Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[hdrider53]

Hey guys, I need a little help. I have about 300 miles on a 95 inch build I did. I put in SE 95 inch flat tops, Andrews 54 cam, SE Performance heads. Big boy calculator for this setup at 5200 feet (my elevation) says 155 PSI. My readings were 155 front & 150 rear. So it seems about right.

However when I first did the test I thought I was supposed to be somewhere around 190 because I forgot to input the right elevation. So I redid the test with a little added engine oil in each cylinder. My readings were 175 front & 170 rear. Does that mean my rings are not seated yet? Again I have about 300 miles on the build and the test actually came out right according to the calculator but the added PSI after oil was added worries me a bit.

[evostroker]

A leak down test is a much better indicator of ring sealing..if the bike runs good and doesn't burn oil I wouldnt be too concerned about the readings

[grc]

What he said.

btw, there is always a certain amount of leakage past the rings, no matter what.  When you added oil to the combustion chamber, it temporarily reduced that leakage.  If your compression readings are in the normally expected range when you do the test without adding oil, don't worry about it.  If you tend to be the worrying type, then do the leakdown test.  Not only will it give you a good indication of the overall sealing of the cylinders, but unlike a compression test it will also help to lead you to the offending area if you have a problem.


Jerry

[hdrider53]

Thanks for the info. No I'm not the over worrying type. Bike runs good and doesn't use oil. I was just confused on the readings. I thought if the numbers came up after oil was added it was because your rings were bad.

[wxdude]

Where adding oil comes in handy is when you have a cylinder that is lower, by roughly 10% or more, than the other cylinder(s).  This helps to determine if it is a ring or valve problem.  If the pressure goes up after adding oil it is a ring issue, however if the pressure stays the same it is a valve issue.  This could also be used when all cylinders are low to help determine if an overhaul is needed or if a valve train issue needs to be resolved.

Remember though this is only used when a problem has been detected in the compression test.  Like evo and grc said, the numbers sound good to me.   

[dlaws01]

If doing a leak down check, piston must be at TDC on the compression stroke and a decent figure would be 90-95% of input pressure.  This is also a good way of checking if the leakdown is coming from the rings, intake or exhaust valve.  Listen for air escaping from out the exhaust pipe for exhaust valve wear.  Air escaping through the intake valve can be heard through the air filter inlet.  Air leaking past the rings can be heard by listening through the oil drain once the oil is drained.  This type of compression check should be done hot.

[Talon]

I'd get some more miles on it first, like over 1,000, just to make sure the rings are good and seated. You have been riding like the HD break in, varying RPM's stuff like that?

Craig

[hdrider53]

I'm good with just the compression test I did. Just wasn't sure about the readings I got with oil added. Runs great and I have been breaking it in properly. Thanks for the help everyone.