BAM Rebuild - Bearings...

[aragorn]

Ok some background, by missus' boss snapped his timing belt on the M6 last month, i diagnosed it and told him to take it somewhere to get sorted. The garage he went to came back with a quote of 4 grand to fix it, so i told him to bring me the engine and i'd sort it for him for sensible money.

When the motor arrived there was heavy damage to all four pistons, so i picked up a spare set of BAM pistons/rods and ordered all the parts to get it sorted.

Sent the head off to have it repaired, and it arrived back on wednesday, so i've started on the motor today.

Removed the olde pistons and honed up the bores, but i've discovered that all four big end bearings are marked/worn.
I thaught that was pretty unusual, so i pulled number four main bearing cap to inspect the bearing, and sure enough its marked as well.

I took some photos:

Any ideas whats going on here?

The motor is sludge free.

 

[beachbuggy]

Mmm.

That isn't damage caused soley by the cambelt breaking it's been there a little while and taken a bit of time to happen. Possibly from manufacture, bad bearings or wrongly torques. Could be an oil issue some where along the line.

Either way, bearings can be replaced,I would be more concerned over the condition of the crank. Get it checked and measured and if necessary reground with oversize bearings. But it might be nothing always better safe than sorry.

 

[aragorn]

Yeh thats what i'm thinking. Its not from the timing belt thats for sure.

I've asked the guy if its ever had sludge issues or similar, and he says its not.

Will get the crankshaft out tomorrow and measure up. Hopefully i'll get away with a polish and a new set of stock bearings, as i already have them here.

 

[s3dave]

looks like a bent crank, that could do this

 

[aragorn]

Hmm that doesnt sound great, i've never heard of a crank bending with these engines. When i took my 200k AEB crank to the shop to get it checked over the guy said the crank is likely to be fine as they're pretty hardy, and sure enough it was.

 

[Welly]

Hmm that doesnt sound great, i've never heard of a crank bending with these engines. When i took my 200k AEB crank to the shop to get it checked over the guy said the crank is likely to be fine as they're pretty hardy, and sure enough it was.

Yeah, the cranks are pretty sturdy - I'd also be surprised if it was that... How many miles on the lump?

 

[aragorn]

Its only done 80k. Engine as a whole looks in really good nick tbh. Its a 2004 motor, no sludge, nice golden insides etc.

 

[Welly]

Its only done 80k. Engine as a whole looks in really good nick tbh. Its a 2004 motor, no sludge, nice golden insides etc.

How weird.... There is no way that is related to the cambelt lets be honest, so that makes that a very unexpected thing to find in an otherwise healthy engine.

 

[aragorn]

Exactly. I even asked the guy if it had ever been run low on oil or suffered any sort of oil related mishap in the past which might explain it and he said no.

Will pull the crank out of the block this evening, and get it off for a measure and if its good i'll get it polished up, if bad then regrind and oversize bearings.

 

[Welly]

Exactly. I even asked the guy if it had ever been run low on oil or suffered any sort of oil related mishap in the past which might explain it and he said no.

Will pull the crank out of the block this evening, and get it off for a measure and if its good i'll get it polished up, if bad then regrind and oversize bearings.

Agreed, no point in chasing the why - might as well resolve any problems and carry on. Put it down to one of those things... lol.

 

[aragorn]

Bit of a update for this.

Got the crank back on monday and set about installing it last night. Crank went in nicely, and i fitted the main bearing caps temporarily using the old bolts while i await the new ones arriving, and in the mean time set about fitting the pistons.

Got the first piston in, and set about attaching it to the crank, when i thaught hmm, doesnt feel right. Once tightened to 30nm the crank was locked solid. Puzzledness set in, plastiguage said the clearance was normal, but the bearings were all scraped and marked from the fitting and removal.

Realisation dawned when i compared the new bearings (which came pre-installed in the used rod/piston set i baught from backdraft motorsport) with the ones that came out, and discovered the new bearings were thicker. Closer inspection finds "U0.25" stamped into the rear of the new bearings, instead of the expected "STD".

Cue MEGA RAGE!