Just wondering if the compression readings should be the same cylinder to cylinder or if one should be a tad higher...for some reason i thought i read somewhere that the pto side should be a tad higher than the mag side..either way my readings were 116ish on the pto side and 112ish on the mag side...is this about right? sled has 1100 miles untouched 07 800 motor..
compression readings
- Thread starter silver 002
- Start date
Cold vs. Hot compression test
It does not matter if your gage is accurate or not as long as you use the same gauge when cold vs. hot temps.
Example - Indications of rings going bad:
cold compression - 5lb(35kpa) or greater difference from mag to pto.
Hot compression - 7lbs (48kpa)(or more less than when it was cold then you need rings.
Hot compression - 10lbs(68kpa) or more less than when it was cold then you need pistons.
Example:
Cold @ 145lbs (999kpa)
Hot @ 138 lbs (951kpa) or less than...
Value difference more than 10lbs (68kpa)
.......if you are very concerned and want to get to the absolute bottom of it, go to the dealer and get a leakdown test, i think that's about an hour labour.
It does not matter if your gage is accurate or not as long as you use the same gauge when cold vs. hot temps.
Example - Indications of rings going bad:
cold compression - 5lb(35kpa) or greater difference from mag to pto.
Hot compression - 7lbs (48kpa)(or more less than when it was cold then you need rings.
Hot compression - 10lbs(68kpa) or more less than when it was cold then you need pistons.
Example:
Cold @ 145lbs (999kpa)
Hot @ 138 lbs (951kpa) or less than...
Value difference more than 10lbs (68kpa)
.......if you are very concerned and want to get to the absolute bottom of it, go to the dealer and get a leakdown test, i think that's about an hour labour.
Joe--
Thanks for the heads up... i would say mine were relatively cold...was sitting in about 40 degrees and hadnt been run for an hour and half...i'm going to take that as im on the border...hopefully they will run this season....
Thanks for the heads up... i would say mine were relatively cold...was sitting in about 40 degrees and hadnt been run for an hour and half...i'm going to take that as im on the border...hopefully they will run this season....
F
FNG
Active member
I would try another compression tester just to double check your readings as anything less than 120 (ish) indicates a tired motor 
. Almost any two compression testers will read a little bit different from each other unless they have been calibrated correctly but one-teens is pretty low for that motor.
It is more important that the pressures are equal MAG to PTO (less than 6 Lbs difference or so and yer good, more than that and yer at least due for new rings). I have never heard that the PTO cylinder should have more compression than the MAG side but I'm just a guy in his garage, not a pro mechanic
.
. Almost any two compression testers will read a little bit different from each other unless they have been calibrated correctly but one-teens is pretty low for that motor.It is more important that the pressures are equal MAG to PTO (less than 6 Lbs difference or so and yer good, more than that and yer at least due for new rings). I have never heard that the PTO cylinder should have more compression than the MAG side but I'm just a guy in his garage, not a pro mechanic
.FNG---thanks for the advice..makes sense to use two testers to cross check eachother...at least they would confirm eachother..i did look through the exhaust ports and noticed some real real slight scratches on the mag piston so i could imagine i am losing some compression there...
One other question for all those who have measured the crank stub deflection...what are you using as a basis to measure the deflection from....i tried laying a level from the secondary to the front belt guard mount but that isnt real ideal. i was told that deflection should be measured in the middle of that stub????
One other question for all those who have measured the crank stub deflection...what are you using as a basis to measure the deflection from....i tried laying a level from the secondary to the front belt guard mount but that isnt real ideal. i was told that deflection should be measured in the middle of that stub????
Shop manual says 1/8" (3mm) from end of stub.
The best way to mount the dial indicator is to take the magnetic base or standard base and put it against the PTO cylinder. With a ratchet strap, wrap the strap around the cylinders of the engine and crank down on the dial indicator base - this is so you have a solid mount to the engine itself. With the stylus pointed down on the stub, dial as shown in the illustration. With spark plugs out, can rotate the engine using the starter pull chord. Zero in the scale and measure runout on crank
The best way to mount the dial indicator is to take the magnetic base or standard base and put it against the PTO cylinder. With a ratchet strap, wrap the strap around the cylinders of the engine and crank down on the dial indicator base - this is so you have a solid mount to the engine itself. With the stylus pointed down on the stub, dial as shown in the illustration. With spark plugs out, can rotate the engine using the starter pull chord. Zero in the scale and measure runout on crank
Joe---thanks for the heads up...i just checked my shop manual out and realized that the dial indicator they are illustrating would be much easier to use than my liitle gadget im trying..
any suggestions for a new bottom end...does anyone do core exchanges for the crank case or what is the best way( quickest since i waited soo long) ?
any suggestions for a new bottom end...does anyone do core exchanges for the crank case or what is the best way( quickest since i waited soo long) ?
