2007 Bayou 250 KLF250A
In an ongoing attempt to find knocking noise on clutch side of Bayou 250, I decided to bite the bullet and totally dis-assemble the engine. I have split the crankcase, and cleaning and inspecting each component. The left side of crank case fell and hit the floor in such a way it hit right on an area, that is used to guide a bolt through to the right side of crankcase that has a threaded hole. Of course the whole crankcase is one cast side. It does not appear to be have damaged the mating surface in any way. There are 13 total bolts that clamp the crankcase together, there is a bolt every 2" ~ 4" around the entire crankcase. With this broken molded piece it will effectively, not allow me to hold that part of the crankcase together in that one location with the torque the manual specifies. What are you all's opinions on the possibility of this point leaking oil? I am going to use some type of gasket sealant when I put the crankcase back together anyway. I could buy some used crankcase off of Ebay, I am interested in everyone's opinion.

 

If the surfaces that mate together are flat and un-damaged they will probably be OK with a bolt missing. Worth giving it a go anyway. Bolts missing below oil level are more prone to causing a leak, for obvious reasons, but as there is a bit of pressure in the crankcase when running, oil vapour will leak out at higher levels if it can.

 

Merryman, thank you for your quick reply. I am sad to say, I did not think about the missing bolt being above or below the oil level. fortunately it is above oil level.
Question: Have you ever heard of bearings, or oil pump causing hard knocking? The reason I ask is, I first addressed the "piston slap" possibility, by removing the piston that I had previously installed to the "original piston", with new rings. That made the top end as quiet as I have heard, you can hardly hear the valve lash. What propelled me to tear it back down to the point it is now, is because putting the "original piston" in, made it easier to isolate the noise to the "right" side of engine, and appears to be louder at the area around the clutch adjustment area. I have checked for slack in the piston rod, which is really what I had expected, but if it has any looseness I cannot feel it, or see it. I have purchased a good used oil pump, because the original oil pump has a scored pump impeller, I have not seen how this impacts noise yet. The area that has noise is in the area of transmission inside the crankcase, but the bearings feel smooth in this area, REALLY every bearing feels good, except one. When I cracked the case, everything had oil on it, but when I rotated this particular bearing there was a Little catch point, I have used foaming engine cleaner and a pressure washer and now all bearings feel smooth. The needle bearings I do not think they could make the sound I am looking for, unless one was coming apart, or damage in some way, and they are fine. Back history, on this ATV, the person I purchased it from, said it couldn't hold oil, and he had little children that loved to ride it. So Its possible, they would run it even if the oil level was low, as long as it started they was good. And it had a broken timing gear, bent valve, worn cam lobes, and stretched timing chain. Now it doesn't leak or burn oil, and runs like a top, just loud knock. I know it wont be like a brand new one, but the maintenance person in me, knows that sound means something. The video "1213-1" is when I first start it with old piston in it, and "after 30 seconds" is literally that engine after it had been running for about 30 seconds, on the same day.

 

It does sound quite bad and is probably something that reciprocates, so either piston or con rod. So, big end, small end, or piston or con rod hitting something else. However I had a similar problem with an Eiger a year ago, it had a badly wrecked big end, rod had got so loose it smacked a lump out of the cylinder, so new con rod, crankpin, cylinder and piston. Wretched thing knocked like that after re-assembly. I took the cylinder off again but couldn't find the cause, so gave the bike back to the owners. As they have the mechanical sympathy of gorillas, the noise didn't bother them and, as it hasn't come back, it must still be running.

 

Update 12-14-25
2007 Bayou 250 noise issue
i think I have found either the single problem causing noise or at least a large contributor. The pencil is pointing to the bearing i found that had a VERY rough spot during its rotation. This bearing is a 6202-z, deep groove, single shielded bearing. The open of bearing receives its oil for lubrication from 1 of the oil supply lines from the other side of engine, and it share this supply with the final drive gear. I hypothesize considering the oil and inside of crankcase was so dirty the oil was pumping into the non- sealed side, along with trash and debris and caused it to have a bad spot. I have been soaking it in a ultra-sonic bath with acetone, just to see if i could get it to free up, but no matter what i do, it still has that spot.It also did not help previous owner said they couldn't keep oil in it. All the other bearings do not have any seals on them. However if i was to remove the shield i am afraid the oil would go in the bearing and out the other side and deprive the final drive gear of oil. I made a mini slide hammer and it popped right out. I am going to order one if i cant find one locally, after i assemble it and test it i will provide an update.

 

Update 12-19-25, Their are 6 ball bearings installed in the crankcase, of my 2007 Kawasaki Bayou 250. Of course this is not including the crankshaft bearings. I have checked all 6 bearings and found 5 of them to have a rough spot in their rotation, some had more than one rough spots. I started checking bearing replacement cost from some online suppliers and found it would not be economical going that route. So I called a local bearing supplier, and they could cross reference the original bearings, and each bearing was $11.0 ~ $13.0 each. The original bearings was "NTN" brand, the ones I purchased is "Nachi" brand. I have a couple of questions.
1. Has anyone replaced the bearings to decrease noise?
2. Has anyone ever used these bearings in place of the original ones?
I do believe there is a quality difference between the NTN, and Nachi, but is there enough of a difference to matter? I think the NTN bearings could withstand more side loading than the Nachi can, but when installed in engine these bearing will NOT be subjected to much if any side loading.Radial bearing strength is rotational. I am interested in everyone's opinion. Keep good clean oil in engine my feeling is I should not have a problem.

 

I wouldn't have thought the noise will be caused by bearings, and won't be any that are not connected to crankshaft, camshaft or balancer because the gearbox bearings are not rotating at idle.

Oddly enough I am facing the same "do I go for cheapo or OEM bearings" on a 500 King Quad front diff at the moment. It was taken in part-ex with 4WD not working. I assumed it was the 4WD motor, a common fault on them, but no, worn splines on diff nose and prop shaft. However on opening up, no oil in the diff, just a small amount of watery grey paste and all bearings shot. Checked on eBay last night and one bearing is £55 for NTN, unless you buy 'em from China where NTNs are listed for under £10, genuine Suzuki is £70. Haven't decided what to go for yet.

 

I agree, for the most part regarding bearing only in motion when moving, verses while at idle. However, 2 of the bearings found with rough spots was balancer bearings. I knew the original oil pump had some bad grooves in metal impeller and impeller plate, so I purchased a used oil pump, from eBay, that looked real good. I was originally cracking the crank case with the thought I would find the crank bearing real rough, however after removal of crank shaft, I cannot detect any roughness in crank bearings, nor can I detect any play or looseness in the piston rod. But I figured while I had the crankcase open, just replace all bearings, and inspect all components as they are being re-assembled. This ATV, had broken timing gear, bent valve, stretched timing chain, severely work cam lobes, and had been ran without oil, until it just couldn't run anymore. I do not know what the stress of being locked up suddenly does the the rotating mass and the support of the rotating mass. I just hope I am not screwing up by using different manufacturer bearings. The strange thing, is the noise I observe with stethoscope appears to be greater from the BACK of the engine and on the RIGHT side (the side that has foot brake pedal on it), I know sound travels, but when I swapped back to original piston with new rings, the sound that I was hearing from the head, stopped to the point I could hear rocker arm lash, but the noise continued from back and right. VERY strange. It doesn't appear to be having an adverse effect on it. It has a brand new primary and secondary clutch on it.

 

If this is a machine you plan to keep and ride hard, a good used crankcase is the “buy once, cry once” solution. If you’re trying to get it back together without overspending, many people successfully run cases with one missing bolt boss when the rest of the hardware is torqued correctly and sealant is applied properly. Before final assembly, it’s also smart to double-check overall engine health and tolerances vin number check tools like https://carfast.express/en/cars/check are useful for verifying related mechanical data and specs so you’re not reassembling around another hidden issue that could have caused the original knock.