I am new to the forum, and have been working on my 1970 GTX for about 2 weeks now. I am having some starting problems, i had the heads done and new valves put in stock GTX heads (atleast that's what the casting number told me). I first set the timing with the car a TDC on cylinder one and then checked for spark. The spark was good and then i did a Compression test. The compression test came back with about 60# on cylinder 8 and 90# on cylinder one. That doesn't seem right. What are some other things to check before i pull it out and take it apart?? The engine is stock as far as i know. Any help would be appreciated. Thanks

-MMMichael

 

Does it do anything, pop through the carb, try to fire, etc?


60 psi is quite low, what all parts have you messed with/ changed? Any chance you have too long pushrods, valves out of adjustment (I know, stockers don't adjust)

Is the pressure low on all cylinders?

Here's how I set timing. First I make DARN sure the rubber vibration damper has not moved by installing a "positive stop" in no1

http://www.purgeraptor1.btinternet.c...oslockstop.jpg

With the battery ground unhooked, wrench the engine around until it stops, and make a temporary mark on the dampener right under TDC on the timing tab. Do the same thing rotating CCW. True TDC will be right between the two temporary marks

Then pull out the stop, hook up the battery, and bump the engine over with your finger in no1. AS SOON as you feel pressure, look at the marks, and bump the engine until it's at about 10* BTC, more if you have a hot cam. Now look at the dist. On a BB/ RB, rotate the dist CCW to RETARD it, then while watching the points or with a test lamp, or while looking at the reluctor, rotate the dist CW so the points JUST open, or rotate until the star wheel is lined up with the center of the pickup core, and the rotor pointing to no1.

By the way, I always take a second, and scribe a light line in the top ridge of the dist. housing to show where the no1 tower is. That way, I never have to haggle with the cap while dropping the dist in.

Once you learn this and do it right, a healthy engine should fire and run just like you parked it last night.

Make sure the plugs are not fouled, and make SURE your fuel is not stale.

(One time at Miramar, a guy was trying to fire a brand new 396 dropped in a 57 Chev. He borrowed tools coils, wires all morning, and finally got me over there. Hands me a Pepsi can and says "we're priming it with that" I smelled it and it had JP-5---that's Kerosene--in the can. I handed it back and said "go get me some gas")

 

I have no idea what is going on with this thing. i swapped out the heads that it had on it that are stock for that car and havent gotten a certain comp. test on it yet. i tested it but only got about 90#. something isnt right. i'm positive i set the timing right.. other than that i was thinkin maybe the pushrods are too long for it which is causing it to hold the valves open too long but then i thought that would make them hit the pistons? i honestly can say im completely stuck.

-MMMichael

 

I assume you have the stock non-adjustable rockers?

Only thing I can think of, you say you swapped heads---this implies someone did a valve job, either just now or some time earlier---is it possible that the valve stems are too tall? I'd check the "installed height" of the valve stems