Compression problem

[Richard H.]

Hi

I have a problem with a small block motor compression. I am trying to get some miles out of a small block while big block is being rebuilt.


Initially motor had low compression and did not run well. So the motor was dissassembled and cleaned. Broken ring was found in #1. A new ring set was installed. Bored seemed fine showing little visable wear valves cleaned up well with no visable burned areas. Re-assembled and compression was again checked no compression. The lifters were replaced and all cylanders initially came up to over 165 psi. Re-assembled engine thinking problem solved. Tried to start, it would not start. After lifters pumped up I recheck compression and reading came up under 50 psi in each cylander. I lossened rocker bolts and compression came up as valve rockers were backed off. Rockers seem too loose but copression came up. I did replace the timing chain so that could be the problem. The timing marks were lined as best as I could. The original problem of no compression still exist when valves are tightened to specks. Does anyone have any possible solusions?

Rich Harris

[William C.]

Re: Compression problem

I'm making the assumption that this is a hydraulic lifter engine. If so, your likely problem is that you are over tightening the rocker adjustment. The hydraulics need oil pressure to allow then to be adjusted properly. Start the engine in the "too loose" state and then run thru the factory adjustment with the engine running. That should solve your problem. If not, I'd check to see that the "new" lifters you installed are correct for the application.

[Richard H.]

Re: Compression problem

I put hydraulic lifters in, I think the ones I removed might have been mechanical lifters. not sure if they were mechanical or stuck Hydraulics?

[William C.]

Re: Compression problem

What is the tach redline starting at? What is the oil pressure gauge calibrated to, 60# or 80# max? What intake manifold and exhaust manifold is on the car? Are any of these known to be original to the car?

[Michael W.]

Re: Compression problem

The original problem of no compression still exist when valves are tightened to specks. Does anyone have any possible solusions?

Rich Harris

What specs/procedure are you using to adjust them?

[Richard H.]

Re: Compression problem

The car I believe was originally a L-72 big block built sept 65. The story is the engine was stolen or removed for racing. The tac is 6500 and the oil gauge is 80 pounds. The engine in it is a 67 657 block believed to be a crate motor-no stamping on pad. It has high preformance large valve heads 68. The intake is a high rise edlebrook and the carb is a 600 cfm holly. It ran great for several years and I let students at a local high school work on it and the problems began. I am pretty sure the rockers are too tight. Today I am going to adjust them to 0 lash and check compression? As soon as they get too tight I loose all compression! Thanks for your help

[William C.]

Re: Compression problem

OK, do you know for sure what lifters you bought? Have you checked them to see if hydraulic or solid lifters? When setting to zero lash, how are you going to accomplish that, how will you determine for sure that each lifter is on the base of it's lobe when setting the lash? That is the real crux of the issue when setting lash on an engine that is not running.

[Domenic T.]

Re: Compression problem

Richard,
If they are new hydraulic lifters then you will be able to push the pushrod seat down in the lifter body because they are empty.

You need to fill the lifters with oil, some say to submerge the lifter in oil and pump it with a pushrod but I use a squirt oil can and fill the lifter thru the hole on the side till it comes out of the top hole where the push rod seats.

If you adjust a dry lifter you may be bottoming out the hydraulic part and making a solid lifter out of it by turning it down to far.

You can tell by the threads above the nut (how many) but If your lifters are empty that will beat the cam lobe till they fill, If they fill and you will have to do the adjustment with the engine running if you are lucky enough to get it started.

DOM

[Duke W.]

Re: Compression problem

"I put hydraulic lifters in, I think the ones I removed might have been mechanical lifters. not sure if they were mechanical or stuck Hydraulics?"

I'm amazed that you didn't confirm what kind of lifters were removed before installing new hydraulic lifters, but assuming you still have the old ones, now it the time to verify what they are. The piddle valve mechanical lifter used in big blocks looks very similar to hydraulics- two piece held together with a snap ring. You have to disassemble one and see if it has a spring inside. If not, they are mechanical lifters, which have a "piddle valve" inside.

If you install hydraulic lifters on a mechanical lifter camshaft, it won't have much compression and probably won't start once they fill up with oil. A mechanical lifter cam will hang the valves off the seats in the ballpark of 450-540 degrees of engine rotation with a filled up hydraulic lifter.

Duke

[Richard H.]

Re: Compression problem

I backed off each cylinder with the compression gauge screwed in. When the copression came up to 140 I went to the next and so on. The engine started!. Tomorrow I will try to set the timing. It is running but does not idle yet. I did not let it warm up because the exhaust manifolds were painted and they smoked. The lifters I put in are definitly hydraulic. I still am stumped as to why the lifters have to be so loose to get compression. three quaters of a turn is the differance from 45 psi to 150 psi

[Richard H.]

Re: Compression problem

All I am sure of is I could not get any give to the lifters I replaced. I do still have the lifters. The engine did start today. I will try to time it tomorrow.

[Domenic T.]

Re: Compression problem

All I am sure of is I could not get any give to the lifters I replaced. I do still have the lifters. The engine did start today. I will try to time it tomorrow.

Richard,
Do your self a favor and ADJUST the lifters FIRST.

If you did fill them then dis-reguard, but if you didn't and they are not filled to get hydraulic action then you will not idle and eventually burn a valve.

When all the lifters are adjusted the rocker studs will have the same amount of threads abvove the nuts, No exceptions or you have another problem.

the procedure to adjust partially filled lifters is best done with the intake off and watching the compression of the lifter but if they are full then things are easier.

I think your safest bet is to back each lifter (with engine running ) off untill it clatters then slowly turn the nut in till the clatter stops, Then do the turn in and I suggest 1/4 turn not 3/4 as the book says. 0 is the optimum but thats another story.

If all are clattering at once then cup the rocker you are adjusting with your hand and it will amplify that lifter noise over the others so you can silence it.

I did this on a daily bassis when I twisted a wrench at the dealership.

Q, did you pre fill the lifters?

DOM

[William C.]

Re: Compression problem

Because the 3/4 turn is the difference between bottoming out the valve in the hydraulic lifter and hanging the valve open vs letting it close. Now that it is running, do a proper lifter adjustment by backing each rocker off one at a time with the engine running, back one off until it begins to "tick" then tighten until the click stops then add 3/4 turn. Do that for all 16 and you will be close to proper adjustment on all of them

[Richard H.]

Re: Compression problem

Hi and thanks for all the responses so far.

I still have no solution as of yet. I did get it started it runs but terribly and it does not idle. I believe that is do to low compression. These are the things I know. When I put in the new lifters and check the compression before the lifters pumped up it tested 165 psi in eah cylinder. I believe that tells me the cylinder is healthy and I am losing compression through the valves and not through the rings? The original lifters I can not push on them and get them to give at all. They maybe solid lifters but they have a snap ring inside them. I did replace the timing chain, the original was very loose. It maybe off a tooth when I put it in, although this is still the original problem that started this quest in the beginning.

[Duke W.]

Re: Compression problem

I still have no solution as of yet. The original lifters I can not push on them and get them to give at all. They maybe solid lifters but they have a snap ring inside them.

The problem and solution are pretty obvious to me. Did you read post #9? Pay particular attention to the construction of piddle valve lifters used in mechanical lifter big blocks.

Duke