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MG MGB Technical - MGB engine evaluation

Hello,

I imagine my interrogation will upset many people.

But I own Bs for many years now and I try to evaluate the B motor.

My perception is that B's motor is not so good.

1- I have almost never seen a B motor without a need to be rebuilt after 100,000 miles
2- Head are famous for their crack
3- Problems with cooling
4- Oil presure is on the low, after 30,000 miles
5- Design from the stone age with pushrod and siamese intake
6- Leaking oil or coolant from many places

I remember when I bought my first B-GT, I also owned a Volvo with the same type of motor, but with more HP and without any drawback. And after 300,000miles, Volvo B20 engine was still working well.

After reading my evaluation, some will believe I do not like my B. Which is not the truth. But only impression that B engine was not the best thing for B after all.

Am I alone to have that impression?

Cheers,

Jean G.
Jean Guy Catford

Jean,

you are right!
The B20 is known for it's relaybility, and the B-Series engine is a rebuilt candidate after 100K mls.
This is the experiance i can share after nearly 35 MGB jears.
When i was in the situation to rebuilt the engine of my 1973 GT in 1981, i took the Rover V8 and it is running fins since 27jears now, although the 2nd. gear synchro of the LT77 geqarbox is becoming a little bit weak now. Thew engine has covered more than 200K mls now, the LT77 may be 180 K mls.

In the roadster, i have a rebuilt B-Series engine since 4 jears now. Although built up with all the precision possible and tuned to stage 6 (according to the ST-Tuning Manual) these engines are rather 'historic' and do not meet our demads of quality these days.
If it would have been possible here in Germany to have an other (forign) engine to be legalized in a mgb roadster, i would have chosen a Vauxhall 2 litre dohc CX20E with cosworth head and stock 150 DIN HP.
These units do 200K mls without any trouble and fit the engine compartement, are light wight (~90KGs instead of ~160 KGs for the B-Series), and there are the right GM gearboxes available that fit without dramatic mods as has to be made going the V8 way.

When the B-Series engine was designed, it was considered for cars lasting 8 to 10 jears and an anual averadge of 8 to 10 K mls, i think.

Ralph
Ralph

I have owned my B since 1983. It came with 43k miles and about ten years ago I had the gearbox changed to an OD box and recored the radiator. Since this work I have had to do very little on it at all. I swear it seems to run a bit on the cool side mostly with some warm periods in very slow stop and go traffic. As far as oil leaks go I have changed lines to the oil cooler once and the metal line to the oil preasure unit. I have also once gone under the car and slightly tighted all the screws on the oil pan. I've done nothing at all on the side of the HIF carbs. I lose a drop or two of oil occasionally, Its no concern at all. I do not work on it mechaniclly myself as I figure I will just screw it up. I for a while tried to lean the carbs and years later found out I was actually enriching them? I'm no mechanic. At this point I have 125K miles on her and she runs great so long as I leave her alone. Years ago I had a new Chevy van and when I reached 98K miles I had to replace the engine. All things considered I think the old MGB engine is pretty good. The head has never been removed since I have had it. I,d like to have it port and polished to the econotune spec because a little more power would be nice. With the bad reputation heads, I am just passing time for now. I'm afraid if I remove the head I may find a crack. From the outside and in driving it I do not think I have a crack but I just do not want to find out. I really love my car...motor too! Bob
Bob Ekstrand

Ralph,

Unfortunately here in Canada, Rover V8 or Vauxhall are oddities. It is difficult to do such modification.

Your opinion confirm me to rebuild my MGA Coupé with a Volvo B21 sohc + 4sp-OD + 2 Sromberg, as I want a daily driver to travel across america. But this is aside my impression of B motor topic...

Cheers,

Jean G.

Jean Guy Catford

Jean - the Volvo B21 is a fine motor but won't give you the same pleasure as the Buick 215.
To put the record straight the MGB engine will also run round the clock three times but it does need frequent oil changes - 3K if you are using (in UK) 20-50.

I don't give two figs for originality when it comes to the MGB - there are very few originals anyway but the MGA is getting scarce over here and most prospective new owners will be looking for originality or a very very low price.

It's good to hear the car will be a daily driver - good luck with the conversion.

Roger
Roger

Jean

Spent my teen summers working in my uncles machine shop back in the 70's. You listed the one engine that did get over 100,000, the Volvo. Until the toyota's came out, very few car engines got over 100,000 miles without an overhaul.

Got to remember, until the Japanese, the Swedish built one of the most reliable cars out there. Until Detroit started playing catch up and the government started requiring the automakers to look at ways to reduce emissions and increase fuel economy, there was not much incentive to change.

You are also correct in saying the design was well lets say dated. I have not seen the engine in the last of the MG's (one's the Chinese are making) but I have to believe the engines are more like modern ones.
Bruce-C

Jean,

If you are going to put a Volvo in an MGA, I think the B20 with twin SUs would look more at home. It used to be a fairly common conversion. If you do it, of course keep the original stuff and try to avoid cutting, and save the cut parts if you must cut.

If you go with the overhead cam Volvo, I think the B230 weighs less than the B21. If it is from a 240 it should have the block mounted distributor and so be a bit shorter than the one with the distributor on the head. Also, you could use the M47 full five-speed instead of the overdrive. I think 5th in the M47 is an overdrive ratio, but check my memory for yourself.

Charley
C R Huff

Well,

Thanks for your input. But my basic interrogation was on my impressions concerning B engine. I had feelings for many years that B motor was always on the edge of being in trouble. Many MGB owner told me during these years that B motor was very good.
But like people impression on cars. Sometimes it has a bias. Like here in my region, it is mandatory to believe Japs car are the best. But having owned 3 japs cars, I am not so found of them at all.

I made a digression here, but back to the B motor. It is true that B engine is easy to rebuild and could be improved with some gizmo, like a croossflow head
Jean Guy Catford

I have had British cars to drive EVERY DAY & work on for 38 years. I have built a LOT of motors with the help of a man that worked on all type of motors from the end of WW2 till the day he died 4 years ago. He would say as he was building the B motor (This is a OLD BUCKET OF BOLTS BUT IT IS A TOUGH LITTLE MOTOR) I have motors that we have built & put 200,000 miles on, pulled apart & the bore was fine, with the crank, put it back together & sold it to a man that is still running it. I have a 71 B motor that I put 150,000 miles on & thin a deer plowed in to me & I had to drive 5 miles to get of of 95 were the tow truck would not rape me for 5-600 dollars. Put in another raid & drove her home. Re torq. the head, but she blew the head gasket a 1,000 miles later. Rebuilt her in the car with rings, bearings, lifters & a valve job (no cracks) & have put 15,000 more miles on std bore. It is HARD to beat a VOLVO motor even with what is made today! I have one B20 that will go in a B one of thes days.
Glenn Towery

I have to speak up here. I agree with Glenn. The MGB egine is a tough unit. I am the original owner of a 1973 MGB with 155,000 mi. on the original engine and it runs extremely strong, using basically no oil. I always chaged the oil at the specified mileage and I think that has made a huge difference. I was going to re-do the body and while everything is apart I thought I might rebuild the engine, but I have decided not to, since it has so little wear.
1) It has over 155,000 miles and does not need a
rebuild. I figure it will easily make 200,000 and
beyond.
2)Head has never cracked
3)Has never overheated once in 35 years.
4)Oil Pressure 50 lbs at idle, 70lbs driving
5)Pushrods are not that bad of a thing. No rubber
timing belts to break or long overhead cam timing
chains to break or develop tensioner problems and
jump timing like Datsun 4 cylinder engines of the
same era. (From personal experience/ multiple
problems)
6)No Coolant leaks at all. Leaking a very small amount
of oil from the rear main seal.

I agree with Japanese cars being overrated. There is a reason why you see very few older than about 10 years.

Ralph
Ralph

I just tell myself those oil leaks are there on purpose to stop the bottom of the car rusting :)

If you come to NZ you'll see loads of Japanese cars older than 10 years. My daily car is a 1991 Toyota and that goes perfectly. Easy to maintain, cheap to run. We get a lot of very cheap cars imported from Japan (who drive on the same side of the road as us) so I would think older Japanese cars make up the bulk of the market down here.

The B series engine is the first one I have ever rebuilt and I liked that it wasn't really that difficult to do!

Simon
Simon Jansen

I can only agree with Ralph. My B has only 90K miles on it but the last 25K with a supercharger. It leaks no oil, does not need topping up between changes (3k miles) never overheated, 75lb Oil Pressure, or needed the radiator topped between service. I pulled the head at about 80000 to fit a Payen gasket and ARP head studs to be on the safe side and there was no lip what so ever in the bore. Like any early design engine they need regular servicing. They say that oil does not wear out but the anti wear additives in the oil do, so the oil must be changed often. The early Volvo is a good engine but the cars did not last long in our sun. Denis
DENIS4

Hi all..

My 1969B engine has run trouble free for over 250,000 miles. I have been fussy about oil changes...oil and filter changed every three months religiously. This car has run in stinking hot Australian conditions with never an overheating problem. I blew a clutch recently so plan to take the motor down for a look and will report back. The only time this car has ever stopped on me is when the fuel pump failed (twice).

From anecdotal evidence it appears daily drivers have more longevity than cars used only occasionally. Any thoughts on this theory?

Kind regards
Mick
Mike Donaldson

My '72B now has 107,000 miles, and I change the oil each fall after an average of 1000 miles of summer weekend fun. Each year of the last 8 I have owned it, I do a compression test as one measure of the health of the engine. For the 7 previous years, I had 150 PSI of compression across all 4 cylinders, with no more than 5 PSI deviation each. This year, for the first time I noticed that #3 cylinder was low, @ 120 PSI. I decided to run it another summer, and remove the head next fall for rebuilding. I tested the compression with the engine cold, but will retest when it gets warmer up here in chilly New England. Any opinions if it is more likely the head than the rings in #3 cylinder causing the lower compression? Do you think the performance will be seriously impacted by one cylinder being down 30 PSI? It has always had good power/torque climbing the hills where I live. I did check the valve adjustment, and did not encounter any serious problems there, all were close to being correct with only a few of the valves requiring minor adjustments.
Joe

I'm glad so many others have piped up. As far as points 2 to 6 go heads are not *famous* for cracking. Yes they do crack, and there were mods during production to strengthen it. If it were that common all the original engines would have died long ago, as it is you can get engines from scrappers and dismantlers because it is usually the body that causes the demise of a car, and even then there are many thousands of these cars in regular use all over the worls. There shouldn't be any problems with cooling, these cars run in desert states with no problems. If yours has cooling problems then *it* has the problem, not the design of the engine in general. If your oil pressure is low after 30k then again there is something wrong with *your* engine, not the design in general. Design is from the stone age? Given the MGB is 35 years old, and the engine dates back quite a bit earlier than that, then it's hardly surprising that it is considered 'old fashioned' today. Doesn't make it any the less a reliable, long-lasting and torquey engine even if it doesn't have the performance of a modern engine. And as for leaking oil and coolant from many places that is purely down to you, my son, neither of mine drip either.
Paul Hunt

Interesting guys,

To see a variety of opinions. But after reading for years many post on this forum describing all type of MGB troubles, mentioned ealier, trigger me to have such interrogations.

As I noticed there is owners which seems to "never" had any problems and a multitude of the others.

I believe my B-GT is a great car fun to drive, but I could also see weak point on it. But it is possible to correct them to some extend.

Cheers,

Jean G.
Jean Guy Catford

an interesting point that Mick from Australia is making I think - my B is a daily drive, and though its only 4 years in my ownership, never misses a beat engine wise. Friends with lovely bodies (you know what I mean) whose MGB's spend a lot of time in sheds unused for the winter months do seem to suffer not only more teething issues, but also are having more serious issues also. maybe these wee engines were meant to be driven (into the ground?). My engine is the 1973 original, just over 90K on it (10k a year since I got it, and has even compression accross the cylinders, good oil pressure etc - I also do regular oil changes (one of the few things I can manage not to screw up so I do every 3K miles). And having said that it will now slap me in the face by not starting when i leave work in ten minutes!

But like Paul from West midlands says above, given how old the B series is, its bound to be a bit old fashioned by todays standards. However, that it starts, stops and works as it should after all this time to me is testament of an oldie but a goldie! Long live the B series, as its the olny engine I have even a remote understanding of (and even better, SUHS4 carbs are also understandable, unlike my friends webber which clearly is the work of the devil as regards my understanding of it now that he has it in bits!)
mick

The only weak point IMHO is that 1798 cc siamesed bores is getting towards too much piston and not a lot of block. The only failure I have had was when the head gasket failed between 2 and 3 cylinders on my cars original engine at about 80K miles. Knowing what I do now I do not think I would have that problem and my engine still shows the same oil pressure as when it was last rebuilt 13 years ago, although it has not run many miles, about 40K. It uses almost no oil and does not leak any of it's fluids either. Of course it can't compete with a modern short stroke 16v DOHC fuel injected electronically managed engine, but how many of them will still be in daily use 60 years after the first one left the production line?
Stan Best

Hello,

The point is not to compare with "modern" engines EFI, remember Jag in the 1950's had DOHC. Light years from american V8 or 70s jap cars.
I remember have owned a 74 Corolla 1.6L OHV, which engine was a junk compare to MGB engine.

But I remember many years ago an evaluation of MGB where the writer said Brittons made MG from a part bin.
Also another point, as it is written in my Haynes handbook for TR6, replace engine bearing at 50,000 miles??? Like if it is just like changing points. I imagine it is the same thing for B as it is similar engine conception. It is why I have obsolete design in mind
Thanks Stan, I forgot to mentioned blown head gasket in my list.


J.G.
Jean Guy Catford

J.G.
There you have it - the MGB's motor is good agricultural equipment which will run to very high mileage provided you change the oil regularly. The UK cars now tend to have cylinder heads modified for lead-free gas which has meant new gasket and in some cases valve gear. A lot of lead-free heads have also been cleaned up to give more torque and better MPG.
Some of us have taken the opportunity to fit high-rise camshafts although the original would still do the job. It was normal a lifetime back to work on the main engine bearings between 30 and 50K but that was on those engines not fitted with bearing shells. It was never the normal drill for the MGA or MGB motors.

Some Haynes' advice on general maintenance is non specific and needs to be read with caution. The TR motors were long life too but their drivers had trouble keeping them on the road which explains the low numbers now.
Roger

"Brittons made MG from a part bin"

They did, but that isn't the same as saying they were used from parts from a rubbish bin!

All 'parts' bin' means is that all the various marques Morris, Wolseley and MG and later on Austin used common parts where they could to reduce costs (something that went sadly wrong when Leyland/Triumph/Jaguar 'merged' with them).

Haynes may well say to change big-end shells at 30k and main bearings at 50k, but the Leyland Workshop manual doesn't. And in any case common sense dictates if you are going to go to those lengths you would do both at the same time. But I bet the number of people who do change bearing at those periodicities is minimal, myself included, and we don't suffer what you seem to as a result.

Bugatti had twin OHC engines in the 1930s, but look at the price range and market of Bugatti, Jaguar and MG and you will see why MG used basic technology longer than the other two, and to extremely good effect. Keeping a classic Jaguar running as an every-day car, let alone a Bugatti, is a very different matter to keeping a classic MG running.
Paul Hunt

Hello,

Paul, nobody never said MGB was made from rubbish bin. The MGB being a great car for a "reasonnable" price. In america in 1973 it was $4500, which mean $1500 less than a Corvette. Concerning economy at BL, I was upset in those days to see my new 1986 XJ6 with the same 2 cents door lock than a B or the same fender side lens also.

Regarding the motor now I begin to tink that B engine is good, Moped type to repair with many drawbacks.
No matter of opinions, it was the choice BMC made when they designed that car.

Cheers,

Jean G.



Jean Guy Catford

There are few mysteries about the engine employed in the MGB. This is not a state-of-the-art, fuel-injected, dual-overhead-camshaft, four-valves-per-cylinder, variable-valve-timing, microchip-controlled technological wonder, festooned with interconnected sensors and switches, all linked to mysterious black boxes, and guaranteed to both intimidate and befuddle NASA engineers. Instead, this engine is something more along the order of an archeological relic from a bygone age of motoring, something that was intended be maintained by its owners with simple hand tools and to also be produced in alternate versions that were to be installed in farm tractors and diesel-engined taxis. In today’s world of laser weapons, it seems as anachronistic as a sword. Crude, yet still highly effective in a very intimate way.

Keep in mind that the design of the B Series engine was started in August of 1944 when it had become obvious that the defeat of Germany was close at hand. Leonard Lord, Chairman of the Board and General Manager, gathered together his three top engine designers from the engineering staff at the Austin Design Office, Eric Barham, Jimmy Rix, and Bill Appleby, and gave them the assignment of designing a pair of all-new engines that would enable the company to get a jump on the competition in the soon-to-come postwar market. The ultimate evolutionary results were the legendary A Series and B Series engines. Such was their development potential that they both remained in production well into the 1980s.

Although the B Series engine design is truly a compromise, it is a brilliant one that modern mechanics recognize as being one that was far ahead of its time when introduced. It was further improved with the introduction of its five-main bearing version. Certainly there were other new engine designs that were even more advanced in the mid-to-late 1940s, but this one was intended to be available in cars that ordinary people could afford to own and operate. In those days, that made it special, and its designers had every reason to be proud. During an era when full race engines struggled to reliably produce 1 BHP per cubic inch, when the 18G Series arrived in 1962 it boasted 95 BHP from a mere 110 cubic inches, giving it a specific output of .864 BHP per cubic inch, and this was an engine that could reliably be used as a daily driver! In its heyday, it was impressive indeed. Pretty fantastic for a relic whose basic design is almost two-thirds of a century old! A true classic engine design for a true classic car!
Steve S.

"I was upset in those days to see my new 1986 XJ6 with the same 2 cents door lock than a B or the same fender side lens also."

Not half as upsetting as when Ford used Mondeo switchgear in an Aston Martin!
Paul Hunt

IMHO the MGB engine with a proper exhaust system has a great exhaust note. It is a beautiful thing, and with a performance exhaust or headers sounds way more powerful than it is. Many times I turn the radio off, especially at night with the top down on a quiet curving country road. Have I mentioned I can't wait for spring?

Ralph
Ralph

Interesting comments here!

From new owners seem to suffer less troubles than others, it's turning out to come from a maintenance
issue. It's difficult to trace back the past from our cars after nearly 50 years. This makes them more sensitive to problems. But fixes are available to cure the main part of issues. From the fuel efficiency point of view, and despite of the exhaust note, I hate its engine because it's dating back to 1944 and it 's a sort of a compromise between economy and industry. It's a basic reliable and easy to maintain unit but we have to consider these terms in the 50-60's meaning and context. It's a pity MG factory did not implant the 2.0 australian BMC version tested by 1963, that could have opened doors. Adding to this, a real uptodate 60's cylinder head! But sincerely, I like this car for its style, its associated image and a part of dream, sure.
MG Madness?
Regards.
Renou

This thread was discussed between 05/01/2009 and 11/01/2009

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