Polishing Crank Journals?

[jap-car]

I'm just starting on my first full engine rebuild. My crank journals need a polish and I'm told that "crocus cloth" or grade 2000 wet and dry is the thing to use. Can anyone tell me where can I buy these at less than £10/sheet + P&P ?!! :rolleyes:

Also, best place to buy plastigauge?

Cheers,

Robert

[eliot]

www.realsteel.co.uk/ sell plasiguage.

Wouldn't worry too much about polishing your crank.

[jap-car]

eliot said:

www.realsteel.co.uk/ sell plasiguage. Wouldn't worry too much about polishing your crank.

Thanks for the plastigauge link.

The journals definitely need a polish as they have some very light scoring (just about detectable with finger-nail). A bearings specialist has told me that they will be OK without grinding but a polish is a good idea.

[boosted ls1]

I polish journals with 800 grit wet and dry and a flat boot lace. I use wd40 as a lubricant. You could start with a 600 grit if you wanted. I've even finished some cranks with a 1000 grit but that's just me being pickey

Boosted.

[eliot]

Oops, Misread your question. Thought that you wanted to polish the actual crank.

[Nick_F]

You could radius - I'm sure that isn't really a verb - the oilway holes whilst you're at it.

Make sure you keep all the swarf out of the oilways, though.

[rw774]

You could work on the crank webs,make them a little less like a brick.
Taper the leading edge toward the rear of the web.
Polish all the marks out of the web, then get it balanced. Introduce a scaper plate and tailor it to within a 1.5mm max of the crank. This should give you a few extra horses. The idea is to aerodynamic the crank and remove all the oil mist. A crank can carry alot of oil mist, effectively slowing it down.

[jap-car]

boosted ls1 said:

I polish journals with 800 grit wet and dry and a flat boot lace. I use wd40 as a lubricant. You could start with a 600 grit if you wanted. I've even finished some cranks with a 1000 grit but that's just me being pickey Boosted.

Hi Boosted, can I just ask, does that grade of grit remove a significant amount of metal? Ie does it mean under-sized bearings?

Thanks, Robert.

>> Edited by jap-car on Monday 3rd October 20:16

[jap-car]

Nick_F said:

You could radius - I'm sure that isn't really a verb - the oilway holes whilst you're at it. Make sure you keep all the swarf out of the oilways, though.

Is that where the edges are chamfered? If so that's already been done on my crank.

rw774 said:

You could work on the crank webs,make them a little less like a brick. Taper the leading edge toward the rear of the web. Polish all the marks out of the web, then get it balanced. Introduce a scaper plate and tailor it to within a 1.5mm max of the crank. This should give you a few extra horses. The idea is to aerodynamic the crank and remove all the oil mist. A crank can carry alot of oil mist, effectively slowing it down.

I see what you're saying and it sounds good.......but this is my first full engine build and I wnat to keep things simple (well as simple as it gets with a Mitsi GTO). Thanks though


>> Edited by jap-car on Monday 3rd October 20:20

[dilbert]

jap-car said:

boosted ls1 said: I polish journals with 800 grit wet and dry and a flat boot lace. I use wd40 as a lubricant. You could start with a 600 grit if you wanted. I've even finished some cranks with a 1000 grit but that's just me being pickey Boosted. Hi Boosted, can I just ask, does that grade of grit remove a significant amount of metal? Ie does it mean under-sized bearings? Thanks, Robert. >> Edited by jap-car on Monday 3rd October 20:16

If you have the tools to measure for "out of round" to maybe a tenth of a thou (vernier mic), then polishing might do you some good.

Otherwise I'd leave well alone.

If the grooves are small enough that you need to remove less material than that, then it's unlikely to need polishing.

On the other hand, if the gooves are that deep, then you need to make sure that the job is still "round" afterwards.

[boosted ls1]

Jap car,

If the groves are tiny you can initially use a 400 grit. This is what crank people use and they usually don't go any finer. They leave it at that. Draw a penny across the journal and see if it 'picks up'. An 800 grit leaves it very smooth and I like that. If you want to call give me a bell.

As for knife edging, I've never done it. There are 2 schools of thought on this. Knife edge the forward edge or knife edge the trailing edge. A bullet is more aerodynamic flying backwards!

A scraper is a good idea if you want to do it.

Boosted.

[jap-car]

boosted ls1 said:

Jap car, If the groves are tiny you can initially use a 400 grit. This is what crank people use and they usually don't go any finer. They leave it at that. Draw a penny across the journal and see if it 'picks up'. An 800 grit leaves it very smooth and I like that. If you want to call give me a bell. As for knife edging, I've never done it. There are 2 schools of thought on this. Knife edge the forward edge or knife edge the trailing edge. A bullet is more aerodynamic flying backwards! A scraper is a good idea if you want to do it. Boosted.

Hi Boosted - I just looked at your site and you like like the perfect person to talk to! If you could spare a couple of minutes then I'll definitely give you a bell this week. Basically I've used a vernier caliper on the journales and they seem to be dead on the 60.00mm they should be but they have got scoring which I can just pick up with my nail. I was hoping to polish these up without removing a significant amount of metal.

Thanks again, Robert.