The Stovebolt Site Forums The Shop Area Engine Shop OK, why the low cylinder pressure?

Hi, Guys, I just got this truck home from a guy who said he had the engine rebuilt 8 yrs ago and only drove it to work and back. He went out in Dec of 06 but the truck wouldn't start. He replaced the coil and battery thinking it was an electric issue. I've checked and I do have spark, but still no fire. There does also seem to be a fuel delivery problem, but when I did the comp check there was a heavy fuel smell. I did a compression check (with 2 different gauges, by the way) and all my cylinders are running about 35-50#. Is the engine worn out and all the cylinders have worn out with such even compression? Am I looking at a rebuild, or am I missing something fairly simple? :confused:
Thanx, Chris
P.S. I did do a search on the forum and couldn't come up with a satisfactory answer, sorry...)

Chris,

The chances that these readings are valid is pretty slim. There is probably something else going on that is not allowing the cylinders to pump up. The obvious first check would be the valves. They could be gunked up and not closing, or they could have been adjusted much to tight.

A pretty standard method to take a compression check is to pull all the plugs, open the choke and wedge the throttle WOT, ground the coil and crank at least five or six times per cylinder.

The screw in pigtail for the compression gauge works the best..no pop offs. Is this how you did your test?

The engine wouldn't run with pressures like you found, and those low values wouldn't just happen overnight. Could the seller have seen you coming?

Squirt some light weight oil into the cylinders, let it soak for awhile, and while it's doing its thing, pull the valve cover and see what the top end looks like. As you roll the engine over with the fan, each rocker arm should, at some degree of rotation, become loose and you should be able to twirl the pushrod. Dig around some, all is not lost quite yet.

Stuart

If the cylinders have been Gas washed, you will have
low compression, squirt some oil in the spark plug holes and you'll find the compression will be a lot
higher. Look for a sunk Carb float.. That will explain a lot of things....

definaltely check your valve lash ...first ...might be too tight

Thanks for the info, guys. I can build and diagnose a small block chevy, but this straight 216 (waddya mean, no pressurized oil pump and what are these things you call "babbit" bearings??? ) totally throws me for a loop.
I'll try to track it down, starting with pumping oil into the cylinders and retaking the test. I already bought a carb rebuild kit and I did note what seemed to be an awful lot of gas at the bottom of the intake. As far as checking the valve lash, I'll have to learn that.
So that I can get more input, please check for my question in the general truck talk regarding looking for the best book to pull out the 216 and rebuild it. When I was a kid, I used the Chilton Motor Manuals, but haven't seen those around for years. I guess I'll be looking for the "Step by Step for the complete idiot" guide... Thanks again, and I'll keep you posted on what I find this weekend...

Okee Dokee! Well, I went out and did a wet compression test. I got about 35# or so dry and about double that with a squirt or two of oil. I moved the fan with the valve cover off and saw that all the pushrods seemed to be moving well and was able to twirl each one by hand. I guess I'm going to be looking at a rebuild, yes?
I'll be ordering a shop manual and assy manual next week, but in the meantime, I've heard I have to remove (practically) the entire front end to yank the motor-is this true?
Be prepared for lots more questions, OK? I appreciate the help so far...
For info, I'll have to do this rebuild quickly (though it won't be a "rush" job) since I'm giving this truck to my dad (he's 76 and I WON'T give it to him if it's undependable) when he comes to visit the first or second week of August. Oh Boy! I can feel the stress now! WooHoo!
Any help will be appreciated... Thanx again, Chris

Certainly is easier to remove the engine straight out the front but if this seems discourageing think of it this way;
you'll never get a better opportunity to flush out the readiator, replace worn engine mounts, straighten or replace broken grill parts, etc.
As you get into the engine remember the tapered crank journals and don't loose the shims. The rest of it is easy enough for a good 350 man.

Certainly is easier to remove the engine straight out the front but if this seems discourageing think of it this way;
you'll never get a better opportunity to flush out the readiator, replace worn engine mounts, straighten or replace broken grill parts, etc.
As you get into the engine remember the tapered crank journals and don't loose the shims. The rest of it is easy enough for a good 350 man.

What are tapered crank journals? :confused:


Stuart