The Stovebolt Site Forums The Shop Area Engine Shop Valve Sticking?

Hello All,

I just bought a 1950 Chevy Pickup with a 235 engine in it. The seller told me he thought it had a valve sticking. How do I figure out if i have a sticking valve?

thank you for any help.
Mike

do a compression test first. suspect any cylinder thats low. Then you can repeat the test on the low cylinder, but add some oil (~ 1/2 oz) first. If compression improves, then worn rings are likely the cause.. if not, then look to a valve problem (worn, sticking, etc)

Be careful on an engine that has been sitting for a while, a stuck valve can result in a bent pushrod, so always oil the valve stems making sure oil runs down the guide. Gently tap on valve with soft hammer or 2 x 4 to make sure they all are free.

Ed

I checked compression on the engine. Here's what i came up with. #1 - 15 psi, #2 - 100 psi, #3 - 110 psi, #4 - 115 psi, #5 - 30 psi, #6 - 30 psi.

now i'm concerned. Any suggestions?
Mike

Tom C, sorry, I didn't read your instructions very closely. Reminds me of high school. I retested as suggested. Here is what I got.

#1, 15 psi dry, 27 psi wet.
#5, 32 psi dry, 65 psi wet.
#6, 40 psy dry, 90 psi wet.

does this mean i have worn rings?
Mike

those are very low readings. It looks like you have some ring wear, but all old engines do. If I had to guess, i would say you have a valve problem on #1 and the head gasket leaks between 5 & 6...

as Ed says, you can tap on the valve stems to make sure they're free. Then unfortunately you are looking at pulling the head - It won't run with compression that low.

should i pull the head and get it machined and then see how it runs or just tear down the complete engine? I really don't know. I also realize you may have nowhere near enough info here to respond. Thanks for any help.

Mike

It’s worn out. Time for a rebuild.🛠

Do it right rather than struggling for each new failure. Cost is low.

Ed

With readings that low and inconsistent from one cylinder to another, there's not much point in trying more specific tests like cylinder leakdown, etc. Have you run the numbers to determine what vehicle the engine came from? A 1950 pickup wouldn't have had a 235 from the factory unless it was a special-order low oil pressure type with Babbit connecting rods. Post the stamped number on the machined pad behind the distributor and maybe the block casting number down low on the block around the fuel pump, and one of our number-crunchers can tell you which engine to order your rebuilding parts for.
Jerry

If you had a stuck intake valve, you may now have a bent intake valve.

Treat yourself to to the shear joy of a complete rebuild. There are few moments as rewarding as driving a brand new Stovebolt engine.

Thanks for the input guys. Guess I'll be rebuilding the engine. A few of the main things that concern me:
1. parts availability
2. getting the right parts for the rebuild
3. never having done a rebuild.

am i off my rocker to attempt this? i know you can't really answer this but i'm very determined with a good level of mechanical competence.

thoughts?

99% of your rebuild parts are readily available through the various FLAPS, Evilbay, and the restoration websites. Read up, study and ask questions. These engines have some unique components and procedures to rebuild them so the more you know the smoother the process will be.🛠

Just asking, what type and brand compression tester did you use and how did you conduct the test? Your readings and retest numbers are all over the place. Before you start tearing that motor apart, let’s make sure you tested properly and confirm that you actually have a compression issue.

Dragsix, thank you for the response. I used an IEC compression tester. As far as type, i'm not sure how to answer other than it has an adaptor that screws into the spark plug hole. Choke was fully open, coil disconnected, plugs removed as i tested each cylinder. First i tested each cylinder without adding oil, then i added about 1/2 oz. of motor oil and tested again. Hopefully that answers your questions.

Was the throttle plate fully open?

Try it one more time. As above, make sure the adapter is screwed in properly. Let’s make sure you have accurate numbers. Now, bear with me here. Do all of the cylinders dry. Then do them wet. Let’s see what you get.

Ran compression test again. Confirmed throttle was fully open. Here's what i came up with.
#1 - 15 psi dry, 31 psi wet
#2 - 110 psi
#3 — 115 psi
#4 - 115 psi,
#5 - 40 psi dry, 110 psi wet
#6 - 50 psi dry, 155 psi wet.

Well, from the cheap seats here, it looks like your motor needs some overall refreshing/rebuilding.

Thank you so much for your time. I am starting a new thread asking for resources on rebuilding a 235. i guess i'll start by pulling the transmission.

If you've got a couple of weightlifter friends and adequate storage space, pulling the front fenders, grill, and radiator support as a unit is the simplest way to access the engine compartment. The hood can stay put, just raised and supported by a rope or a ratchet strap to the tailgate so you don't get any painful surprises while you're pulling and installing the engine.
Jerry

With the engine assembled remove the valve adjusters from the rocker arms (identify them if possible and replace where they were).
Now all 12 valves are relaxed and fully seated.
All the intakes, and all the exhausts should be very close to the same height (but different intake vs. exhaust).
Any short? That's the problem valve. If it's an intake it may also be bent, and won't come out easily when head is off and the spring is released.

One thing I always like to do before I jump in head first into a rebuild is to go through the disassembly process slowly with the purpose of determining what is causing the problem as I go.
As panic mentioned above, pull the rocker arm assembly before you pull the engine. Once that is out of the way, take a dead blow hammer and rap each valve stem and watch for a rapid return to fully closed. There should be a satisfying thunk when they close. If they rebound slow or you don't hear a nice thunk, the valve guides may be gummed up.
Since all of the valves will be closed with the rocker arms removed, you can now apply air to a spark plug hole and listen for where the air may be leaking out. Some compression gauges have a fitting for an air compressor on them.
1) past a burnt valve.
2) past week rings.
3) into am adjoining cylinder due to a bad head gasket.

Jerry and Ed are right on the money, at lot of the old engines can be gummed up due to non detergent oil or no oil change. I have one right now in the shop that has what looks like dirty black grease through out. As Ed and Jerry suggest pull the head. And by the way if you see micro cracks in head have a machine shop check it prior to rebuild. Many times the cracks can be minor. Doc.

Question- - - - -have you actually had the engine running yet? Somehow, I doubt it. If not, grab a good 12 volt battery so you can spin it over fast enough to build some compression pressure, make sure you've got the valves adjusted properly, clean points, fresh gasoline, and properly set ignition timing, and fire that sucker up. Even if it only runs on a few cylinders, get it thoroughly warmed up and recheck the compression after running it a while. I've been successful at starting a few stovebolts that wouldnm't even make a full turn with a pry bar on the flywheel teeth when I began working on them, and they continued to improve in performance the longer thery were run.

Tinkering with an engine like the one you're working on is the equivalent of giving a brain tumor patient a big dose of aspirin for his headache- - - - -you're treating symptoms, not the root cause of the problem, but at least you'll get to hear it run before you bite the bullet and do what all of us know needs to be done- - - - -rebuild it!
Jerry

Thanks for all the pointers. I haven't heard it run so i'll do that first. i have electricity to the distributor cap but nothing from there. Plug wires have little to no continuity. I'm ordering wires, distributor cap, rotor cap, and condenser. points look good. Would love to see it run before i start tearing it down.

i need help please figuring out what year my 235 engine is. Block has number 3836233 GM5, head has number 38359/8 GM1. Any ideas on where i can look?

Radio noise suppression ignition "wires" can have up to 1,000 Ohms per inch of resistance, measured with a digital ohmmeter, and they will carry spark just fine. Metallic spark plug wires are as obsolete as Acetyline gas headlights, hand cranks for engine starting, and squeeze bulb horns.
Jerry

3836233 = 1955 2nd series truck and it could be 1956 car or truck (engine block).

Find and post the following codes (for better identification):
- head & block casting codes
- head and block date casting codes
- engine serial number

The head number is probably 3835913 which is 55 possibly 54, maybe a bit earlier (casting date late 53 for the 54 model year.) Both the 54 and 55 heads used the four screw perimeter valve cover with the 54 cover having two vents/slots punched in the top of the cover. The 55 valve cover did not have the slots. 53 used the earlier two stud and nut arrangement. The 848 head entered service for the 56 model year so I don’t think it’s 56 head.

Mike, If you pull the valve cover, about the center edge on the drivers side, you will find the casting date for the head. If you post it here we can sort out when it was cast and get a more accurate date on the head.