Another different pushrod length WTF
05-05-2015, 09:46 PM
#1
Another different pushrod length WTF I know this has been asked here before....once by me.
I know its normal to have different lengths between intake and exhaust but what about between cylinders?
Last build on this short block I had to run 7.40 on driver side and 7.325 on the pass. Engine ran fine.
New build, same short block untouched, same heads and valve train, new head gaskets. Measure for new pushrods and come up with 7.40 intake and 7.325 exh. Brian T. valve train kit with morel lifters and comp pushrods.
Zero compression on numbers 4 and 8!!
If I loosen the rockers I get full compression. Which tells me one or both pushrods are too long.....BUT WHY ON THOSE TWO ONLY? All other cylinders have 180 (well except number 6 which reads 150)
Now, I had the heads checked and milled to clean up. Checked valve install height, etc and all checked out. Morel lifters have less than 5k miles (albeit hard) and using 50 thous pre-load. New cam built by Martin at Tick.
Any thoughts? Bad block casting from GM? Lifters install height difference with no lifter tray?
I know its normal to have different lengths between intake and exhaust but what about between cylinders?
Last build on this short block I had to run 7.40 on driver side and 7.325 on the pass. Engine ran fine.
New build, same short block untouched, same heads and valve train, new head gaskets. Measure for new pushrods and come up with 7.40 intake and 7.325 exh. Brian T. valve train kit with morel lifters and comp pushrods.
Zero compression on numbers 4 and 8!!
If I loosen the rockers I get full compression. Which tells me one or both pushrods are too long.....BUT WHY ON THOSE TWO ONLY? All other cylinders have 180 (well except number 6 which reads 150)
Now, I had the heads checked and milled to clean up. Checked valve install height, etc and all checked out. Morel lifters have less than 5k miles (albeit hard) and using 50 thous pre-load. New cam built by Martin at Tick.
Any thoughts? Bad block casting from GM? Lifters install height difference with no lifter tray?
05-06-2015, 10:00 AM
#3
Was hoping that was it so I took the rockers off, checked them, replaced them and nope.
I'm not sure which or if both are too long. I will loosen one at a time tonight and see.
I didn't personally check all the valve heights so maybe those two are off. I would think that even if the others were even open a hair (5 thousands) I would have crappy compression if at all???
I'm not sure which or if both are too long. I will loosen one at a time tonight and see.
I didn't personally check all the valve heights so maybe those two are off. I would think that even if the others were even open a hair (5 thousands) I would have crappy compression if at all???
Last edited by edge04; 05-06-2015 at 10:38 AM.
05-06-2015, 07:07 PM
#4
back messing with it
I had 7.325 laying around. Installed those in both intake and exh and no compression.
Well since last time the difference between the driver's side and pass was exactly .075 I figured the intake side must be ok as I am going from 7.40 to 7.325 but the exh I'm going from 7.375 so only lowering them by .050 and yep full compression with exh rocker loose. So now I have to order two 7.30 pushrods
So my set up is all cylinders have 7.40 intake and 7.375 exh except cylinders 4 and 6 which will have 7.325 intake and 7.30 exh
Why just those two? Any theories welcome. I going with valve install height and poor quality control from the builder. Any way of checking install height with them fully assembled and mounted?
I had 7.325 laying around. Installed those in both intake and exh and no compression.
Well since last time the difference between the driver's side and pass was exactly .075 I figured the intake side must be ok as I am going from 7.40 to 7.325 but the exh I'm going from 7.375 so only lowering them by .050 and yep full compression with exh rocker loose. So now I have to order two 7.30 pushrods
So my set up is all cylinders have 7.40 intake and 7.375 exh except cylinders 4 and 6 which will have 7.325 intake and 7.30 exh
Why just those two? Any theories welcome. I going with valve install height and poor quality control from the builder. Any way of checking install height with them fully assembled and mounted?
05-06-2015, 07:49 PM
#5
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Well that's a tough one.
I'm guessing the cups in the hydraulic lifters were not at the top of their stroke (already depressed). Then when you added .050" preload it pushed them all the way to the bottom of their stroke. After you started it they pumped up and unseated the valve.
Could the pushrods be mismarked?
I'm guessing the cups in the hydraulic lifters were not at the top of their stroke (already depressed). Then when you added .050" preload it pushed them all the way to the bottom of their stroke. After you started it they pumped up and unseated the valve.
Could the pushrods be mismarked?
05-06-2015, 08:27 PM
#6
but I measured on number 1 and 6 and those are fine.
Well that's a tough one.
I'm guessing the cups in the hydraulic lifters were not at the top of their stroke (already depressed). Then when you added .050" preload it pushed them all the way to the bottom of their stroke. After you started it they pumped up and unseated the valve.
Could the pushrods be mismarked?
I'm guessing the cups in the hydraulic lifters were not at the top of their stroke (already depressed). Then when you added .050" preload it pushed them all the way to the bottom of their stroke. After you started it they pumped up and unseated the valve.
Could the pushrods be mismarked?