Topic: Engine knocking

[jlatkins83]

I just rebuilt the top end of my engine but checked the rod bearing clearances while I was at it. Everything was in spec and the top end went together great. But now when I hit around 3000-4000 rpm I hear a "knocking" sound. It sounds like its more of a vibration of metal than a hitting of metal. I'm not sure what it is, thought it might be loose exhaust but I have those tightened down. Any help would be great! Thank you.

[jlatkins83]

I forgot to say, the engine runs great at idle and start up. I also haven't timed it running yet, only static.

[City Boy]

Hi.An oil pressure check with a gauge may be helpfull.How did you check bearing clearance with only top end apart?

[ekpent]

Not that its your problem but I had a vibration between a certain RPM range on a CB900F that was freaking me out,thought the top end had a major problem. Checked it out carefully with my helmet off and found it it was the glass in the mirror housing vibrating and rattling in that range.  Try to see if you also can get a better idea in the shop as to maybe what part of the engine is making the noise.

[jlatkins83]

Hi.An oil pressure check with a gauge may be helpfull.How did you check bearing clearance with only top end apart?

I fully rebuilt the top end and had the cylinders off, but I also had to split the case to find a dropped pinion clip. So I went through and checked for play in the rods and on the crank. I guess I should of mentioned that so I don't sound like an idiot. Thanks for the advice.

[City Boy]

Ok.If the bearings passed the visual and measurement tests you are likely looking elsewhere for the problem.You also checked the main bearings right?

[Danno]

sure you got all the wrist pins right?
also you can get vibration from baddly synched carbs it makes the primary chain slap back and forth by the pistons being out of sync

[jlatkins83]

Bearings are good, as for synch that can be out. I need to rebuild my carbs but it is like looking for atlantis to find a rebuild kit for 78' keihin carbs. However, I got a tell tell clue today that makes me think the noise is still in the exhaust. The mounting flanges are much thinner then the stock finned type and I think that the cylinders with studs (long story why only some have studs) aren't able to tighten all the way due to lack of thread on the stud. I also checked the whole engine by listening to it in various spots with a rod (sorry I don't have a stethoscope)  and all sounds are like normal running condition. I will keep posting when I find the issue. Thanks for all the help, it can be a bit lonely and frustrating in the garage by yourself.

[ekpent]

Somebody over in Seattle give that guy a HUG if he is lonely in the garage and lend your ear also.  Seems to be some peeps over there I bet 

[scunny]

group hug.
since you say the exhaust isn't being clamped fully, is there any sign of blowby, it can make a wierd sound.