viper piston question help!!!

Concept Carbon

Concept Carbon

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Joined
Jan 31, 2006
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Age
45
Location
Ottawa, ON.
I pulled my cyl's yesterday to get ready to swap in a srx base gasket. So decided might as well change my rings.

I beleve I may need to change my pistons as well #$%&* ( not in budget)

I measured my pistons 10mm from the bottom with a dial caliper and got 2.7095 on all 3 and they are supposed to 2.7143-44. Im going to try to get a micrometer on them and check my caliper at work to make sure its calibrated.

besideds that can i just change the rings?

here is a pic of my pistons

pistonclearenceuy7.jpg
 
^^ I agree. Instead of saying this my own way, here's Mrviper's post on my pistons that were .008" out of spec.

Got your pm. I would personally replace them if it were mine, .008" wear is pretty significant, sure it will still run but the piston will never have the stability it had when it was .008" larger. The rings are what keeps the piston stable and once the rings wear the piston begins to rock back and forth in the bore, this is what wears the skirts down as you have seen now, replace the rings every 2500-3000 miles and the pistons last a long,long time.
Theres alot of people who think just because its a yamaha it will run for 20,000 miles with no tune up, and it will, but it will never hold pressure in the cylinder for very long as it will have blow by. the blow by ontaminates the fresh charge in the case by leaking spent exh. gasses into it and this lowers the power output, think of it like a EGR valave stuck on in a car, they dont run too well unless wide open when that happens. The thing is this blow by happens over time and the rider usually doesnt notice the power loss so much as all of a sudden the sled wont pull the current clutch weight anymore(low rpm) and when they get the sled rebuilt topend wise they think its fast as heck again...LOL!
The black below the second rings is blow by, I have seen worse then yours but its still there none the less.


I see everything in your piston that I saw in mine, only you have some good rub marks on the intake side of your pistons. I never had these that bad.
 
Get new pistons, rings, wrist pin bearings, and a gallon of amsoil interceptor. Get it back together and run the snot out of it this winter.
 
I see signs of a cold seizure there at one time by the looks of the mag piston, Not enuff warm up time before lettin her have the throttle. I would not reuse those in my own engine let alone someone elses, I know they are expensive but replacement would be wise. Your engine, your call. Plenty of blow by happening there.
 
mine were worse yet but still pulled 110pto 130 center and 130 mag kinda strange. I cleaned up the pistons and there fine, no scoring or any scratchs for that matter. they dont look like they have any wear on them. Only 2600ish miles on mine too on mostly yamalube, then I switched the amsoil.
 
thansk for all the help, im going to get new pistons and rings. Can I reuse the rist pins.

mrviper do you add oil to your gas when you do break ins. also would it be a good idea to add a little oil to my crank while its open.

my cyl look brand new. do i need to use a 240grit flex hone, or can i just wet sand with 600 quickly.

sucks cause im going to have to break in my engine with srx pipes for the first time. Il jet il jet it rich 160s and 45s then when switch to 157.5 and 42.5.
 
you want to run yamalube for a tank of gas to break in your new top end. then switch over to yamalube.

You have to take a close look at your wrist pins. If they are like a dark purple color and appear to have been under alot of heat stress, can them and get some new ones.

The wiseco wrist pins are good to get. They might be cheaper too and are only 2/3 the weight of a stock yamaha wrist pin (less reciprocating mass and little faster rev)

I never added oil to my gas except when the sled was delivered from the dealer. Just soak all the new parts in 2 stroke oil and install them. Lube up the cylinders and rings reall good during the install.

If you stop for the night cover it up real good and while working on it so you dont lose a circlip or anything small like that in the crank case
 
ya, you most likely could just clean them with laq. thinner and a scotchbrite pad.

if the cylinders still have factory crosshatching and are not all glazed and shined up, you dont need to hone them, just use a scotchbrite pad, laq. thinner to cut any deposits and clean/scuff them up, install new rings/pistons and run it. I dont ever put oil in the gas, this actually leans out a engine, as the oil displaces the gas and leans the fuel mixture, thats a old habit of yesterday........... the new rings and platings of today will be fine with just a couple of heat cycles, then ride the sled as normal, you can simply heat cycle it 2 times in the garage, run engine varying throttle till warmed up, let cool and repeat, thats all I ever do and I have never had a failure yet using this method of break in.
 
If you need a wrist pin puller, I can lend you one, also have a 280 grit 3 stone hone I can also lend you. Look up in working log, crank & cases...We are most likely neibourghs…LoL…
 
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