Question about rebuild???

yamvip

yamvip

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Jan 27, 2004
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I'm thinking i might do a rebuild on my viper,it has 4500 miles,is there a need for a total rebuild or just rings???Not sure if it really needed,new pistons,clips,etc.Wondering how many of you did the total rebuild,and who didn't.Another thing is I haven't got into to engine yet.Obviously if the skirts are worn,then a total.I would like some opinions??????
 
There isnt anyone with a good working crystal ball that can see inside your engine to tell you if the pistons are worn!!, it comes down to alot of differnt factors, and oil type is number one reason. The better the oil, the less wear! take it apart and measure the piston skirts and see if they fall into the correct specs. You may just need a set of rings and some gaskets and your back to new like performance.
 
Measure the piston skirts,??See that is why i asked didn't know that,do you know what the measurements are???,and or how i can get them??
 
pretty simple, get a set of digital calipers and check the size of the skirts below thw wrist pin, your checking the diameter of them basicly, so youd put the calipers on the front and rear of the piston, they should be checked approx. 10mm from the bottom of piston, they should be 68.944-68.947mm

BTW- if you plan on doing this and dont really have alot of expertise in this area, it would be best for you and your sled to simply purchase a yamaha shop service manual, it has diagrams showing what I am explaining and it gives you all the information needed to complete the job, such as torq specs for bolts/nuts, and procedures to go thru in steps to complete the job correctly, they are a great asset to have.
 
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they should be 68.944-68.947mm
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.003mm is equal to one ten-thousands of an inch, pretty much impposible to measure that with a caliper! Thats .0001 of an inch! If you drove the sled 500 miles the pistons would be out of spec. This is the factory sizing when they manufacture the pistons, I know they say to replace them if they are smaller, but you need to take this info with a grain of salt. If you really want to know if the pistons/cylinders are worn out, the best, and cheapest way is to remove the rings, and put the cylinders/pistons back on the motor(you don't need to torque them down). Then turn each cylinder to top dead center, then try to slide in a .004 feeler gauge between the piston and the wall. This will give the most important reading of wall clearance. Even if the .004 will go but a .005 won't, I would still just throw a set of rings in. If the cross hatch is gone, you will need to scuff the walls with some 600 grit wet/dry sand paper. Deff get the manual!

Almost forgot the feeler may be easy to get in at the top, but skirt clearance is what we want to measure, so it needs to go all the way down. If it does that they are out of spec.
 
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ahh...... those are the specs for the piston being new, the largest, under the minimum worn, so yes its that easy to see if they are worn below 68.94mm!!!! if they are worn they will not only be worn by .0001", it will be much greater, once the rings have gone south and the piston begine rocking back in forth in the bore a good bit of piston skirt will be worn away. You will also see what looks like a dime sized flat smooth spot worn right on the skirts from rubbing the cylinder. Dont make this out to be rocket science cause its far from that!!!!, most guys here do this for fun, I make a living doing it and I use a micrometer, most here probally dont know how to read one!!, this is basic stuff for guys to start learning how to do self repair! Dont confuse people!!!
 
so yes its that easy to see if they are worn below 68.94mm!!!!
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Buy a brand new one, and measure it!!!! use a mic.
I GUARANTEE that it will measure out at 68.95mm (2.7145")
Stock bore is 69mm (2.7165")
That leaves .002"-.0023" Clearance new from factory(tight).
.004" is better for a hard runner, not so many squekeies.
Just saying clearance is the issue, better gauge of acceptable tolerance.
Hell a viper is within spec at .009" over skirt/wall clearance!
 
Again, lets not cloud the water for others!! Why must people make mountains from ant hills here on this site? A basic question was asked by the original poster, and he was given a correct answer, the correct factory specification answer! end of discussion!

The entire reason yamaha made the powder forged piston was to run a TIGHTER skirt to cyl wall clearance, this provides BETTER ring seal and BETTER piston stability, the piston does not expand rapidly like a wiseco forged unit does!! Running it looser in the bore is completely wrong, you lose performance that way! a looser skirt to wall does not make the engine any less prone to squeeking a piston, thats from incorrect warm ups and /or lean jetting! The std wear limit is .002"-.0027", pretty simple, will it still run if looser??, sure!!, is it to factory specs....NO!

If you want to make specs other then what the factory reccomends for yourself fine, but dont cloud the water for others trying to learn the basics. For first timers your making them feel like its something they cant handle and its quite the basic repair, or preventive maint.
 
they should be 68.944-68.947mm
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=.003mm or .0001"

The std wear limit is .002"-.0027", pretty simple
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=.0007" or .017mm

Now your giving two different sizes. Which one is it then? I would like to see you get an accuate measurement with a caliper below .001"
http://www.onlineconversion.com/length_common.htm

A basic question was asked by the original poster, and he was given a correct answer, the correct factory specification answer! end of discussion!
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HERE YA GO RIGHT FROM THE MANUAL! This is whats important. I'm just saying the SRX specs are a little tight, ya can get away with more skirt clearance and not have a any problems. YOU guys can do what you want, but just measuring pistons isn't telling you the whole story.

Manual says .004" (.10mm) maximum skirt clearance For 01 SRX
manual says .010" (.25mm) maximum skirt clearance for 02 VIPER

a looser skirt to wall does not make the engine any less prone to squeeking a piston, thats from incorrect warm ups and /or lean jetting!
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Lots of guys who race run lean jetting. Answered that one yourself.
 
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LMAO @ triplexxx!!! ya just cant quit can ya?? go on with your bad self....LMAO!!!

Yamvip: dont worry, get a service manual and check your stuff out, dont get all taken in or intimidated by some arguing non pertant information, you need not look any further then a hundreth to see if your pistons are in spec or not, if under 68.94mm or 2.71" they are worn. Take a peek at the skirts and see if they show "bald" spots or semi flats worn in them, will be real smooth as the rest of the skirt will have tiny ridges in them, this is a tell tale sign they have been let go too long between rings. It pretty much boils down to how good the oil was that was run for 4500 miles and the type of use, easy,hard,or beat.....LOL. I have seen sleds with 7000 miles and the stock pistons in yet and check good, but they have had rings replaced every couple thousand miles, and synthetic oil used. good luck!!
 
68.944 millimeter = 2.714", low side tolereance on original post.

NOW it's....2.71 inch = 68.834 millimeter

HUGE difference between 2.710", and 2.714"

I was just saying that if you were to measure them according to the original info provided, they probablly would not have been within spec. But could have been totally useable. At least now you won't be wasting money on pistons that are still good. The original spec of 68.944mm-68.947mm is way to tight for junking out pistons, and is actually the yamaha's factory tolerance for manufacture of pistons.
dont get all taken in or intimidated by some arguing non pertant information
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Not hardly, I would have not argued this unless I knew it was wrong. Just trying to clear things up for you. Don's not stupid he knows who is right.
 
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