No compression... But odd results.
12-09-2019, 05:44 PM
#21
Either way you either have to pull the head or get checker springs to see if the valves are binding. Valve spring seat pressure should have been more than enough to close the valves completely with the rockers off. If you saw the valve pop up when the cylinder was pressurized then you have a problem of some kind.
12-09-2019, 08:20 PM
#22
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Originally Posted by Philhippy45
how does one fix that or what causes that?
12-10-2019, 07:30 PM
#23
Maybe the valves are binding up in the guides somehow for some other reason, perhaps deposits or the clearance just not being enough.
Just shooting in the dark here.
Just shooting in the dark here.
12-10-2019, 08:22 PM
#24
So I decided to get smaller pushrods for the driver's side. The ones i had in were 7.575" the ones I tried were 7.550" and 7.525". The ones that work are the 7.525" but I kept pass side the 7.575" I cant figure out why if the heads are suppose to match why the differences? But anyway now they all hold compression and are all within 1 to 2 psi of 180. So I guess I can't complain... Figured I'd give an update and my solution.
12-10-2019, 08:43 PM
#25
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If you measure for pushrods what do you get? Those numbers seem high for stock lifters, stock head, stock rocker setup.
12-10-2019, 08:55 PM
#26
they're ls7 lifter and prc 247 heads. When i measured I got the 7.575" but then I had to get a new head because the first one blew up on dyno and their was almost 5 years between castings. The machine shop now thinks that's the issue they may have casted it different or used longer valves.
12-10-2019, 11:07 PM
#27
So I decided to get smaller pushrods for the driver's side. The ones i had in were 7.575" the ones I tried were 7.550" and 7.525". The ones that work are the 7.525" but I kept pass side the 7.575" I cant figure out why if the heads are suppose to match why the differences? But anyway now they all hold compression and are all within 1 to 2 psi of 180. So I guess I can't complain... Figured I'd give an update and my solution.
12-11-2019, 05:34 AM
#28
we thought it was hanging open but wasn't what gave us that illusion was the oring was bad on the compression tester and we though maybe a valve was hanging because what else could it be. After doing a leak down we ruled that out so I started to put Teflon tape on the compressor tester threads and bam now have compression so I had to do that every time I took it out and put it in.
12-11-2019, 10:34 AM
#30
i went by what the machine shop said I didn't actually measure anything myself. That's what he told me to put in. Hes been building engines for 50 yrs doubt it's inexperience but never know **** happens and the problem is fixed took it to dyno this am and not one issue with it. This time it actually was tunable. Now runs and drives great.
12-11-2019, 10:51 AM
#31
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they're ls7 lifter and prc 247 heads. When i measured I got the 7.575" but then I had to get a new head because the first one blew up on dyno and their was almost 5 years between castings. The machine shop now thinks that's the issue they may have casted it different or used longer valves.
My old 346 build, the heads were aftermarket AFR castings with thicker decks, the lifters were solid, AND the base circle was shorter than yours is. My pushrods were 7.425". The only times I've ever seen longer than that were:
1. Short travel lifters were used, in which case pushrods ended up being 7.7" long
2. Tall deck block
Many of these aftermarket heads are lifetime castings. You may need to redo the valves, etc, but the castings are extremely good. Are you SURE it was a casting failure that caused it to blow up?
12-11-2019, 10:52 AM
#32
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i went by what the machine shop said I didn't actually measure anything myself. That's what he told me to put in. Hes been building engines for 50 yrs doubt it's inexperience but never know **** happens and the problem is fixed took it to dyno this am and not one issue with it. This time it actually was tunable. Now runs and drives great.
12-11-2019, 11:31 AM
#33
they're ls7 lifter and prc 247 heads. When i measured I got the 7.575" but then I had to get a new head because the first one blew up on dyno and their was almost 5 years between castings. The machine shop now thinks that's the issue they may have casted it different or used longer valves.
12-11-2019, 11:34 AM
#34
I'm so confused to everything I read. The banks switched from the beginning to the middle, valves moving when air pressure applied and with springs installed doesn't make sense. No matter who or what anyone says, you MUST measure your pushrod preload. Even the 3/4 to one full turn method (When done correctly) works. I've had to use different sized PR's due to install heights being different between the intake and exhaust but it was only a difference of .025".
The car runs fine which tells me something was way off with your method of doing a leakdown. Glad it's running though.
The car runs fine which tells me something was way off with your method of doing a leakdown. Glad it's running though.
12-11-2019, 12:16 PM
#35
I'm so confused to everything I read. The banks switched from the beginning to the middle, valves moving when air pressure applied and with springs installed doesn't make sense. No matter who or what anyone says, you MUST measure your pushrod preload. Even the 3/4 to one full turn method (When done correctly) works. I've had to use different sized PR's due to install heights being different between the intake and exhaust but it was only a difference of .025".
The car runs fine which tells me something was way off with your method of doing a leakdown. Glad it's running though.
The car runs fine which tells me something was way off with your method of doing a leakdown. Glad it's running though.
12-11-2019, 05:10 PM
#36
Methinks you should have someone else knowledgable look at it with a calm objective eye. You're too invested and flustered, and that's when you make mistakes checking stuff.
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