wondering if i have a bent valve or lifter set too many turns. did a compression check after cam change got 210 rear but 180 front. i hear a weird gurgling sound through intake manifold while doing compression check only on front cylinder. absolutely certain cams are in right have done 4 sets so if some one says cams are in wrong no way.
i pulled lifters out because of a weird tapping sound and found lope pitted on lifter and a few flat spots on lobe, a bit of scratches on cam lobes. wondering if it was not compressing on occasion and valve may have dinged piston and that was the random tap i heard once and a while it was a different tap then tappet noise.
any way thinking about hooking up compressor with guage to compression test hose get cylinder near tdc on compression stroke with valves closed, acr wires disconnected and pressurize the cylinder about 150 lbs and see how fast it leaks down. anyone ever done this, heard of leak down test cant think of any other way to do this.
I am expecting to hear a leak through intake valve out intake manifold while throttle plate is forced open.
anyone one know what leak down time is acceptable, its not gonna hold pressure forever like a pneumatic cylinder would with a completely round seamless piston cup. rings have gaps.

 

air through intake shows that valve is not seating- unless the cam ( you are on compression stroke, right?) or a misadjusted push rod is holding it open...

you have to pull it apart and solve the problem

( and air through the exhaust would be an problem with the exhaust valve. air through the crankcase vents would be bad ring seal)

mike

 

A leak down test isn't time based, it's the percentage of air that "Leaks" past rings and/or valves.

 

it must have a time base line to establish an acceptable leakage.
example 150 lbs in cylinder shut off air pressure trap in cylinder. it may take 15 minutes to drop 20 lbs. if rings or valves are not seating it may loose the same 20 lbs in 5 minutes you can graph this and compare one to the other.
same procedure is used for testing gas line connections pressurize to set pressure and check so many hours later. if it falls below a set value it will not pass and leak must be found until time over leakage number is in spec.
i undstand where it will leak- valves or piston rings so please no offense if people ell me this but its kind of a no brainer. im really looking for acceptable numbers to compare what i get. i hope i miss adjusted push rod , but i am going to see a builder monday concerned about how well my rings seated on the last ring change and would like to walk in there with good accurate data that buildesr use and decide weather im going to tear it down in winter and change heads and pistons or keep my mvs heads with a possible bent valve from the lifter screwing up unless I overturned it while setting it

 

Aircraft use leakdown tests all the time and they are percentage based. A leakdown tester
has two gauges. The primary which is your supply air and the secondary gauge is what the cylinder is capable of holding.
For example, you may have 100psi shop air going in but the cylinder is only capable of holding 60psi, or 80psi or whatever. It will always be 15psi or so lower. Any more than that and it's time to start looking at intake and exhaust valves and rings. You would have to hold the prop because the air wants to push the piston down. In fact, you can watch a cylinder seal better as it is approaching TDC, since the rings will be seated against the bottom of the ring lands.

Take care,
Dave

 

im taking that staetment more a measure of how many cu inches the cylinder will hold before it becomes completly pressurized on second guage

 

but since you hear air at the intake- it doesn't matter what a leak down test shows...you already have a demonstrated problem.

mike

 

i havent tried it with compressed air yet, just heard the gurgle while starter was turning the motor over with compression guage on it wouldnt get over 180 im assuming its comming out valve, it could also be going out piston rings and comming back out pcv system into breather pick up .
which now makes me think ill pull bolt out of intake mount on breather and see how much air leaks out of crankcase while its pressurized

 

When doing a leak down test you don't pressurize the cylinder and then shut the supply off. Every leak down tester I've ever seen and used has two gages, one that shows supply pressure and another that shows percentage of leakage. A high end race engine will leak zero when fresh. While I'm sure you could do the math and come up with this percentage, I don't know the formula off the top of my head. If you're going to talk about this with an engine builder he's going to want to know what percentage of leakage you have, not time and delta.

 

well guess i wont be doing that test. will still try to blow some air in to cylinder to see it i get air back out valve, will check push rod turns if i get leakage then looks like head will be comming off .