When I recently purchase another KLX with the Bill Blue 351 kit and pumper carb installed I expected some differences. The extra power and instant throttle response is great. Love it! The extra noise from the engine is a change I did not anticipate. The new bike also has a Q4 muffler with the power bomb header, so the exhaust noise is pretty much acceptable.

The engine generates vastly more noise than my other KLX250 and am wondering how much of the noise is normal for this big bore engine.

There are basically two noises of concern. The first is a heavy clicking noise, that diminishes, but does not go away, as the engine warms up. Actually contact Bill Blue about this one and he suggested I go with higher octane fuel. I'd been using 91 already and did manage to find some 92 octane, which may or may not have made a difference. I checked the valve lash this weekend and found all to be within spec. While I was at it I also removed and reinstalled the timing chain tensioner, to give it a chance to reset itself. This seemed to help, but really not sure. I have a Kreiger manual tensioner on its way.

The other noise from the big bore engine not heard from my '06 is a noticeable, but not too loud, whine or whirring noise. It sounds something like a vacuum sweeper and changes with the engine speed. I thought this might be coming from the air box, since its lid is off, but this does not seem to be the case.

I also realize that all of this extra noise might be normal for this larger piston and greater displacement, but would like to know for sure if possible.

Can anyone tell me if any of this noise is normal based on their experience?

 

Both those noises sound like normal engine noise from the KLX.

The clicking noise which goes away as the engine warms up? That sounds like the cam-chain. Mine clicks like crazy when cold but is completely gone when hot. BTW, I am using the Kreiger manual chain tensioner.

The Whirring/Whining noise which changes with engine load? that sounds like the pressure relief valve on the oil filter. The oil filter on our bike has a little metal gate backed by a spring which seats in the smaller diameter rubber ring. When you back-off the throttle, but the gears are still engaged, there is a higher oil pressure created. I have found that my oil filter makes a whine which goes away once the engine is hot. BTW, i have tried both the Kawi filter and the K&N filter.

Then again, i just have a 250cc... the 351cc is on the list!

 

Thanks for the opinion. I have my doubts about the oil filter bypass theory, though. As I stated, I also have a '06 KLX250, which produces no such noise. In fact, beyond exhaust noise, the '06 engine literally sounds like a sewing machine once it warms up, which may be making the new 351 bike sound loud in comparison.

 

Do you have the airbox lid on the '06 KLX250? Removing the airbox lid can actually increase the intake noise (rather than reduce the noise). If you have the airbox lid, you could try running it with it in place and see if the noise diminishes.

 

Good idea. Yes, I have the lid on my '06. I run it without the snorkel.

Oh, and one more point I meant to mention: The whirring, whistling sound is more prominent at low speeds. At higher speeds other noises overwhelm it.

Thanks.

 

I had a rod bearing failure on my '12 that coincided with the install of the 351. I don't know if it was initiated before I added the big bore but I will say that it was immediately evident on the first start-up. I even pulled the jug to inspect everything but I couldn't find the problem at that time. I ran the bike for almost another year and 5k miles before it got to the point that I knew I had to tear it apart.
Bill was very helpful on repairing the cylinder damage and I have not had any issues since I rebuilt the bottom end. The only thing that I wish Bill would do on this kit is to add a dry film coating on the piston skirt to reduce thrust wear on the bore and piston. The rest of the kit should be just as durable as the oe components.
On fuel requirements- I calculated the compression ratio at 12.3:1 with the base gasket installed and minor bowl cleanup(removal of material around valve seats to reduce shrouding). I have tried using 87 octane and the engine will spark knock under load so I always run minimum 91 octane to eliminate knock potential. The other reason I do this is that when you get spark knock it transmits a tremendous load to the piston and rod/bearing and I don't want to give the crank another opportunity to go south.
I will also say that after installing the manual tensioner the engine is quiet after it warms up so the oe tensioner did seem to add some racket during operation.

 

Thanks for all the insight. I have tried replacing the air box per previous suggestion, but made no apparent difference beyond making throttle response a bit sluggish.

I've tried to imagine what in the crankcase could be making the whining noise and am now wondering if it might be related to the timing chain. Hopefully, the Krieger tension adjuster will make a difference.

 

My bike started to make a weird noise, found it was the roller that hits the chain
tightened up the shock spring a little never came back




maybe you have something inside like bearings

do those big bore cause engine venting issues not venting enough
where you could get fuel mixed into the oil which eats away at the crank bearings on cold startups


drain oil and smell, if you smell fuel in the oil its a bad sign

 

All of the bearings in the bottom end are either ball or needle bearings so they are pretty impervious to fuel contamination issues that will kill a plain bearing crank.

 

The whine, I've concluded is timing chain which is not a great concern. What about the knock? I now have the Krieger tensioner.