I was thinking this as well, but still makes no sense as far as compression goes. 0 - 5% leak down on most cylinders at 100 PSI.

 

Zero sense whatsoever. We are thinking whatever is wrong has to be in the heads. Only 1 gasket per head, pistons? i'll have to get back you on that one. i dont remember so i'll have to look up the order. The only thing i DID NOT order on this build was the heads. My builder said he had some that were better and would last longer. He said alot of the dodge heads crack (both were on this one) so thats the only thing im unsure of as far as parts go.

 

But you say 0-5% leak down, if it was valves, rings leaking/blowby you would not have a reading of 0-5%. What are you thinking headwize for a problem? Need more info about the heads and pistons.

 

The only thing I can think of is cam timing, but I'm not sure if one tooth off either way would open the valves up enough to get such a low reading. I'm thinking they should be well north of 150psi...

edit: My ZJ book I have says the exhaust valve opens at 56 degrees BBDC, so 34 degrees after TDC. How many teeth would you have to be off?

 

3 or 4.

Given the current info, it almost has to be a cam timing issue. Yank the cover, see what ya got.

Also, what cam is in there? Timing set? (is it adjustable?) I wonder, if an adjustable set, if the wrong marks weren't lined up.

Suppose another way to test would be with a degree wheel.

 

Well my buddy who is a mechanic made the comment that if the combustion chamber in the heads was too big, we could get a low compression reading like that. Say the stock heads flow 65cfm and these heads flowed 95 cfm, but the motor isn't pushing that much air into them. Kinda makes sense, but won't know until i get specs on the heads here in a couple hours.

 

.480 206 cam with a 110 or 112 LSA. cant remember which. No adustable timing set. stock set. I remember reading that one of the gears in there has 2 different marks on it, maybe its on the wrong mark? but wouldn't it idle and run like crap? Besides lack of power, the thing idles and runs smooth. The idle does drop really low, and sometimes motor cuts off when i approach a stop sign, but cranks right back up. I assume that's due to the low compression.

 

If you say had open chamber heads and deep dish pistons yes this would explain the low comp numbers. Or a piston set with the wrong pin height or wrong length con rods.

 

If i remember correctly, pistons were slightly different than stock, but nothing crazy. Rods were same length, i did check that. I'm sure when he put it all together, at least 1 or 2 of the pistons were at TDC. I would think he woulda noticed if it didnt come all the way to the top of the block.

 

One would think he would, it should have been measured for clearance as well. I will wait for head info and piston part numbers.