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MG MGB Technical - 80 MGB Engine Performance

Have an 80 LE in great condition, but want to add a little "oomph" especially on low end. Don't plan to spend the money for crossflow head, supercharger and such. Hoping some of you gurus can tell me about some less expensive enhancements and what's the best improvement for the money spent.

First, the 80 LE is desmogged, don't know that I agree with this, but seems common and would have to go to e-bay and hope to find the gear. Any suggestions appreciated.

Second, it has a Weber DGV, but I have a set of SUs from a 70 engine (have complete engine).

Third, the exhaust manifold is a pre-1975 (thankfully) and I have added the Monza system. Is there any real performance change by adding a performance header?

Fourth, the ignition system is probably stock and there are lots of aftermarket. Any opinions/experiences appreciated.
Rick Penland

Fit the SUs and put K&N filters on them perhaps? I don't know about more 'oomph' but they will let the engine breated better.

Simon
Simon Jansen

I agree with that suggestion. The car is scattered in my shop for a total refitting of all bushings and it's 20 degrees fahrenheit now, so I have a couple of months to play with it. Might as well refit anyway since I have the HS-4s. Besides, I can rebuild and tune SUs in my sleep (still have SU wrenches), but the Weber is something of a mistery. Will need to study hose routing options since the HS-4s feed through the "Gulp" valve and then to smog pump that shares with the rack and "anti-backfire" valve. My pump on the 70 engine is siezed so of no use. I'll watch e-bay for a pump. Also, will need to add manual choke for HS-4s. The 70 engine complete with smog was a "screamer" compared to this 80 engine.
Rick Penland

I went from a DGV to a 38DGES(Outlaw) with a GREAT performance. You don't need to change the manifold, only the carb...
CDD Dewey

Rick,

Change you smog cam for the early cam. Than get a Eurospec Distributor 41610 distributor from Brit-Tek.

Check out my web-site. This is a 1977mgb with a supercharger. Take off the supercharger part and read the other information. Maybe you can find some items of interest.

Any more question just ask.

Ray

http://www.treasure-island-jewelers.com/1977mgbSupercharged.htm
Ray 1977mgb

Rick. First, you need to define what you mean by "oompf". It sounds like you mean somewhat more power, especially at the lower rpms, from what I am reading. Is this correct?

Most of the things that can be done to increase the power in your stock engine have already been done. Removing the restrictive intake/exhaust manifolds and replacing them with a factory exhaust and a good intake/carb will result in a significant increase in power. Removal of the air pump will free up a couple more horsepower. (While I would prefer the twin SU carbs, the DGV 32/36 can perform well with an engine such as you describe.)

So, only minor increases in power are going to be available to you based on what you currently have. Ray's comment about replacing the distributor is well worth checking out and considering. If the distributor is worn, rebuilding or replacing it is a good idea and will result in more consistant ignition--better balanced cylinder firing and a smoother, more powerful engine--but, only slightly.

The cam used for the rubber bumper cars was actually optimised, by changing the cam timing four degrees either advanced or retarded, for midrange power. The heavier weight of the RB cars made this desirable. Thus, simply changing a good RB cam for a new CB cam will make very little difference in low end power. However, there is another point here which may allow a cam change to give you a significant increase in power.

The RB cams have, for many years, had a reputation for being "soft". Like your "oomph", "soft" is an undefined term which could mean many things. (A "soft cam" might be one which is not optimised for performance or it may refer to poor quality of metal used in its production, or a good quality metal being used with a an improper heat treatment resulting in a rapidly wearing surface. You see why I do not like undefined terms.)

In the case of the RB cam, my experience is that the quality of the metal, or the heat treatment process, was inferior and that some of the lobes on the cam, varying from cam to cam, will tend to wear down. My experience is that only one to three lobes per cam will demonstrate this excessive wear. This results in the cylinders being out of balance with each other. (One or two will not fill with fuel/air as effectively due to the intake valve not opening properly or the exhaust valve not opening properly and not allowing the burned mixture to be evacuated so a fresh fuel/air charge can be drawn in.) When some lobes are worn, the push rods do not move the valve open as much as the unworn lobes will. Thus, this can be measured with either a dial indicator, to show the rise of the rocker arm at the push rod, or with dial calipers to measure the how far the valve has been pushed downwards when the tappet is on the peak of the cam. This is little more complex than setting the valves and should not be a difficult measurement to take.

I use a dial indicator because it is more exact and I have several. Dial calipers, on the other hand, are almost as useful (you do not need exact as the difference will be fairly large--more than .025"). Dial calipers can also be used for any number of other things associated with the with the car (measuring bolt sizes, piston diameters, crankshaft journal diameters, etc.) and are relatively inexpensive. The less expensive, stainless steel, "Made in China" dial calipers can be had for under $25 from a number of sources and are as accurate as the far more expensive brands.

If the distributor is worn and/or the cam is worn, you will benefit from replacing them. If they are not, little benefit is to be derived. If the cam needs to be replaced, replace the lifters/tappets at the same time.

Beyond that, the best way to increase the power of your engine, at all rpm ranges, is to rebuild it. The use of high compression pistons (the factory standard 8.8:1 are fine) is a good idea and results in better performance. The single best thing to install is a modified cyinder head. The Peter Burgess "Econo Tune" cylinder head, his lowest performance option, will result in a significant increase in useable power when combined with a factory cam. Cylinder heads that have been more highly modified need a modified can such as the Piper 270 to take advantage of the increased fluid flow allowed by the more highly modified head.

Bottom line is, except for the cam and distributor, which are currently unknowns, you have about as much as your engine is currently capable of providing and performance increases will require rebuild/modification of the engine internals.

Les
Les Bengtson

Thanks for your comments. Found Brit Tek and the Ultimate Ignition kit looks intriguing. Sounds like a couple of months of blowing the spiders out of the HS-4s and equipping with that ignition kit is a good place to start. The cam is my next point of research. If I read all correctly, the old 70 is an 18GH WE H high compression engine and the 80 is an 18V884AEL low compression engine (8.8 to 1 versus 8.0 to 1) so I'm sure performance will never be the "push you back in your seat" that I had in the 70, but I'm sure I can get a little closer. The valve duration is significantly longer in the 70 engine. Hence, need to determine if the increased fuel delivery from the HS-4s and hotter ignition will be a moot point if I don't increase the valve duration (need an automtive engineer for that one). By the way, no plans to race this thing (too old for SCCA again), just want to drive it and enjoy it.
Rick Penland

Les, thanks for your comments. I was typing the reply above this one when you entered yours. That's the kind of info I'm looking for; what will really make a difference versus lots of expense for very little effect. Yes, "oomph" means low end. The 80 LE winds up fine, but seems weak below about 2,500 rpm. Sounds like I need to do some more engine diagnostics and precise measurements. I've mainly been rebuilding the suspension on this car that has obviously sat unattended for some long period in its life, but into the engine very little. I replaced the head gasket because of obvious leaks and used the proper copper one instead of the "cheap one". Learned that lesson long ago the hard way. Tops of the pistons looked good and cylinder bores showed very little wear. Pistons fit tighlty. I pulled the oil pan because of obvious leaks and noted the inside of the block is red which is often the color of primer that we used when refitting an engine after hot tanking and there are two colors of gasket sealent, white and red. I never use a sealant on new gaskets, just lots of heavy axle grease and clean the surfaces thoroughly. Someone has been in the engine, but I have no information (neither does the previous owner) on what was done or why. I suspect the distributor was not touched and needs rebuilding or replacing. Hence, I haven't seen the cam or its condition. Odometer shows 77K miles.
Rick Penland

I forgot to add that my engine is a desmogged US one. When I rebuilt it I changed the LC pistons over to +20 (I think) high compression ones. I haven't run it yet though so I can't tell you what difference it will make!

You might want to get a copy of the Peter Burgess "How to Power Tune Mgb 4-Cylinder Engines (Speed Pro Series)" book.

http://www.amazon.com/gp/product/1903706777/qid=1133817724/sr=8-1/ref=sr_8_xs_ap_i1_xgl14/104-1018288-2685559?n=507846&s=books&v=glance

I think you'll find it very useful and it will discuss a lot of the things you are thinking about.

Simon
Simon Jansen

Rick and Les,

Rick, Les brings out some fine points, but I would also like to elaborate a bit further on the cams.

The early 18G used a double row timing chain and this is what retarded the timing 4 degrees. When the early 18V came out the cam was really almost the same but than they went to the single sprocket which basicly kept the car a 0 degrees instead of retarded 4* like the earlier years.

When the Rubber bumper MGB came out it had a new cam that was advance 4 degrees witht he single sprocket.

So lets look at it again. The double row timing chain retarded the timing giving more mid range torque.

The early 18V had the single timing chain keeping more low end torque.

The later RB had a 4 degree advanced cam to try and bring more low end torque because of the weight,but it was also a smogger cam. As your car is desmooged having this cam, if it is still there has no benefit at all. This is why I suggested using the earlier cam but not using the double row timing sprocket. Use the single row to keep that low end torque.

Les, if I am incorrect please let me know. This is from the information I have and I feel would be best with his car. Just a suggestion.

And Rick the Ultimate Ignition Kit is the one for you.

Ray
Ray 1977mgb

Ray. My understanding was that it was the actuall cut for the woodruff key that determined the cam timing, not the camshaft sprocket. But, I have not bothered to compare the two sprockets. When using the double sprocket set on a reground RB cam, it timed correctly. When using the double sprocket set on a new CB cam, it timed correctly. Hence, I did not bother to do any further research.

To the best of my knowledge, the change in cam timing took place when the RB cars, with their heavier weight went into production. Others may have more information on this.

As to Rick's comments about 77K miles on the engine, this is an interesting point. Unless you have documentation to demonstrate that this is 77K, rather than 177K miles, such things are very hard to determine. When we purchased my daughter's 77B, there was a great deal of PO documentation to demonstrate that the odometer was on its first trip around. Thus, I was confident in the actual milage. With my 68GT and 79 LE, I am far less confident as there was not documentation from PO's as to how many miles the cars had actually seen.

For some 37+ years, I have used my MGs, and a few Austin-Healeys, as my primary means of daily transport. This tends to skew my perspective. Perhaps, I lack self restraint. But, to me, owning a British Sports Car to drive only it infrequently is not "part of whom I am". Driving, under the current situation where I live, is not fun to me. Driving a Brit Sports Car, however, makes this less of a chore.

How much wear your camshaft will demonstrate at an actual 77K miles is hard to determine. The ones I have examined have had about 80K+ miles on them and have shown significant wear on two-three lobes. My daughter's engine, at a documented 97K miles showed a very signficant amount of wear on two lobes and a lesser amount of wear on another lobe. Once again, actual measurement is indicated. Rutland Tools has a website and is a good source for things like dial indicators and dial calipers--these are things you will find many uses for and are not expensive.

In the final analysis, the single best investment I have made was in having Peter Burgess build a cylinder head for my daughter's car when I rebuilt her engine. Again, this was his "bottom of the line" cylinder head, the Econo Tune model. A spendid addition to a stock engine which I cannot recommend highly enough. My car (the 79 LE) has a Mike Brown cylinder head and a slightly larger bore. Otherwise, the engines are identical. Theresa's car will out perform mine any day of the week.

Les
Les Bengtson

Les,

I do think it is the sprocket not the woodruff key.

My double row came with a straight key with no offset. When I time mine is was 4 degree retarded.

Here is a archive post on this:
R.T. Whitfield, East Tennessee
A long time ago I found out the only difference between the older (chrome bumber) and newer engine tuning was the cam timing, not the cam.
The easist way to improve rubber bumper car engine performance is to replace the single row timing chain and sprocket with the older style double row.
Look at the specs for the two cars and you will see the cam shafts are the same, only a few degrees difference in timing.
Check it out with a cam timing wheel. When I showed this to Jonathan Twist of University Motors even he could not believe it, but check his web site out, he was amazed to find this out even after all his years of experience. This is also documented in the MGB tech archives.

Hope this helps.

Ray


Ray 1977mgb

Ray. As I tried to mention, perhaps I was not clear, the one RB cam I timed with the double sprocket checked out the same as the camshaft had with the single sprocket. Thus, my belief that the camshaft cut for the woodruff key was the determining factor, not the sprocket. However, my experience, based on a single example, is not definitive. Several people have reported that the camshaft they installed had significant variance from the reported standard--up to eight degrees. Thus, all we can say, in any form of definitive manner, is that degreeing in the camshaft is a good idea.

Les
Les Bengtson

Ray, Les, Simon and Dewey, thanks for your insightful comments. Your experiences and knowledge will save me lots of fruitless labor and money spent. I'm especially intrigued by the comments about the timing chain and sprocket. I think the 70 engine has the double row timing chain. Hence, using that and the HS-4s from it along with adding the Eurospec distributor are my choice at this time. Les questioned the 77K mileage and I concur. MGs used to be famous for odometers that didn't work. I have no history beyond the immediate previous owner who owned for less than a year, but I bought the car for the body which is absolutely perfect. I've inspected the floor pans and hidden places like the battery housing and think the mileage is close to true. Otherwise there would be more deterioration.

I may hold off on extensive engine work for another time. Since I have the 70 engine, I will probably get tempted to build it up over time and drop it in rather than spend too much on this one. I've always kept a spare engine when I had Bs so that I could be building one while driving the other. The best of both worlds. It's great to be an old man and have a B that I don't have to always drive. I enjoy tinkering with them as much as I enjoy driving them. As a younger man, I've been up till nearly dawn replacing a clutch and such so I could drive it to work the next day.
Rick Penland

In case it helps anyone contemplating these changes, I switched the sprocket from single to double row as an afterthought on an engine a while back, having already timed in the new cam. Doing so gave a 4* change. As the key and the cam stayed the same, it must have been the sprocket that altered things.
Steve Postins

Steve,

There are many post in the archives on this subject and mostly everyone who has changed from single to double sprocket had the same results as you and me. I agree with you 100% that it is the sprocket and not the cam or the key that changes the timing 4 degrees.

Ray






Ray 1977mgb


Les,

Can you tell me how to check the cam lobes for wear using a dial indicator? My '80 LE doesn't have as much power as it should, and I suspect the cam may be worn.

Many thanks,
Dave
Dave Plantz

Ray, et al. I have only timed a single RB cam when changing over to the duplex timing chain. I did not bother to check what the timing was before replacing the sprocket. My general advice to anyone changing over would be: "None of us know, exactly, what we are talking about and you need to dial in you cam". I do not know of anyone who has done a "before and after" timing check. I do know that people I consider reliable have reported that their cams were up to 8 deg (crankshaft) off when they were installed. The factory solution, "align the dots" has been the system used by most of the people who have assembled engines in the past. I used this for something over 25 years and have built some very good engines that way. However.

If it really matters, I will admit that I am wrong about this as long as everyone will agree to use a degree wheel and properly time their cams. One degree off on the sprocket, out of 360 degrees, and one degree off on the camshaft (in the same direction) out of 360 degrees will equal two degrees variance at the camshaft and four degrees at the crankshaft--the variation we are speaking of here. Thus, my advice to all is "don't listen to the old folks about what is the cause--just us a timing wheel and degree the camshaft in properly". That is the bottom line and the rest is, quite simply, something that us "old folks" would like to know--if it is possible. DEGREE IN YOUR CAMSHAFT!!!

Dave. Sorry, I have been busy and did not answer this thread as quickly as I should like. Hence, the foregoing.

In answer to your question, a worn lobe will not lift the pushrod as high as a non-worn lobe. If the pushrod does not move up as far as it might, the rear of the rocker arm is not lifted as much as it should be. The rocker arm, then, does not depress the valve as far open as it might if it had been pushed upwards by the action of the pushrod, being activated by the tappet, on an unworn lobe. So, the basic mechanism is clear to you--the worn lobes do not raise the rear end of the rocker arm as much as an unworn lobe would. However, we have to consider the "rocker arm ratio" which means that the back end of the rocker arm, being the shorter arm of the lever, does not move as much as the front of the rocker arm which bears on the valve. Thus, the front of the rocker arm moves more, in relationship to the back end, making it easier to see small differences because they are magnified by the "rocker arm ratio". (From memory, this is something like 1.2:1 which means the front, valve, end moves 20% more than the rear, pushrod, end.)

To use dial calipers to measure this relationship, put the transmission in neutral. Put on the hand brake or choke the wheels so that the car cannot move as you lean against it. (At my age, I lean against it a lot.) Get out your Driver's Handbook or workshop manual that gives the order for adjusting the valves. (No reason not to check the valve clearances while you are doing this and "kill two birds with one stone".) Use a 1 5/16" wrench to turn the engine over, using the order given in the workshop manual. Then, adjust the applicable valve clearance. Before going on to the next, measure the height of the spring cap above the surface of the block. Write this measurement down. Go on to the next valve adjustment and do the same thing--set the valve clearance and not the height of the spring cap above the surface of the cylinder head. When you are done, you will have your valves set to the proper clearance and you will have noted the relationship between the valve spring caps and the upper surface of the cylinder head.

As in compression readings, there are guidelines, not absolute rules. The factory has not published "acceptable vs. unacceptable valve lift". Thus, we get back to my own experience which may, or may not, be absolute. The camshafts I have examined, out of the engine, which had worn lobes showed something like .100" of difference between the lobes which seemed to be original and the lobes which demostrated a significant amount of wear. This is augmented by the "rocker arm ration" of something like 20% more movement at the valve than on the cam side.

As such, my best guess is that if the heights of the valve spring covers vary by more than .050" it is an indication of significant cam lobe wear and the cam, and tappets, should be replaced. But, I would point out that this is just a guess. The cams I have examined have been from RB engines I was rebuilding and the lobe wear was much in excessis of this measurement. But, the owners still thought, until some other problem developed, that "the engine was running fine". Problems which develope over time are seldom recognised until something breaks badly. My daughter drive her 77B, with a broken exhaust valve, until I took the car out for a drive and, immediately, recognised the problem. My cars ran much better. Theresa, only drove her car and did not recognise that the power of the engine was deteriorating. I, immediately recognised the problem upon driving it, did a compression check and recognised a valve problem on number three cylinder.

Thus, the .050" figure is not an absolute, just a best guess based on my own experience. The metal of the RB cams seems to wear quite rapidly when the surface hardness is breeched. This may also be true with other cams, but most of my recent experience is in rebuilding the engines for our RB cars. In any event, if you have a difference of .050", it will only get worse as the engine is run more and the power that engine is capable of producing will only get to be less as time goes on. But, I am not competent to say at what point the excessive wear will become objectionable and the engine will be declared "under powered"

Hope this may help. Les
Les Bengtson

I did a definitive test and report it on my website engine building section - http://www.octarine-services.co.uk/5.%20degreeing_the_cam.htm - the difference with the double sprockets is 2.25 degrees.
Chris at Octarine Services

Sorry - the URL go split over 2 lines!

http://www.octarine-services.co.uk/5.%20degreeing_the_cam.htm
Chris at Octarine Services

OK - so you need to copy & paste to the address window....
Chris at Octarine Services

Here is some information from the MGB shop manual, Haynes MGB manual and The Original MGB by Clausager.
It appears there may have be two different single row sprockets. Note that in June 77 only the cam sprocket was changed. It looks like this may have been done to give a 4* change in timing. I'm talking design/theory differences, measured differences may vary due to production tolerances and stacking errors. I did the lobe center calculations, they aren't in the refernced books. The appendix in the Peter Burgess book tells us how to compute lobe center calculations from cam opening and closing information. These computations are valid only on cams with asymmetric lobes, same opening and closing rates for the lobes.

The original MGB used a double row roller timing chain and sprockets. The MGB 62-74 shop manual gives the following timing settings.
Intake valve, opens @ 16* BTDC, closes @ 56*ABDC
Exhaust valve, opens @ 51* BBDC, closes @21*ATDC
This timing gives the intake a lobe center of 110*ATDC, exhaust lobe center is 105*BTDC. LSA (lobe separation angle)is 107.5*. Camshaft is retarded 2.5* ATDC

In October 72 the chain and sprockets were changed to a single row on NA engines 18V 673. No mention is made of a change in timing.

In December 74 NA rubber bumper cars with 18V 797-798 engines on had a new camshaft #1156. The Haynes MGB manual provides the following timing data for those engines.

Intake valve opens @ 8* BTDC, closes @ 42*ABDC
Exhaust valve opens @54*BBDC, Closes @ 18*ATDC
New cam gives intake lobe center of 107*ATDC, exhaust lobe is 108*. LSA is 107.5*. Camshaft is now advanced .5*BTDC.

In June 77 cars with 18V 847 engines for the home market UK received a new cam sprocket.

The Haynes MGB manual gives the following timing for those engines.
Intake valve opens @ 20*BTDC, closes @ 52*ABDC
Exhaust valve opens @ 55*BBDC, closes @ 17*ATDC
Intake lobe center is 106*ATDC, Exhaust lobe center is 109*BTDC. LSA is 107.5*. Camshaft is advanced 1.5*BTDC.

Moss and VB lists the same sprocket single row part numbers for all 18V engines. They go on to say the early double row sprockets and chain can be used on all 18V engines. What is not known is which single row sprockets are being sold now if there were ever any any differences, is it a UK spec sprocket?

In my 74 engine I went from a single row to double row chain and sprockets when I rebuilt the engine. I checked the timing prior to removing the old chain and gears and found there was a small difference about 1.5* -2* from the double row settings. That could be an actual difference or it could be caused by wear and stacking errors. I had my old cam reground so I don't have valid after rebuild comparisons.

Les has given the best advice for anyone planning to change a cam. Degree it with a degree wheel and dial indicator. With all the variables in cams, gears and manufacturing tolerances we don't know what we have unless the cam is properly degreed.

Clifton


Clifton Gordon

Rick- Soas to give you a comparative understanding, my 80 LE with 53k original miles, bone stock and just after completing smog inspection, was pushed over to the Dynomometer, and showed a stunning 54 HP at the wheels. This'll give you appreciation for the hand delt you. My 71 produced 87 hp years ago with near stock setup. To be blunt your best bang/buck would be to pop for the $2k supercharger from Moss or the Han's Hotter. If your stock gine is less than, say, 80k miles, you should get years of utility and smiles if you keep the boost around 5-7#. FWIW Vic
vem myers

Les,

I agree with you that we still must use a degree wheel to be absolutely postive of our cam timing. All sprockets made are not all 100% accurate and could have a slight flaw in manufacturing.

Steve and I only gave examples of our sprocket change and both of us had 4* retarded timing. There has been many post in the archives and most end up with the same 4* and I have read some also that were 8* off.

I respect your knowledge and your help in the past and I am only saying that at an average I would say that if anyone did change from a single to double sprocket expect a 4* change, but to be sure You Must use a degree wheel to set your cam timing accurately.

Merry Christmas to you and Your Family Les,

Ray
Ray 1977mgb

Ray. There is a lot of this stuff that none of us knows well. As Clifton notes, there have been several changes over the years and most of us, myself included, do not have examples of each variation to research. Thus, we become "the blind men describing the donkey". We try to describe what we know and why we believe what we believe. In my case, I do not believe that I will ever know the whole truth about things MG and must content myself with learning what little I can. I think most of us understand that and feel that way.

Therefore, there will always be room for discussion of what we have each learned, either as an individual or through reading what others have learned. Through this process, we are able to muddle through to a vague understanding which is more than we understood before, but less than a comprehensive understanding of all things MG. Peter Burgess, John Twist and a very few others, after years of work and study, seem to have reached a comprehensive understanding. Few of us hobbyists ever will and I know for sure that I will not.

Merry Christmas to you and yours also. Les
Les Bengtson


Les,

Thank you for the thorough explanation of cam wear and how to diagnose it. Hopefully I can check mine this weekend when I get home from school. I'll also need to pickup a dial indicator.

I also read your post about selecting the correct cam for these later engines. It seems that most people switch their timing gear to the double sprocket, so I'll plan on doing that while I have it apart. The thing that I'm confused about is using a RB or CB cam. From the discussion, it looks like the only difference is cam timing between the two (according to Ray's post).

Many thanks,
Dave
Dave Plantz

Dave, I'm not sure you can still get a cam like those used in rubber bumper cars. Moss lists the same part # for 65-80. According to Paul Tegler's website the cam on rubber bumper cars has less intake duration than the cams used in chrome bumper cars.
http://www.teglerizer.com/mgstuff/mgbcamspecs.htm
Here is a repeat of part of my above post.

"In December 74 NA rubber bumper cars with 18V 797-798 engines on had a new camshaft #1156. The Haynes MGB manual provides the following timing data for those engines.

Intake valve opens @ 8* BTDC, closes @ 42*ABDC
Exhaust valve opens @54*BBDC, Closes @ 18*ATDC
New cam gives intake lobe center of 107*ATDC, exhaust lobe is 108*. LSA is 107.5*. Camshaft is now advanced .5*BTDC."

The information about the camshaft change in 74 was taken from Clausager's Original mgb book on page 141.
The valve iming figures were taken from the Haynes MGB manual engine specifications on page 24.

Add the intake opening and closing figures to 180* and you get a duration of 230*. Look at the valve timing for the early cars on page 22 in Haynes and add the intake opening and closing figures to 180*, the duration is 252*. The intake valve is open 22* longer in the early cams. Longer duration in this case means better performance.

Clifton
Clifton Gordon

Dave,

As Clifton stated above the 1156 cam was used on the rubber bumber. From 65-74 they used the same cam just different sprockets (Double and Single). I did a lot of research before I changed my car which is a 1977 MGB. I had the 1156 cam with single row. When I changed my cam back to the earlier one and also changed the single to double sprocket my car turned around completely. It had a better pick up and also went further into the rpm range. When I added the supercharger it only made it better all the way around.

Moss Motors now only sells one cam for all years as nobody would install the 1156 cam anymore during a rebuild. So please understand that there were 2 different cams. Some prefer to use the earlier cam and stay with the single sprocket while some prefer to use a double sprocket and use a woodruff key, while other like me used early cam with the double sprocket and took the 4* retarded timing.

Ray
Ray 1977mgb

This thread has been rich with information and I thank all of you as well as wish all of you a Merry Christmas. I'll have to read a lot of the articles that several of you refer to. I've been spending a lot of time researching and too little turning nuts the last couple of weeks. Sounds like I need to get some tools and do some precise measurement and adjustment. Many of you are highly technical and I'm, at best, an experienced "shade tree" mechanic.

I want to get my suspension back together right now and won't spend that much time on the engine until later. However, I need to change the timing gear cover gasket because of noticeable oil leaks so will look at changing to the double row sprocket that is on the 70 engine. I'll need to inspect it closely. I rebuilt the 70 engine at about 75K and noted some cam wear, but only changed the cam bearings at that time. Will need to inspect the chain for wear since it has about 150K on it. I pulled it, dropped in a rebuilt 71 that I had for a spare and the 70 has sat since. That was about 1985 or 1986. I bought the 70 when it was a year old and drove it until 1987.

The engine in the 80 LE has been worked on per my visual inspection, but the previous owner has no history. When I changed the head gasket, the cylinder bores were in better condition than I expected for 77K and the pistons fit snug with minimal play. It has been my experience with older Bs that the cylinder walls are usually OK, but worn enough at 75K for honing, piston knurling and oversize rings, but need rebore or resleeve next time. The older Bs had chrome moly rings and the 2 engines that I've redone were high compression with the extra ring. Hence, probably wear faster.

If the 80 engine has been rebuilt, might have a replacement cam. I don't think I can be sure without tearing the engine down although some of the instruments you all have suggested might give a hint.
Rick Penland


Clifton and Ray,

Thank you both for explaining the cam differences to me. I now understand them.

Rick,

Good luck with your '80 LE. ' Guess we're sort of in the same boat with the engines. It looks like mine was rebuilt at some point (or re-ringed and honed) as there was cross hatching on the cylinders when I had the head off. Mine has 97 K miles and I have no idea if the cam was replaced. Hopefully I'll know this weekend after I take some measurements. I can't wait until I get this thing running with some power! It kind of wimps out when the rpms go up.

Cheers,
Dave
Dave Plantz

Dave, sounds like we can save each other some dollars by experimenting and reporting back. Unfortunately, don't know that I'll get anything done this weekend and gone all of next week (travel all over north America extensivley), but hope the week between Xmas and New Year to get the front suspension finished, torqued, off the jackstandsdone and run it to a car wash, clean off the grease and oil and start on the rear suspension. I'll do the timing gear change and take some measurements then fit with the Hs-4s in January. Also, sounds like a dynomometer benchmark would be worthwhile, but I'm in the hills of Missouri where they still measure mules. Not sure if I can find such for automobiles.
Rick Penland

This thread was discussed between 05/12/2005 and 09/12/2005

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