Engine Knock

Need some expert opinions/advice. When I first start my J, it sounds fine. Normal ticking valves and such. fine for about 15 seconds. Then, it develops a noticeable knock. Can't tell where it is coming from, but does not sound good. After about 30 seconds, it completely disappears and I don't hear it again until the bike sits overnight. The ritual described is consistent and it has been doing this for about a year (granted I've only put about 1000 miles on it in that time). Ay thoughts? Thanks.

maybe a little back ground on the bike, how many miles, any known work done to it.
oil and filter change

11K miles that I know of. Entirely stock as I can tell. Have owned it for 2 years, it runs great, and I change the oil and filter every 1000 miles using Valvoline dino 20W-50.

A knock is often a rod bearing. I would put an oil pressure gauge on it and see what the pressure is at startup.

If it was a 'clacking" sound it might be the primary chain slapping around.

You know it may be more of a "clack" than a knock. Would the "noisy right after a cold start and then disappears" condition be consistent with a slapping cam chain? Thanks.

A primary chain in a 1000J? I don't believe they have one.

Rod bearings can cause a knock, as can main bearings and pistons, and wrist pins, and a few other bearings. But bearings that knock don't get any better when the motor gets warmed up. Piston slap (sounds like a knock) can go away when the motor warms up.

I think the J motors were notorious for piston slap, APE Jay told me one time that he made a significant sum of money installing 1075 kits in J police bikes because of cylinder wear (causes piston slap).

Kind of hard to diagnose over the interweb though, so it might be something else causing it

Appreciate the info guys. I think bountyhunter may have been referring to the cam chain (rather than primary). My scoot has made this racket for the 2 years that I've had it and it doesn't appear to have gotten any worse. If I recall from my younger days, and my younger days are way way too long ago to remember, piston slap had a sort of ringy/hollow sound to it (if that description makes any sense). But then, could have been caused by the hollowness between my ears. Who knows.

grumpy56 wrote:

Appreciate the info guys. I think bountyhunter may have been referring to the cam chain (rather than primary). My scoot has made this racket for the 2 years that I've had it and it doesn't appear to have gotten any worse. If I recall from my younger days, and my younger days are way way too long ago to remember, piston slap had a sort of ringy/hollow sound to it (if that description makes any sense). But then, could have been caused by the hollowness between my ears. Who knows.

No, I meant the primary chain because I didn't know they made one without it.:laugh:

If it's a clacky sound, it might be a cam chain. have you checked the chain tensioner assembly?

Don't tell me it doesn't have one of those either......:blink:

grumpy56 wrote:

Need some expert opinions/advice. When I first start my J, it sounds fine. Normal ticking valves and such. fine for about 15 seconds. Then, it develops a noticeable knock. Can't tell where it is coming from, but does not sound good. After about 30 seconds, it completely disappears and I don't hear it again until the bike sits overnight. The ritual described is consistent and it has been doing this for about a year (granted I've only put about 1000 miles on it in that time). Ay thoughts? Thanks.

Another theory --
Clogged oil pump screen or oil journal.
Residual oil from last run lubes for 15 seconds.
Then knocks for 30 seconds until oil arrives.

Could use stethoscope to help locate knock source.
And as already suggested, use oil gauge to determine pressure at start-up and extent of any delay in building pressure.

Good Fortune!

If oil filter failed or collapsed, the by-pass might kick in.
But am uncertain whether that could cause the symptoms as described.

Wouldn't hurt to check integrity of the filter.
And could also test run for effect without the filter.

Good Fortune!

Great suggestions. Am going to work through them starting wih the stethoscope and checking the oil pressure. Thank you all.

bountyhunter wrote:

grumpy56 wrote:

Appreciate the info guys. I think bountyhunter may have been referring to the cam chain (rather than primary). My scoot has made this racket for the 2 years that I've had it and it doesn't appear to have gotten any worse. If I recall from my younger days, and my younger days are way way too long ago to remember, piston slap had a sort of ringy/hollow sound to it (if that description makes any sense). But then, could have been caused by the hollowness between my ears. Who knows.

No, I meant the primary chain because I didn't know they made one without it.:laugh:

If it's a clacky sound, it might be a cam chain. have you checked the chain tensioner assembly?

Don't tell me it doesn't have one of those either......:blink:

Nope, bevel gear drive!!






Just kidding :laugh: