big end shells.

[bl1300]

How much movement would you deem acceptable in a big end shell.

I have always presumed none whatsoever. The reason I ask is that I am changing the engine on a Mitsubishi L200 due to big end failure. I dropped the sump of to swap it as the new engine has come from a Pajero and they have different sumps. Whilst in there I decided to rock the bearings.

On the old engine number 4 had perceptable play of maybe 1mm overall deflection and was knocking badly. The new engine has maybe 1/2mm of overall deflection on 3 big end bearings. I was assurred by the seller that this engine was a well maintened, sweeting running low mileage unit.

[Kieran]

Play along the crank (ie journal to journal) is fine but any play within the bearings themselves is going to get worse quickly, as the big ends hammer the soft shell bearing into tinfoil I would have thought.

[jrevillug]

There might be just about perceptible movement in a healthy big-end, but not even close to 0.5mm. With oil in there it'll be hard to move about anyway, but the running clearances on BEs are tiny. The Imp workshop manual gives the running clearance as 0.025 - 0.067mm: micrometer measurements, not ruler or vernier measurements.

If it's been well maintained, what killed the big end? There's rarely a manufacturing fault that shows up after, say, 80,000 miles with BEs: they'll either be fine for years, or die soon after it's put into use. So I think it'll be neglect one way or another, and that all the BEs will be worn, even if not quite as badly as No 3.

Best thing to do is to whip the caps off the rods and look at the shells - the surface of the bearing material will tell you a HUGE amount about how well an engine's been built and maintained, and will normally show why it failed too.

Finally, the chances are that the crankshaft needs regrinding - even if it's not been worn undersize it'll probably be oval and scored.

[bl1300]

Thanks what i should probably have noted is that this play is sideways and along the crank. There is no perceptable movement perpendicular to the journals. Bearing one I can't move by hand all of the remaining 3 big ends have this journal to journal play. I can't say I'm happy about this engine as with the way it was described 104k on the clock serviced every six months for the whole of the cars life and only 2 owners the last thing I expected was to find play in the bearings. Unfortunatly the seller won't take it back as he says it runs sweetly. I was very reluctant to put the engine in the vehicle without seeking some other opinions on its opinions as it was certainlly not the easiest job ive ever done to remove it. The engine is the mitsubishi 4D56 2.5 diesel and ive heard a few stories about them killing big end bearings fast.

[jrevillug]

A little end-float on the rods is normal, yes*. If it's all nice and clean in there with no sludge in the sump then I'd bung it in.

Clean out the old sump and oil pickup meticulously before fitting to the new engine.

If you don't the metal shavings from the bearings in the old engine will kill the bearings in the new engine. Obviously new oil and fiter are essential - and I wouldn't fit anything other than a Mann+Hummel oil filter just in case there's something you missed.

*EDIT: there's very rarely a clearance quoted for this. However, every engine I'd had apart has had easily-preceptible play there and on most the con-rod itself acts as the thrust bearing. I wouldn't worry about it.