The Stovebolt Site Forums The Shop Area Engine Shop Chevy 235 Health Checkup

Hi all, finally got to go about seriously checking out the engine in this '58 Apache.

After driving it around town a bit I've noticed that it smokes a decent bit out of the valve cover. It's burned a couple quarts of oil over the last month, and I've noticed some water in the valve cover. After reading lots and lots of forum posts I think this is just condensation, I don't see any signs of major water buildup.

Here's the smoke out of the valve cover
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and
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First I did a vacuum test, and got a low vacuum at idle, with a bouncy needle and an occasional fall.
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I had a feeling it was idling too low but I didn't have a tach meter so I rigged up an oscilloscope. It's kind of the long way around, but it's cool to see the dwell in real life. This is at 323 RPM with like a 30% dwell.
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Brought the idle up, and was able to get a better vacuum with screw A on the Rochester Single Barrel. Vacuum's still jittery. Oh, and I checked the timing it was good.
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Then I pulled all the plugs, each one was oily around the threads and in the recess of the plug
1-6 Top to bottom
1-6 Left to Right

Then I did a compression test and obtained the following:
Cylinder 1 - 87 PSI
Cylinder 2 - 65 PSI
Cylinder 3 - 70 PSI
Cylinder 4 - 82 PSI
Cylinder 5 - 80 PSI
Cylinder 6 - 103 PSI

After that it rained and I had to pack up. I didn't get to do a wet test or a leak down yet. I don't think the numbers above look great, but I've never worked on an engine this old. Thoughts?

Those are very low compression values.
130 psi was "normal"

The difference between readings/cylinders on you engine are quite large.

MY PC is having trouble opening your vid's but I'm pretty sure it's my PC and not your vids.
Your engine should be set to idle between 500 to 600 rpm.

Blowby, you get that when the rings are worn to a point where combustion gasses escape past the rings into the crankcase and vent out the top. Based on your compression readings I'd say your engine is worn past it's prime and or it hasn't ran in quite a while and the rings are stuck in the piston grooves.
Condensation increases as blowby increases, they go hand in hand. It's pronounced in colder weather to hardly noticeable in warm weather.
The 216 in my 49 has been exhibiting these same characteristics for 21K miles. These are signs of a need for a rebuild.
The oil burning is also due to worn rings as the cyl sucks in oil past the rings on the intake stroke. Air always rushes to filla vacuum and it carries whatever's in the air with it.

Sounds like your engine is due some internal attention.

GB,

Those plugs look like AC 43. That's a really cold plug for puttin' around town. In tinkering with my restored '36 Chevy pickup that I've owned since 1965 I've found that with optimum carburetor jetting an AC 46 plug gives a perfect color in short drives around town, like over to the park for a picnic lunch with my wife. If you PM me your email address I'll send you a plug color photo I just took for comparison purposes in before and after my PCV fabrication.

As Tim points out those compression pressures are not good, as is the "bouncy" vacuum gauge reading. There are online tutorials showing you what various vacuum gauge behavior tells you about your engine.

An easy valve and ring condition test can be done by making a fitting to go in the spark plug holes and pressurizing each cylinder with compressed air with both valves closed. Then listen at the exhaust pipe, carburetor throat and draft tube outlet for leaking or burned valves or severely worn rings/bores. That technique is below low tech but it sure works!

Good luck!

How long has this engine been sitting without being run on the road? It could just be that you have gummed up rings. That would account for all of the blow by.
If it were mine, I would (as per Hotrod Lincoln's recommendation for un-gunking engines) change the oil and add 2 quarts of diesel fuel so that the dipstick shows 2 quarts over full, and run the engine above idle speed for 20 minutes. DON'T DRIVE IT! Then drain the oil and refill with fresh oil and see if it improves.

Is anybody else having trouble seeing the vids? This is the first time I have used google drive to host videos. Let me know and I will fix it.

The previous owner says he rebuilt it, I'm waiting to hear what all that entailed. If he did put in new rings, and they are stuck... because it did sit for about two years... wouldn't driving it 100 miles have loosened them up?

They are AC43. I don't know a lot about "hot" and "cold" spark plugs, other than what I read in the manual. I planned to change them, but I figured deciding if I needed a rebuild was more important ATM. What's the difference?

Yes, the compression is low. Try doing the compression again but this time put a couple of good squirts of oil in each cylinder. If the compression improves, the rings are likely the culprit which explains the blow by. If it does not, valves, valve seals, valve guides are the likely culprit. I agree, the plugs are a little cold. If you can’t find the AC plugs, Champion j12yc or j14yc or the resistor variant will work. I run j12yc in my 235 and 261 builds. More out of habit then anything else.

I was able to download and run your vids, it was my PC.
The blowby isn't that bad. I should do a vid of my 216's blowby, it was about triple what I'm seeing in your vids. With use it's decreased to about what I'm seeing in your vid and I've put approx 21K on the engine since I got it running.

You say the engine has sat for 2 yrs. Altho that wouldn't usually be enough time to "freeze" or "stick" the rings in the piston grooves, I've gotten to the point where I try to never say never as theres always exceptions to the rules and I seem to run on to them LOL.

Plugs 5 & 6 look like they have some oil/combustion residue built up. As pointed out try out the recommended plugs.

You need to get/have 3 necessary tools if your going to wrench an old Stovebolt engine, a timing light, a tach/dwell meter and a vacuum gauge. I really like the O scope tho.... I'd really like to get my hands on an old Sun 1020 diagnostic machine....
Your vacuum reading improved when you increased your idle, make sure you're idling between 500-600 rpm with 550 being optimum. Lugging an engine be bad bad bad....
Using your vacuum gauge, adjust the idle/low speed carb adjustment to get max vacuum reading. If rpm increases back it down via the idle speed adjustment. Set it to the point where it just makes max and not beyond as usually this will enrichen the mixture too much. Well worn engines need to run richer, good tight engines will run leaner.

With that done check and set your timing to spec. Usually theres a BB embedded in the flywheel. It's not unusual to run these engines more advanced than the old factory spec so take note before you adjust as you might find it likes the original setting better. Some folks use max vacuum to set the timing but I've found that it usually advances it too much. Another method is to disconnect the vacuum and plug it, using an adjustable timing light set the timing with the engine rpm between 2.5K -3K rpm. At this rpm the mechanical flyweights should be at max advance and then set your timing to the TDC mark with the timing light set to 30-35 degrees advanced. This is probably the best method but you need an adjustable timing light (more $$$'s).
The deciding timing factor is the road test. If it pings loudly under load it's too advanced. If it hessitates on acceleration and lacks power it's retarded too much. A very slight almost can't hear ping under load is optimum.
Some folks successfully use just the road test to set the final timing. YUMV....

In summary, if the engine isn't making any unusual noises, bangs, clangs, etc. Is making good oil pressure and not overheating I'd change to hotter plugs, check/set the carb and timing then run it like that for 500-1000 miles then recheck. With use it could loosen/straighten itself out. These engines like to be run.....
Don't go fixing anything thats not broke LOL.
Dave

Thanks for the replies. This is all really helpful.

I talked to the previous owner, and he said he didn't know the extent of the rebuild. He said some guy in Oklahoma did it for him. He said he got pictures and it all looked clean, but he didn't have them anymore, and from the sound of things he was pretty young probably 15 when it happened.

Yeah, I figured I could just go to Autozone or Harbor Freight or anywhere and get a dwell meter... but I could only find a crappy digital one. I'm having friends dig through their dad's stuff looking for an analog one. If not I'll just find an MT415 on ebay or something. But for now I can use the O-scope. It's really cumbersome though.

Nice everybody is telling me to set it to 500+. As I recall it was MUCH happier around 525-550 RPM. In the first vacuum video I think the idle was 330ish, and for the second I had adjusted to 475 (as per the Chevy Service Manual). I have checked my timing, and it is good at idle. I do have a timing light with advance! I do not yet understand this distributor, and it is not spinning when the engine is revved like I believe it is supposed to do...so I have been hesitant to rev it high.

@yar, I don't know what you mean by color. I'm guessing you mean that my plugs should look sort of tan/grey and dry like they do in a good engine? Not black and slimy like mine?

I will do a wet compression test, and a leakdown test soon and post the results. Rain, school, work and other "unimportant" things are getting in the way - I imagine this will happen Thursday night. I am going to go ahead and pull the carb and the distributor as they are a total mess...and pick up some AC46 equivalents.

I've been thinking it might be nice to take the front fenders off until I get the engine sorted. How hard is that?

GB,

Here are some color charts to illustrate the concept:

https://www.google.com/search?q=spark+plug+diagnosis+chart&sa=X&biw=1440&bih=794&tbm=isch&source=iu&ictx=1&fir=iYoXqSLc98lKNM%253A%252CMycfoz0dCKMYOM%252C_&usg=__SIdHvbKy1tqUC2YRNsa3XPh_rjM%3D&ved=2ahUKEwjt5MaY_tDaAhXrz4MKHdHcDecQ9QEwAXoECAAQOw#imgrc=iYoXqSLc98lKNM:

The terms "hot" and "cold" with respect to spark plugs describe how fast the plug dissipates heat to the cylinder head it is screwed into. A "cold" plug dissipates heat faster and vice versa. In a property jetted engine that is not drawing oil into the combustion chamber the color of the porcelain is an indicator of the plug's ability to "burn off" combustion deposits. In other words, it is a thermometer telling you things about your engine.

Changing the jetting will change the spark plug color. However it is critically important to understand that jetting has to be correct for the engine, not for the spark plug. For instance, if excessively "cold" plugs are in an engine and the plugs indicate a "rich" condition, leaning the jetting to improve the plug color may make the mixture excessively lean, with the potential to burn valves and/or melt holes in pistons.

Plug "reading" to jet an engine is possible and is done successfully all the time but tech savvy people (I'm not one of them) do the job much more accurately with an O2 sensor in the exhaust pipe and an air-fuel ratio gauge.

Have fun!

Ray,

If you "Use Full Editor", there is an option on the right of the edit window/menu (a globe with a chain-link under it). That allows us to put URLs/web-addresses in a message with a short name of the link/purpose.

Your very long links/web-addresses mess up some peoples' browser viewing - they have to scroll to the far right because your long URL, which for some reason, does not "word wrap".

Thanks for considering doing this in the future.

Tim

The vacuum advance may be part of your running issues. There is a diaphragm in the vacuum advance unit. Not uncommon for the rubber to be blown out. These distributors use a ported advance port in the carb for vacuum signal to the advance diaphragm. The vacuum port is above the throttle blade, on the atmosphere side of the throttle blade. So there is little to no vacuum at idle with the throttle blade closed or mostly closed. As you open the throttle, the port starts to see vacuum as the throttle blade opens, the position of the blade dictates how much vacuum the port sees. The vacuum advance unit will advance the timing depending on the vacuum it sees, until the throttle blade is open so much that there is no vacuum signal and the distributor rotates back. That is the movement you see. If you are not getting any movement, either the rubber diaphragm is shot, the distributor advance is frozen or jammed, or the motor is not making sufficient vacuum when the throttle is opening to actuate the advance. So I would start with the diaphragm. Make yourself up a little steel line and fitting to install into the vacuum advance unit with a rubber hose on it. Disconnect the line at the advance unit, install your little tool and gently blow into the rubber hose, If you are blowing through the diaphragm, no resistance in other words, the diaphragm is shot and this is the first thing to get replaced. If you do not blow through it, suck on the hose to create vacuum and see if the advance moves. if it does, the diaphragm is good. If it does not, twist the distributor to see if it is frozen or jammed.

If the advance is good, then you have to see if the port in the carb is clogged. Hook up a vacuum gauge to some port that is full manifold vacuum (vacuum source under the throttle blade). On the later 55-62 intakes, there is a place for the vacuum hose for the vacuum wipers, this is a full manifold vacuum port. Not sure about your intake. See what full manifold vacuum you have at idle, and a little off idle, say 2000 rpm.

Then, connect the vacuum gauge to the end of the steel line at the advance. At idle, you should have little to no vacuum. Then crack the throttle and gradually open the throttle to 2000 rpm and see what vacuum you have. If no vacuum, the line may be clogged or the port in the carb may be clogged or some other issue that will need further diagnosing. that is how I would approach the problem.

"If you "Use Full Editor", there is an option on the right of the edit window/menu (a globe with a chain-link under it). That allows us to put URLs/web-addresses in a message with a short name of the link/purpose."

Tim,

Thanks for that information. I will ask my wife to explain it to me. I'm about as computer illiterate as a person can be and still be breathing but I will definitely try to do as you suggest.

"The vacuum advance may be part of your running issues."

Mike,

Should he also check the centrifugal advance for proper function?

You can check the mechanical advance with a dialback timing light and a tach, start at tdc, few rpm, dial back to tdc, few more, back, few more, at some point you should be able to graph out the advance vs. rpm curve and the total centrifical advance. If you tell me the Delco Remy number for the distributor, I can sort out what the mechanical advance curve should look like, I.e., when it should start, how much at what rpm, total at what rpm. Then you can compare. If you have access to someone with a Sun or Allen distributor machine, that exercise is much easier and a bunch more accurate.

I just rebuilt a 2403 55-62 235 distributor. Had it on the sun machine for an initial look see and discovered that the mechanical advance was coming in very late and the total was coming in at an rpm that was way too high. The advance on these things is under the breaker plate so you have to take it all apart to see what is going on. Found a broken pin and advance spring, the spring had wedged under one of the weights and rust had accumulated, as well as a thick coating of dirty and heavy grease. Once I rebuilt it and ran it on the Sum Machine, the advance came up to perfect specification. So if your curve is way off, then something else is up and it might need a little more attention.

The first time I had a distributor rebuilt I could not believe the difference in starting and running. So if your distributor is really not close to the specification it’s supposed to be, consider having it rebuilt.

No new test results yet... but I found out where all my oil was going.

Out the Tailpipe

Are you sure that's oil and not just dirty condensation from the exhaust system?

I think it's oil. The entire exhaust system is about a week old

Keep the chatter going guys, I am trying to dial in a 1960 235 in my 1950 3100 and all the advice in this thread has been wonderful! I think I'm having carb issues, but I'm going to go buy a vacuum gauge and pull out my other toys and try everything that has been shared here before I drop $300 for a newly rebuilt Rochester. Thanks!

Guys,

Sorry for disappearing. Life happens. I did the oil in the cylinders for a few days then I drove it hard for a few days, then a few hundred miles over the next few months. The smoking and oil consumption has not gotten worse or better. In the meantime I obtained all the rest of the parts (including two other 235's) from the previous owner. I have decided to open another discussion thread, and get another engine running while I continue to drive it. I'll return to this thread when I pull the engine that's in it and tear it down.

Thanks for the help! See you in the other thread for now.

-GB