Compression problem

[Richard H.]

Re: Compression problem

This is a small block crate engine, did they use mechanical lifters in a small block? I have the old lifters, if I put them back in how do I adjust them?

[Duke W.]

Re: Compression problem

I have no idea what you have, but my suggestion was to disassemble one of the old lifters to determine if it is mechanical or hydraulic given that the piddle valve mechanical lifters look like hydraulic lifters. Your symptoms indicate the possibility of hydraulic lifters on a mechanical lifter cam.

If they are hydraulic, the adjustment procedure is in any service manual. At TDC #1 and TDC #6 of the compression stroke you adjust eight specified valves - tighten them until there is no clearance - then 1/2 to 1 turn down. They do not need to be soaked in oil or prefilled.

Out of curiosity, why did you install new lifters on the existing camshaft?

Duke

[William C.]

Re: Compression problem

As Duke mentioned, you FIRST MUST figure out what the cam is in the engine before you go anywhere. Do you have receipts for the crate engine? The part number of the engine should let you figure the original camshaft installation. If not, I'd think about buying a GM cam and lifter set and installing the matched assembly.

[Domenic T.]

Re: Compression problem

I have no idea what you have, but my suggestion was to disassemble one of the old lifters to determine if it is mechanical or hydraulic given that the piddle valve mechanical lifters look like hydraulic lifters. Your symptoms indicate the possibility of hydraulic lifters on a mechanical lifter cam.

If they are hydraulic, the adjustment procedure is in any service manual. At TDC #1 and TDC #6 of the compression stroke you adjust eight specified valves - tighten them until there is no clearance - then 1/2 to 1 turn down. They do not need to be soaked in oil or prefilled.

Out of curiosity, why did you install new lifters on the existing camshaft?

Duke

No you do not have to fill them or infact anything else BUT if you have respect for your cam that is what should be done with hydraulic lifters so they do not beat the cam lobe in it's break in. Very important to get the lifter turning ASAP during the cam break in.
The other reason is to establish when thelifter is at O lash BEFORE you tighten it down.

A empty lifter that cannot be seen will give NO resistance when tightened down,hence holding the valve open, no hydraulic action, no compression.

That was one of the mistakes I found that was made the most by inexperianced mechanics, tightening a dry lifter till it put pressure on the valve stem, then tightening it 1/2 or more.

DOM

[Duke W.]

Re: Compression problem

No you do not have to fill them or infact anything else BUT if you have respect for your cam that is what should be done with hydraulic lifters so they do not beat the cam lobe in it's break in. Very important to get the lifter turning ASAP during the cam break in.
The other reason is to establish when thelifter is at O lash BEFORE you tighten it down.

A empty lifter that cannot be seen will give NO resistance when tightened down,hence holding the valve open, no hydraulic action, no compression.

That was one of the mistakes I found that was made the most by inexperianced mechanics, tightening a dry lifter till it put pressure on the valve stem, then tightening it 1/2 or more.

DOM

With the crankshaft properly indexed, you wiggle the pushrod up and down while tightening the nut until the clearance just reaches zero. Anyone should be able to do this, including first timers. Then the additional 1/2 to 1 turn. Some say rotate the pushrod back and forth with your thumb and forefinger until rotational resistance is felt, which indicates zero clearance. This won't work very well because the amount of rotational resistance once clearance is zero or less is not that much more and can be difficult to detect.

The lifters will likely fill up during cranking or shortly after starting. A preoiler will fill them up for sure if you rotate the engine through at least two revolutions while running the preoiler.

Duke

[Richard H.]

Re: Compression problem

I replaced the new hydraulic lifters with the original ones assuming they were solid lifters. I adjusted the rockers to a .30 over 0 lash and turned the key. The engine started immediatly and it sounded great. With a few small adjustments it idled at between 700 and 800 rpms. I will not know for sure how it runs until I take it for a test drive tomorrow. We will see! I am only trying to get some additional miles on the car with this small block while the big block is being rebuilt. The way it sounds I maybe putting the big block on a stand! Thanks to all for the help, hopefully I will have a good report tomorrow.

Thanks,
Rich harris

[Domenic T.]

Re: Compression problem

With the crankshaft properly indexed, you wiggle the pushrod up and down while tightening the nut until the clearance just reaches zero. Anyone should be able to do this, including first timers. Then the additional 1/2 to 1 turn. Some say rotate the pushrod back and forth with your thumb and forefinger until rotational resistance is felt, which indicates zero clearance. This won't work very well because the amount of rotational resistance once clearance is zero or less is not that much more and can be difficult to detect.

The lifters will likely fill up during cranking or shortly after starting. A preoiler will fill them up for sure if you rotate the engine through at least two revolutions while running the preoiler.

Duke

Duke,
With all do respect, I have done this profecionally at a chevy dealership and still do it here in my shop today.

There was no mention of a pre oiler and what psi do you pre oil at?

I use 80 to 100 psi on lifters that are REQUIRED to be installed without oil and it takes about 6 revs by hand to do it at that pressure.

Over 80 % of aircraft engines fail because the engine is started with dry lifters and the cam is allowed to be beaten by the lifter for 40 min.

The old chevy manual says, if I remember right 20 min.

If the lifter is filled the first timer will be able to feel resistance and NOT tighten down a empty lifter to the point of holding a valve open.

Most good cams are case hardened about .050 and once a lifter beats thru that it's over for the cam lobe.

I use a much more accurate way than the finger and thumb way and bolt the covers down, run the engine for 20 min at 1800 and close the hood.

This is not a easy thing for a first timer.

DOM

[Duke W.]

Re: Compression problem

How do you think Flint adjusted hydraulic lifters back when they were building several hundred small blocks per year.

They certainly didn't lavish the attention on engine assembly that we do today.

Likely they adjusted empty lifters as I described, and the 30 second hot test filled them up, then it was off to the plant. There was no dedicated cam breakin.

After installation in the vehicle the engine went through at least a couple of dozen cold starts while it was jockeyed around for shipment to the dealer and movement on the dealer lot, spending most of the time idling, and the engine rarely achieved operating temperature during these brief periods of operation.

The bottom line is that these brand new engines received the absolute worst treatment you can give a new engine, yet the survival rate was in the ballpark of 99.9 plus percent.

Duke

[Domenic T.]

Re: Compression problem

How do you think Flint adjusted hydraulic lifters back when they were building several hundred small blocks per year.

They certainly didn't lavish the attention on engine assembly that we do today.

Likely they adjusted empty lifters as I described, and the 30 second hot test filled them up, then it was off to the plant. There was no dedicated cam breakin.

After installation in the vehicle the engine went through at least a couple of dozen cold starts while it was jockeyed around for shipment to the dealer and movement on the dealer lot, spending most of the time idling, and the engine rarely achieved operating temperature during these brief periods of operation.

The bottom line is that these brand new engines received the absolute worst treatment you can give a new engine, yet the survival rate was in the ballpark of 99.9 plus percent.

Duke

That makes one think and discounts a lot of cam break in instructions.

Believe this or not as they were his words:

In 1970 when I was working at the dealership I was told by the service manager that about the time that break in oil was discontinued (I think he said in the 50's) the dealership was instructed to remove cams and coat them with a special lube because of failures they were having. New cars and that's hard to believe because it would be preventative MTC. and I don't think the word recall wasn't born yet.

Those are not my words but his and it would be interesting to see if any of the old timers here ever remembered that happening.

When I went to work it seemed that there was always a BB cam replacement job in my stall and that was what prompted the conversation.

DOM

We had to use a break in lube on any cam or lifter we replaced under warranty and that's why (he said) we did have