I recently picked up a 2011 Brute Force 750 that has a Knocking sound coming from the engine. The prior owner ran it very low on oil. I'm trying to confirm if I spun a crank bearing.

below are two videos of the engine running...



After listening to the knock does anyone have any input?

Before I go as far as cracking the case I would like to rule out any potential smaller problems that could be making the noise.


* Stretched cam chain (make sure tensioners are fully extended)
* Clutch noise (Run engine with belt removed to see if noise stop.
* Cam

what else should I check? Thank you!

 

Almost certain that knock is valve related. I don't know the big Kawasakis at all but I'm sure they will have roller bearings anyway. I have had Honda 350s making that sort of noise and it was a loose valve seat. Also Suzukis with worn out cam followers. Re-set the clearances and see if that helps. Don't think it is chain, but the tensioners should NOT be fully extended.

 

I adjusted the valves to the manual specs. They were all a little tight, but not too far off. The chain tensioners both appeared fine with the tensioners only extended about half way out. The noise is still there. I did find an exhaust leak, see attached picture... this was on the front cylinder pipe and was in a concealed area of the pipe. Any chance this could be causing some of the noise?

 

No, I still think cam, followers, or a valve seat loose. You are going to have to take the head(s) off anyway so also check the pistons and bores for wear, piston slap makes a somewhat similar noise, but less sharp and faster, as a rule. Use of a screwdriver/stethoscope may narrow down which head is giving trouble.

 

This is not me.

 

I did a leakdown test on both cylinders. I got approximately 24% leakage on the rear cylinder and 60% leakage on the front cylinder, with much of it feeling like air was coming out of the exhaust and intake on the front cylinder. Should I now concentrate on pulling both heads or just the front? Thanks!

 

Take a look at the front for the compression issue, but I would check with the stethoscope first, noisy valve gear doesn't always mean low compression, so the noise could be coming from the back cylinder head. I don't have a leak down tester, a compression test tells you if something is wrong, and inspection tells you what, when you take the head and cylinder off.

 

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I checked the compression and got 50 on the rear cylinder and 32 on the front cylinder. The manual calls for 36 - 66 psi. I pulled the front cylinder head to take a look.

I am not quite sure where to go from here... Thanks!

 

Can't tell much from photos. Measure Piston(s), rings and bore(s) for wear. Remove valves and check seats are not loose. One cam follower seems a bit odd, but you can tell better than me. Measure cam lobes for wear, Check rocker shafts for wear. Something is worn somewhere to make that much noise, you just have to check everything to find what.