The Chopper Compendium

well, just when ya thought this build log was done...here we go. not exactly what i was hoping for from the first day-long ride i was gonna take.

-dan

Hi budoka, sorry to see that you are having engine problems. By the looks of that picture looks real bad, good luck man in the repairs and a major thank you for setting up another awesome bike forum. I am sure we can all make it as good or better than the old one.

Nasty looking wound. Just a burnt piston or more damage?
Jim

That piston looks like it had an argument with my plasma cutter....and lost

I hope you get it sorted and running strong again soon

Have you figured out what caused it yet Dan? Weak mixture? Advanced ignition? Don't know a lot about Knucks but I bet some of the other members can help out with this one

Maz xx

that really sucks dan but at least we know ya ridem hard . wish i was there to help love tearin into the old bikes . hope your able to get all the pieces out without too much trouble

thanks folks. Maz, you were naming all the exact questions i was asking. Tomo and i looked at it and discussed it, and we had a guy who works on knucks a lot here look at it, as well as a guy who used to work on Toyota's racing team building engines, and the conclusion we collectively reached is that it was a crappy combination of factors all piling up that caused it.

for one, i may have had the timing just a hair too high, but not so bad that it was pinging or even kicking back when starting it. not nearly enough to cause that. secondly, seems there was a tiny hairline crack that had developed where the old intake ports were welded up when the heads were converted for dual carbs. my guess is that the engine running for 1500 miles or so with those huge, heavy SUs hanging off of it may have caused that. i know, i know, i *should* have done a pressure test to check for leaks, but the engine had been running like it was, so i thought it was probably ok. expensive lesson learned. third, i may have had the carbs running just a slight on the lean side since i had been playing with the jetting to alleviate an overly rich condition, but again, not so bad as to cause any pinging, and the plugs were looking real good (if anything the plugs were saying it was still just a slight bit rich, but i had decided to stay at that jetting since a little rich is always better than too lean). lastly, the guy who used to build engines for Toyota's race team swears that the rear piston either had a problem in the casting, was dropped at some point, or was hit with something at some point, otherwise a piston that thick wouldn't have burned through anyway.

i'm taking steps to address all those possibilities as i put it back together. right now i have it torn down 100 percent to clean all the piston trash out. believe me when i say it got *everywhere*. good thing i got it shut down real fast. not sure when exactly i'll be riding again, but i'm gonna take my time and make sure i put it back together right.

-dan

I think you're doing the right thing Dan, even the smallest bit of old piston material could wreck the oil pump or lunch a main bearing etc.....its a gut-churning moment when you first see all that shrapnel but it has to be cleaned out. As for the reasons, I was just going on past experience (with my old Sporty).... nearest I ever came to that kind of damage was a similar combination and on one really bad occasion when a valve dropped.........I'm sure that you will get her sorted and back running as sweet as ever.

And thanks for finding time to get this new board up and running despite living in the ongoing turmoil of earthquakes, working, martial arts and family stuff.....as well as trying to fix your bike! What a guy

Maz xx

sometimes i think its more fun wrenchin em than ridein em its the sinkin money into em that sucks

We only ride em so we have an excuse to take em apart again to fix em......

Maz xx

Sorry to see that Dan!

Man...that sucks.Hope you're back rollin down the highway soon

With everything you went thru just to get the bike to Japan you sure didn't need this. But don't worry, it may take some time but you will get it going and be on the road again.

What a bummer Dan! I know all about those intake leaks with the Pan. I stuck a piston a few years back. Pressure test can be a bitch sometimes because you are testing a cold engine that is not representative of the actual enviroment that it lives in. I have been think about a plate with a big o-ring to bolt to a head to check the heads out completely before assembly. I would like the o-ring to be able to take up to 300* F so I can throw the head in the over for awhile before doing the test. I will do this before my Pan get put back together. As soon as I get this other chopper out of my shop, it is full steam ahead on the Pan.
Keep us informed on what you find.

Scott

thats wild, i just seen a flathead 80 in the same shape. crappy pistons. who built the motor? If i remember right you bought the motor from billy lane. He is some times hard on motors and bike. I am sorry to see that happen to you, the Keith black pistons are a good replacement choice. But hey I still think a broken knuckle is cooler than my evo. The boys a deluxe here in denver do alot of knuckles so if you need any help getting parts let know. I bet the first ride down the road was just short of watching your children being born.

Chris

dan do you have the springer build photos? if so that is something that would be good to post up for these guys to see.