Viper Blow-by

[sxr_700]

I noticed last fall my viper had compression on the lower side for only 2500mi. Ive come down to the conclusion that from starting it up and letting it idle alot before I drove it brand new, the cylinders glazed before the rings seated. All three pistons have blow by all the down past the wrist pins in spots. The cylinders are good and still have a visible cross hatch, no bad scoring or anything and the pistons look to be in good shape with no scoring or anything else. I think I've found out why it doesnt have the snap it did when I first bought it. Whats your method of breaking the glaze on these cylinders??? On my motocross bikes I just use a green Scotchbrite pad with WD-40 and then wash them really good in dish soap and those get rebuilt once a year, will that work or would 140g emery cloth be better??? Can I reuse the y-pipe gaskit or will I have leaks? Also do you recommend that while its apart I use the SRX base gaskit?? Thanks

 

[redsnake3]

srx basegasket is only needed if the sled is piped, even then im not sure it will work as that is a trick used on vipers and as for the blow-by you will want to get new rings installed and have the cylinders honed.

 

[sxr_700]

Ive had bad luck with a dealer honing a cylinder on my old 04 YZ125, as far as honing, they used a finger hone which chiped the plating on the exhaust bridge. This is why I only use a scotch brite and some oven degreaser. It breaks the glaze quite well and it wont remove any material from the cylinder. But dont leave it on too long. If I had a ball hone then I'd do it, around 240 grit aluminum oxide and 10% smaller than the bore. I would use the srx gaskit if It helps with cooling incase I pipe it this year as I'm undecided.

 

[sxr_700]

Reringing it is my plan.

 

[redsnake3]

i dont think that the srx gasket will fit on the redhead engine. as for the hone you need a good hone, the x pattern is very important.

 

[change_up]

It's not a red head motor. The title and first sentence in his post says "viper".

 

[redsnake3]

It's not a red head motor. The title and first sentence in his post says "viper".

just goes to show my attention span, lol. i seen his name and figured it was a redhead. so do the gasket change when you pipe the engine, till then the viper one is better stock. still gonna want to hone the cylinders.

 

[sxr_700]

What hone do you reccomend?

 

[daman]

What hone do you reccomend?

The only one that should be used on a 2-stroker is a 3 stone spring flex hone in 240-280 grit stones, but IMO it's not really needed, Nic. is some hard stuff(very tough) to tell ya the truth a hone really won't touch it much

 

[redsnake3]

i disagree, i have done this myself a couple times, all that is need is a little more spring pressure on the stones and a little higher rpm.

 

[daman]

i disagree, i have done this myself a couple times, all that is need is a little more spring pressure on the stones and a little higher rpm.

Well the ones i did it really didn't do chit,so i don't waist my time, sled rings today are desighnd to break in with out honeing...

 

[sxr_700]

See thats what I was thinking. My YZ's and RM's have never had any blow-by/low compression/rings not seating issues. Those bikes also wear quite a bit more by sucking in dirt through the filter and are always screaming, atleast mine are lol. Oven cleaner breaks the glaze with a scotch brite pad. If your cross hatch is gone after deglazing then it needs to be replated. I've had cylinders redone at US Chrome and they use a diamond hone to cut the cross hatch in plated cylinders because the plating is that hard. I'll measure the ring end gap and let you know for each cylinder. My guess is it wont be that loose but just didnt wear to the cylinder to provide a good seal.

 

[sxr_700]

Also does anybody know the torque specs for the cylinder base nuts and head bolts.

 

[daman]

Check tech it should be there,if no one jumps in..

 

[sxr_700]

Ok tech says 20 on the heads and 24 for the cylinders. THanks

 

[sxr_700]

The ring end gap on all 3 was anywhere from 0.18-0.20 which isnt all that loose, but IIRC my compression was only 110 on pto and around 130ish on center and mag. The pistons show a lot of blow-by and I know they didnt seat for shit so I'm thinking thats my problem. Anybody know if you can reuse the y-pipe gaskit???? I'm ording everything I need tomorrow so anyhelp would be appreciated. Thanks

 

[mrviper700]

ya, its steel, you can reuse it, I would spray it with some hi tack gasket spray.

you do know that the pto cylinder in a viper will always read lower then the center and mag due to the combstion chamber being larger then the other 2 are, this is how yamaha used straight jetting in all 3 and to compensate for the added heat given off by the pto cylinder/clutch.

I would just quickly run a 240-280 grit hone up and down a few times then install the new rings with the "T" mark facing up, and just use plain ol yamaha lube to break it in for the first couple heat cycles, then rip it as you ride it. You can just heat cycle on a jackstand. vary the throttle openings, run till warm and let it cool completely, do it 2 times and shes ready for action!

 

[sxr_700]

Yes I realize that the viper compression is lower, but I'm thinking all 3 #'s should be higher considering the blowby. What type of hone would you use? Ball type flex hone?

 

[mrviper700]

I use a flex hone, 3 stone hone, have used it for 10-15 years and have yet to damage a cylinder.

 

[daman]

Do not use a Ball type flex hone...

ball hones are junk and they dont cut evenly in a 2 stroke, the balls flex in and bounce off the sides/edges of the exh port and transfer ports, you get a much better job with a 3 stone spring flex hone..