Stovebolt.com Forums The Shop Area The Engine Shop Is a full rebuild in order?

Greetings, fellow stovebolters! I am very new to working with engines, in fact, this is my first one.

I find myself facing a puzzling issue with my beloved 1954 Chevrolet 235ci straight 6 stovebolt engine, and I'm seeking the wisdom and expertise of this esteemed forum. When I push the pedal to the metal, I'm met with troublesome sputtering and misfires that just won't quit. On top of this, a 50 mile journey will use about a quart of engine oil. I've already taken several steps to address the problem, including carburetor balancing, replacing a bent pushrod (located on cylinder 3), and fine-tuning the tappets. However, my efforts have yet to yield the desired results. Furthermore, I'm getting a top speed of 45mph on the flat (which im happy with) but if it sees any hill it drops significantly, down to about 20mph.

In my quest for answers, I conducted a compression test last night, and the results left me scratching my head: Cylinder 1 showed a meager 65psi, Cylinder 2 recorded 75psi, Cylinder 3 revealed a worrisome 25psi, while Cylinders 4, 5, and 6 displayed a more promising 75psi each.

Tonight, I am going to push compressed air through the spark plug holes to see where the air comes out of, I've seen that this can help identify the issue?
(air out the carb = intake valve, air out the exhaust = exhaust valve, air out the breather = piston leak? )

Upon inspecting the spark plugs, I discovered that they were all dirty but dry, as I had anticipated. However, Cylinder 3 stood out with its dirty and wet plug, indicating a potential anomaly.

Adding to the puzzle, I couldn't help but notice an intriguing phenomenon with the pushrods. While the pushrods on most cylinders exhibited a ticking motion as they spun, Cylinder 3's pushrod spun freely and continuously, setting it apart from the rest.

I turn to this esteemed community in the hopes that your collective knowledge and experience will shed light on these perplexing symptoms. Your insights and guidance are greatly appreciated as I strive to revive the full potential of my cherished classic engine.

Thank you in advance for your invaluable assistance and expertise.
Is it worth a full engine rebuild? And is this something I could potentially do myself and learn how to do it? or would it have to go to a specialist shop?

If anyone is interested, I have put a video of the engine tickin over on the youtube link below.

Edit by Moderator: Removed imbedded video and provided link.



[LINK] [youtu.be]

I'm not qualified to tell you whether your engine needs rebuilding but I can give you personal experience with my engine.

I have a 216 with a 3 speed trans. Both are unrestored.

The truck will easily reach 65mph. A new clutch solved the 45 mph top speed issue and 30mph creep up hills.

Each cylinder holds 110 to 120 psi.

When you say plug number 3 is "wet", I assume you are talking about oil. I don't see where you identified the spinning pushrod as intake or exhaust. Oil is probably entering through worn valve guides. I suspect the valve with the wonky pushrod is not seating properly.

My opinion is you need a valve job at the very least.

Just bite the bullet and do a complete rebuild. It’s past time!

Stovebolt machinist in the UK? Hmm.

As with any diagnostic procedure, the cylinder leakdown test has a few details to observe that will assure good results. Unless the piston is at the exact top of its travel when the air pressure is applied, the engine will try to turn. That can be prevented by putting the transmission into top gear and setting the parking brake and/or chocking the wheels. You will get a more accurate test by positioning the piston an inch or so down from the top before locking the engine to prevent the crankshaft from turning. The cylinders do not wear evenly from to bottom. The max wear happens in the top 1 1/2 inches or so. Cylinder wear is corrected by reboring the cylinders and installing oversize pistons and rings.

The oil consumption can be caused by worn valve guides, but the cylinder leak test will tell you if the piston rings are also part of the problem. It sounds like a full overhaul is the best choice, but it's always wise to confirm the engine condition by testing. Good luck!
Jerry

I went through this with my 283 last year. I tried the leak down test with the piston in different positions. I was getting massive losses from 45 to 65 percent! But it ran...... I was conflicted. Ended up with a crate. I figured may as well have a new engine with my new everything else.

Chevydafz1 Sounds like your in for a fresh engine. With little experience at engine work,maybe a good used engine or if you done a crate engine (if available to you) they would require some credentials on who installed it. In the US would be some professional installer. Best bet for the money would be good used if you can switch em and I would want to hear and see the used one running and drive it. In the days past you didn,t want to test engines for the junkyard !! It's easy for them to say oh we'll get you another one !!!

Chevydafz1 Wow saw your video,is a chugger,would be be big fun to rebuild that engine if you have a machine shop and parts available. Once worked in a shop that could get that engine in the morning and get it back to you the next evening fully re-built

Perhaps I'm commenting on the obvious here but #3 cylinder being 25 PSI and with an oil fouled plug argues against only a valve guide leaking oil. Oil coming from guides tends to support compression pressure even on a worn cylinder. Nos. 4,5 & 6 are relatively better but still way low. For cylinder 3 I'd bet on a combination of burnt exhaust valve and, given the rest of your report, broken rings or a burnt piston. As others have said prepare for an out-of-frame overhaul.

It is possible that you have burnt valves and guides leaking oil but the rings are OK; a leak-down test might help diagnose that but you have to develop enough pressure to test the rings and badly leaking valves won't do that. Some other questions: Does it have a lot of blow-by out the breather(s)? Does it hold 10-15 PSI hot and idling? or is it more like 0-5 PSI? Do the rods knock with the engine floating (no load nor overrun)? Do the pistons slap when cold? Can you hear that low-pitched thump of a worn main bearing? How much oil does it leak out the crank seals?

If there's little blow-by, its reasonably quiet, holds good oil pressure, maybe you could get by with a head job. I have seen these engines with badly burnt valves but little else wrong but not often.

Thank you for the information, it's actually a decently quiet engine when its running, and gets good oil pressure. (this drops when the engine is idling down to nearly zero though), the rods dont tap, they used to but the tappits were way out on all of them, so i adjusted them to correct.

i think based on what everyone else is saying, its probably a good idea to get the engine out and rebuilt. I have a 200 mile round trip to do in 3 weeks time, so hopefully it'll get me there and back, then i can work on the engine during my quiet season.