Bonneville America Forums Forums Technical Forums Performance Mods broken cam chain, after 904 kit installed

like the title says, I broke my cam chain which means tearing the engine down to the crank. According to Jojje I can remove the crank without removing the barrels, pistons, or Con rods by flipping the motor over, splitting the cases, and lifting the crank out by unbolting the con rods.

The cam chain broke because I (stupidly) did not reset the cam chain tensioner (yes, I am stupid), there was too much tension on the cam chain (yes, stupid), and the chain snapped after about 10 miles.

Hopefully no valves are bent, but I won't know until I pull the head off which will be either tonight or later this week. I hope to have the cases split by the end of this weekend.

Yes, stupid, but I will fix it! and ride as soon as possible.

Right now, the tally of what's damaged includes the cam chain, and the 2 cam chain guides. The cams and the top side of the head are ok. Judging by the position the valves/cams were in when I opened the cam cover the valves may be ok too, if that's the case then I got lucky. I'm still expecting at least 2 bent valves...dammit. Hopefully the crank is ok, and from looking down the cam chain tunnel it looks as if the chain wrapped around the crank, which should mean the crank cam chain gear is intact and undamaged. I'd hate to replace the crank, at $900.

Oh well, live and learn! I'll be sure to post pics of the damaged parts here.

Hey Jeff sorry to hear that. I know from the fact with you tearing it down yourself you know what you are doing so I would not venture to insult your intelligence, with that said I did not see in your posting a mention of the conrods or piston damage if you have a bent valve. I've seen several damaged pistons and bent conrods in automobile engines from timing chain failures and piston valve contact. I hope you the best and she has no colateral damage and goes back together smoothly. And get back out there and RIDE! Take care T

Jeff, good luck and hope damage has been kept to a minimum. I really respect someone who can openly admit their stuff ups. Good onya mate cos your explaining this may help someone else not do the same. That's why this site is such a beauty because everyone shares their experiences both good and bad so that we all learn from each other. That's the spirit I see anyway and you've re-iterated it. Hope you are back on the road soon and given the talent of some of our fellow members, we might be able to assist with suggestions on the rebuild.

If the conrods and/or pistons are damaged the bike will sit idle until I can afford carillo rods and an 1100cc piston kit. If I have to break this whole thing down and replace significant parts I might as well replace with better parts.

Hopefully I'll only need a cam chain, the 2 guides, and maybe a pair of valves at worst.

update, the motor is starting to go back together. The damage was limited to a broken cam chain and 2 bent intake valves that have already been replaced. I'll have all my parts by Monday so I'm expecting to be up and running in about a week.

Bent valves but piston is OK?

indeed

Frank

The piston is ok. The rod is ok. There is a very tiny mark on the piston where it hit the valves, but there are no cracks or anything like that. The valves were barely bent too, you couldn't tell by looking at them until I filled the combustion chamber with WD40 (spark plugs still in, head upside down on the workbench) and it ran past the valves. I got lucky.

We're holding our breath Sweat. Keep us informed

mike