The Stovebolt Site Forums The Shop Area Engine Shop Compression test results

Just finished the test (twice) on this 56 235 and:
1 - 85
2 - 90
3 - 90
4 - 95
5 - 85
6 - 70
Motor starts and runs fine, a little bit of smoke but not ugly, have not had a valve adjustment in 4 years with approx . 1500 miles driven since last adjustment. Time for rebuild? Or adjust valves and test again. This motor is original and probably has never been rebuilt or out of truck. Probably set a long time before I bought it. Thoughts??

Dale

If it runs fine and doesn't smoke too much, I would be happy!

Well, I'm not unhappy, just surprised at how low the compression is compared to the 130 the shop manual says they should be, and #6 close to only half of that. Is valve adjustment worthwhile with those readings?

if it runs, drive it til it doesn't - the absolute reading isn't as important as the 25# spread between the highest and lowest, the manuals states that with more than 5-10# difference the engine cannot be tuned properly, I'd consider the engine thrashed

Bill

I agree - until the smoking GETS ugly, or it doesn't run, run it!

Of course, the curiosity would kill me - I'd do a valve adjustment and test again, just for because.

-Michael

The older MOTOR or Chilton manuals give the proper procedure for a compression test. Did you block the throttle open on the carburetor when you ran the test? Did you have all the plugs out, or only the one on the cylinder you were testing? Did you go back and squirt oil in each cylinder and check it again? Has the engine sat idle for a long time? (The one cylinder with 70# might have a sticking valve.) Not trying to be a smart a-- but if you did it all correctly, it STILL seems to be a drivable motor, and it gets real costly to overhaul one, especially if it doesn't need it. I'd run the valves again and drive it.

i was told as long as the numbers are all close to each other, then that should be enough

Thanks everybody! I plan to do a valve adjustment, then re-d o the comp test just to make sure of what I am getting. So you know- I start this truck almost every day and drive it at least 2 or three days a week - just terrorize the neighborhood, then back to the garage. Will let you know how the test turns out as soon as I learn how to and do the valve adjustments.I am following ths shop manual best I can-- fun!!
Dale

Dale,

My all-time-favorite Stovebolt hint is how to adjust the valves with just 2 turns of the crankshaft:

Setting Valve Lash

Saves time - brilliant. It can seem intimidating, but it's really quite easy once you get into it. Post if you need more help!

-Michael

Thanks Michael - Your "setting valve lash" will probably work great for me if I knew just a little more. I do have just a few questions, never having done this and being the amateur extreme 1) do you set to #1 using the rotor position after removing the distributor cap, or just by observing the valve/rocker arm opening? 2) Do you need to remove the plug wires and spark plugs? 3) can you "turn" the motor (crankshaft) by hand using the fan, or do you need to use the starter? These are the little details that are not readily obvious to me and in which the shop manual is no help. I appreciate your offer to help before I take off on this. I'm sure you're right, having done this once it will undoubtedly be more simple next time. It's doing it right the first time that counts. Thanks again,

Dale

Dale & Mike,

I hope you do not mind me entering this discussion.

1) Since you will have the valve cover off, and you will be able to see the valve stems and tappets, you might as well look for both #1 cylinder valves being closed/shut (rocker arms being loose). I also check to see if the timing ball on the flywheel visible (it may or may not be lined up with the pointer, depending on the year/model flywheel).

2) There is no need to remove plugs/wires. Be sure the ignition is off.

3) Turn the crankshaft any way that works. I use the fan-belt and/or harmonic balancer. Or, I use a flywheel turner. Using the starter would be OK, i guess.

Be sure to let the engine run for at least 30 minutes after reaching operating temperature before stopping the engine and removing the valve cover.

Tim,

I'm pleased that you entered the discussion, as I'm sure so would Mike be. Thanks for the follow- up - it all goes together now and I am on my way - one more dumb question though --- what's a flywheel turner look like? I have never heard of one far less seen one. Not to worry - can figure out how to rotate now, just didn't know there was such a tool. Sounds handy. Thanks again,

Dale

flywheel turner

A big screwdriver or small pry-bar as a lever between the flywheel and the lower side of the clutch housing also works.

cameo1956

here is a quick video i made last time I set my valves on my 54 235
...link...

Please ignore the comments on the bottom of the video as they may be misleading. I've heard the method I used described as "The Numb Skull Method"


Follow the instructions from Tim's page above especially his note on TDC.

I was able to move my flywheel with the fan.
good luck

Nice video, DADS50

I especially like the sound track.

Thanks

Thanks for the video DADS50! -- thought it was excellent. I never did use the distributor rotor, just followed Tim's advice on rotating with the engine fan. Turned easily. Did it according to all information provided, Tim, Mike and everybody. Had to adjust 4 gaps - all openings adjusted were found way too tight. Especially the #1 intake. (which I had listed mistakenly as #6 in my first post above - reversed the order my mistake). I'm learning and I think I did it all right as far as I could tell. Wish I had run the engine with the valve cover off like DADS50 did so I could have checked the oiling, but I had already put it all back together, started up, runs fine, no leaks. Now off to do the compression test again. Will post results (the right order this time) when I get done. Thanks everybody!

Dale

The open valve cover is not necessary. I just didnt know it at the time.

Compression test results - before and after valve lash adjustment -

Before After
1 - 70 - 80
2 - 85 - 90
3 - 95 - 100
4 - 90 - 100
5 - 90 - 95
6 - 85 - 95

Some change, but not so much in the lowest- #1. For now I will just take some of the advice above -- it runs great, so, at least for this cold winter I'm just going to drive it and enjoy. Rebuild later down the line when troubles appear. Thanks again everybody - I feel like I learned a lot.

Dale

Right now you have a good engine that may be least expesive to rebuild. You may be able to avoid a lot of machine work.

I would start stashing money in piggy bank for a rebuidl in about at year.

Dan Bentler

I had a '49 Pontiac that had compression like that, one low cylinder. I drove it for about 10,000 miles that way, even on trips of 2000 miles. Unless you drive it a lot, if it runs fine, I'd leave it alone. I'm a cheapskate.

I agree with Christopher, drive it.

And, Dan has it right - drive it and start saving. It could last a long time, depending on how much you will drive it.

You know, it's heartening to hear so much support for just driving this old truck,until it begins to fail. So far, for something this age,it has performed admirably, and I forget sometimes, that's exactly why I bought it in the first place. Like I said, I learned a lot here that I won't soon forget, and for now - I will just keep on driving this old beauty. Thanks again for all your help.

Dale