Guys got to working on my 340 challenger again.. we did a comp test first and then a leakdown.. the engine was cold, but it gives us a baseline to go by.. what I found is quite odd and I am not sure what it all means? Can u look at the following pic and let me know your thoughts! Something is wrong somewhere ,but where? When @ TDC #1 the balancer is at zero or close to it and rotor pointing at #1 also, I get comp not real good ,but good enough, but when i do a leakdown on that cylinder it's basically dead along with 3 others.I only took it to 70 psi to test it with incase anyone wonders, also I could not hear leakage from anywhere? a little out breathers ,but thats it!,nothing out exh or thru carb, thats why I am baffled!.Also #2 cylinder is very high too!. is it cam timing? or what? Also the car starts and runs not too bad, is responsive and throaty too , but isn't making alot of vacuum like 7-9? Smokes some too off and on.. and has it warms up has a inner knock what sounds like inside the motor somewhere too.. the oil has been checked and filter cut open no bearing stuff!... At this point were going to pull it and have it gone thru. unless u guys see something we don't

Looks to me like something is wrong with your test proceedures. Did you run the comp test with the carb butterflies open, plugs out, and do the same number of pumps for each hole? Looks like you did some of the leak downs on the overlap stroke. Are you sure you were on the comp stroke for all 8 cylinders on the leakdown test? The car would not run "ok" if those numbers were real - although the vacuum is real weak - should be double that.

Hi thanks for the reply. yes I held my finger in the plug hole for each til it blew my finger out,verifying i was on the compression stroke then manually moved it so it was exactly at TDC, each test was done with 4-5 pumps each hole. Carb was wide open also.

Comp test; looks like you ran 3 tests on #2 and got a variation of 40 psi?? Something changed. Maybe cranking rpm? The leak down test should have been run with 100psi input. The lower the input pressure the greater the leak rate will be as the higher pressure will push the rings against the ring lands and make a better ring seal. Even at 70 psi input, with 15 psi on the "leak gauge", you should have been able to hear / feel the leak. Just to verify that you have a problem with the holes that show a major leak, I would run an rpm drop test. Run the engine at a steady idle rpm and pull the plug wires off 1 at a time and record the rpm drop for each hole. If your suspect weak holes line up with holes that show very little rpm drop, time to pull it apart.

The most reliable way to do a leak down test is with the rocker arm gear removed. Then you are sure the valves are closed. As was mentioned use 100 lbs to do the test. If you still get real high leakdown you should be able to hear the air escaping out the carb, exhaust or thru the breather. If you hear the air comming out the carb or exhaust try hitting the valve and retainer while there is air in the cylinder. You will nlotice the guage drop for a second and then it will come back up when the valve is back on the seat. You may have build up on the valves that is keeping them from sealing.

If you hear air comming out the breathers then your rings are shot.

Raul

Ok Here is the results from test #2. without the rocker shafts on..piston at top of cylinder. At this point it looks like the pushrods are wrong for the cam.. cam is unknown, also I should point out this motor is new rebuilt according to previous owner was taken apart and reused pistons etc.stock bore supposedly yet too.. So Next question is those two cylinders that tested low # 3 #7 after i tested second time they gained compression.. whats up with that? Also how does one go about measuring for correct pushrods on a shaft mounted system? The ones now are approximately 7 17/32 long.. also their one piece not ball end ones either that came stock on these.. thinking the guy had no idea what cam is in there and used the stock rocker setupand rods?

Think you need to take the motor down all the way and check it over. Just too many issues and unknowns. Sorry I couldn't help more, but that's what I would do at this point.

Are you using stock or adjustable rocker arms? If they are adjustables you need to have 2-3 threads showing from the bottom of the rocker arm. If you have a cam with a lot of duration (overlap) it will cut down on the compression since the valves are open for such a long period of time.


Raul

I honestly don't know if there stock or not Is there a way to tell? This is a 69 340 with X heads, has 2.02 int valve.Only single valve springs tho? is that stock? I am actually helping my brother on this car it's his car I am A pontiac guy,lol.. so not too familiar with the rocker set up on these dodges? I know there shaft mounted and when i loosened them they seemed tightened down tight. Not adjustable like mine..Thanks guys!. this is a pic of my car.ran [Email]11.95@114[/Email] on a new motor @ 4600 pds..pump gas 91.. 560 Hp.. 600 ftlbs

What does it mean with out pushrods?

i think at this point we will get a pushrod checking tool and get the right preload. Obvious now without the rockers on it is sealed pretty well.must be too much preload pushing some of the valves open when they shouldn't be?What were stock on these for springs? cause i can take my fingers and push down on them opening the valves!

Might pick a cyl that's at TDC & make a mark on both of that cyls pushrods up top in the valvetrain area referenced to something stationery nearby (for a height change measurement)then bolt on the rocker arm assy and measure how far it depresses the 2 pushrods for a preload measurement. I thought I read that you are able to depress the valve springs w your finger but they cant be that weak.

I was reading on comps site about that also, about using the valve cover gasket base as a reference point. by getting those two measurements how does that tell us what length pushrod i need?.. also I meant my thumbs ,but yes i can take my two thumbs and push down on the springs opening the valve!

Yea me too, I only know Gm's... This is all new to me. please forgive me but what is the site? hughes? do u have a web address?

The leakdown on #3 & #7 look pretty bad. Did you try squirting some oil in and re-test? This may help point to rings and not valves, but either way I think your going to have to tear down the engine (at least the heads) to fix it?

I didn't do any oil on leakdown only on the comp test.and that helped very little.. ,but after i removed the rockers shafts on the heads i had good readings, so something in the valvetrain geometry is screwed up... cam is unknown, need to get a pushrod tester and find the proper length for the right preload..