I"m in.....

Measures 94.82mm, spec is 94.945mm.....after 200 hours.

Wrist pin assembly is no longer within service limits

Piston color indicates a rich mixture or gas with a lot of additives

I would guess a little of both.

stockpiston_zpsc130af3e.jpg

Edited by Krannie

Measures 94.82mm, spec is 94.945mm.....after 200 hours.

Wrist pin assembly is no longer within service limits

Piston color indicates a rich mixture or gas with a lot of additives

I would guess a little of both.

stockpiston_zpsc130af3e.jpg

Are you sure your micrometer is accurate? The spec limit is 94.965. According to your measurement the piston is almost .006" undersize which I find incredibly hard to believe. How does the skirt look? I am familiar with Coop's bike. If anything it is jetted on the lean side but CA pump gas may be a factor. Crown looks pretty normal to me.

Edited by PBDBLUE

Are you sure your micrometer is accurate? The spec limit is 94.965. According to your measurement the piston is almost .006" undersize which I find incredibly hard to believe. How does the skirt look? I am familiar with Coop's bike. If anything it is jetted on the lean side but CA pump gas may be a factor. Crown looks pretty normal to me.

We measured in it 10 places on the piston.

We measured in it 10 places on the piston.

We measured in it 10 places on the piston.

The spec only applies to the measurement across the skirt 8mm from the bottom. Coop is pretty anal about maintenance. With .006" of piston wear + whatever cylinder wear usually results in a cracked skirt. Really doesn't matter as the piston with that many hours should be replaced anyway while your in there.

Edited by PBDBLUE

The spec only applies to the measurement across the skirt 8mm from the bottom. Coop is pretty anal about maintenance. With .006" of piston wear + whatever cylinder wear usually results in a cracked skirt. Really doesn't matter as the piston with that many hours should be replaced anyway while your in there.

Yes.

Since I did not own the bike, and 200+ hours, I needed to see inside.

I'm putting in HotCams WR cams too.

Everything is just fine so far.

Piston and wrist pin are toast

2008wr006_zps019a3f07.jpg

2008wr007_zps52aa113e.jpg

Cylinder has piston rocking marks, and substantial ring landing grooves.

All will hone out with a dozen or so passes.

2008wr005_zps10378a19.jpg2008wr005_zps10378a19.jpg2008wr003_zps757c0548.jpg2008wr002_zpse0626b3f.jpg

Rod small end is perfectly fine

2008wr010_zps7a9dfd52.jpg

The Valves appear to be very much in spec, especially the middle intake.

I will take it out to inspect, and to then re-shim, if needed. I doubt it will need a re-valving.

HotCams cam in today!

Thanks for sharing the photos and details! If you get into the carb I would very much appreciate photos and explanations. You seem quite knowledgable, especially in the area of getting carbs dialed in.

Thanks for sharing the photos and details! If you get into the carb I would very much appreciate photos and explanations. You seem quite knowledgable, especially in the area of getting carbs dialed in.

I won't post carb details, as the only thing I am changing is the needle (to NCVS) and tuning the apump timing.

Read this, if you want a great trip through the FCR:

http://www.dirtrider.com/features/protips/141_0707_keihin_fcr_carb_rebuild/

thanks for sharing the pics Krannie. I think I should pull my piston out just for the wristpin..

Well, the exhaust valves are pitted (visible with the naked eye), and the center valve was not seating correctly (asymmetrical wear marks), so I am doing a full OEM valve job. The center intake was also starting to mushroom, but could have gone another year.

We could have gone 100+ more hours, or probably more, but what's $600 between friends, anyway??

Seriously, the pitting on the exhaust valves is a sign of extended wear, regardless of visual appearance of the the intake valves, so why wait.

Headlight shell and cams came in

HID (FOR SALE $100 without rectifier or harness, but all ballasts and switches)

2008wr013_zps693f2ad9.jpg

2013- (which is a direct fit, no mods needed for mounting to 2007-2011 and maybe others)

2008wr012_zpsb50fd4c2.jpg

CAMS

2008wr017_zps25e2b5f0.jpg

Edited by Krannie

What cams did you go with?

Good choice to replace the valves....would really suck to pop a poppet and ruin all the other work you put into it.

What cams did you go with?

Good choice to replace the valves....would really suck to pop a poppet and ruin all the other work you put into it.

Hot Cams makes a 'YZ spec' cam with out the YZ decompressor misalignment issues.

I don't think the valves would have gone catastrophic for years.

Yammies usually don't do that.

But, the hard starting, monthly shimming, deceleration popping, and eventual 'deadness' is much easier to avoid, with the head in my hand, rather than a tow rope in hand..........

I am noticing that the shifting is extremely notchy, and I am wondering if there was not some longer than needed oil change intervals, or, less than stellar oil brand being used here.....which could explain the Wrist pin near failure....

I've got gallons of Motorex KTM Racing blend 4T oil that I got from my dealer when I bought the KTM.....which is thankfully GONE from my garage....which will do fine after a 30 min dino oil break-in.

Edited by Krannie

Put the Headshell and front fender on today to check fit and appearance.

The fender require all new holes, but the headshell bolts right on.

wr001_zps5d395e3a.jpg

wr002_zps3c64c0bf.jpg

The forks that are coming off look really good. Nearly new.

wr011_zpsc9109b17.jpgwr009_zps46a6cbed.jpgwr004_zpse079d3a3.jpgwr007_zpsf1dc4b19.jpg

Edited by Krannie

I have to say, a piston at 94.82 would be rocking around all over the place in the bore, with the resultant damage to the ring lands on the piston

With that much cyliner clearance, pistons tend to tilt over and punch their way out of the cylinder

I think you mic needs calibrating, or at least a zero (75.00mm) check.

If the piston really is that small, then odds on the cylinder is gonna be oversize (and you've already noted the marks where the rings stop at TDC & BDC) so a hone will do nothing to improve the clearance issue, and you need a re-plate and hone back into service limits

Edited by GuyGraham

I have to say, a piston at 94.82 would be rocking around all over the place in the bore, with the resultant damage to the ring lands on the piston

With that much cyliner clearance, pistons tend to tilt over and punch their way out of the cylinder

I think you mic needs calibrating, or at least a zero (75.00mm) check.

If the piston really is that small, then odds on the cylinder is gonna be oversize (and you've already noted the marks where the rings stop at TDC & BDC) so a hone will do nothing to improve the clearance issue, and you need a re-plate and hone back into service limits

Micrometer is fine.

Cylinder is fine, or will be with honing. It mic's in spec, top, bottom and middle.

Piston is not fine. Way out of service.

A worn piston has nothing to do with a worn cylinder, unless there is catastrophic failure.

The Cylinder is 1,000 times harder than the piston.

The motor had audible slap at idle.

I believe this motor has been running on poor quality oil, and/or for more than 200 (more like 400) hours.

...which is irrelevant, cause it's mine now. I cast no aspersions on the previous owner. Caveat Emptor.

You are making tons of assumptions and guesses.

Enjoy.

Edited by Krannie

As you provided no size info for the bore dia, of course its guessing and assumptions!

As you provided no size info for the bore dia, of course its guessing and assumptions!

You can tell by looking. No damage to the Nikasil coating other than superficial.

I'm curious to know what size it is - you said above that it mic's in spec at the top, middle and bottom, so what did it measure?

Personnel experience tells me one you can feel the ridges where the rings stop at TDC & BDC the cylinder is o/size and from your photo's those ridges are clearly visible

I'm curious to know what size it is - you said above that it mic's in spec at the top, middle and bottom, so what did it measure?

Personnel experience tells me one you can feel the ridges where the rings stop at TDC & BDC the cylinder is o/size and from your photo's those ridges are clearly visible

I'll see if I can get the numbers, or if it's still apart.

Hopefully the cylinder is back on already. We are waiting for intake valve parts.

You can feel the ring landings, but just barely.

There is nothing in the cylinder that will catch your fingernail.

The deepest wear will be at the back of the cylinder at piston skirt contact

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now