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On-track mechanical (with video)

2K views 18 replies 4 participants last post by  MGFChapin 
#1 ·
Was at the track this weekend, And on day 3, I had a mechanical issue when downshifting into turn one -- a sudden buzzy noise coupled with a loss of thrust. Quickly got a hand up, then pulled in the clutch and brought it off track.

You can see it in the video here:

Any idea of what this might be? I'll bring the bike by the race shop this weekend or next but was interested in any preliminary thoughts on whether this might be engine, transmission, clutch, etc.

I was thinking transmission or clutch since the engine kept revving after I lost thrust, but in truth I have no idea.

Bike is a track-only 2006, 11k miles (3k track), valves recently checked, regularly maintained, etc.
 
#7 ·
Sadly yes, final drive is in tact. Pulled the plugs to do a compression test and found that one had been pounded flat. So my guess is that I dropped a valve, which then did who-knows-what to the piston and cylinder lining. Going to have it scoped this weekend to investigate further.

Photo attached for your viewing pleasure.
 

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#8 ·
I was afraid of that but didn't want to bring it up since you said it ran fine afterwords.

When I was watching your video I was cringing on your downshift into turn 1 you really revved it there. Sounded like it probably went over the rev limiter. We lost a cylinder on a race bike at the last shop I worked for because the rider did that going into turn one at PIR.

How much are they charging you to scope it? I have a scope.

We took our race bike motor down and started rebuilding it and it was cheaper to just get a used motor and combine the two.
 
#9 ·
Mac,

Thanks for the kind offer. I'm short on time this weekend so will go with the local shop for scoping, but may ask your advice during rebuild.

Interesting that the video shows (1) beyond a doubt that this is due to operator error (like most things) and (2) my memory of the engine being something other than instantly trashed is completely wrong.

Preliminary questions on the rebuild.

If I did in fact drop a valve and turn my engine into a blender, I assume this means I have damage to: cylinder head (maybe), cylinder sleeve (maybe), valves, and piston. How many of these parts can/should be swapped in from a donor engine, and how many should be purchased new?

While I'm in the engine, anything that's worth replacing as a matter of course? Bearings, going to kit valve springs, etc.? Or is this just a good opportunity to do a full refresh and check each component for spec against the shop manual.

Any common failure / wear points I should be on the lookout for?

Thanks as always. Free beer is always available in Seattle if you're around.
 
#10 ·
Pretty much guaranteed you're replacing an entire cylinder, piston, valves, etc..

Something to consider though is you can usually pick up a used motor for less than the parts and labor to repair if you aren't doing it yourself. If you are doing it yourself be sure and contact Cascade Moto Classics in Portland and Latus. They both may have used parts.

Any time you have the motor apart you should plastigauge the crank. Beyond that it would be worth replacing the wrist pins. When replacing the head watch out for wear in the cam ladder especially on cylinder 1. This would also be a good time to upgrade the oil pump and install the updated oil pan gasket/baffle which comes with the new pressure relief valve. I wouldn't do kit valve springs unless you also do the kit valves. Stock valves on these years were a 2 piece valve and they're really not up to the added abuse of the kit springs. As for checking the spec on everything it never hurts if you have the time and know how. However the big things are directly related the actual combustion Pistons, Cylinders, Valves, Rods, Crank. Inspect those and you should be good. I have a bore gauge set you can borrow if needed and I can show you how to use it. I might have a a set of high accuracy calipers of the correct dimension for measuring piston skirts as well. I would have to check the size of my calipers though. I got them for measuring BMW twin pistons which are significantly larger than our bikes pistons.

Let me know if I missed something or you need more detail.
 
#11 ·
Thanks! I pulled the engine last night. Am on the hunt for a fresh one, and will refresh that before installing. Also plan to tear into the old one to see what can be saved.

From peering down the intake, I see a decapitated and sideways valve head, bent valves, and a pile of rubble on top of the piston.
 

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#15 ·
Yes, thanks. Ordered everything, including the pump, pipe and gaskets. Do you happen to have the frame and swingarm tools? I know they're not strictly necessary -- count threads on the swingarm and make a diy tool for the frame -- but thought I'd ask anyway.
 
#17 ·
Got the engine installed last week in time for the track on Monday!

New engine ran great. I was pleasantly surprised that the install wasn't too difficult. Just went slow and followed the shop manual.

I'm now the proud owner of both the swingarm and engine tool. You're welcome to borrow them anytime. I'll trade for use of the fork servicing gear :)

Thanks for all the help!
 
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