While trying to set the timing chain up, I may have inadvertently bent a valve. If I did a leak down test, what percentage should I see on a brand new machined engine? How much variation is acceptable between cylinders. Explanation of what I did below.
I was trying to draw up the slack on my timing chain. My tensioner tool had prongs that went past the tensioner gear hole, so as I tried turning it counter clockwise the peg from the tool was hitting something behind the gear, stopping it. After several hours of this, pulling sprockets off the cams, playing with the chain. I decided / thought I would rotate the engine. Obviously, the slack in the chain resulted in timing off. I went very slow rotating the crank until about 3/4 around on the first turn when I felt some resistance (valve I assume). I reversed back to tdc and about an hour later figured out what I was doing wrong. Now, I have everything timed perfect, but I’m worried I bent that valve, so I thought I’d to a leak down test and see what I destroyed in my moment of ignorance. Engine is out on stand, so now is the time.
Welcome to the club. I did this last year. The valve was bent only slightly, however there was a substantial difference between cylinders. In my case, you could hear the air escaping on the exhaust side.
I would recheck your valve clearances. I they haven’t changed, you just might have lucked out. Just depends on how much resistance you felt before backing off the crank. They are easier to bend by independly turning the cams. If bent, they will stick open and you will measure more clearance.
I tried the compressed air trick, but I really didn’t hear any perceivable difference between cylinders. There is no way I bent all of them bc I stopped right away. I think i can hear leaking out of all cylinders, but a very small amt. When I remove the air source after several seconds, the pressure still releases (a big puff) out the spark plug hole, so I’m keeping my fingers crossed. Im heading to harbor freight tomorrow to buy a tester and give it a go.
Steven,
I am with Kris on this. Measure the valve clearances and watch the tappets fall and rise with the cam lobes. If the clearances are still good and the valves open and close properly then you did not bend a valve. If a valve is bent then your valve clearances will be off.
Nah, bent valve, so long as you catch it before you start the engine, is an annoyance. This was a big pain in the wallet. A brand new custom ground camshaft.
Ok… I anxiously checked valve clearance. Here is what I got. It doesn’t make sense. If exhaust valve 2 was damaged, wouldn’t it sit high, not so closed I couldn’t get anything in-between?? I checked and it doesn’t seem stuck. I had larger exhaust valves installed by machine shop if that matters.
Exhaust 1. .010. Intake 1.009
Less than .0015. .010
.011. .010
.012. .009
.010. .011
Exhaust 6. .009. Intake .011
I doubt it was a flaw in the cam. It was a Dema Elgin regrind of a low milage S3XJ6 cam. Somehow I put it in a bind drawing down the journal caps after the second go-around adjusting the valves with the head on the bench. Didn’t quite feel right, then - CRACK.
Im struggling with the leakdown test. Engine is out of car and I’m waiting on my new starter, so can’t really do pressure. Cams installed and I used a feeler gauge to make sure that valves not touching as I did each cylinder. No oil pan or breather installed, but not sure how much that matters.
Cylinder one measured about a 20psi difference (70-50). Cylinder 2 was about 62psi difference. That’s the one with no gap at all between cam and valve. Cylinder 3 was 14psi difference. Cylinder 4 was 32 psi difference. Cylinder 5 was 12 psi difference. Cylinder 6 is a 10 psi difference. I went back twice and was in the same ballpark. I used a max pressure of 70 psi and even then I was having trouble holding my breaker bar still. I even used a dial gauge to measure tdc on cylinder 1 and blindly checked my cams with my tool and they both were perfect. I’m either missing something or I went through and damaged a bunch of valves before I finally felt the one.
