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Author Topic: oops.  (Read 10540 times)

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Offline racer142

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oops.
« on: July 27, 2013, 06:05:46 AM »
Well I went riding today. made about three sorry practices before the bike gave up. Opened it up and found this

Crank is locked up but the cylinder and had are fine. I found no damage other than the piston and crank. My question is how long should a crank last? I would guess this one hat 100 hours on it pretty easily. Curious if that sounds about average or not. About to buy a new crank and need to know if I should stick with hot rods or go wiesco or oem. Any thoughts?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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oops.
« Reply #1 on: July 27, 2013, 07:59:33 AM »
After watching swappers vid of his sons 85cc hot rods crank big end seize after sub 5 hours riding I think and hearing all the dreadful things about wiseco cranks that I have, I would stick with OEM. And 100 hours on a 125 big end sounds pretty close to right. Depending on how much you flog it and how lubed it gets.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline evo550

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oops.
« Reply #2 on: July 27, 2013, 11:09:11 AM »
Are you sure the crank is not just jammed with a piece of the piston?
How many hrs on the piston ? A broken skirt is usually caused by to much clearance between piston and cylinder.
Looks like a 125 piston, so 100hrs on a 125 crank is getting long in the tooth.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline cnrcpla

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oops.
« Reply #3 on: July 27, 2013, 01:30:34 PM »
Quote
Are you sure the crank is not just jammed with a piece of the piston?
x2, check this out. If there is shrapnel in the bottom end, the crank has very little clearance between the cases and itself, so even a very small piece can be jamming it up. Also could be pieces in the main bearings.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline racer142

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oops.
« Reply #4 on: July 27, 2013, 02:18:16 PM »
Its a 250 and yall will think I'm crazy but the piston had over 100 as well. The crank is likely just jammed but while I'm there to clean it out I might as well replace it.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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oops.
« Reply #5 on: July 27, 2013, 02:30:54 PM »
Examine your cases very carefully in the crankcase area as well. That piece of piston skirt may have become trapped between the con rod big end and the cases.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline motoman356

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oops.
« Reply #6 on: July 27, 2013, 07:51:32 PM »
even if its just jammed with the metal bits youll want to still replace everything and split the cases. your gonna want to get all those metal bits outta there so they dont do more damage. ive ran oem and hot rod cranks and i didnt have any issues with aftermarket however most engine builders will say stick with oem.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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oops.
« Reply #7 on: July 27, 2013, 09:31:04 PM »
x2 on what everyone else said. And I made the 125 assumption by teh size of the piston relative to your hands. So i'm now thinking you have mammoth hands. Rule of thumb for replacing pistons is every second ring(s) change. Piston and rings, rings, piston and rings, rings, piston and rings, rings etc.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline racer142

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oops.
« Reply #8 on: July 27, 2013, 10:43:47 PM »
Yeah I was never going to keep that crank I don't know how that got brought up. This is the second rebuilds I've done on this bike. Last time was March last year. I was just curious if that was average for a crank. Im a mid pack to front of the pack b rider at the National level so I'm no slouch on the bike it has been ridden hard nearly weekend for a year and a half. Id say 25 races which is Saturday practice Sunday race with 20 plus practices on top of that. I'm probably going to stick with the hot rods crank since it worked before. Just curious of yalls thoughts. Also how tight should the clearance between the piston and cylinder? Mine seems smooth but I can fit a .007" feller gauge and don't have a service Manual for it.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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oops.
« Reply #9 on: July 27, 2013, 10:52:30 PM »
.007? You mean .07? A feeler gauge that is made to 7/1000ths of a mm is rather small... I've always gone by no more than .04 mm clearance.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline cnrcpla

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oops.
« Reply #10 on: July 27, 2013, 11:04:00 PM »
He means .007 inch. Welcome to the American system  :P
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline racer142

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oops.
« Reply #11 on: July 27, 2013, 11:10:29 PM »
Yes it's in inches that's the " behind the number. But it was .178 mm I believe
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Stusmoke

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oops.
« Reply #12 on: July 28, 2013, 03:28:23 AM »
Ah I should have figured that. .178mm bore clearance is masses too much.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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oops.
« Reply #13 on: July 28, 2013, 04:20:02 AM »
How many motors have you built Stu?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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If you don't fall off you are not going hard enough

Offline Stusmoke

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oops.
« Reply #14 on: July 28, 2013, 04:40:14 AM »
Is my information wrong?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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