I think I have a strong indication as to my problem is but ask for some reassurance. I'll start wih my setup stock original 99 LS1 shortblock 22K miles,G5X3 camshaft,Absolute Speed 5.3 heads,Comp R lifters,stock rockers,Comp 977 springs, Crane pushrods.

I decided to do a compression test just to see the general health of the motor as it's gets it's share of high rpm's (High stalled A4) and came up with a wide varience. I realizd thru reading here the actual numbers were not as important as the difference between each cylinder. So with that said 2 cylinders were down about 30PSI compared to the avearge of the others. Next step is of course a leakdown test. I did not have a leakdown tester handy so I button it up for the day and fire her back up. Major lifter tapping and a cylinder not firing off as I guess a lifter bled down from all the cranking during the compression testing. I did disconnect the coilpacks and the fuel injectors for this testing. After a few minutes idling she simmers down starts to run OK.

Yesterday I do a leakdown test wich came back with all 8 cylinders having 5% or less wich I know are well beyond acceptable. I do another quick comp test after this leakdown and tho' like a dummy this time I forgot to open the throttle blade wich threw the numbers off from last time the same 2 cylinders come up with a large margin lower. And again on restart lifter making a racket and rough idle for a few mins. I brought along my infared temp gun and hit the header tubes on each side during start up and one of the cylinders that has a low comp reading was about 100 degrees cooler at the header during this settling process but comes up temp. The motor settles and lifters quiet down but a slight tick has been present in this motor for some time now.

Question in short can a faulty lifter throw compression numbers off? Obviously the leakdown results show rings/heads are in good working order. I did some searching and the Compr R lifters have had their share of issues but back 6 years ago when this thing went together they were the only game in town. Thanks in advance for any input here on something I may be overlooking.

 

Hmmm nobody with any sound tech advice for me?

 

I would assume that it could, for instance if the one intake valve is not opening as much as the other intake valves due to lifter bleed down. I dont suppose you plan on pulling the heads anytime soon do you? You might consider it as those comp-R lifters are known to destroy the whole motor when they go. Probably not what you want to hear right now, but better safe than sorry. Even if its not the cause of the compression test variation between cylinders, it still sounds like a lifter problem.

 

Yes I actaully do plan on pulling the heads actaully the whole motor. I'm goona do the rod bolts so I figure now is the time to do this all. I guess the Caddy lifters are the way to go? The Morels are pricey but if that a better option i'll spring for them. Not looking to do this again. As of course with a different lifter will come preload specs/measuring for a possible pushrod swap as well.

 

Theres the LS7 lifters too... What length pushrods do you have now?

 

They are 7.400 Cranes I did not set the heads up. Something tells me I need a bit longer pushrod as when I rotated the motor over by hand and put the lifter on the basecircle I could move the rocker arms up and down ever so slightly probably talking thousandths. But from what I've read if there is any preload that should not be possible. So in short I ordered a pushrod checker and will be going thru the motions upon reinstall. I really appreciate the reponse this thread lay dead for a couple of days. My mind has been burning the midnight oil.