Various screeching rattles above 4k

[ninja]

Hello all, I'm crossing fingers that this place is still active.

Got myself a '92 Revere. Managed to ruin one engine already but thats another story. 

I've recently installed an unknown/untested lump in. She runs well, has good compression and if you left it at idle you wouldn't ever think it had problems. 

It's when it gets to 4k on the rev range. It's a strange, rattly, screechy noise I've never heard on an engine before. It'll stick with the rev range from 4k all the way to redline. anything below that and its fine. 

I'll get a video of it later on hopefully, but I'm just wondering if anyones had a similar noise before and was able to pinpoint it?

It's definitely not the driveshaft, clutch or transmission. I've ruled these out already.

Also, it doesn't run any differently with this noise, it'll still pull like a train. It does bog down a bit when coming off the revs and going back on, but I imagine that to be carburettor related, something I can sort later.

I'm rebuilding the old engine with nice shiny parts, but its a long project on my budget and I'd rather not have another one go on me.

Judging from the cam chain wear, I'd put the engine at around 50-60k mileage. 

Will update when I get a video, cheers in advance!

[searj]

the oil pump drive chain has no tensioner and can rattle around a lot, pull the side covers off the engine and have a look around for any fragments? mine makes an odd chirpy squealy noise at just above 4k when at a constant speed and has done for the last 40k, and probably most of the 70k it did before i owned it.

bogging down on power could be battery or spark plugs as well, mine useed to bog and it developed into a massive stutter on acceleration, turned out to be a dead battery which confused me as in normal riding youd never have noticed it and it always started up really easily!

[ninja]

Thanks for the reply buddy!
Yeah, a chirpy rattle sounds about right.
The rattle I was describing that I thought was the oil pump drive chain has since gone away, however the chirpy rattle has gotten seriously bad. I can no longer accelerate past 4k without the chirpy rattle becoming very obvious, power loss is complete and it feels like the engines about to drop itself. Go below 4k and it runs fine without issue.

I'm definitely gonna whack the camera on and go for a ride to explain this, hopefully I can pick the noise up.

Spark Plugs are brand spankers, standard NGK recommendation. Battery is also brand new, nice Yuasa one, also same as recommended by the manual. 

[ninja-thelazyone]

Just to follow up with this, it was a conrod bearing. Allowed massive movement which let the piston play with the valves.
Rebuilt old engine, all smooth sailing now.