ENGINE REBUILDERS PTY LTD
7 BARRETT STREET, FLEMINGTON VIC 3031,
TEL: (03) 9372 3111, FAX: (03) 9372 3122
ACN: 006 798 492 ABN: 74 006 798 492
TECHNICAL NEWSLETTER OCTOBER 2007
PRECAUTIONS AFTER A COMBUSTION CHAMBER BLOW UP.
We have just examined a Subaru H6 engine after a piston disintegrated into hundreds of pieces following an internal problem. One of the oil ring rails was found jammed between a valve and valve seat, and piston fragments were throughout the ports of the head. Needless to say, the sump was also quite a mess with evidence of some of the smaller pieces having circulated through the oil pump and into the crankshaft bearings. We know that some of these small particles will also be found inside the oil galleries within the cylinder head.
We will remove the oil gallery plugs from the heads and from the crank cases to ensure that the engine goes back to the client totally clear of the problem.
WHAT ABOUT THE ACCESSORY ITEMS THAT WILL BE CONTAMINATED?
The following applies to all, but in particular to modern, engines:
The motor mechanic must be alerted to thoroughly clean out both the intake and the exhaust manifolds. Should the engine be turbo’d then the turbo must also be cleaned. Should an intercooler be fitted, this must be cleaned together with all plumbing.
Where the engine has an oil cooler, unless the mechanic can absolutely guarantee that it can be cleaned, then it must be replaced. Likewise all oil lines external to the engine have to be cleaned out.
Where the intake manifolding design has large runners be aware that a cup full of oil could be laying in the intake ready to go straight on top of the new pistons at the first crank over of the new engine. This could bend a con rod. The oil will have come from the crankcase pressure up into the intake system past the broken piston and intake valves. We have seen this with the Audi APK DOHC engine design.
With Subaru, blow the exhaust manifolds out as we have seen debris from a blow-up pulled back into the combustion chambers at start up. We have seen heads removed only to discover loose carbon from the exhaust sitting on exhaust seats stopping the new engine from running straight after a repair.
How clean is clean?
Consider that a hair from your head will measure four times thicker than the oil clearance in most modern petrol crankshaft bearings, you can’t be clean enough.
Attention to detail please; particularly if you are working on one of our engines.
H James.