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MG MGB Technical - 125K on engine

I bought my 74B in 1983 with about 43K miles on it. I drive it well and never over-rev the engine. Oil gets changed twice per year and it is running about as well as it ever has. I have thought seriously about having the head done to econotune specs. I mentioned this at our club meeting and one member said I must rebuild the engine 1st to avoid damaging it using a stronger head. What do you guys think? Necessary? What gets redone on the engine? Does this include crank and cam bushings? Any comments are most appreciated. Thanks
Bob Ekstrand

I don't think you MUST rebuild the engine. What damage is likely to be done? I would think the worst that could happen would be some oil burning.

It is true that putting a good cylinder head on a worn engine can show up weaknesses. On my previous MGB I fitted a Burgess Fast Road head to a 100K + motor. It ran well but gradually began to burn oil. Peter told me that the extra cylinder pressures caused by the head were causing the worn rings to let more oil blow past. I just used the car because it was running so well, and in fact sold it without ever touching the engine, having put at least 20K more on to it. If I were you I would do the job and see what happens. You will probably go for years before you feel the need to rebuild. I'm sure you won't wreck the engine.
Mike Howlett

Bob, if oil pressure is still high and the engine is not burning much it will probably give you another 100K miles. The valve gear has a shorter life and is probably already a little tired. You would get useful power from a simple head refurbishment,more still from a ported head although you won't get the full benefit unless you improve the breathing. Neither level will have much effect on the life of the engine. I would go for the former but include timing chain, tensioner,valve springs as a matter of course and be prepared to change cam followers, pushrods and some rockers.
HTH
Roger
Roger

Thank You, Mike and Roger for your response. I really appreciate it. At about 89K miles it needed a clutch so I had it done and ADDED an O/D box to it and at the time the guy recored the radiator and replaced the timing chain. From what you guys said I feel confident that the econo tune head would still be in order. Thanks again, Bob
Bob Ekstrand

Good move with the overdrive - you are due an alternator and starter motor (just to be cheer you up)
Good wishes.
Roger
Roger

Roger, I know what you mean about the alternator. Since I've had it I have put in about 3-4 alternators. Some were rebuilts from Moss or B V and one was a new one. They do not seem to last long. However, the last one I did I just took the old one to Kragen Auto parts and got a rebuilt with lifetime warrantee. I have had it 5+ years and it still works great! I did a starter the same way but do have a bit of a problem with it. Occasionally I hear a click but get no turnover so no start! I keep a stick in the car, open the hood, and tap it a couple times and she starts right up! I'm glad its easy to do. Take care, Bob
Bob Ekstrand

Yes - been there and got the scars. I am sure the answer is to use the equipment as often as possible.
Roger
Roger

Bob, if it's running that good, I understand your conclusion to leave it alone. A complete engine rebuild at that mileage (excluding the head) is likely to reveal enough cylinder wall wear to warrant knurling the pistons or boring the cylinders and totally new pistons. The crankshaft is likely to require polishing only at this point and replacement of all bearings. Camshaft and tappets are usually worn by that point. Being a kid that grew up with very little money and a fascination with cars (mostly flathead Ford and Merc V8s), we survived doing some things that most mechanics would never do. If you opt to do the head only, I would suggest at least dropping the oil pan and inspecting the connecting rod bearings and main bearings. Worn piston rings and camshafts aren't likely to blow your engine up, but worn connecting rod bearings will. It's possible to replace bearings from underneath and without machining the crankshaft, but only if you can determine that the crank journals are not significantly worn and if done carefully. Replacing bearings this way onto worn or damaged journals will do more harm than leaving the old ones in place. There is no truly accurate diagnostic tool for determining bearing condition other than a visual inspection. Oil pressure at idle will reveal some information. You've driven it long enough to know if your idle oil pressure has decreased over time.
Rick Penland

This thread was discussed between 08/06/2009 and 12/06/2009

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