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Does my crank need regrinding
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advinnie
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PostPosted: Wed Oct 29, 2014 12:11 pm    Post subject: Does my crank need regrinding Reply with quote

Hi all I have a crank where all conrod journals are good and so are the three main journals but the small main journal is showing a small bit of wear but is it enough to warrant a regrind? 
The dull rings in the photos measure 39.98 to 39.99mm but the shiny rings in the centre of this journal measure 39.92 to 39.94mm is this a problem? Here's the photos
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jsturtlebuggy
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PostPosted: Wed Oct 29, 2014 4:20 pm    Post subject: Reply with quote

Yes it would be wise to regrind the crank with the dimension being undersize.
Since you are not showing any of the other journals, did you do the fingernail test on the #2 main bearing journal?
What is the drilled hole in the bearing surface for? I never seen that in any crankshaft.
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bugguy076
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PostPosted: Wed Oct 29, 2014 6:40 pm    Post subject: Reply with quote

It will need to be ground. I have the same problem on a 69mm C/W crank. The problem is for what it would cost to resurface and ship the crank, a little more would buy a new one.
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modok
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PostPosted: Wed Oct 29, 2014 9:38 pm    Post subject: Reply with quote

The #4 bearing is not very important, so I'd have no problem turning a blind eye to .05mm wear, but he says it's even worse?? yikes.

It's a shame to grind all the mains if only the little helper bearing needs it.
My crank guy would do it for 40$ to just grind one!! but then you gotta find one odd bearing.
If you have to buy bearings anyway then maybe grind all the mains, and in either case.........please check runout on the main bearings AND gear and pulley areas. Could be the casue of the problem in the first place if it's BENT!

I do know what the holes are for. You'll laugh........it's so simple. They drill two or three of those around the journal, at any given position one will hold one hole worth of oil. Prevents rattle on startup!
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advinnie
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PostPosted: Thu Oct 30, 2014 1:32 am    Post subject: Reply with quote

Ok but it this way it will cost me £150 to get the crank regrinded but I also have a good 74mm counter weighted crank now with the 74mm crank I will have a 2054cc engine and with the 78.8mm crank I will have a 2188cc motor now would another 134cc really make that much of a difference in performance?
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fastfil
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PostPosted: Thu Oct 30, 2014 1:58 am    Post subject: Reply with quote

Clean it up with some 400 emery tape, then 600, 800+. Just enough to get rid of any high spots. Mount the crank up so it can spin, get a mate to spin it while you polish the journal. Maybe you could do it in the case half - running on some old bearings. If you're worried about it being undersize, just keep your fan belt 5% loser, because that's all it's holding.
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PostPosted: Thu Oct 30, 2014 6:14 am    Post subject: Reply with quote

If I had that in the shop here, I would polish the crank first and then measure. It really depends on how undersize it is. Some you can get away with and some have to be ground.
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advinnie
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PostPosted: Thu Oct 30, 2014 6:23 am    Post subject: Reply with quote

Right it's had a bloody good polish and clean up here's the mic readings the widest section is 40mm the thinnest section is 39.92mm
Is this a regrind ?
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Quokka42
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PostPosted: Thu Oct 30, 2014 6:33 am    Post subject: Reply with quote

It grew with a polish? You are measuring with a digital caliper, right? Assuming your measurements are accurate, are you saying it is thick at one end of the journal and thin at the other?
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advinnie
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PostPosted: Thu Oct 30, 2014 6:39 am    Post subject: Reply with quote

T honest area is the shiny ring in the middle of the journal and is 39.92mm the dull colour rings are 39.98 to 40mm and yes I an now using a calibrated digital mic
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modok
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PostPosted: Thu Oct 30, 2014 4:45 pm    Post subject: Reply with quote

advinnie wrote:
Right it's had a bloody good polish and clean up here's the mic readings the widest section is 40mm the thinnest section is 39.92mm
Is this a regrind ?


It "should" regrind it....... but if you asks what will happen if I run it??? It'll probably work ok.

Something is wrong with the economy if it is cheaper to make a crankshaft than regrind it.
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mark tucker
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PostPosted: Fri Oct 31, 2014 5:20 pm    Post subject: Reply with quote

yup there is a problem with the prices of reground cranks these days. but thats not the issue.(well it is but not this thread) if it all checks out good for the app it is intended for I would use coated bearings(well I use them on everything) but a slightly thicker coating on that bearing. but more importaint...why does that have a hole drilled in it and whoo doned it???
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raul arrese
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PostPosted: Fri Oct 31, 2014 5:23 pm    Post subject: Reply with quote

The drill hole is to hold oil just incase it needs it .. lol
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mark tucker
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PostPosted: Fri Oct 31, 2014 5:30 pm    Post subject: Reply with quote

oh I see, most people use a oil can.I just keep oil in the sump and let it use what it needs.almost a qt a year.
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Danwvw
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PostPosted: Fri Oct 31, 2014 6:04 pm    Post subject: Reply with quote

I have run much worse cranks but that is me! Sometimes I just took some 400 Emery Paper followed by 600 and then 2000 then 4000 to them just by hand. Never had one cause a problem doing it that way.
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