Lifter/lash adjusters fill driving, but don't bleed back, then no compression

[LiquidGS-T]

the car is a 96 GS-T

OK, we did a full engine rebuild. Stroker kit, Head rebuilt and decked, 272 comp cams, stock oil pump, balance shafts removed, translator w/3g maft, and a 16g. stock lash adjusters, 680s, walbro 190, blah blah blah

Tried to start it up, no compression. I've run into this before. Pulled out the lash adjusters and bled them down the best i could (pin in the top and pump). I got a lot of oil out.

Put them back in the car, fired it up. Had bad valve chatter obviously. We started driving the car and the chatter quieted, car was running smooth. then at low rpm it started to develop a stutter. Compression test showed cylinder 2, 3, and 4 with 150psi, cylinder 1 had almost nothing.

The intake lifters seemed higher than the rest on cylinder one. Pulled them out and drained them again. Put them back in, compression test was great. Started the car ran smooth. Got about 3 blocks with it and it started to stutter again. If you get it moving and take it over 2500rpm it runs smooth. Get below that, its missing. SOMETIMES it pulls out and doesn't stutter at all, but thats seldom. We thought maybe they needed to run a little while. Car's got over 100 miles on it, and no change...

Tried replacing the intake lifters on that cylinder with another pair, but got the same result. The car never had an oil problem or problem with cylinder one...

We ordered 3g lifters for it hoping that they drain better and won't build up like that. Can't figure this one out tho. The oil pressure is normal.

Couldn't find any threads with this problem before.

 

[nuclearr]

Humm interesting I havent heard this before and am interested in find out what your problem is.

Could it be your oil pressure is to high?

 

[LiquidGS-T]

i thoguht that, only judging off the stock oil gauge, but its normal.

 

[SrKegler]

To rule out lifters, try swapping cyl 1 lifters with cyl 4 lifters. See if the low compression moves to that cylinder. If it doesn't I would suspect weak valve spring in cyl #1.

On 2d thought, just check #1 valve spring pressure. Just noticed you replaced lifters.

 

[Defiant]

You've bent valves in #1.

 

[LiquidGS-T]

i didn't think about weak springs...? I'm gonna run the car with one lifter out and see how it does. then i'll move to the other, see which one is doing it, i just can't believe that its both. we've been working on it for quite some time so its driving me nuts.

Defiant, thanx for the reply, I actually used my compression tester to fill the cylinder with air manually and see, the engine holds air well until you let it go and the piston pushes down causing the valves to open. BUT compression test on drained lifters shows 150psi. Bent valves wouldn't be anything.

 

[TurboAnything]

I am having the same issue with a car right now. Built motor Kiggly springs,supertech valves,crower 272 cams bla bla.

The compression on cyl 4 is low 60psi but 1,2,3 are 170psi. I take out the intake valve lifters on cyl #4 and bleed the down and recheck and it will got to 170psi. If i let the car run for 5-10min it will start missing and the compression goes to 60psi again. I have repeated the test 3 times with same result.

 

[Calan]

John... pull the lifters (either #4 or #1) and rotate the engine until all valves are definitely closed, and lock the engine so it can't turn... and do a leak down test with the highest pressure you can inject... 100-120 psi. It could be that the lifters are masking a compression issue caused by something else. (Like compression falling off after it heats up?)

If it can hold everything you can throw at it with the lifters out and the valves closed, swap the #4 lifters (both intake and exhaust) with another cylinder. If the problem stays with #4 regardless of the lifters, get hold of a cam degree kit and check the valve travel, and start looking at valve springs or the rockers on #4. If the problem follows the lifters, replace them.

 

[killercolt]

It sounds like the lifter is bottomed out from over cutting the valve seat or not trimming the top of the valve stem correctly. You can check this by depressing the bleeding the lifter all the way. Put the lifter and rocker arm back in. Rotate the base circle of the cam love over the rocker arm. Basically you are at zero lift. Push down on the rocker arm where it engages the top lifter. You should have good amount of up and down sponginess here.

If you have no play, this means that the lifter is bottomed out. This can cause the valve to open when the engine is hot.

You got a few options:

1. Take the lifter out and grind the base of the lifter to shorten the lifters a bit. You got a lot of material that can be removed. Repeat until you get sponginess.
2. Go to over size valves to make the valve stem seats lower
3. Get a new head
4. Have the machine shop trim the top of the stem. Be careful. Too much can cause rocker arm to retain interference.
5. Cry
6. Curse
7. Drink beer then curse

Good luck.

 

[BogusSVO]

I would have to agree with killer colt, valve tip height is too tall, so soon as the HLA gets any oil pressure it cracks the valve off the seat.

If you have a regrind cam, install it and see if the issue goes away.

The head you are having issues with, did it bend valves/crack guides before and you go back with STD valves?

 

[TurboAnything]

I tried shaving down the lifters. I removed a good amount off the bottoms and the lifter was sitting no where near bottoming out. Started the car and the problem still happened 60psi on cyl-4. Leak down test shows the same on all 4 cyl so the valves are sealing when set in the closed position.

I then decided to remove one intake rocker at a time and do the comp test. With the left most rocker removed compression stayed at 60-70psi. I then reinstalled the left most rocker and removed the inboard rocker. Low and behold compression jumped to 160psi. I started the car and let it run for over 10min. The compression stayed good. I shut the car off and check it and its holding 175psi now with just the left most rocker installed.

I have already pulled the head and it is back at the machine shop to find out why the valve will seal when fully shut but when fallowing the cam profile it hangs up and does not want to close all the way. Cyl #2 was showing only 150psi so i that will be checked as well.

Thank you guys for the help I will update this when i know more.

 

[BogusSVO]

Sounds like one of two things... Cam base circle larger than spec, or valve tip height too tall

 

[TurboAnything]

well got the head back today. I put it on and it did the exact same thing as last week.

I am at a loss. I think i am going to just build a new head and see what happens. Only thing i can think is the head is tweaking when torqued down causing a valve to not seat.

 

[BogusSVO]

If the valve was cracking off the seat when the head is torqued down, it would not hold for the leak down test with the cam out of the head. Nor would the compression come up when you bleed down the HLA.

Also if a valve job was done and the seat was crooked in the head casting, compression would be low no matter what

 

[TurboAnything]

Ok as a last ditch effort I put a stock intake cam in. Low and behold compression is now holding fine with all rockers in place. I have driven the car and all is good. I have a hard time believing the crower 272 is to blame but that's how its looking.

 

[BogusSVO]

Have you measured the base circle of the crower cam lobe and compared it to the stock base circle of the stock cam?

 

[bastarddsm]

If the valve is sticky, and basically floating, it will cause this. Could be that the crower cam, has a ####ed up ramp and letting the valve float. Are you sure the kiggly's are installed correctly?