04 Mt. Viper--Just rebuilt but still low compression???

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04viper700

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Okay so I just bought this viper the other day, I did a compression check because it wasnt running right, PTO cylinder was 85Lbs other two were 120, I know vipers had staggered compression but this was too much different so I torn her down. PTO was a little scored but very savable so I decided to put three new SPI pistons in it, Cleaned and reset power valves, and lightly hone the cylinders with bead hone......Got done with it yesterday and heat cycled it a few times. Today went out and rode it and ran GREAT (aside from running out of gas). When I got back to the shop we pulled a Compression test and it came out at right at 100 PSI on all three holes??????
We've done alot of motors and never had anything like this happen, Has anyone ever had this happen on a viper motor????
 
Use a different compression gauge. My guess is you are okay and don't run out of gas again (causes a lean condition, etc.).
 
Used two different guages ( one snap on and one craftsman) already same reading, it runs great and holds about 8800 rpm great....just weird......

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That sounds low. My old 8000+ mile venture has 128 psi in both cylinders. I was shocked when we just did a compression test. Yeah the reeds were needing replacement, but the top end was sound.
 
Im just dumbfounded by this, I keep going back thru my head making sure i didnt miss something inside....only thing I can come up with is the new head gasket (windrosa) seemed a bit thicker than stock.


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that could do it. also, did you break it in using synthetic?? synthetic isn't as good for breakins because it does its job so well it doesn't let the rings seat as quick.
 
I did drain the oil tank and and fill it up with klotz....when assembling used fogging oil for all surfaces for start up, wonder if I just give it some ride time if the compresion will come around?

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After market will lower comp. I know this to be factual with Winderosa for red head engine. Has head ben cut? AKA Bender mod? If head is still stock I see no reason why comp should be even. If you have the head off again I would consider putting an opticool gasket in there.
 
As far as I know head is stock...I think ill pull the head and have a look.

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Poped the head off this thing today and switch gaskets to OEM and still no difference in compression, Thinking Im going to take out the KLOTZ and put some mineral oil in it and run it a while and see what happens.....:o|
 
Thats Correct it is a windrosa base gasket also, However I did verify that that was the same thickness as OEM with a micrometer.
 
Well, took out the klotz oil and put in some mineral oil....went and put on 25 miles and it ran beautifully 8500-8800 rpm and seen 90 a couple times riding the river....got home and pulled a compression test and still only 100 psi
..., Ive been around sleds and alot of yamis my whole life and never seen this happen, how could it be running this good with that kind of compression....goes against everything i know..... just plain wierd......on the up side I spanked an 08 800 rev :D

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Yes i did, well wothin spec...I own a power sports store and we do alot of motors, so all the technical stuff is done on every motor we do....

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My Viper also runs low compression (100-105) but runs excellent....although will not beat an 800 rev lol. I bought it just before this season and the previous owner told me it had a brand new top end....I was a little worried but figured the rings would seat themselves in after a couple hundred miles. They should be seated after this but I'm still cranking the same compression (got 400 miles on so far). But like I said, I'm getting the exact same numbers you are.
 
Im running stock spring with two 17.2 rivets in the weights....only thing im really worried about is if it will run fine at altitude 7000+ ft. Guna weight it with 13.3 outer hole and 13.9 inner...if it wont pull rpm i guess ill grind out the outer rivit and hope for the best

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