Main bearings

[minor65]

One of our minors developed a bad rumble /knock when over around 2000 rpm. Immediately we presumed big ends. Although no loss of power, no smoke, oil pressure good, oil and water good. So we pulled of the sump and removed big ends. All excellent and not too old. Removed the centre main cap to find this. Brass showing on it. Is it knackered ??? Also does the crankshaft need removed to remove numbers 1 and 2 main caps??[frame][/frame]

[bmcecosse]

It's well knackered - down to the phosphor bronze. - what does the crank look like ? And yes - engine out job. Someone has fitted new big end shells in the past I guess - they're easy to do! I would fit a new oil pump too - and check the plate and spring are present in the filter can.

[minor65]

Aye thought that. Crank is good and yes oil filter is all good too.

[ACDodd]

No good just looking at journals they need to be measured accurately. I would very much doubt your main journals are still in spec with shells in that condition. Haul it out and have a measure up and decide from there what needs to be done. Let measurements guide you to success.

Ac

[oliver90owner]

It is an simple job to replace that centre main. Likely been done before as a 'quick fix'. Almost certainly needs the crank regrinding and undersize bearings fitted for a proper repair. It may even require line boring.

RAB

[bmcecosse]

Absolutely NO point renewing just the 'centre main' - indeed the front main can also be done with a bit of dismantling - but no hope for the rear main - which when worn allows oil to flood the rear labyrinth and drip out the bellhousing/soak the clutch. An exchange recon crank from the likes of Bull Motif is probably easiest way to go - AND a new oil pump... may as well do the timing chain and bottom sprocket when in there any way.

[minor65]

Well, due to time restrictions i will replace the centre main bearings in the meantime. But it won't be used for a while, so it looks like the winter project is sorted. I have all the new parts anyway for a spare engine, so we'll just use them.

[bmcecosse]

That will just be a waste of a set of bearing shells - the crank will be 'unbalanced' dangling on the new centre shells. May as well do nothing and save the new shells for later. Or build up and fit that spare engine.

[oliver90owner]

As I said, a quick fix, but not when completely gone like yours. The usual trick was a new centre bearing and piston rings on a poorly engine, the sell it on quick. Piston ring grooves out of spec, stepped top ring to avoid the wear ridge in the bores, but who cared, it would last out the warranty, if there was one worth having.

First 'trick' I came across was the dealer replacing seals in a leaking macpherson strut. Lasted about two weeks before it knocked the top out of the strut. They then did/had to do the proper thing and replaced the strut as I had a written 3 month warranty. Come to think about it, that was first of only two second hand vehicles I have ever bought from a dealer. They knew too many tricks.

RAB