I may have to take legal action about this one but i want your opinions if it's going to cause a problem.

 

Basicly i took my crank to the engine shop for some work and they scratched the main bearing journal on the crank now they were very honest and pointed it out to me but said it was cosmetic and not going to cause any problems.

 

My mechanic has said it's fooked and not to be used, he has asked other peoples opinions on the scratch and they say the same thing. They are also saying you took it to them in good condition all machined to size and got it back like that. Now this rebuild has just dragged on and i don't really care about that as i just want it back but if it is going to cause a problem then i need to get it sorted.

 

So what i'm asking is, would a scratch to the main bearing cause any problems or is it purely cosmetic like the engine shop recomends?

 

Thanks in advance.

A scratch if you can feel it with your nail is a problem.

I think you should trust your mechanic more :)

Do you have a picture of it ?

 

If the scratch has raised the surface at all then it's no good.

If it's just a scratch then it could break the oil film and then can't be much good for it either.

 

I'm sure it can be repaired by metal spraying and regrinding. Many places can do that sort of thing, but these people are generally accepted as being good. http://www.thurstonengineering.co.uk

yeah you can feel it with your nail.

 

good point Andy.

 

I'll get some pics of it.

if the bearing is scratched, then your messing with clearances and hence hydrodynamic lubrication, take the shaft and stick it up the moron who did it, and tell him to empty his piggy bank to pay. If you take something to a professional to be machined then you dont expect it back in a worse condition than it was in before.

Is it really worth the agro, buy a good crank on here second hand and tell the machine shop to foot the bill or you will report them to trading standards?

Well i have spent close to £2000 on the crank. (not just with them, went to another engine shop first)

 

I took it to the supposibly best engine shop in the area paid over the odds as i wanted a top job.

 

Apart from the scratch the knife edging they done looks like they attacked it with a angel grinder. Maybe that's how it is meant to look but to me looks like a lumber jack had a go.

 

Could i have a list of possible problems the scratch could cause so i know what i'm arguing.

is the bearing you are talking about actually integral to the shaft ??? it must be able to be removed surely??? ive not seen one of these cranks so dont know. Or is it just the end of the shaft thats scratched and that sits in a shell type bearing ???

it's the end of the shaft that is scratched rather than a actually bearing.

What size is the journel, if it is at the last undersize then its past a polish or grind and you need to be building it back up. If it say at 10thou under then maybe it will polish out or grind to the next size, get the bearing supplier to change the shells for the next size.

oh dear, right. have you had a good look at it under a magnifying glass, it is probable the edges will be raised even if it doesnt appear so. Any raised edge on the journal is not what you want. Like scrawni says it maybe possible to get rid of it but, you gotta be very careful to what you are taking away. I would presume that unless i'm corrected that journal and bearing are lubricated "hydrodynamically" if this is the case the you cant afford any raised edge at all. the oil wedge formed by rotation, will break down and you will get excessive wear, you will also most probably get turbulance which is also a no no. I would suggest that you will need to get rid, but you must make sure you know exactly what tolerances you have, because if you dont it will be in the bin time. I can right you a whole page on bearing problems materials etc.. if you like but it well boring.

What size is the journel, if it is at the last undersize then its past a polish or grind and you need to be building it back up. If it say at 10thou under then maybe it will polish out or grind to the next size, get the bearing supplier to change the shells for the next size.

 

the Bearings came from the states and i don't really want to have to get another set because the engine shop couldn't do their job properly.

It all depends which way the scratch goes.if its across the journal from web to web it will loose oil pressure but if it runs around the radius of the journal and its not jagged and doesnt reach the edge then its fine.

oh dear, right. have you had a good look at it under a magnifying glass, it is probable the edges will be raised even if it doesnt appear so. Any raised edge on the journal is not what you want. Like scrawni says it maybe possible to get rid of it but, you gotta be very careful to what you are taking away. I would presume that unless i'm corrected that journal and bearing are lubricated "hydrodynamically" if this is the case the you cant afford any raised edge at all. the oil wedge formed by rotation, will break down and you will get excessive wear, you will also most probably get turbulance which is also a no no. I would suggest that you will need to get rid, but you must make sure you know exactly what tolerances you have, because if you dont it will be in the bin time. I can right you a whole page on bearing problems materials etc.. if you like but it well boring.

 

It's getting complicated lol.

 

nope i will have a proper look myself when i get it off the mechanic, i've seen it but not really studied it and at a quick look it looks messy.

 

Would it make any differences that i will be running high boost on this crank and allot of bhp?

 

So basicly as the crank stands it's not acceptable, but.... if it's deep or raised it's really bad.

 

If it's only slight i might be able to get away with it.

 

So in other words for a highly recomended company to scratch this part of the crank is a no no for what it cost as it could cause a serious issue.

 

*take a deep Breathe* i better have a word with the engine shop.

 

What should i be happy with as a outcome to them buggering it up?

 

e.g. repair or machine a new crank to the same specification and leave it as that or should i push for more as in get compensation on the cost for the hassle, stress and timescale this has caused.

my personal opinion is, any machine shop worth its salt would never hand back a damaged component, sorry to say but they sound like butchers!! expecially what you said about the knife edge!!, is trhe crank still balanced??

 

listen dude you have paid top dollar for what was prommised a good job from a reputable machine shop, & i know the rebuild has been dragging on but its the main component in the engine & its the one thing that will f@ck up if it isnt 100%

 

take it to another machine shop see what they say!!

 

best of luck fella.

if you can get a pic up sometime, that would be helpful. but if the opinion is its unacceptable, then the machine shop is obligated to rectify there mistake regardless of the cost to themselves, if it turns out the mistake is difficult to put right, then they have no choice but to machine another.