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MG MGB Technical - Another Timing Question

I've been through all the archives and the manuals to try and figure out what to do about the timing on my 73 B. While they have helped I'm at a loss on what to do next.

Near as I can tell the timing pulley has been installed improperly when the engine rebuild was done by the PO.

Cyl # 1 fires when rotor is at ~8 oclock position, instead of 2 oclock. Cyl # 4 fires at ~2 oclock.

I tried to conduct a static timing. When cyl #1 is at TDC the timing marks on the pulley are at ~6 oclock (facing the front of the car). For the pulley timing mark to line up close to the timing indicators, Cyl #3 is at about 20 deg BTDC. When Cycl #3 is at TDC the pulley timing marks appear ~20 deg ATDC. The car seems to run ok but seems to be running rich.

Before I start playing with carbs I wanted to make sure the timing was set up. The dwell is at 58 deg.

My question is can I simply rewire my distributor cables so that cyl #1 fires at 2 oclock and by redoing a static timing, paint a new timing mark on the pulley to indicate TDC for cycl #1 and use that for conducting dynamic timing? I don't want to go to the hassle of having to pull the timing pulley.

Thanks

Mike





Mike McKinnon

Mike,

First the pulley - yes you can paint a new mark - it soundslike you have an early pulley (marks at the bottom) with a later timing cover (pointers at the top) - use a probe and dial guage to find TDC the way to do it is to rotate the engine (always clockwise) until the No 1 piston is 1 thou before max lift and make a small mark on the pulley next to the TDC pointer. Rotate the engine until the piston is 1 thou after full lift and make another small mark . True TDC lies halfway between the two marks - use a hacksaw to cut a fine groove at this point and paint white.

Second the dizzy - the problem here is the way the drive has been installed - set the engine to TDC no 1, firing ( both rockers should have clearance) take out the dizzy and remove the dizzy clamp plate, undo the screw holding the dizzy mounting to the block and withdraw the mounting. Use a long 5/16 UNF bolt or stud to screw into the dizzy drive in the block and withdraw it, turning it clockwise as you do so. Reinstall it 180 degrees round so that the larger lobe of the drive is at the top - put it in with the slot just past hrizontal going clockwies and rotate it anticlockwise as you push it in. The slot should end up pointing upwards towards the engine number plate if you have it right.

Reinstall clamp plate and dizzy and now the rotor arm should be in the 1 o'clock position.
Chris Betson

Chris, I strongly suspect my distributor is 180 out, despite being told that's impossible. Unfortunately, I'm having a hard time visualizing what you're saying. Pulling the distributor is no problem. That's done. It's being 100% sure I'm putting it back in right that's got me stymied. It does only appear to go in one way.
Baxter

Baxter. The distributor has a "drive dog" secured by a cross pin on the bottom of the distributor shaft. This is a circular section of steel with another piece attached or machined at right angles to it. This right angle piece inserts into the "distributor drive", which has a groove machined into it to mate with the drive dog. Both of these parts are machined "off set". In other words, they are not on the centerline of the distributor shaft or distributor drive, but are off to one side. This means that, for the two pieces to mesh properly, both have to be offset to the same side when inserting the distributor. So, if the offset portion is installed towards the upper right hand side of the engine, it is installed "180 out". (Based on my rapidly failing memory that the correct orientation is with the offset oriented towards the lower right hand side of the engine. I always look at the book before installing the dizzy drive.) This works for the dizzy drive. HOWEVER, is is possible to assemble the distributor "innards" improperly so that, even with the correct orientation of the distributor drive shaft and distributor drive dog, the timing is 180 out. The points cam is attached to the distributor shaft with a screw. This is the one on top which is covered by the rotor. If you take a look at your workshop manual, it will describe how to take the dizzy apart. What it does not really tell you is that, when you assemble the distributor, you can re-assemble it correctly or 180 our. (The distributor drive dog has a series of curved "teeth" which mesh with a series of curved "teeth" on the camshaft. The drive dog can be incorrectly inserted in a number of different positions, normally referred to as "one tooth off" or "two teeth off". The distributor can only be re-assembled either correctly or "180 off". So, the basic cure for "180 out" is to remove the dizzy, remove the base plate, remove the top screw, remove the springs, lift and rotate the points cam 180 degrees, then reassemble.

Mike. In addition to the above, which may be of use to you, I tend to agree with Chris that you, most probably, have an earlier crankshaft pulley mated with an 18V timing chain cover. Your concern that the PO assembled the crankshaft pulley incorrectly is possible, but highly unlikely. Both the camshaft and the crankshaft have a "partially circular" groove machined into them. (Think of this as a "semi circle" not fully cut.) Into these grooves fits a "Woodruff Key". This is like taking a circle and cutting off most of it leaving a rounded bottom and a flat top end. These Woodruff keys are inserted into the camshaft and the crankshaft and "drive" the cam timing gear and crankshaft timing gear (through a chain connecting the two of them to allow the camshaft to turn at one half the crankshaft speed) and the crankshaft pulley. If the Woodruff keys were not there, the entire assembly would be held together, and kept from slipping, solely by the crankshaft pulley nut. It is possible such a system would work, once, but very unlikely. Thus, there are two possible alternatives. First, the one that Chris mentioned--you have an earlier model pulley and an 18V (correct for your year) timing chain cover. This equates, almost exactly, with what you describe. The second possibility is that they "crankshaft pulley", which is, actually, "a harmonic balancer" has "delaminated". The harmonic balancer is designed to contain or eliminate some of the vibration of the engine. It is composed of three parts--an inner ring (with groove to fit over the Woodruff key), an outer ring (with the groove for the fan belt) and a rubber ring which bonds the two together. If, as will happen over time, this rubber ring begins to fail, and the bond between the outer ring and inner ring becomes uncertain, the outer ring can rotate, in relation to the inner ring, and the timing mark becomes inaccurate because of this change in relationship.

What to do? First thing is to use a straight edge and an artist's brush to make a line across the face of the pulley. Then, start and stop the engine several times. If you see the line "break", you may have a seperation of the parts due to breakdown of the rubber bonding ring. If not, assume you have the incorrect harmonic balancer and replace it with a good one. Bob Schaulin, at gbmg@aol.com ,can supply an early 18V harmonic balancer at a fair price. To me, replacing with the correct part is easier than "jury rigging" the existing system. Doing the job correctly is not "a hassle" but is "good shop practice". Les
Les Bengtson

Whoa Les - no need to take the dizzy apart yet - let's make sure the drive shaft is installed correctly first!

Baxter - get the engine to TDC with No 1 firing - look at the engine with the dizzy off.

There is a clamp plate attached by two 1/4 inch bolts - undo them ( unless you already did so to take the dizzy off)

Now there is a "plate" held on by a countersunk slotted screw - undo the screw and tap the plate round to loosen it and pull it out - it has a long collar that slides into the block.

Now look down the hole - there is a round "plate" with a slot across it and a threaded hole in the centre. Insert a long 5/16 inch UNF bolt or stud and screw it into the hole.

Pull the drive shaft out - look at it and you will see the slot isn't actually in the centre - one side is bigger than the other - this side needs to be uppermost when the drive shaft is installed.

I have posted a picture of a correctly installed shaft on my website at www.octarine-services.fsnet.co.uk

Chris Betson

PS - should have said - look under the FAQ link ....

http://www.octarine-services.fsnet.co.uk/faq.htm
Chris Betson

Chris. I have had a chance to rebuild two engines over the last year and strip down a couple more. Far less, probably, than what you do on an annual basis. However, the one, universal, problem I have been having is the distributor drive hold down--that silly slotted screw is almost impossible to remove because it has become rusted in place over the years. When you eventually get it removed, the hold down plate, which has a somewhat oval shaped top grafted onto a piece of tube shaped metal extending down into the hole to hole the dizzy drive in place, is rusted at the top and, at the bottom, seems to be glued in place with old oil residue.

My solutions to these problems have been to make another tool, from an old 1/2" grade 8 machine bolt, to use as a screwdriver. The shaft of the bolt is about 3/4" long and it is milled to make a common screwdriver-like end, then polished to remove the sharp edges. This allows me to use a socket wrench or impact wrench to remove the screw after it has been soaked in ZEP-45 penetrant. At the same time, the penetrant is sprayed around the distributor drive retainer and, after the screw is removed, a brass drift is used to cause the retainer to rotate around the portion sitting inside the engine. By doing that and adding penetrating lubricant, you can remove the distributor drive hold down--eventually.

Hence, my most recent experience with these engines indicates that, especially when being taken apart for the first time or after many years of being asssembled, the successful removed of the distributor drive dog is going to be a very tedious process. Especially when it it done while bending over the fender of the car. It is difficult enough with the engine out of the car, special tools at hand and the engine located on a disassembly bench.

The engine I am currently disassembling was rebuilt a year ago. The hole into which the distributor drive dog fits, followed by the distributor drive dog hold down, was flap sanded to remove all rust and the hold down itself was throughly cleaned and polished. Anti-seize was used when assembling the hold down to the block and the screw through the hold down and into the block. Everything came apart with a twist of the fingers. So, in such a situation, I would consider removing the distributor, removing the hold down screw and the drive dog hold down/retainer, removing the drive dog, rotating the drive dog 180 degrees, re-installing the drive dog, re-installing the hold down/retainer, re-installing the hold down screw, re-installing the distributor and time the engine.

If, however, I had any problems getting the screw and hold down/retainer out, it is nice to know that five minutes of work with the points cam can achieve the same effect. Les
Les Bengtson

Well, after fooling with it all day, I think I've got the timing sorted out or at least in the ballpark. Except for one thing. After checking and rechecking, then checking again, #1 cylinder lead is going to about 10 o clock on the distributor? Is that OK?
Baxter

Baxter, If running ok it will not hurt anything. It's nice to have it at the specified location but not essential and no harm will be done if it is timed at some other location, but you should make a note in case you forget and try to use the standard 1 o'clock position. FWIW, Clifton
Clifton Gordon

Les - I never have any problems removing the drive retaining collar - I use an impact screwdriver with a blade that fits the screwhead ( very important!) and once that is out, rotating the collar (using a drift and hammer if it is tight) always pops it straight out.
Chris Betson

Chris. That is why you are a professional and I am not. Thanks for sharing that particular tip. I can see where it would make life much easier. I just tore down my daughter's engine. The one that had the oil hose leak and cause it to run out of oil as she was driving along. By using a little "anti-seize" on the screw and the hold down, they came our very easily. But, the sump was full of bearing metal and the rod journals are all showing evidence of scoring. I am planning on having the block hot tanked, the crankshaft turned, new bearings and thrust washers and the block honed. There was no damage to the cam and the lifters were in excellent shape. Not signs of any metal flakes above the pan area. If I am missing something, please let me know. Thanks, Les
Les Bengtson

Chris/Les and others, now that the screw is out and the drive withdrawn, have either of you noticed the "shape" of that thing. I miked the one out of a 1979 with 80k and it was beyond worn out. Popping for a new from Moss and comparing the measurements was enlightening. The old one was nearly 30 thou under in diameter with a swail worn in the center. The remaining drive gear teeth were sharp as a razor. I can only guess at the subsequent timing variations produced by this sloppy drive. Comments?
vem myers

To let you know how it came out... while I undoubtedly had some timing issues, and the plugs may have been on wrong, I had a combination of badly gunked up DCOE and the coil was wired in backwards. Now, it runs. Its running rich, but pretty well, all things considered. Now to start setting things properly.
baxter

Vem - yes but wear on the drive gear is only half the problem, the camshaft gear wears as well but is less noticeable because the pattern of wear is equal over the teeth whereas the wear on the drive gear occurs in the centre of the drive side of each tooth.

This only really causes a problem at idle when the drive gear chatters on the cam - above idle the resistance offered by the points smooths out and the drive settles down.

This is one of the reasons that electonic (magnetic or optical) ignition smoothes out the idle so much - the drive does not cause the chatter.
Chris Betson

Vem and Chris. I pulled a dizzy drive yesterday and another one today. While both show some polishing, I can detect no true wear. In other words, the polished area is in no way dished or gooved, nor am I able to measure any wear. (A somewhat difficult concept as the surface is curved, so this observation may not be totally accurate. If, however, there is wear it is less than .001".) Both of these are from later model RB cars, a 77 with a documented 100K on the part and an 80 with unknown miles. The wear that Vem notes I have not seen. But, I pulled several RB camshafts before I first saw one that has badly worn with one lobe almost circular rather then egg shaped. So, the conditions I found may not be typical of the breed. Comments? Les
Les Bengtson

Les - no, not typical. 9 out of 10 drives I see are serviceable. The wear shows up clearly when I sandblast the drive - normally this is a shallow dish about 1/4 inch long in the centre of the drive side of the teeth - probably less than 1/2 thou deep.

Cam lobes are often worn, usually one or two more than the others but 8 out of 10 are reclaimable. My problem is that I have to buy whole engines to get new core stock for regrinding - new cams on steel stock are expensive!

Anybody want cheap engine blocks??
Chris Betson

I have checked three distributor drives recently and as Les noted on his, mine show very little wear. They had a visable shiny area where they meshed with the cam but I could feel or detect any wear.

I wish I could say the same for lifters. The three enigines I disassembled all had some badly pitted lifters. I don't know the maintenance history of the engines. In the 68 GT the cam may have been original, it had the long lifters and about half of them were pitted and some cam lobes were worn over .025". I have owned the 74 since Jan 98. About 8 months ago I rebuilt the engine, it had a Crane cam in it so it had been replaced, two of the lobes were worn around .012" and three or four lifters were pitted. The engine from a parts car had recently been rebuilt? The cam looked to be almost new and had no identifying marks but the lift and duration were near stock MG cams. Two lobes had some damage, caused by some pitted lifters. The lifters were not all identical, two had holes drilled and the others did not so the lifters may not have been replaced when the cam was replaced. FWIW the PO had been using Amsoil (sp) synthetic in the 68 GT engine, the engine was very clean inside so perhaps the lifter and cam wear was present when he started using the synthetic oil.

I had Mike Brown build a head to go on the 74 after the engine rebuild. I installed it after around 1700 miles on the rebuild. I decided to check the lifters and it made me sick to find three of them pitted. The lifters were replaced at rebuild, I used a reground cam, all parts were coated with assembly lube or cam lube. I used Castrol 20-50 oil run the engine around 30 min. at 2200-2500 on startup. The oil pump was primed prior to startup. Valves adjusted after initial running and oil changed at around 100 miles.

It seems that number 1 and 4 exhaust lifters will usually be bad. All the lifters I used were in Moss of England packages, I don't recall if the label sain made in UK or a product of UK. Les, I noticed you said the lifters were good in your daughter's engine, where did you get the lifters and were they recently replaced? I sent Piper an email asking about lifters and they never responded, I guess because I am not using their cam.

The lifter issue has been discussed several times and it seems to be a major problem either because of poor lifter quality or a design flaw in the engine. I talked to an MG owner a few weeks ago and he has torn down several engines and noted lifter problems in them. Now before you say I have no lifter problems, you don't really know because everything will work ok with pitted lifters but they will gradually eat the cam lobes and not make any unusual noise.

Chris, I think I remember you indicated you use Piper cams, do you also use their lifters or is there just one source for lifters?

Sorry about the length of response, Regards, Clifton
Clifton Gordon

Clifton - lifter wear is very typical of the breed, 9 out of 10 lifters I take out of engines are pitted or unevenly worn. But then they are all engines that are taken in exchange for reconditioned units and you don't pay good money to change a good engine - do you?

Yes I use Piper cams but I buy lifters in bulk from XRN - County brand.

Proper bedding in of the lifters and cam will help ensure long life but these are highly stressed items.

I surmise ( but can't be sure) that engines used for short town journeys will exhibits more pits than engines used on long high speed journeys - simply because there is more stress and worse oiling at or near idle speed so sitting at lights and in traffic promotes lifter wear.
Chris Betson

Chris, Thanks for your response. I do very few short runs, I'm retired and use the MG's for pleasurre only. I live in a small city and when I take the car out I usually avoid most of the traffic lights. I guess what disturbed me most was the new rebuild having bad lifters after less than 2k miles. I would have never known if I had not changed to the modified head and decided to inspect them. Perhaps it would have a long time and never given a problem. Thanks for the lifter source lnformation.

Regards, Clifton
Clifton Gordon

This thread was discussed between 14/10/2002 and 17/10/2002

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