The Stovebolt Site Forums The Shop Area Engine Shop Major engine problem

Hi Guys, can't stay away.
48 2 ton, splash oil 235, you'll remember the build. Dual carbs and exhaust, 700r4 trans.
Just heard from owner. driving home on the pike, 65 mph. Everything fine all day. suddenly looses a lot of power, won't go over 30.
Starts and runs a little rough. Spark to all cyls. Compression check = 80-83 in all cylinders!
Sounds like cam jumped a tooth, but???
Input anybody? It's gear drive, no timing chain. Gears are both steel, no fiber gear like old Volvos to wear out.
I'm diagnosing remotely so I can't see or hear it and nobody has a vacuum gauge.
No bad or funny noises. Carbs sound ok, miss can be heard in exhaust
However #5 doesn't make a noticeable difference when the wire removed, changed plug, no difference.
Could be a secondary problem, vacuum leak, too lean?????

My guess is a broken rocker or a pushrod to #5. Had a cruisin buddy had a similar problem on his 52 chevy 235 car.

Compression check = 80-83 in all cylinders!
Most likely not your problem: nice that they are so close, but so-so readings

Did you try a different wire on #5?

Check for a bent pushrod or a broken exhaust rocker arm on #5. If it can't get the exhaust out, it can 't make any power on that cylinder, but the compression will still be there.
Jerry

Jim,

Here's a discussion on Chevy Talk that says compression on a '54 235 is just under 125#.

http://www.chevytalk.org/fusionbb/showtopic.php?tid/282437/

So low 80s# on that 'engine might be a clue.

According to this even a '48 216 has compression pressure of 110#: http://www.secondchancegarage.com/public/361.cfm

In the past I've adapted a spark plug base to accept compressed air. If that air is whistling out the carburetor or exhaust pipe(s) with the valves closed a burned or bent valve would be a suspect.

Compression @ 80s in all cylinders sounds strange. Did they remove all the spark plugs before running the compression test and have the throttle pushed open (WOT) ? The air tight seal on the intake manifold (and carburetor/throttle body mounting to the manifold) is so vital for smooth performance on the Stovebolt. You have 2 carburetors, so twice as many odds of something not right with the pressure (and vacuum) and possibly the fuel or both. Granted I'm a newbie to this, but I'd start with very close examination of the carburetors, hate to say it, but even removing them, checking the float bowls, checking the gaskets on the throttle/intake manifold plate, gaskets on the manifold to block, etc...

The Shop Manual shows we should hope for 130 or better (I am happy with 125 or better).

I am just hopeful for a compression gauge which functions consistently from one cylinder to another. I do not care what the actual numbers are. That "number" is merely a function of calibration, not accuracy. One only needs to focus on the percentage differences between the 6 cylinders.
If one wants to obsess on the calibration of a compression tester, then one should contact NASA to find out where they buy theirs and who calibrates them.
Carl

I appreciate the come backs.
The last compression test (less than 2500 mi ago) was 125 - 128 with the throttle closed .
Yes all plugs were removed. yes there was plenty of spark to the plug (mechanic wasn't used to plug wires that don't have boots)
The valve cover was removed and " everything was moving fine". They were looking for the #5 problem, but I will have them be more specific tomorrow.
I see nobody has any comments on the cam timing. Loss of power, consistently low compression and low but steady vacuum are the common indicators. I've seen it in a number of engines, just none with 2 steel drive gears.
I just don't see 1 cylinder out killing that much power. I had a head gasket blow completely between 4 and 5 on that engine on the highway and got it home getting 35 on the level with it firing up through the rear carb.
I will try to get get more info tomorrow. If We can't find the problem, it will probably be shipped back here.
Thanks

It would be almost impossible for that style of cam drive system to jump a gear tooth and it if did' the engine probably wouldn't run. Maybe a sheared off woodruff key that lets the cam or crank gear slip? I've never seen that happen. One way to check would involve watching the valve action in relation to the pistons- - - -#6 valves "rocking" as either #1 or #6 piston is at the top of the stroke. It would require a bright light or a borescope through a spark plug hole to see the piston movement.
Jerry

Just a shot in the dark, but could the distributor have been left just loose enough it has moved (turned) and make the timing quite slow?

This happened on a 216 once I was called to work on. Next time it is running, give the distributor a slight twist by hand and see if the engine sounds better.

I like the cam timing theory, but I too doubt it "jumped a tooth", more likely sheared a key, though that also sounds remote..
Here's the page in the shop manual for checking such a problem.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0606.htm

Grigg

I've asked them to calibrate the compression tester on a known good engine and reinspect the rockers and push rods.
Checking ignition timing is a bit of a problem. Having an automatic trans means the flywheel is gone. When I rebuilt the engine, I filed a notch in the damper pulley that lines up with a stamping on the front cover at TDC for assembly and setup on the stand. Once the engine was in the truck it is very difficult to see. I set the distributor timing by vacuum .

It's been 2500 miles since rebuild. The power loss event was sudden.

Anything they've done recently to the truck? Even something seemingly innocuous? Just thinking if there's any clues there.

For example: Oil change ---> overfilled crankcase ------> gunked up rings -----> Loss of compression.

I wouldn't think such an event would cause such an even loss of compression. Just throwing stuff at the wall.

Did the camshaft on the splash oiler 235 have a notch in it to clear the crankshaft? If so would it still turn over at all? Can't say I've worked on one, but vaguely remember something about a notch in a cam to clear the crank. And I might be (very well could be) wrong on that.

I'm still leaning to the distributor has moved on you.

Just how rough it is running?

What kind of throttle linkage does it have? If there are any clamp type bell cranks in the linkage, then maybe check the throttle linkage at WOT to make sure pedal to throttle-to-pedal is still adjusted properly?

Roy,
The distributor moving, suddenly out of time, can cause loss of power, but reduced compression across the board points to valve timing, not solely ignition timing.

Say the cam timing changed, then so did the ignition timing.
If you then only correct ignition timing to gain some power back you've ignored the possible source of the problem, something within the timing gears. If valve timing is off much it still won't run as nice as it did before even if ignition timing is best it can be given the situation.

Updates:
Remember this is long distance trouble shooting.
Compression gauge was 15 lbs low when checking with another known engine. That makes them 95 and no faith in the gauge.
Everything to do with the valve train has checked out OK.
Confirmed spark at the (new) plugs.
Cyls 1-2-3-4+6 all making good power, 5 makes no power.
Think it's a lean problem.
Reading the plugs finds 5 of them all clean and at most, 2 have very slight tan color. In other words very good.
#5 plug is toasty brown, like a perfectly toasted marshmellow. Running very hot and lean.
Offenhauser manifold w/2 W-1 carbs.
Manifold gaskets checked, tight and no detectable vacuum leak. Cyls 4 and 6 running fine.
With engine running at about 1200 (to take the idle circuit out of the picture), #5 still not firing. Slowly dribbled gas into the rear carb. # 5 started firing and engine smoothed out. slightly more gas and engine started to stall.
I think we have a cylinder head with an internal crack in #5 leaning it out.
If the leak was any closer to the intake port, #6 would be affected too.
During the build I rejected 3 heads for cracks before the 4th magnafluxed ok.
Next thing would be to pull the head, What do you think???

Is the distributor breaker cam ok, any reason to suspect weak or erratic spark on that one cylinder?

Something dropped in and partly plugging #5 intake port?

Just guessing and covering bases, not suggesting.

You don't want to hear it, I'm sure, but you've got one too many carburetors on that engine!
Jerry

Wouldn't the head crack show on the compression test?

Grigg, good thought on the distributor. In this case that cylinder is always dead and each time it was checked, the spark was good.
It will be easy enough to check the intake chamber in the head when I get the manifold off on the way to removing the head.

Jerry, I know you think carburetors should go through life like hermits, alone. But many years of working on imported cars, of which 80% had a minimum of 2 carbs, says that if you size them correctly, they work very well.

At least they keep the mechanics eating regularly and driving cars with one carb! I had lots of fun and fed my family pretty well while spending other people's money on stuff they thought they just had to have! Press on!

Jerry

Compare valve lift with dial indicator, wiped cam lobe for #5 cylinder?

If hydraulic lifter, one collapsed?

Maybe a broken valve spring? They said valve train looked good. Is it possible #5 Valve Spring (Intake) is broken? Did they visually inspect the action on the valve train (cover off) while the engine was running? If the spring is not broken, maybe sitting up too high, the valve stem lock is off or slipping.

Engine was run with the cover off. Close attention paid to #5 valves by an experienced (diesel) mechanic.
I'm afraid this repair (if it is a new head or not) is going to be a hard sell. Client is 15 - 20 years younger than a lot of us. Enough so he doesn't get into the drive, repair, drive, repair.... thing.
All those little things like points closing up, rockers that need adjustment, float valve sticking and so on that are normal on this era engine make him want a "Modern, Dependable engine".I know that is going to come up again tomorrow.

In my experience the original Stovebolt engines are dependable, I've put a lot of miles on them, some trips thousands of miles, coast to coast once.
Veering much from stock is asking for more trouble, dual carbs as mentioned, adaped automatic transmission, what else? All that seems simple and reliable enough, but they're changes and in general changes are either asking for trouble, or take some time to work out the bugs and become reliable.

A heavy truck, with a load, driving fast; perhaps just asking to much for what it is.
Have you ridden along for a road trip, is it just being flogged trying to get the job done?

It sounds like your client needs a new F-150 with a bumper to bumper warranty. Didn't Rolls Royce once do things like lock the hood down and only allow their factory certified mechanic to touch the car?
Jerry

This is confusing maintenance with repairs.

I used a 1950 F-1 as a daily driver for 2 years. Fixed what was needed, then put
it on the road. Never afraid to drive it any where and never had a problem.

Yes they work well when designed that way from the factory by engineers
that have all kinds of test equipment to verify they have a system that works.


I knew two brothers. They were going to be drag racing legends. In their
quest for speed they would read the hot rod and racing magazines and
install parts in their quest for more speed. With every change their
engine sounded and idle more like a real racing engine.

With every added part to their engine their car went slower.
The only thing they did that gave them more speed was the
first thing that they did. That was changing the rear end ratio.
Jeffrey

OK, so there is certainly something strange going on with #5 cyl. so it's pretty certain that the head will have to come off.
All other speculation will be put on hold until I do a compression test with my equipment and put a vacuum gauge on it.

As predicted, the client is taking this opportunity to talk about replacing the engine.
He really likes the truck, loves driving it, but his one lament has always been " I'd drive it more if it only had more power".
So before we do anything to this engine, he wants a list of options , degree of difficulty and cost, of different engines.
It goes against the grain a bit because I do restorations. However, I'll comply.
I only see 2 options - late model 261 or early small block (283, 302, 327).
All of those should bolt up to the 700R4 with little problem and both will need new front engine mounts. I have an old 283 in the back of the shop so that could be built up as any of those 3 sizes.
261 would have to be bought remanufactured.
Guess I will have to shift that discussion to the modified forum to find people who have done it and what the clearance and installation problems are.

261 is the logical choice and still resemble original.
A GMC 302 can also fit with some radiator adjustments. The front mount crossmember is different between GMC and Chevy, so could swap it, or modify/adapt.

Have you checked lift on the cam?
I'd check everything that's easy to check before pulling the head, might not be any trouble under the head.

I plan to do a complete diagnoses when I see the truck, but the client has to have it trucked down to me first.
That won't happen before I report on the replacement options.
You know how it is, he has to decide what he wants to do (and pay for) and I have to deal with schedules on space and time. A big bolt takes the entire center bay in the shop. Can't store it outside so it is truly the elephant in the room. It effects all of the work in the rest of the shop.

Jim,
How did the 235 perform with the 700R4 right after the installation, in your opinion?
Even though the extra gears, which are fairly close together, will help get a little more out of the 235, there is probably a measurable loss of power due to the nature of a stock automatic transmission. Did you notice anything like this when you test drove it?
Was the buyer happy with the performance prior to the sudden failure?
The reason for all of these questions is because if there wasn't much in the way of added performance from the addition of this combination of dual carbs and 700R4, then I wouldn't expect much more from a 261 with this setup. So if your buyer wants more power which he can feel, then you will need to go with a V8. If you up-sell power steering, air conditioning, with a serpentine belt setup, you might be able to charge him enough to come out ahead with the engine plant change.
Carl

I actually think that the 700R4 was an asset to the old splash 235.
The obvious advantage of standing starts with a load. The shifts were adjusted to really match the engine load, and the great asset of the 0.7 OD which allowed the truck to run on the highway without reving it's heart out.
I did choose to not connect the torque convertor lockup so the engine had a little relief when pulling hard. (like when the OD would shift in a little early under no load driving.
I feel there was a power increase by letting it breathe better. Maybe 10% or so (originally 94 hp adding another 9 was a lot)). Enough so that the A/C compressor or the 90 amp alt charging the big accessory battery after using the electric powered lift to raise a loaded bed, didn't make it feel it was dragging an anchor.
He really loved the transmission. He often said it seemed like the engine was working hard, or just needed more power.

I had the same feeling about the 261, I think it would be just an incremental change. It would be an easier install, but I don't think it will make him happy.
I think a small block putting out a solid 250 hp is the answer. Pretty easy to get out of a 283, even easier from the same block punched to 302.
Wish I could find a good way to put power steering onto a 2 ton.

I have no first hand experience with a 261. But would sure think that 150ish HP vs the current 100ish HP would be a noticeable difference.

Then again, he's running all those accessories.....

I just like it when these trucks retain a 6 cyl.

I think the difference between the 235 and 261 would be very noticeable. I replaced my 235 with a 261 and the difference was night and day. The 261 came out of a 1960 Viking series 60 school bus. That bus had no problems even loaded rolling down the road at the speed limit at the time. And would pull hills like crazy. I put it in my little 58 half ton pkup and could haul anything I wanted and had plenty of power.

Ditto to what Roy posted.

My 1960 261 (150 hp) is very noticeably different/stronger that the 1954 (high-pressure) 235 (135 hp) it replaced.

The 1948 (low-pressure) 235 was rated even lower (90-93 hp).

Well, Jerry, I have dual Rochester b carb on my 1954 up until the issue I asked you about I have had no problems with the setup. My fuel mileage is off by 5 mpg average at highway speeds. I have not had it checked by my mechanic, he has been busy with the end of the year car shows. BTW the truck has 32000 miles since the engine overhaul. Jim, I hope you figure it out.