Klx250 piston vs cam chain noise
 

I just purchased a 2006 klx250 with a top end noise. PO stated that it would need a piston. This model seems prone to cam chain issues so I'm wondering how I tell the difference. It is not loud and the frequency/ sound is very similar to 2 stroke piston slap. I pulled the chain tensioner and it looks fine but did seem to be most of the way out. The bike has 17,000 miles

when you're revving up, does the clatter get louder, or faster, or what? does it change when it's under load or in neutral? if it sounds like a 'clack' that hits every revolution, it's not the cam chain. a failed cam chain kind of sounds like your engine is full of gravel (random clattering)

you can mostly inspect a cam chain in place by just pulling the valve cover. after a few engine rotations by hand with the tensioner in place, there shouldn't be much slack at all in any part of the chain. also spin the engine to top dead center and see how close the cam sprocket alignment is, with a stretched chain they'll never line up properly.

you can try to check for piston issues with a bore scope, a badly failed piston will usually eat the bore, so there might be evidence without tearing the top end down.

with that mileage, if it was me, i'd just take 'er apart and replace piston/rings/cylinder as required, lap the valves, and change the chain just for peace of mind

I just threw on the Krieger manual cam chain tensioner. That got ride of a lotttt of noise. My 09 is also at 17,000.

I'm thinking I pointed out how to detect where the noise is coming from in a post at the ADVrider forum, but here it is again.

Use a long handle screw driver or a mechanic's stethoscope. Put the handle of the screwdriver against your ear, put the tip down at the tensioner area and listen. Then put it down on the cylinder around the front and back where the piston skirt would actually be hitting. Remember too, this is a liquid cooled engine and piston slap may be muted a bit by the water jacket.

I also find it hard to believe there would be enough wear in that low of mileage to develop piston slap. It isn't a common thing like it can be on a two stroke. My bike has 15,000 on it and had a bad tensioner. Looked pretty much like the following picture. Unless you use a strong magnifier on the tensioner you won't see what the damage actually is...

https://cimg7.ibsrv.net/gimg/www.kaw...cfd8735a36.jpg


The wear pattern here and that one polished tooth is the problem. The tensioner is junk.

When the engine decelerates the momentum of the cams pulls the cam chain tight on the back side, pushing back on the plunger. Normally the pawl would engage the tooth enough to hold it, but the top of the tooth has chipped and rounded as probably has the pawl. Now the pressure pops the pawl up and the plunger pushes in five teeth. The pattern is where the rack pushes back out Part looks good, but it isn't. The back side of the plunger will actually be polished due to the metal on metal sliding. None of that should should be there. It should click forward and hold, but it isn't doing it. A stronger spring is not the answer, the goal is to have as little actual tension on the chain as possible with as little chain slack as possible.

From personal experience and some friends that race, I found a manual tensioner does the job with a reasonably simple adjustment process and absolute reliability as long as the lock nut is good and tight. Adjustment interval is only when clicking returns when fully warmed up and is no more frequent than a reasonable valve check interval. Even when loose it is only a few thousandths, far less than that of a bad auto tensioner.

So if you find the noise is loudest at the tensioner area/cam drive, don't hesitate to go to a manual ajduster, besides it is less than half the cost of a new OEM unit and will never wear out.

Plus, knowing what I know about Kawasaki singles and most definitely the 250/300 series engine I would say it is a cheap non-invasive first step that takes a half hour to install and adjust. Would you rather spend a wad of money on a top end only to find that the tensioner was the issue, or buy a tensioner that runs $43.20-72.25 depending on the country, with the great possibility it will solve the problem? That is why most people pick up the tensioner and 99.8% of the time it solves the issue.

Tear down sounds like a good idea but I'll do some more investigation first. I have one of those mechanical stethoscope things so I'll send some time this weekend sourcing the noise. I just did a short test ride so would like to know more before tear down

I did spend time looking at the tensioner teeth but it is hard to tell

Another indicator would be what's in the oil filter. If the piston or crank is eating itself, there will be debris in the filter. If it's the tensioner/chain, not much debris. When my bike started to clatter, it turned out that the big end bearing in the crank was hammering itself to bits. Ended up also destroying the piston because of all of the metal floating in the mix.

I made a video.

I also listened around the engine with one of those HF mechanical stethoscopes, The noise is definitely loudest at the valve cover area right outside what must be the the area of sprockets on the cams. It is louder on the right (cam chain) side than the left I still get some noise down on the cylinder where the piston would be running but it is louder on the left and right vs front and back which does not seem correct for piston slap. I have not drained the oil yet to see what is in there.

It could possibly be the decompressor which is mounted on the exhaust cam.

With that much noise at the head on the right, do not run the bike again. From what I know and have experienced, if it is the tensioner and I am fairly certain i is, that one is so bad that it is totally possible the cam chain could get loose enough to jump time at the crank and stick a valve in the piston. If it was a piston it would be a more rapid clack and not really that loud, with the miles on that engine. Besides from what I've experienced and what others here have experienced, the 250 engine is barely starting prime time at 10,000 miles, so 17,00 miles is so low in that aspect that it just doesn't make sense. I am sending an email to you.

Time to pull the valve cover and do an inspection. Take a close look at the decompressor, make sure the springs are in place. Also, try to determine if the chain is loose. That will also be an indicator for the tensioner.