I have a 1990 Mustang that I swapped a rebuilt 302 and t5 into, I got gt40p heads and upper and lower intake, got the heads rebuilt and bought some 6.250 length pushrods with some pro form sbf rockers, was cranking the engine over with a wrench to do a spark plug thumb test and the only cylinder with compression enough to blow my thumb off was cylinder 5. Most other cylinders besides 6 had no air coming out at all, I did the rockers all the same way to spec 20lbs and am not sure why one would have good compression and the rest don’t
Roller rockers with no compression
- Thread starter DPORTER0729
- Start date
Mcmahst
5 Year Member
I don’t think I fully understand your question. You’re using like a socket and ratchet and you’re not getting compression turning it with that? As you do that, do you see the valves open and close? Using the starter motor will create a better environment for a compression test. Did you select the pushrod length by testing your specific roller rocker arms and a push rod length gauge? Explain the pushrod determination process. Good luck.
I have several thoughts after reading this and through. The only one came to the surface is...
What?
I am only certain that I don't know what is going on, yet.
What?
I am only certain that I don't know what is going on, yet.
I don’t think he followed the directions on adjusting the pedestal rockers. Probably needs shims and/or different pushrods. Who knows as the info is kinda lean.
Sorry for the lack of information, I did use a pushrod length checker and the rockers I am running to determine the correct length. After adjusting the tool to 6.250" and checking every rocker by rotating the engine over a few times the sharpie mark was completely centered on all of the plungers after torquing them to spec, I did all of the rockers at the same time the same way as shown in multiple videos and I'd agree that the pushrods are too long or the rockers were too tight but number 5 cylinder has almost perfect compression. i dont have the starter hooked up yet so i dont know the actual numbers but the spark plug thumb test gave me accurate enough results to realize that 7 out of 8 of the pistons had 0 compression. I didnt use any shims on the rockers and the pushrods were a different style bought from summit racing but still stock length. played aroung with the rockers on number 1 cylinder and could not adjust to produce any compression. My main question would be how is it possible one piston is perfect when i did every one the same exact way?? Thanks for all the quick responses, will keep everyone updated
Mcmahst
5 Year Member
I think posting some pics of the work you’ve done will give us a better idea of the situation. Also, you think the pushrods are different than the stick ones? Explain that better and pics of both would help. I’m wondering if the end of the purchased pushrods is actually increasing the length of it. You could try swapping cyl 5 pushrods with cyl 1 to see if the issue moves with the parts. Good luck.
I think I would loosen up all of the pushrods then turn it over by hand and see if you have compression....
The part about wetting your finger and stuffing it into the hole doesn't strike me as a good measure.
Perhaps a gauge for the next test?
Perhaps a gauge for the next test?
Blackhawkxx
Advanced Member
- Mar 3, 2023
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Do what Limp suggested and if all lease fails do a leak down test. You can rent the tool at parts stores but you will need an air compressor.
I'm away on vacation right now but I will try loosening the rockers and rechecking compression as well as uploading pictures, the difference in pushrods is the stock ones have the ball part almost tacked onto the rod itself whereas the summit racing ones are billet one piece that tapper up to round, unfortunately I sold the factory pushrods along with the stock block so I won't be able to post a comparison but they are 100% the same length as factory. I have been researching and it's possible the geometry is barely off by having the heads resurfaced and using an aftermarket head gasket, but I'll try the easiest options and hope for the best before trying shims and whatnot, thank you all for the help, it is greatly appreciated!
i should have told you he was just baiting you
Now, I need a "Who Me?" smiley.
I switched to those type of pushrods on my " P " heads and did not have any problems....
NEVER sell any parts until your project is DONE AND RUNNING.......
NEVER sell any parts until your project is DONE AND RUNNING.......
oz
Founding Member
To prove your theory that the pushrods are too long, just loosen both of them on one cylinder and redo your 'wet willie' compression test on that one cylinder...
If that solves the issue, you've got your answer.
If that solves the issue, you've got your answer.
Is there any way that my timing is off? I'm 99.9% sure that the engine was at top dead center on cylinder 1 when I installed the timing gears but I always end up second guessing myself... I feel if the timing was off cylinder 5 would not have accurate compression each time and it would throw off the whole geometry.
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