1986 ATC 250es Engine Tick/Rattle

[MN250R]

Need some help. I got this tick/rattle I cant figure out. Its actually louder in person.First off, the machine runs awesome! Aside from the tick. The weird thing is it only does it under a load.Once you get in the rpms it goes away. If I ease into the throttle, it won't do it either. It's when you stab the throttle under a load. Motor is completely rebuilt with a new 11.1 wiseco piston, piston/cylinder were matched at a machine shop specializing in race sleds/atv building. New did timing chain, valve lapped with new valve springs. I have tried multiple pensioners with same results. I even tried another rocker cover I purchased, Same thing. Engine leak down test showed no leakage at all. Not to mention setting the valves at .08 numerous times.I even did a smoke rest on the exhaust thinking it was leaking st the manifold. Which it wasnt. I'm at a total lost.
Other than that annoying tick. It runs great. It didn't make this noise until after my rebuild. But I replaced clutches, stator, centrifugal clutch etc at the same time so it's hard to pin point it. Hell, I even added 95 octane thinking it was pinging. Any ideas would be great if anyone has any or ever experienced this noise. See videos below. You will hear it. Thx!


https://youtu.be/zcf91kDpxUY

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[shortline10]

Did you check how tight the upper rod bearing / wrist pin was ?

[ps2fixer]

I second the wrist pin knock, comes and goes with rpm/load. Sounds real similar to the 250sx I had with a bad rod which was worn on one side making an egg shape and would only knock at just the right rpm. Engine was ran like that gently for years till the rear end splines slipped and I bought it. I cheated and just did an engine swap since I had a ready to go spare and traded to my cousin. Pulling straight up and down it felt tight, but you could twist it side to side and see the piston move a lot more than it should.

Not really advising to keep riding, but I've bought a Toyota Camry from a lady that had the same problem. I asked her how long it's been doing that noise and she said since she bought it like 100k miles ago (it had like 280k miles or something like that). It came with really good tires + a spare set of really nice winter tires for $500 back when scrap prices were up, couldn't pass up the deal.

[shortline10]

Using a straight weight 50 or 60w motorcycle oil will help with the knock . Just make sure you give it a few minutes to warm up .

[MN250R]

Thanks for the reply! , I couldn't feel any movement when I had it apart. But it never did this before until after I did the rebuild.

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[MN250R]

Using a straight weight 50 or 60w motorcycle oil will help with the knock . Just make sure you give it a few minutes to warm up .I read the question wrong, I didn't check how tight the wrist pin was in the bearing on the connecting rod. I only tried to move the connecting rod when I had the piston off for play. I might just have to pull it
apart again and see. Do you think a bent valve could cause this or a worn cam? Thx!

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[ps2fixer]

It would run poorly with top end issues. You can validate the top end, head gasket and rings are holding up well with a compression test. Normally a top end noise always clicks reguardless of engine rpm and it physically sounds like it's coming out the top of the engine vs the mid to lower end. Probably not too hard to check the wrist pin, don't have to remove the piston to check. Sadly to replace it's likely the connecting rod where the slop is at which means splitting the transmission and either paying a shop to replace the rod and big end bearings, or buying a known good crank with a good rod (more risky).

Generally bent valves either makes for low compression or no start, worn cam just makes low compression (less lift to open the valve). In extreme cases, the surface the cam rides on could make a bit of noise but never personally encountered that issue so not sure what the sound is like exactly but read it's somewhat common if the oil filter gets installed backwards and the top end is starved of oil.

[shortline10]

Being that the noise is only present under a load is tell tail sign of a loose rod bearing or possibly piston slop .
Like I said just run some heavy weight oil and see if it gets any better .

Edit :
Just noticed your running a high compression piston !
Could be spark knock from low octane fuel . Do a compression test , if your over 210 ish you might need an additive or race fuel .
Did you check piston deck height ?




I read the question wrong, I didn't check how tight the wrist pin was in the bearing on the connecting rod. I only tried to move the connecting rod when I had the piston off for play. I might just have to pull it
apart again and see. Do you think a bent valve could cause this or a worn cam? Thx!

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[MN250R]

Being that the noise is only present under a load is tell tail sign of a loose rod bearing or possibly piston slop .
Like I said just run some heavy weight oil and see if it gets any better .

Edit :
Just noticed your running a high compression piston !
Could be spark knock from low octane fuel . Do a compression test , if your over 210 ish you might need an additive or race fuel .
Did you check piston deck height ?Thanks for the reply, I did not check the deck height. I purchased the new piston wiseco piston from a member on here. .I did talk with the machine shop that did my cylinder work and they also thought it could be the rod. They said I would have to pull it apart again and check for any slop up and down. I also am running the accelerator octane to my non oxy that puts it around 95 octane. I'm running gn 4 10w 40. I was running 15w-40 rotella t before the rebuildhttps://uploads.tapatalk-cdn.com/20191216/af562a8818fdb284bd584a5dc8fe896a.jpghttps://uploads.tapatalk-cdn.com/20191216/4c97b7abcffa06c4caf44c1cf831d46a.jpg

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