how and what to check on a crank?

Hey guys.  putting a new head on my bike.

 

also have a new 13.5 JE piston I was going to install.

 

problem is ive got nearly 400 hours on my OEM crank I was told that not only are rings harder on a old crank, but a high comp piston is basically asking for trouble on such an old crank.

 

while im in the engine and got the cylinder off to put new rings on at a minimum.  how can I check the crank for wear?  just left to right movement or what?  im not interested in pulling the engine, splitting the cases, and doing a bottom end rebuild.... ill take my chances.

 

thanks

Edited by coryf89

400hrs on a crank, you're gonna install a 13.5 piston, and you're gonna take chances? I would bet against this working out...

ok, I see in my manuals all you do is just measure the side to side play on the big end of the rod.... anything more than .6mm and shes worn out.  can this be done in the bike?  the 2 manuals ive got both show it being done with the crank out of the bike.


400hrs on a crank, you're gonna install a 13.5 piston, and you're gonna take chances? I would bet against this working out...

not going to put the piston in anymore. just new rings (well see when I pop cylinder off)  dont know what ill end up doing with the 13.5 piston now.

 

my current piston is a 12.1 with 140 hours on it according to my maintenance logs.

Edited by coryf89

Take the crank out, measure it, then put in a new crank. That's what I would do.

yeah I figured you were gonna say that...

 

why cant it be measured in the bike?  if im taking it out theres no point in measuring it because id throw a new one in anyways. but im not about to pop the engine out and tear open the bottom end.

 

not gonna lie, ill probably keep running it.  not sure if im just a cheap ass, or a risk taker.  well see how it looks when I pop the piston off and feel how the crank rotates and what some of the measurements are.

Edited by coryf89

You will know when a crank is done. Hopefully you don't break a rod and the bearing eats it.

Any Up and down play is a sure sign the crank is worn. Problem with old cranks is that when the rod goes it normally destroys both cases. at 400hrs you are taking a huge gamble. At least throw a new rod on it, which can be done cheaper than a new crank. I hope ur not riding on an MX track where crank failure can lead to serious injuries.

no. no mx track... just 10-15km into the mountains haha.

 

its not the price im concerned about, its just the work and downtime/time it takes.

if the crank goes, ill either buy a whole new bolt in engine off ebay, or maybe take this as a sign to finally upgrade bikes to something way newer. could be a blessing is disguise ;)

 

ill let ya guys know what I figure when I check the crank out.

It'd be a hell of a lot easier to replace the crank than to drag a dead bike 10-15 km out of the woods, then find a second hand engine (a new set of unknown problems) buy it, ship it, pull and replace. Measuring the crank won't tell you if the rod is fatigued and that's the worry. Replacing the crank, once the engine is out only takes about two hours. You only need a couple gaskets and it's done. While you're in there, I'd have you replace the bushings in the trans. But do your worst, and don't forget a tow rope.

Melk man, how many hours are you getting on your cranks??.... you seem to have a dozen bikes with over 1000 hours each :p

pull the engine out of a 2010 crf250 today... 2 guys working on it, took 17 minutes!! not too bad.  makes me reconsider being lazy and not doing my crank now.  still would like to hear from melk man

Why ask for advice then ignore it?

I didn't have an hour meter on my purchased new 06... Had lots of hours though... Didn't rebuild it till 2013 believe it or not... Crank measured ok, but no reason to chance it.

Do the rebuild correctly and have the piece of mind that you have a like new engine.

I had good luck with mine. I'm not going to chance it on my new bike... I will do routine rebuild(s)

My dad is still riding his all original 06. Never changed a clutch, shimmed the valves etc. He doesn't over rev it, but I keep telling him to at least check the valves.

I have pressed many cranks apart that measured perfectly as far as side clearance and up and down  just to have the bearing cage fall into several parts  thats to many hours and your bearing cage is wore out .

I have pressed many cranks apart that measured perfectly as far as side clearance and up and down  just to have the bearing cage fall into several parts  thats to many hours and your bearing cage is wore out .

 

Do you have a source for the left side main bearing, other than HotRods?

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