dean51267

sounds like a plan, I will get the tech to load the cylinder with air and then see if there is leak down, and if so, where. I will keep everyone posted once we get that far.

BillK

Dean,
They should be able to do a quick check on the cam by removing the rockers and checking the lift at the pushrod. If they are engine builders, they should have no problem doing this. You mentioned that the rockers were loose after the engine sat ? All of them, or just the ones on that cylinder ? Its normal for the lifters to bleed down after sitting, so unless it was just the one cylinder, I would not worry about that. An easy, quick check on the ignition is to hook up the timing light to that cylinder's plug wire and see if the light flashes. If it does, then the ignition is "probably" ok. Could be as simple as a bad spark plug too.
Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

dean51267

Thanks Bill. There is spark at the plug, and there seems to be adaquate rocker arm movement (indicating no work lobes). We swaped plugs, so I think that stuff lines out.

I think someone hit it on the head when they said 80# compression and no leak down are mechanically incompatable, I am thinking I am going t ofind something in the cylinder area. IF we pump air in and no problem there, then I think I will have them swap distributors and verify nothing funny there, but right now there is two incompatable facts on the table, zero leak down and no compression. Gotta eliminate that problem first.

800XCR

Changing your distributor will not resolve your issues - it has nothing to do with compression or leakdown and you say it has spark. What would be the purpose of the swap?

GOODT

it IS possible to have 80lbs compress and 0 leak down usually a burt or sucked valve or a small hole in the piston.. you have to remember a compression tester itself holds press, a leak down tester does not

Olds Eddie

My friend that builds race engines recently had a new engine on the dyno that wasn't making the power it should have. After checking cam timing, valve adjustment and everything else he could think of he tore it back down. He discovered that a ring was too thick and was seizing in the groove which wouldn't let it seal properly. He usually hand laps all the rings to prevent this from happening, but this was a piston/ring combination from a reputable race part supplier so he didn't. I'll bet he won't do that again. He said that it didn't show any leak down, but as the piston warmed up it would grip the ring and not allow it to follow the bore properly. It sounds alot like what you have.

Dave_N

You can have zero leak down and low compression if you have a flat cam lobe or collapsed lifter that only allow the intake valve to open very briefly and will not allow much air into the cylinder to be compressed. Then you would have low cranking compression in the cylinder, but could still have zero leak down.

Dave

dean51267

Dave,

After talking with Terry this morning (Terry runs a well known small block race building shop) he said it almost HAS to be either rocker adjustment or lifter problem, for the exact reasons you stated.

The heads are new Darts' when Terry puth them together they were vacume checked and all that stuff.

Man, I am having to learn all this motor head stuff all over, I forgot WAY to much since I took a desk job.....

Everyone is thinking cam is bad, but it is brand new, and other motor is fine, both got exact same treatment, so I am thinking it is something else.... now I am thinking lifters or rocker adjustment....

Dean

Wobble

All you need to do is measure valve movement relative to valves on good cylinder with dial gage on top of the rocker arm. It has to be lifter or lobe issue IMO.

It is possible that the cam lobe is not cut in the right place causing to much overlap and compression loss.

With a degree wheel and a dial Gage you should be able to rule that out and also rule out bad lobe.

Collapsing lifter would be left as most likely.

Lmarth

I usually avoid these 'unusual' problems because you're not right there to see everything for yourself. On the topic of poor leakdown numbers, some of you guys are completely losing me. You do a leakdown test at TDC when both valves are closed (lifters are on base circle of cam).It's just a static test to see how much air pressure is lost. As was noted in one of the earlier posts, backing the rockers off takes any involvement of the valve train out of the picture eg. an improperly ground cam lobe(s). You can take a perfectly blueprinted motor, leak it and then remove the cam,lifters and distributor and if the cylinder is at TDC (fairly easy to do with a degreed balancer) you'll again get a good leakdown number. As for lobe wear, when they go, they usually go completely. Just cranking the engine over and observing the rockers usually will tell ya pretty quick if you lost a lobe. Again, a worn lobe won't affect leakdown. Not trying to sound like a smart azz, but always welcome to a little enlightnment from the many folks here that know far more than me.