compression differences 80 FI spider

[narfire]

Had a bit of time to putter with the car today. Tried out the new compression tester and found some differences. #1-130 psi #2-100 psi #3-125psi and #4 120psi. the rings were put in correctly less than 400 miles ago, so I'm wondering if the valve/cam gap is out of whack. I'm getting a 1800 head done with oversize valves so I wanted to see what if any comp. difference there might be. The engine does run rough at the moment.
Any coments,going to wrestle with the valve covers before dinner.
Thanks
Chris

[So Cal Mark]

#2 is a concern especially if the engine runs rough. Have you done a cyl balance test to see if 2 is causing the roughness? I'd do a leak down test to see where the leakage is. With only 400 miles it's possible the rings haven't seated in 2, but I'd think a problem is more likely.

[rlux4]

My '82 ran slightly rough when I first got it. I had one cylinder that was about 15 lbs. lower compression than the others. When Alvon (Ventura Ace) graciously offered to help me check valve clearances we found that cylinder to have a valve that was off by several thou. After changing out the shim to get the correct clearance, the compression readings were close on all four and the car ran great.
Ron

[narfire]

Hi guys, yeup #2 seems out of whack more than the others. If I have done this right then
Intake #1--.012 # 2 .005 #3--.012 #4--.011
Exhaust #1--.014 #2 .016 #3--.016 #4--.018

My newly bought shim tool is at the mill so I'll be spending a few evenings getting this sorted. I would just leave this till the 1800 head is ready and do this on a bench but I need the car to get to the paint guy. Never done this stuff before but seems straight forward (kind of). I'll might even have to read some instuctions but if I do I'll never tell.
Chris

[rlux4]

Sounds like you have a handle on it Chris. Way to go buddy.
Ron

[narfire]

Yea it works!!! re-shimed the motor, even got one machined down to the right thickness and presto... good/same compression on all 4. 135,130,130,130. Can't believe that a couple of thou. makes that much difference but I guess it does.
Not bad for a logger
Thanks guys&gals
Chris

[rlux4]

Woohoo!
Kudos to Ace.
Ron

[TulsaSpider]

Awesome! I'll have to try that. I have one cylinder that's a little down from the others as well.