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.
Exactly. Sounded like the engine was still revving, but with the addition of the buzzing noise, and no power to the rear wheel. Happened quickly so I'm not 100%, but that's how I remember it.
So you haven't started the bike since? Have you tried shifting the bike with the motor off? The sound reminded me of a lot of things but if the bike runs normally then my guess would be a transmission problem with the gearbox being stuck between gears for some reason.
I don't like to be the guy running around diagnosing things just because they happened to me, but it's a quick check. Chain still on the front sprocket? Happened to me out on the track...
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.
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.
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.
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.
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.
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.
I don't. I've been looking for a used one. I want one just because I'm a toolaholic. Also I know how critical it is to stress the frame correctly. If I were to make one it would be with a socket so I could use a torque wrench on it. Maybe I should just buy one and rent it to everyone.
@dlk7u let me know if/when you want to do a fork service. It's kind of a lot of tools and they're expensive so I don't lend them out, but you're welcome to tackle the job in my garage with my guidance, or I can do it for you at a reasonable price.
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