Compression ratings

Hey guys I have a 93 seca 750 that I got from a bud who says it has low compression, What are the actual compression ratings?

 

150 psi is new , 120 to 125 is acceptable but low , if any are less than 100 psi you have rings or valve sealing problems , this is why you should check valve clearance ,sometimes this is enough to bring compression up a little.

 

I ran a compression test and here is what I came up with testing each 3 times. Cylinder #4 - 115-117 and it jumps about 5-7 psi with each stroke once its at max, and when I stop cranking on it leaks down fairly quick. Cylinder #3 - 93-95 Same it jumps around, and leaks down fast to maybe 40 psi, cylinder #2 - 100-105 again jumps around too but it doesn't leak down as quick. And cylinder #1 is an even 119 with no jumping and doesn't leak down at all when I stop cranking on it. Meaning rings or valves? I should also mention my valve gasket does leak pretty bad it drips while it's running and I plan to replace it, but might as well wait to see if I should change the rings too.

 

Okay question did you have the throttle wide open while cranking ? Did you have all the spark plugs out ? Have you poured a table spoon of oil in the cylinder and see if readings increase? Have you checked valve clearance? I would try what I described first ,if valves have never been done ,which is a good chance this can lower compression as valves will seal but not fully .

 

Your gauge should hold pressure. Nothing to bleed down if using a standard compression gauge. If you are watching it leak down your valve in your gauge is no good. I would check with another gauge and then if low compression is found do a leak down test. Leak down test will show rings or valves.

 

I just checked my ski doo and my buddy checked his truck and the gauge worked fine, but I'll try another gauge but I'm doubting its the gauge.

 

If you can get lets say 100psi it should stay. If not the only cause would be a bad or sticky Schrader valve in the gauge. An engine's cylinder will not hold psi for longer the a few seconds before normally bleeding down to 0 by the ring gaps. It's all in the gauge to record highest psi of cylinder.

Hope this helps.

 

It will read the compression and hold it for 1-2 seconds then leak down to 0 except that one cylinder. It will stay at 119 for about a minute and then very slowly leak down, which is what my gauge usually does on any motor I have tested before. No I didn't have the throttle open or do any of the other things, I had all the plugs in at though.

 

If you have plugs in the other cylinders then engine will not spin up fast enough try to remove all of them crack open throttle and use a fully charged battery and then see what your readings are.