[wbferran]

the only thing i have read about this check is that the lowest reading cylinder needs to be within 75% of the highest reading cylinder.

but there must be some number that would be considered normal for my 351W. before the valve job i had around 150 on the driver side, 5-8. 1-4 had some issues and were well below limits.

after the valve job, i only got 75-95. different gauge than before and the check before the valve job was done with the engine at normal temp. the check after the valve job, i had allowed the engine to cool down a little (first gauge got stuck in the hole!).

anyway, is there a normal number for this engine? someone had suggested there needs to be some minimum compression to create proper combustion of the mixture, and that is why i am asking. thanks-

billy

 

[woodsnake]

What were the issues with 1-4?

 

[wbferran]

What were the issues with 1-4?

around 40 or so in 1 and 2. decent in 3. zero in #4.

don't think any of that changes what kind of compression should one consider to be "good".

 

[Bad69cat]

If your in the 160ish range your probably OK....What caused you to do the valve job? How in the world did your guage get stuck!? Thought I was the only one with those kind of troubles!....jeesh

 

[wbferran]

If your in the 160ish range your probably OK....What caused you to do the valve job? How in the world did your guage get stuck!? Thought I was the only one with those kind of troubles!....jeesh

the gauge was a loaner from O'reilly's. it was brand new. it went into #1 just fine, but when i went to get it out, the hose just spun inside the male end. just a poorly made gauge, or i got it in there too tight. anyway, i was fortunate it was the #1. after removing the battery, i was able to get a long, skinny flat head screwdriver to the face of the threaded male and along with a hammer, gain enough of an edge to get it turning counter clockwise. got lucky there.

i also thought around 160 would be "normal". so the readings of 95 to 75 are either wrong, or the machine shop screwed up. i did the valve job because the vacuum was so low, only around twelve inches at idle. subsequent compression check showed very low, less that 40, in one and two, and zero in #4. the vacuum is back up now to nineteen (brakes work better), but the miss is annoying. if the compression check is accurate, something is wrong with the valve job.

 

[towcat]

On an 351W engine with rings and valves in good condition, the comp. I would expect to see 160 to 180.

 

[Bad69cat]

hmmm, check the valve lash first. might not be the valves....may want to pull the head and check that cylinder, sounds like bad rings or hole in the piston perhaps..? see if it has a deep ridge or any grooves in there --- might be able to run a scope in the plug hole first just for a quick looksee

 

[wbferran]

hmmm, check the valve lash first. might not be the valves....may want to pull the head and check that cylinder, sounds like bad rings or hole in the piston perhaps..? see if it has a deep ridge or any grooves in there --- might be able to run a scope in the plug hole first just for a quick looksee

checked all the cylinders and the pistons when the heads were off. i was pleasantly surprised how good everything looked. i don't think you noticed that the valve job had already been done?