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MG MGB Technical - How much mileage from Reco Motor

Hi, I have just had my Mk1 MGB engine completely rebuilt/reconditioned (5 bearing crank).
The carbs, starter, alternator etc are as they were but the whole motor and internals
(bearings,pistons,crank, timing etc)are all new. It was taken out once before 20thou and that is what I have just had done again. Can I expect the same life as I would out of a new engine or ?? Obviously older parts that were put back on will wear out but what about the basic motor. The mechanic at first said 50thousand miles, then said 100 ??
Also, how many rebores can you do at 20thou??
Craig
Craig Williams

Craig-
Presuming that the only internal components that you reconditioned are the crankshaft and the connecting rods, part of the answer lies in how you break it in, part lies in the quality of the components used, part lies in just how well the machining and assembly was done, and part lies in how you drive. If the first three are all good and the last is "reasonable", you could get better than 100,000 miles out of it.

There are several diferent oversize pistons available. Barring a disaster like a fractureed piston ring, the next oversize should be +.040, with +.060 possible on the next rebore. Beyond that oversize, you're getting into custom piston territory.
Steve S.

You can expect between 50 and 150 thousand miles depending on how you treat it - lots of short journeys and low mileage per year with few oil changes will tend towards the lower life - lots of long journeys and high mileage per year with frequent oil changes will tend towards the higher figure.

Bores, pistons and crank bearings will last longer than the cam and followers - so after 50 thousand I would take out the followers and inspect for wear, replacing them AND the cam if the wear is abnormal.
Chris Betson

Chris - interesting that you mention lots of long journeys would give better mileage out of the engine. I would think that as long as the engine has time to warm up and evaporate HCs and water that it wouldn't make a difference. Long journeys would imply high speeds = high revs = more wear.

Of course your opinion is highly regarded by me and others on the board. I believe the best insurance is frequent oil changes.

Bud
Bud G

Cris is spot-on about longer journeys yielding better engine life. I think it takes much longer to evaporate the bad stuff than most people realize. Long trips don't necessarilly mean higher average RPM's, as there is usually less lower gear work involved.
George B.

I tend to agree with Chris and George B., but for a different reason than George's. He may be fully correct that it takes longer trips to fully evaporate the moisture and gas vapors which tend to collect in the oil and thin it. An old book on sports cars pointed out that, after significant city driving, it was not unusual to have to add a quart of oil after a couple of hours of highway driving due to burn off of trapped water vapor and gasoline vapors which had condensed out when cold and diluted the engine oil. My belief is, however, that the primary reason that engines driven faster and longer will give a longer service life is the rate of wear at different engine temperatures. Rate of wear is highest when the engine is cold. Rate of wear is lowest when the engine is hot (about 195 deg F was near ideal as I remember reading it). Thus, an engine that is driven short trips will have more colder running time than one which is used on longer trips. Les
Les Bengtson

Thanks guys for your comments.
Should I be doing anything special to run it in?
There are two schools of thought here apparently.
My mechanic said don't Push it hard (of course) but said no need to baby it either, just drive it reasonably carefully as you normally would.
He just put Helix oil in it too (I thought I heard somewhere you needed to use run in oil ??)
Craig Williams

Craig, don't let the engine labour under load - better to change down a gear - I would rev it up to 3000 rpm with the occasional burst to 4500. Take it on longer journeys but not at constant rpm.

Do the first 500 miles as quickly as possible and then change oil and filter.
Chris Betson

Craig,

I also had reconditioned my MGB's engine this summer. And the workshop also did not use special run in oil, seems those people do not tend to de-facto-voodoo. The first 250 miles i did not rev higher than 3000. Then I sometimes went up to 4000 or more for very short periods of time. And always take care that you don't drive at constant rpm over more than some minutes. This might be annoying for your followers but i alway kept 'switching' from 2500 to 3000 or 3500 or 4000 when driving on the 'Autobahn'. At least try to 'play' with the gas pedal every once in awhile, even if you do not really change rpms a lot, but it helps I believe. BTW if you feel a rpm-range the engine does not like do this take as a friendly hint to avoid using this range...

Good luck

Mark
(who did 1000 miles in 4 weeks and is now enjoying a well performing engine)
Mark

This thread was discussed between 02/11/2002 and 03/11/2002

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