bent con/crank?

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Hey,
so the NSR is running again and runs/rev's pretty well when stationary, but after getting on there is deffinatly something wrong in there.
The bike doesnt pull very well after 6,000rpm and there is a pretty strong new vibration in there with each compression (engine sounds no different though).

As I recently had a rather large amount of 2 stroke oil go through the engine as detailed here, whats the chances the con rod or crank could have been bent?

I was planning to do a squish test but as the engine compression is down to 110psi I have decided to whip the top off and figure out what bore the cylider is (take it to a bike shop?), and do a top end rebuild.

Whilst I have the top end off, any thoughts on how to check the con rod/crank for trueness? My plan is 1: something straight for the con and rotate the engine to see if the edge of the crank moves up and down.

Any other thoughts would be muc appreciated, I have a whole spare engine runs healthy and strong with a good crank and con rod (and top end to think of it) but the big end bearings are somewhat shagged... Neutral

Any thoughts would be much appreciated.

Best regards

-Jvr

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Pretty much no chance the con rod is bent.

Main reason to bend it would be a hydraulic lock, and while that would be possible with 2 stroke oil it would need to be above the piston.

Only real way to tell if the con rod is bent is to strip the engine and check the rod itself. Same for the crank (take crank out and check it with a dial gauge).

All the best

Keith
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Snorty · World Chat Champion Joined: 13 Oct 2010 Karma :

Might be a stupid suggestion, but is your PV working? On my TZR it doesn't pull well past 7k and tops out at 8k as it has no power valve servo. Gets very vibrate-y at this point too

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Hey,
Yep, powervalve is happy.
The engine runs fine when on the side stand right through the rev range, just under load it struggles at higher rpm.

I'm just wondering what could cause the vibration, it doesnt feel as subtle as bearings, a much shaper vibration.

Will whip off the top end this morning/tomorrow morning, will take it to the bike shop to get it measured (if i find one that will do it for me).

The spare engine will get a rebuild as long as i dont have to pinch the crank/con in which case my current engine will get a rebuild.

Best regards

-Jvr