RD350 engine noise, cant locate

D

dentoncafe

New Member
I just aquired another guys project bike, he put wiseco pistons 1mm oversize in a 350 head on a 250 crankcase, did a great job with the bike, intake is great, reeds are intact, but on kickstart and running, there is a terrible mettalic squeal, squick and its somewhat loud, it isnt really a grinding noise, but ill try and put a video up tomorrow, just wanted to see if i could be missing something before i pull the head off, i dropped oil in the top end and it didnt really go away. It does not have the oil pump anymore, i had to premix, also had been sitting dry from a couple weeks.
 
it is definitely coming from the top end, it wont squeak if i use my hand to slowly push the kickstart, im going to take it to a shop tomorrow to see if they can figure it out before i dive into the motor, if it was coming from the crankcase bearings would it still be loud?
 
That ^ is not as daft as it might sound. Try it to see if it's just the reeds.

My guess would have been a broken piston ring, or leaky head gasket, but I like this idea.
 


Weisco rings in a RD350, one hot run after seating the rings. Made it 3 miles till it started screeching and squeaking, then lost the right piston on the way back home. Total ride time 10 mins before the top of the piston came apart.
 
Spoonz said:


Weisco rings in a RD350, one hot run after seating the rings. Made it 3 miles till it started screeching and squeaking, then lost the right piston on the way back home. Total ride time 10 mins before the top of the piston came apart.
Click to expand...

you are doing it wrong ;D
you really gonna blame rings for that :eek:
 
The ring spun and caught the exhaust port. The ring was made too thin and this happened. So yes I can blame the ring for this. I put factory parts back in mine, and I haven't had a problem in 5k+ miles.
 
Spoonz said:
The ring spun and caught the exhaust port. The ring was made too thin and this happened. So yes I can blame the ring for this. I put factory parts back in mine, and I haven't had a problem in 5k+ miles.
Click to expand...
no you did it wrong
what did you do put wiseco thin rings on yamaha pistons ?
 
Those appear to be very old type pistons that used an L shape (Dykes) top ring. What rings were fitted? Normal late model Wiseco or rings for that old Piston?

Did you build the motor with rings that were clearly too thin for the piston and hope it would be OK or was it built by an OP?
 
Squeaking is probably blown base gasket, acts like a reed as the air comes out, particularly if transfer ports were modified and gaskets trimmed
Could also be from open oil spigot
Blown head gasket can sound the same but you usually see smoke coming out
Either way, it's quicker and safer to pull top end off and check.
New base gaskets are a lot cheaper than new pistons
 
These pistons and rings were to be a matched set from wiseco, older but still new and in plastic. When I put them in, the top of that piston looked nothing like when it came back out. The other piston still looked new. Needless to say it's better to take a more in depth look to see what's causing the noise. Anytime something doesn't sound correct, take it apart and see what is going on. Gaskets are cheaper than engines.
 
The older Wiseco pistons were 'fully variable' quality and size.
It was 'quite normal' to open 20~30 boxes to find two 'close enough' but very very rare to find two the exact same size (or within 0.0005")
You need at least 0.005" clearance with them in an air-cooled two stroke plus the bores may not be the same size
Since they went CNC they have been pretty damn good though
Spoonz,
Looks like timing was over advanced plus a bit lean top end?
 
Spoonz said:
The ring spun and caught the exhaust port. The ring was made too thin and this happened. So yes I can blame the ring for this. I put factory parts back in mine, and I haven't had a problem in 5k+ miles.
Click to expand...

Um, that's not possible. There MUST be a pin in the ring grooves that prevents the rings from rotating around the piston. If there isn't a ring locator pin, then you can't use that piston in a two stroke.

That piston looks melted to me. Detonation is the most likely cause. Too lean, and/or timing too advanced is what I would look at.
 
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