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MG MGA - Main Bearing Condition

What would you do if you saw this around 600 miles? Brand new crankshaft and bearings before the 600 miles...

I think I know the answer...



J DeRienzo

Doesnt look healthy....Who rebuilt the engine, and did they plastigauge the bearings? Glenn
Glenn Hedrich

Does the oil hole in the bearing half still fitted line up with the oil hole drilled in the block?
it looks a bit strange.

Mick
M F Anderson

That big end bearing to the left of the main doesn't look too clever. What was the oil pressure like and are the crankshaft journals damaged to a similar degree?
Lindsay Sampford

What would I do? Before or after crying!

The inside of the engine block looks to be dry? and rusty? Is that an illusion? Looks like it's been running without any oil? If so it's done well to reach 600 miles!
Neil McGurk

More information is required.
Was the engine running before the new crankshaft was fitted?
Any chance that the conrod bearing caps were ground at their mating surfaces, to compensate for worn bearings, and then not bored circular?
Was the engine turned by hand after each assembly procedure?
Were the main bearings line bored?
As asked before, what was the oil pressure?


Mick
M F Anderson

When I look at the image I find it difficult to determine what is oil? white metal? or indeed base metal? So I would find it difficult to make a judgement on this image.
Just regarding surfaces note the main has shiney one side and dull the otherside of the oil way. Are we to assume one side is down to base metal and no white metal remaining? I rather suspect it is oil film as refering to the camshaft lobes they display the same colouring!

Based upon that why has the engine been stripped apart? is there a fault?
Robert (Bob) Midget Turbo

I don't know if the bearings were plastiguaged. The lower end was built by someone who had many years building MG motors.

All the oil passages line up, but the holes in the bearings are a bit bigger than those in the journal. I don't think they are any bigger than what they were whem installed.

The oil pressure was really high when the motor ran. Especially at idle. The needle was generally straight up (can't remember of that was 50ish or 80ish PSI) while running and only dropped 20-30 PSI at idle. The crankshaft journals appear to match their bearing wear.

The reason it looks dry on the inside is because it is. I had the block cleaned from all the impurities resulting from removing a broken head stud. These parts ran in the motor previously.

I am ignorant to turning the motor by hand after each assembly procedure. Does this mean installing each bearing and rotating the crank prior to the next bearing? If so I don't know. Nothing in the motor has been bored to include any conrod or main journals.

The coloring on the camshaft is an illusion. The focus was only in the mide main bearing and the fact that the front side of the bearing is gold colored and the rear section is closer to what a new bearing looks like (a little shinier). There wasn't anything wrong with the motor prior to opening it up (sheared head stud). It sounds like there is a term "white metal.". If the white metal appears to be gone and gold metal is left, is the bearing done?

Thanks for the help!
J DeRienzo

J, was the engine completely stripped to do the head stud? Did it go back together with the original bearings or new? Give us an order of events please.
Lindsay Sampford

At 65K miles the original factory build had a spun #3 conrod bearing. With that failure, the motor was completely stripped, a new crankshaft was procured, new main and conrod bearings installed plus a new #3 conrod.

That build went to ~600 miles where I went to retorque the head studs. I was on the #11 head stud (literally about to be done) and the #11 stud sheared at the block.

Efforts to remove the broken head stud while the motor was still in the car went unsuccessfully. I pulled the motor and completely stripped it to take it to someone who removed the broken stud without damage to the threads! I thought I was going to have to helicoil the block, but didn't have to.

Because of metal shavings, block being out of the car, et cetera I decided to have the block cleaned for good posterity.

I didn't take a look at the condition of the bearings until reassembly (mistake).

Having done a few internet searches, I honestly can't in good conciounce put this thing back together. The discoloration is obviously from a heating of the metal, the crank shaft has some imperfections that are noticibly to the both sight and touch. Both the middle and rear bearings are showing one half of the bearing being this gold (heat induced, I believe) color on the front side of the oil grove and the rear half of the bearing still the original color of the bearing or "white" as has been described.

I think my question now is going to move to what might have caused this to happen? The oil pressure indicated a higher than normal (per the service manual)? The oil pump was new and obviously was pumping oil and it appears that one part of the bearing was getting oil but the other part wasn't. Anyone heard or seen an issue that could cause one side of the bearing to get oil and not the other? Could the bearings just have been installed improperly? What is the exact method of installing the bearings? From what I could see you put all the bottom bearings in the bearing races with the tabs seated in the appropriate places, place the crankshaft on the bearings, place the matching half of the bearing on top of the bearings, then bolt down. Obviously all of this happens with copious amoutns of assembly oil.

Is there something I'm missing???

I'm starting to run out of clues!
J DeRienzo

P.S.!!! Just read the dieseling post and need to add that this motor has ALWAYS dieseled, even when my grandmother drove it as a daily driver when brand new. We had significant enough problem with the dieseling that we were buying 110 octane racing fuel and adding four gallons of racing fuel to the 8 gallons of 93 octane pump gas to prevent the problem. Could this lead to imperfections or issues that could have caused the bearing wear?
J DeRienzo

Did you, or whoever did the rebuild, clean out all the oilways? To do this properly, the little brass blanking plugs need to be removed from the oil galleries and replaced with new ones when the cleaning is complete. I wonder if the new crankshaft had the oilways blocked with packing grease or something. It must be some kind of oil starvation, so I think I would check all the oilways very carefully first if it were mine. Hope it goes well for you,
Lindsay.
Lindsay Sampford

It's unknown to us whether or not the oilways were cleaned. I'm assuming that the oil ways were cleaned when the block was cleaned, but since I never purchased oil plugs, I don't see anyway the guys would have removed and replaced them.

Is a machine shop required to remove and replace the plugs?

Should I have the block recleaned with these plugs out then reinstalled?
J DeRienzo

If you have stripped the engine down yourself, then the best person to clean out the oilways is you, then you will know they have been done thoroughly. I think there is some stuff about this on Barney's site. The blanking plugs are a standard item and should be available from your machine shop. As for "dieseling", it will certainly not do your engine any favours. You shouldn't have to be messing around mixing fuel, just make sure you have the correct spark plugs fitted. NGK recommend B6ES (not BP6ES) http://www.ngkpartfinder.co.uk/car_commercial_search.php?type=SPARK%2520PLUGS&manufact=MG&model=MGA&engine=all fit them and you should have no problems with dieseling or running-on as we call it.
Lindsay.
Lindsay Sampford

I found the gallery plugs it would be good to remove to properly clean the oil ways http://mgaguru.com/mgtech/engine/of101a.htm they are marked 1, 11, 9 and 8 on Barney's photos. If you can't or don't want to remove the gallery plugs, at least flush them through thoroughy with gasolene. There are quite a few other oilway drillings that will all require your attention. Access should be obtained from inside and outside of the fully stripped block, and watch out, as gas squirted in through one hole can exit just about anywhere! Carry on until you are happy that all those oil passages are scrupulously clean, don't forget the crankshaft oilways.
Lindsay Sampford

I would not owrry about removing the oil plugs. This can be a very expensive and risky process. You better have a good machine shop (which is had to find now a dys) you trust. Just remove the filter and base flush the oil passageways with some oil alot and the clean with some brake cleaner. Reinstall the crank and bearings. Hand tighten the main bolts then torque the center cap and rotate the crank to see if there is any drag. Even if there is no drag I would take the cap back off and check to see if there is any wear makrs or shinny spot from the rotation. If you see shinny spots you either have a funny shaped crank journal or block journal maybe bad. Keep in mind that this is just the simple and quick fix to the problem, But should get you going and not have you worring about another 600 mile tear down.
gl mr

J
What does the matching bearing in the cap look like
Did you have trouble getting oil pressure up 600 ago when you first started the engine
To me the no.2 bigend bearing there looks as though it has been starved of oil or a load of rubish has been through it---hard to tell from the pic.
There is a problem with that centre main though- it looks like a tight clearance problem-- maybee some rubish between the back of the bearing and the block---Really there shouldn't be any wear at all as all the load is the other way into the bearing in the cap.
Nice big camshaft you have there--- Willy

Bit late to ask now but was the centre cap fitted around the right way- you might be able to tell from matching up wear marks--maybee
WilliamRevit

Oil film clearance is very small, on the order of 0.001" on the radius. Something as small as a human hair trapped behind the bearing shell can cause that sort of wear pattern. If the "junk" behind the shell was much larger it would cause the crankshaft to seize up and not turn during assembly.

Considering this was a new crankshaft and new bearings, I'd be inclined to put the blame on the bloke who did the assembly. But first you must determine that there is nothing wrong with the bearing journal on the crankshaft.

Gut feeling is that you will be able to polish the crankshaft, install new bearings and it will be fine. Just keep everything clean during assembly, and yes do check that it turns freely after tightening each individual bearing cap.
Barney Gaylord

Use PLASTIGAUGE on assembly. Otherwise what Barney said. Looks like bearing was in crooked/ junk under it.
R J Brown

To me it looks like the kind of damage you would see if the engine was assembled and started without enough lubrication. Make sure you use a good assembly lub and prime the oil pump before starting the engine. I think Barney's site shows you how to prime the oil system prior to starting the engine.

Cheers,
Ian
IJR Renshaw

looks nasty..seems odd that you had very good oil pressure with bearings eaten up..large main clearances always cause a substantial pressure drop when hot.Did you fit a 'spin on' oil filter conversion ?? if so take it off and check the size of the hole where the external pipe enters..often it is under 5/16"..this should be opened up to 7/16" and the corners radiused for better flow.. Barneys suggestion that there could be crud under the bearing shell is also likely ..it dont take much ..
TJ Trevithick

This thread was discussed between 29/12/2009 and 03/01/2010

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