Horrible knocking sound, almost like the piston is rattling in the cylinder, right after a complete rebuild, top and bottom end

[2strokeRobert]

So I just finished building a 2006 cr85r, and it started up on the second kick, got the idle adjusted right, and it was running very smoothly and quite to the point until u gave it a Lil rev. I cut the bike off, because I didn't have time that day to run it through the heat cycles. Everything was fine and dandy, couple days later I had the time to run it through its cycles, so I started it up, let me add that I had maxima 2 Stroke oil at a 32:1 ratio and premium gas, and Honda HP transmission oil in the case, so I started it up, and again it was running smooth, I let it idle for about 5 mins then pulled in the clutch and ran through all the gears, still running smooth, put it back in neutral and let it idle another 5 or so min, giving it a little rev here and there, still sounding great, then a friend is like why is it so quite, I'm like its not quite, lol and gave it a Lil rev, to get that 2 stroke music going on, still sounding good, gave it a little flick flick of the throttle again, but still careful not to pin it, and boom, all of a sudden it goes from running nice and smooth to a loud knocking noise that sounds like its from the cylinder, almost as if the piston is rattling around in the cylinder. So I kill the bike, worried I may have messed something up, give it a sec, and try to start it up again, and as I slowly kick the kickstarter as to not really try to start it, but just bring the piston up and down to have a listen, the same knocking noise is made. It sounds horrible. Like really really bad. So I'm like to hell with it and give it a full kick, bike starts first try, but with the same sinister sounding knock. I don't let it run for anymore than 30 to 40 sec, and I cut it off. Still thinking to my self did I forget something, I know I put both circlips on the piston, each side of the wrestling bearings, and I know I placed the ring in the right place were the gap is on either side of the little spot on the piston where it should be. Lemme add that I used a weisco piston, and a hotrod crankshaft and the stroker Rod kit. So the bike will still start on the first kick, and it will run, but with the nastiest sound coming from the cylinder, and so I've decided to not crank it anymore out of fear that I'm going to mess up the piston or cylinder, if I hadn't already. I plan to pull the head off, and possibly the cylinder this evening to try and diagnose the problem, but if anybody can give me any advise or opinion, or even share an experience where maybe the same or similar thing has happened and what to do next would be extremely helpful. Thank you.

[BarterFreak- 116]

Best thing to do is open it up and see what's up.

[Excitable]

when you ordered the piston did you have the cylinder measured?

if so who measured it?

[KPRacing]

If the bike starts up & runs fine, I would think something came loose In the engine. The bolt on the end if the crank, clutch hub nut, flywheel nut, ect. Definitely check out the top end but I would recommend pulling the ignition cover & right side crankcase cover to have a look.

[2strokeRobert]

No I didn't have it measured, but it was running great and smoothly at first, then it just happened all of a sudden, almost as if the ring wasn't there. If it was running smoothly at first then that wouldn't be the problem would it? Or could it because the metals expanded after it heated and caused the extra space?

[2strokeRobert]

Yeah Imma pull off the crankcase cover too, as well as the ignition cover , it almost sounds like the kickstarter might be catching and clicking as the gears turn, but I know I put that in right because I had to install it a second time after taking the clutch basket off again as well, (only way to install it properly is by taking off the basket) I followed step by step to cyclepedia's directions, as I did for the whole bike.

[Excitable]

No I didn't have it measured, but it was running great and smoothly at first, then it just happened all of a sudden, almost as if the ring wasn't there. If it was running smoothly at first then that wouldn't be the problem would it? Or could it because the metals expanded after it heated and caused the extra space?

it is very possible but not guaranteed your issue.

 

maybe get a vid of the sound?

[Michael1979]

My bike seems to be having the exact same noise. If you could post a video I'd be great to find out the problem.

[Michael1979]

Just to add, the knocking noise on my bike seems occur JUST after top dead center...

[Turboloader]

Sounds like you have mismatched piston in the cylinder. The junk-yard man has a video how to correctly measure cylinder bore out of wear zones, and "fit" correctly! Go stock! I bet your scoot ran great with the stock gear in it!

[mxsteve1968]

hot rods crank???? quite possibly an upper or lower rod bearing, did u check the crank for true, before u installed it? hr cranks are known to fail in the small bore engines if they are not as close to zero as possible. never use aftermarket internals they just dont hold up as well as OEM...I hope its not the rod bearings. GOOD LUCK

[CR250_182]

Check your engine mounts and make sure everything is tight. Not saying it's that, but I've have a problem before where I couldn't tell where a knock was coming from, the I realized it was just the whole engine because the bolts worked themselves loose

[2strokeRobert]

Sounds like you have mismatched piston in the cylinder. The junk-yard man has a video how to correctly measure cylinder bore out of wear zones, and "fit" correctly! Go stock! I bet your scoot ran great with the stock gear in it!

well i never knew what it ran like because when i got it, it had the cylinder off and piston and rod was exposed and bottom end was kinda rusted and the crank was seized, the rest of the parts came in a box, i payed 50 bucks for it so im not really complaining, for a 2006 cr85r you cant beat it.   

[2strokeRobert]

hot rods crank???? quite possibly an upper or lower rod bearing, did u check the crank for true, before u installed it? hr cranks are known to fail in the small bore engines if they are not as close to zero as possible. never use aftermarket internals they just dont hold up as well as OEM...I hope its not the rod bearings. GOOD LUCK

ive built 2 banshees using hot rods crank, one being a stock 350 but with the stroker crank, and another that was bored and ported and polished to a end result of 400cc and both are running great and have held up to the abuse we put them through, no doubt OEM will always be better, but sometimes you cant always get what you want. yeah i hope its none of those things either, i have yet to get a chance to break it down again, just with the holiday season, and work, its hard to find a chance to get to it, but i do this kinda thing for a living but customers have got to come first.  

[2strokeRobert]

I'm a dummy, in the end it was the most simple thing, yet I had Damn near taken the bike apart 2 times trying to figure it out. Removed the cylinder and clutch cover and all trying to find the problem... in the end it was the magneto/flywheel, the big nut in the center had come lose but wasn't able to back off all the way because of the plastic flywheel cover that sits very close to, resulting in the flywheel moving side to side as it was spinning. My fix was put some locktite on the nut, torqued it down with a air impact, and it hasn't given me any problems since.... silly me

[Pygmy Warrior]

What the hell is a wrestling bearing?

[Excitable]

I'm a dummy, in the end it was the most simple thing, yet I had Damn near taken the bike apart 2 times trying to figure it out. Removed the cylinder and clutch cover and all trying to find the problem... in the end it was the magneto/flywheel, the big nut in the center had come lose but wasn't able to back off all the way because of the plastic flywheel cover that sits very close to, resulting in the flywheel moving side to side as it was spinning. My fix was put some locktite on the nut, torqued it down with a air impact, and it hasn't given me any problems since.... silly me

?

 

glad you found it and it was a easy fix. ?

[Turboloader]

A good lesson learned, keep all bolts tight and in torque spec, people!