x-2 compression numbers

chadman154

#Itsonlymoney !!!!!
Location
Dirty south
what should the compression be on a 650 with a mariner head and mariner exhaust. it appears no porting has been done.

i did a compression test and front cyl had 140 and rear 200. tested it three times all the same. pulled head. everything looked normal and in order, re installed head, front comp now 60 and rear 170.

what could cause the eratic compression rates?
 

Vumad

Super Hero, with a cape!
Location
St. Pete, FL
best way to find a problem is by messing with one thing at a time and seeing if anything changes. Your removed the head and you lost compression. The only part of that process that effects the compression is the head gasket or O-ring. I would start there.

You wont be able to see if the lower compression of the front cylinder is because of the rings. The clearances are just too small to see. I believe the only way to test them is to replace them.
 

chadman154

#Itsonlymoney !!!!!
Location
Dirty south
x2 compression

is it possible to have 200 on a 650 with a head? i know the gasket could be bad on the front to cause the drop, but what would make the rear so high before i opened it up?
 
Location
Barrie, ON
The head could nake it that high. When you reinstalled it possibly the rear is leaking a little also. Did you notice any scoring in the low cylinder when you had the head off. I'd pull the cylinder check for damage then install a new gasket. If your at 200psi and only running pump gas that might be why you have your problem.
 

dbrutherford

Parts Whore
Location
Fairmont, WV
All 3 of my 650s are between 140 and 175. All with stock heads and different hours on the engines.

I agree with those numbers.


I ahd a 650 with a Mariner head years back but I never trusted my compression gauge.


Are you holding the throttle wide open with a fully charged battery when cranking the engine over?


You might also want to try a leak down test too for good measure.
 
is it possible to have 200 on a 650 with a head? i know the gasket could be bad on the front to cause the drop, but what would make the rear so high before i opened it up?

haha! psssh 200, is nothing compared to the 235 i had on my old 650 motor, wanst reliable for $#*t BUT it screamed!:brap: i was running a milled ocean pro on a decked and ported cyl with big bore sleeves and 660 pistons. had to run VP116 minimum, and i still blew it up twice a year!

anyways, 135 i believe is stock compression. stock motor with a high comp head should be around 175 or so, depending on what domes your running.


When checking compression 1. make sure the tester is screwed in all the way! ( late night.. too much beer... too little sleep... long story.. dont wanna talk about it..) 2. make sure you have a fully charged battery and you hold it at WOT 3. crank it over till the needle stops climbing, about 5 seconds-ish.
4. repeat.

If your running a mriner head theres a chance one of your O-Rings are bad, change those first since theyre cheap and easy to do. Also MAKE SURE you used the correct torque pattern. start in the middle then work your way out ( a lot of heads are numbered) make sure you torque in steps, toruque them all to about 10 ft/lbs then go back and bring them to 22 ft/lbs ( at least that was the specs for my ocean pro) retest it and go from there. if its still low in one cyl, pull the motor out, change the rings and try again, if its still low, bore it and put in bigger pistons, if you still got low compression, you might want to invest in a new tester.. wait maybe trying another tester should be like the second thing you try.. hmm.. crap...another late night.. no sleep.. except unfortunately no beer this time..
 

agua

FIshing for Stand ups
Location
Seminole, Fl
My x2 has marrener head, pipe, box and it has 185 even a


and thats the highest ide ever wanna go since anything over you have to move into race fuel
 
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