The Stovebolt Site Forums The Shop Area Engine Shop 1955 1st Chevy 3600 compression test results

Hi there

Just waiting on some parts to get this truck started, or attempt to start, after sitting for more than 20 years. I spun the engine over with the starter to do a compression test, and the results are as follows:

#1 - 140 psi
#2 - 65 psi
#3 - 70 psi
#4 - 145 psi
#5 - 155 psi
#6 - 150 psi

I was happy with all but #2 & #3, i sprayed penetrating oil in and let it soak for a day, then added some ATF and soaked for two more days with periodic cranking by hand. We did the test on #2 & #3 last night and the compression came up to 115 psi on both. This is better but still along way from the rest of the cylinders. My assumption is that there were a couple of stuck rings after sitting so long, and my questions are:

1- have any of you had similar experiences with sitting engines?
2- Is my assumption of stuck rings correct, or at least possible?
3- Do you think that these could free up once the engine is running and warms up?
4- Is there any precautionary advice to offer before i fire this with the current compression test results.

Thanks in advance
Jeremy

Did you confirm all valves are free moving not Stuck?
Focus on the valves for #2 & 3 cylinder.
If stuck I took a rubber mallet & wood block and knocked on them.
On my old 216, which did the trick for me.
Hopefully others will chime in soon.
Todd

Since the readings came up 40 lbs or better your reckoning of stuck rings may be right. But, be sure your valves are not sticking or bent push rods from cranking the engine. Good luck.🛠

Thanks for the response

Before i did anything i pulled the valve cover and cranked by hand to ensure the valves moved freely, it turned over quite easily. i will check bent push rods, but wouldn't that shorten the opening of the valve, rather than affect the closing? Or am i checking bent rods to see if they may have been caused by a stuck valve?

Thanks
Jeremy

Valves that don't open far enough (especially intakes) will affect compression by restricting the intake path. Starting farther below atmospheric at the bottom of the compression stroke effectively reduces the compression.

Ahhhh thank you, i never thought of that but totally makes sense!!

One quick way to find a bent pushrod involves watching the engine at idle with the valve cover off. A straight pushrod will spin at random. A bent one will stay in the same position with little or no rotary motion. It's almost impossible to eyeball a pushrod and see if it's bent, unless it's rainbow-shaped from a badly stuck valve. Another checking technique would be to remove all the pushrods and roll them over a completely flat surface like a sheet of plate glass.

My favorite method of freeing up sticky piston rings is to run the engine at a fast idle for 15-20 minutes with a fresh fill of cheap 30 weight oil and a couple of quarts of Diesel fuel added to severely over fill the crankcase. The crankshaft counterweights splashing into the oil/solvent mix will scrub the crankcase, pistons, and rings like they were in a washing machine. DO NOT drive the vehicle or put any load on the engine while the Diesel fuel is in there. Drain the stuff out while the engine is still hot, change the filter, and refill the engine with oil. I like 15W-40, but opinions on oil are like "noses"- - - -everybody's got one, and some are pretty smelly!
Jerry

Thanks for the info

I like the diesel suggestion, but do you think I risk any internal damage as this unit does not have the optional oil filter?

I've used many gallons of Diesel fuel that way, and the only engines that gave trouble were worn out already- - - - -the solvent bath just dislodged some of the gunk that was keeping worn out piston rings pushed out against the cylinder walls. You'll either improve things, or confirm that the engine REALLY needs a rebuild!

If you do have to rebuild it, at least you won't have to scrape as much crud out- - - - -splashing the Diesel around inside does a better job of dislodging sludge than hours spent with a brush and solvent after removing the oil pan.
Jerry

Thanks Jerry

I will give it a try, 5 litres (quarts) of oil and 2 of diesel. Hoping the carb kit shows up on Friday and i will get it fired this weekend, i will post how it went.

Jeremy