Forum for competition engine enthusiasts. RIP Guy Croft 09/11/2020 - This forum will continue both as a source of information and as a memorial to Guy.
Ok i have just started taking apart a spare engine i have for a rebuild as the engine in my car is knocking, this one was knocking as well so i thought i should rebuild this one and swap them.
This is what i found
This was the centre main bearing
And this was con-rod number one big end bearing
What would normally cause this??? bearing in mind it had very good oil pressure.
Odd bit is its has not marked the main juarnal at all but the rod juarnal is quite badly marked???
When the main and big end (one or more) has suffered damage, leaving aside dirt in the oilways on build, it is most often caused by chronic contamination of the oil by gasoline or just simply by oil starvation (eg low oil level, very high G cornering, pickup starved against sump base).
I will say from the outset that when you confronted by simultaneous main and big end bearing damage it is always better 'not to try and save money' but to just scrap the old crank and rods and start with good used or new.
In terms of what you do by way of overhaul here are some tips, none of which, owing to the peculair behaviour of metals after a major 'event' will guarantee that the motor will be as good as it was before..
You need to get the crank crack tested. That's the first thing. Now, I don't know what the crank is made of but if induction hardened (ie: pretty thick hard layer) it should be grindable, seek the expert advice of an FER engine reconditioner on that or get the OE manual out and see what it says (if you can get one) and it needs checking for straightness because it may be bent. Although you get the journals lined up again by grinding there is a risk of the thrust faces being out of true if the crank has got bent. A good grinder can dress these and supply oversize thrust washers. If the crank flange has gone out of true (and you can check the FW runout by putting the crank between centres and measuring with a dail gauge) it is often possible to correct the rotating imbalance it causes by re-balancing crank fw together. If the runout is a lot then you could be in trouble, the swashing load that the clutch imposes when the pedal is released can break the bolts just as easily as imbalance. I've not been able to find data on runout but on a good crank-fw combo I would not tolerate more than 0.001-0.002" runout at the outer radius of the friction face.
The rods need to be checked with a bore gauge, they may well have gone out of round. Crack test. They may be twisted too. These things need expert checks. The rod bolts may have been overstressed. The main bearing housings need checking for true, they may be out of round now as well. It goes on and on.
GC
