Got the itch today to here the old viper so started it for the first time since winter. Took about 10-12 pulls to get it fired up. After running for 2-3 min I did a compression test ( was just curious ) and numbers were as followed
Pto- 120
Center- 120
Mag-100. Maybe 102
Question is should I pull the head and check the cylinders. Could it just be a stuck ring.
I redid the mag side b4 last winter cause it was low on compression and mid season about 500 miles did a compression test and they were 120 across the board. The sled has bender pipes boysen cages. Opticool head gasket.
Should I pull it apart or just run it. Suggestions please. Thanks
Pto- 120
Center- 120
Mag-100. Maybe 102
Question is should I pull the head and check the cylinders. Could it just be a stuck ring.
I redid the mag side b4 last winter cause it was low on compression and mid season about 500 miles did a compression test and they were 120 across the board. The sled has bender pipes boysen cages. Opticool head gasket.
Should I pull it apart or just run it. Suggestions please. Thanks
viper don't have 3 cylinder heads volume the same from stock factory //this is why u got a lower cylinder compression
Agpetro
Member
modsrx said:
It could be the same compression across the board if the bender head mod has been done to even out the compression because of triple pipes. if the mod has been done they should be all the same.
super1c
Super Moderator
And its the PTO (clutch side) that's 10 or so lower not the mag (chaincase) side. Are you calling the cylinders by their right name. Cause 120-120-110 sounds money if your going mag-center-pto
It had a head mod done from rollform tooling. They were the same compression across the board. After mag rebuild. And mid season. When checked. And now at 120 120 100
No it's the mag side. That is low. ( chain case side )
different story now........
I know the offset compression a stock viper is usually low on pto side. But this is the mag side. Plus the head mod is done. I mean that's the only real way to find out is to pull the head off and look at the cylinders correct.
super1c
Super Moderator
Yup time to pull the head and see what's up.
did you pull the head and inspect the mag side piston?
Well finally got the time to pull the head off today and see what was going on. The mag side piston on the exhaust side was rounded or burned off. Wich to me means it's lean. Or possibly crank seal might be leaking. Any suggestions on jetting 02 viper with srx carbs. Bender pipes. Head are 22cc domes. Boysen rad valves. Stock air box. Haven't had a chance to check crank seal yet.
Backwoods M Max
New member
Are you going to pressure test the bottom end? or just do the running crank seal test with a can of carb cleaner sprayed at the seal. From what I have seen. The crank seals on the yamaha's are incredibly durable, and mounted between the 2 pto bearings so if something goes wrong with the seal it's going really wrong. I always do the spray test in the fall when bringing her back to life, but I have been told they should be a non issue for the life of an overhaul if the sled is ridden every year and not left to sit. I lost my bored out indy wedge due to a bad pto seal, but that is a whole different animal. Single seal on the outside of the bearing and just a plain lip style seal. The sled had been sitting for 10 years too. $500 backyard sled from the neighbor, but I learned a lot from losing that motor. Mostly that an erratic idle is a symptom not to ignore.
Motor is currently apart. Am going to visually inspect the seals and prob do a running crank seal test once it's back together. I donot currently have a leak down tester.
staggs65
Moderator
If you've got it apart, crank seals are cheap, just replace them. It's also a good time to change all the water pump seals. jmo