KevB220

Just had the engine rebuilt after it had a drink of water! The big ends were shot and the engine was rebuilt. The crank had some marks on the journels but the garage had it tested and repolished the journels. It was tested within tolerance and was advised it was OK to reuse. New bearings were installed and engine rebuilt. Everything was OK for the first 700 miles when it developed a knock. Taken back to the garage and restripped and bigend 4 had spun in the rod, flattened the shell and damaged the crank.
I was running in without going over 4 - 4500rpm except once when I changed down to overtake on a hill and the revs went to 5500rpm when the knock started 670miles after rebuild.

Any advice on why this has happened because it was implied the engine was overrevved for this to happen! I don't think this is the case.

The car is a UK99 classic. Thanks

WMS

iTrader: (2)

If an engine is built properly it is very unlikely that the revs you have used would cause damage, I have done 'last minute' builds on rally car engines that have gone virtually straight on onto the stage and had no problems. Although it's best to gradually build revs/boost up over a few hundred miles I think the problem is down to something else myself, could be oil pump, engine not cleaned properly etc etc.

KevB220

It had a new oil pump fitted.

Anyone else got any thoughts?

WMS

iTrader: (2)

Did the engine suffer big end failure? It's very very rare that a crank is ok if the big end does fail. To be honest it's almost impossible to say over the forum, it would need inspecting. Has the garage that done the work had previous Impreza engine experience?

KevB220

Plenty of experince on the engines. It now turns out that all 4 big ends have gone. May be faulty bearing material? Standard Subaru ones used.

WMS

iTrader: (2)

Very strange, is the garage footing the repair bill?

merlin24

iTrader: (1)

It could be a case of poor engineering hygiene - there are a lot of places the debris from the previous failure can be trapped - crankcase oil gallery's,modine,under the sump baffles,behind the oil restrictors in the heads etc etc.
It only takes a small amount of debris to jam the oil pressure relief valve open and results in very reduced oil pressure,quickly followed by big end failure.

Mick

KevB220

So debris could be the problem. Ok thanks.

WMS

iTrader: (2)

First thing to check is the oil pump pressure relief valve, could be jammed, and for all the bearings to be shot it must be major oil starvation caused by something. If the garage re-used the crank and just gave it a polish, it could be debris in an oil gallery on the crank itself?