Thundercat project begins

Not going to rag on the condition of it or the trade. If you're happy then good for you.

You'll want to do yourself a favor and have the frame measured at a frame/suspension shop to be sure it isn't tweaked. Do the same for the forks too. The one slider higher than the other "supposedly" doesn't cause problems according to a couple suspension guys I've talked to, but it would definitely affect me mentally while I was riding....

Good luck with it, hope it comes together for short money!

Thanks.
I'd already had my fun with the gun, it was time to pass it on.
Besides working on it a good reason not to get done the other less rewarding tasks, like housework, laundry, etc.

One of the forks is bent, so at a minimum the tube slider it being replaced.
I don't see and signs of frame or tripletree tweakage quite yet, but I haven't gone over the frame yet, I'll keep an eye out.

Any Metallurgists in the house?

J B weld to the rescue!!

oser

Uf da. You got your work cut out for ya on this job.

Oh dear.
Well good thing you got a cheap crank.

JB weld? You think I'm made of money?
I'm hot-gluing this mother back together

Weird. I've never seen one fail like that before.

I've never heard of it either, didn't find anything googling it. maybe the rotor had something fall off and became unbalanced?

Show that to Yamaha.

YZFs had pretty thin/weak side covers (in fact most racing orgs. mandate aftermarket case covers for them). Elwood said that the generator cover was damaged. If the bike were crashed on the left side and it distorted the stator enough to bind on the rotor attached to the crank, that would be enough to snap it off.

Guess you are going to need that ebay crank after all. LOL! Just don't re-use the old plain bearings. Measure and buy the correct sized ones.

Yea, new bearings are a very good investment in this case. You don't want to pull the engine apart again because of blown bearings.

And buy a pair of racing case covers!

You can do it!

oser

Elwood,

You have quite the project there!

Just suggestion word from an old guy with many projects under my belt. Find a good used motor and replace it.

Yamaha makes stout engines. This bike has been obviously abused. By the time you fix everything you see wrong (not to mention the things you may not see) you will have way more money in the bike than it will ever be worth..

Just keep any good parts off the old engine for spares.

Best wishes.

Good advice. That's a serious failure, and there's no way of telling what else may be damaged or weakened. It'd suck to get your project up and running, only to have the engine blow up after a thousand miles.

Yes, if the engine is that bad, the tranny may be very abused as well.
Maybe fix the crank on that engine and ebay it off, then buy another engine.

Besides the bad karma from doing that, how do you know he won't get someone elses' slapped together time bomb?

The OP stated he's just doing this as a project, and replacing a crank isn't that hard (relatively). Just follow the instructions and don't cut corners and it should be as good as new.

I'd venture to guess that either it took a hard impact to that side of the engine, or they wheelied the crap out of it and ran it out of oil. If those bearings get hot enough, it can actually cause the crank to lose temper and snap.


Otherwise, I'm stumped. In all my years of racing, I've only seen a handful of busted cranks.

I realize its probably cheaper to buy a used engine, but this is mostly just a project to see how to (and if I am capable of) rebuild an engine.
This isnt my only transportation so if it blows up later I'll be fine.

The ebay crank came in, I'll take a look at it tonight.

What corners have you guys seen cut that come back to bite people in the ass?

I plan on new bearings, connection rod bolts, and maybe a cam chain and sprocket.
There's marking on the crank that correleate to bearing sizes, but I'm not sure if thats a good baseline, or what exactly to do with them. There's also about four different part numbers from the bearings, I think they're sizes but I'm not sure how to find the size in the part number.

The tranny has worn dogs on the 2nd-6th gear mesh, which I think was pretty common on these, The rest of the gears look pretty good, the forks and drum look good too.

Thanks for all the input everyone, if you guys want pics of anything in particualr let me know and I'll post em.