Compression Numbers?

D

doug

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Feb 1, 2005
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38
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Mid-Michigan
I'm planning on checking the compression on my sled tonight. It's a 2000 SX700R with about 8,000 miles on it, never been touched engine-wise. What should I expect to see psi wise? Or, what would be the minimum I could live with before I do a re-ring? The sled runs great and doesn't foul plugs, but I've never had a sled this many miles, so I'm starting to think about things to check so it doesn't leave me broke-down this winter.

Also, the compression tester is a ten year old Craftsman, used occasionally. Should I trust it?

Thanks
 
I wouldn't even bother checking, it is time for new rings if they have never been done. Guarantee you are getting blowby and that the ring end gap is quite a bit bigger than new ones. Everything wears, new rings are cheap insurance and you will notice the increase in performance from the tighter rings.
 
This makes me think, I've never actually checked the manual for the compression spec. Anyone know off the top of their head what the compression for a 700 SX should be?
 
Yamaholic, yes I agree, but the problem is time. If the engine meets the minimum compression spec, I would prefer to run it this winter, and I'll have more time this summer to go through it, and do the reed stopper mod, etc...

Anyone know the compression service limits?
 
doug said:
Yamaholic, yes I agree, but the problem is time. If the engine meets the minimum compression spec, I would prefer to run it this winter, and I'll have more time this summer to go through it, and do the reed stopper mod, etc...

Anyone know the compression service limits?
Click to expand...

Also do a leak down test if posible that will tell ya more than a com. test.
 
a sled will run with 90 psi a cyl or on a cyl. if yer over 110 psi id leave it for the season and tear it down in the spring.
 
more importantly make sure they are all within preferably about 5% of each other. Anything over 115-120 is good at that mileage.
 
Thanks guys, I now have my work cut out for me. Finally got it in the garage last night (my brother-in-laws Skidoo and my wifes Polaris have been in there for a month in pieces waiting on parts), and looked under it to discover a broken W-arm! Luckily the front shock looks OK. All the bushings are wasted and most of the wheel bearings sound dry. While I am bummed about the W-arm, I have to say that I have broken this arm on every sled I've ever owned, and the Yammi one has lasted twice as long and been jumped twice as hard as the rest of them. Hopefully the compression is OK, as I concentrated on getting the skid out of it so I can order parts today. I'll post the numbers once I'm done.
 
My sled broke a ring at approx that mileage, cost me approx $1000.00 to rebuild and I did the work. The pistons were worn pretty good, 1 was at max approx .005 wear, the other 2 were at .003 wear. I was pretty suprised at the amount of wear, seeing as I use synthetic oil. So three new pistons, rings, wrist pins w/bearings, replaced PTO crank breaing which has integral seal and mag side seal(which was in dire need of replacenent), gaskets and rebuild 1 jug is expensive compared to a set of rings and maybe a set of pistons. My base gasket and head gaskets I could have reused but I'm not a big believer in that, I know that a lot of guys do reuse theirs. just my 2c.
My W arm has cracked twice, but now I welded a brace on it so it should be good now.

:yam:
 
because of this thread i checked compression...12000kms and still puttin out 125psi across the board.


Just wondering if your 125 is warm or cold Blue?
Cold I am 125 across the board.
Warm I am about 105 across the board.
 
97 V Max with one new piston and rings, one 2500 mile or so piston and ring measured warm yesterday:

old: 106 psi
new: 109 pis

Not bad if I do say so myself.
 
oooooooo i just hit 10 000 km so 6000miles, i guess time to do a compresion check poop. Well ethier or i will replace the rings prob this summer.
 
my two 700's one a 97' one a 00' both run 120 on all 3 the 97' has a singl layer hg, the 00' has a peak w/ 21cc, those numbers are cold. the 97' has 6000 mi the 00' has 100mi
 
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