Thoughts on compression change

journeyman

journeyman

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Joined
Aug 11, 2003
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1,181
Age
61
Location
Prior Lake,Mn.
Well most of the longterm guys on here have known I have stated over the years that I have had a strong running stock Viper. The last two years things have kind of been a bit less than stellar or inconsitent I should say for my 'ole VIP. I have now 7650 miles on it. Yesterday I went down to our family shop where I keep it and drained the gas out for the summer. For the heck of it I decided to check the compression just for the plain fact that something has been nagging me. I put on probably about 1200+ miles on this year and about 1000 last year. It was two seasons ago I had the sled re-ringed by a buddy that used to own a Yammie dealership and now works out of his garage.......I didn't have time to do it myself. I had not done a compression check since before the new rings to this day. Anyways I just have noticed the sled isn't as stout as normal. My always fast father's Viper was pretty much ripping me up all winter. Here is what we always used to have for compression:

Mine use to be 127/142/142
His 130/145/145

Here is what I found yesterday:

Mine was lowest ever at 119/130/134
His was at 130/147/147 (his now has about 3200 miles)

I used to run a close second to him but this winter he was eating me up.

My questions are.......did my buddy (which I haven't talked to for awhile...long story) use OEM parts or did
he used aftermarket rings and gaskets. I talked with my machinist buddy and he thinks he might have used an aftermarket head gasket lowering the compression.



Any theories?
 

couple other possibilities
1: did he hone the cyls to get a good crosshatch for the rings to seat properly?
2: did he check the pistons to make shure they weren't under spec?
 
did he use a winderosa gasket kit? i believe their base gaskets measure like .018" thick, instead of .010" thick like the OEM gaskets. if so, that would explain compression drop. then again, that would have shown up immediately right after rebuild, so i doubt its that. same thing about head gasket...if it was thicker than OEM, that would have shown up immediately w/comp loss after rebuild. your experiencing a compression loss from ring sealing/seating issues. maybe he did use aftermarket rings. maybe he ground the ring end gap a little on the large side, which is really starting to show a compression loss, as the rings are wearing?? remember, if you want it done right, you gotta do it yourself.....LOL.
 
mopar1rules said:
did he use a winderosa gasket kit? i believe their base gaskets measure like .018" thick, instead of .010" thick like the OEM gaskets. if so, that would explain compression drop. then again, that would have shown up immediately right after rebuild, so i doubt its that. same thing about head gasket...if it was thicker than OEM, that would have shown up immediately w/comp loss after rebuild. your experiencing a compression loss from ring sealing/seating issues. maybe he did use aftermarket rings. maybe he ground the ring end gap a little on the large side, which is really starting to show a compression loss, as the rings are wearing?? remember, if you want it done right, you gotta do it yourself.....LOL.
Click to expand...

Thanks for the input. It may have been from the beginning being I never did a compression check after the rebuild. My father owns the shop where I keep it
and he starts it for me along with his once and awhile. He said he has noticed over the past 2 years that mine pulls over easier. Also that old friend was known for using parts from places like Parts Unlimited. He has since went to selling insurance and I dropped him being his rates were too high and we haven't talked since. (that was another reason he did the work...I had called him on the overcharging rates for home/auto insurance...did work for nearly free) Anyways, I really need to do a thorough cleaning etc. of the sled this summer. I might replace the jackshaft bearing and the clutch side and some other things. Maybe I will put in new gaskets. I have a spare Viper head, but by the looks of it ,milling wouldn't be a good idea. I also picked up some used clutches on here that only have 1000 miles on them from a member. I cleaned them up last night and they show little wear like mine do.
 
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aftermarket gaskets could very likely be the cause, as mopar said, a thicker base gasket will raise the cyl & head a bit. I have had this issue on my srx with winderosa gaskets, the base gasket being thicker than stock. SRX's use o ring head gaskets so no issue there, but a combo thicker head & base will definately lower comp. #'s
 
ottawaair said:
aftermarket gaskets could very likely be the cause, as mopar said, a thicker base gasket will raise the cyl & head a bit. I have had this issue on my srx with winderosa gaskets, the base gasket being thicker than stock. SRX's use o ring head gaskets so no issue there, but a combo thicker head & base will definately lower comp. #'s
Click to expand...

Yeh and the Viper has a one piece head with a head gasket similar in material to the base gasket. It has two or three layers to it.
 
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