Got a big problem.  I've got a hard knock in the bottom end, it's occurs idle-4500rpm but clears up after that. I know about the timing chain"slap" and it sounds like much more than that to me  but I'm not completely sure. I tore the motor down and everything looks good. I need help b/c this is my first time building a bike. Any help is appreciated.



04 gs500f no mods 11k miles

Quote from: ahuggins on November 01, 2013, 11:38:29 AM
Got a big problem.  I've got a hard knock in the bottom end, it's occurs idle-4500rpm but clears up after that. I know about the timing chain"slap" and it sounds like much more than that to me  but I'm not completely sure. I tore the motor down and everything looks good. I need help b/c this is my first time building a bike. Any help is appreciated.



04 gs500f no mods 11k miles

Which side ?

And "tore the motor down" means what? Did you separate the crankcase completely and see the crankshaft and balancer shaft?

Sorry it's taken me so long to reply. I split the case and checked the bearings, looked fine to me.(I've built plenty of small block motors so I'm not new to mechanic work, just bikes). The knock sounded much harder on the left side of motor(sitting on bike).

Did you mic the crank to check that the roundness is within 1/1000"? If there's an "eggshap" to the surface it'll cause the knock. Also, plastiguage the surface to the bearings to check clearance. Haynes manual will help with that. Out of spec in the thousands of an inch can cause knocking.

Have you been driving with a low oil level lately?
If that is the case I'm afraid your big end bearings are the cause of the knock.

Didn't mic the crank or rods. But someone told me it could be carbs out out of adjustment. It makes sense, a richer mixture on one side would cause detonation, Which would cause a knock until the mixture in both cylinders evened out. Does this sound right to anyone?  And the oil was good when I bought it and I kept it topped off.

Quote from: ahuggins on November 05, 2013, 02:56:20 PM
Didn't mic the crank or rods. But someone told me it could be carbs out out of adjustment. It makes sense, a richer mixture on one side would cause detonation, Which would cause a knock until the mixture in both cylinders evened out. Does this sound right to anyone?  And the oil was good when I bought it and I kept it topped off.

Detonation could cause knock. But the more likely (though hopefully not) is that you've got an issue with a bearing. You've got the crankcase open, you should mic the surfaces and refit spec'd bearings anyway if it isn't the knock cause. Honestly though, you won't be able to know if the journals are warped by naked eye, you've got to check it down to the 1000th of an inch.