The Stovebolt Site Forums The Shop Area Engine Shop 235 Distributor shaft not rotating

1955 First Series 3100 H55L001xxx. Original 235 truck engine 0014xxxF55X.

Driving yesterday with a load in the bed, highway cruising at 55 mph (3.91 gears). Suddenly a short pop or backfire occurred, followed by no power. Sensation was like turning ignition switch off while at 55 mph. Coasted over to the shoulder, engine would not restart. Called AAA for tow.

Did some roadside troubleshooting while waiting for tow. Have narrowed it down to the distributor shaft/rotor not rotating while engine is turned over by hand.

AAA provided 80 mile tow back home. (AAA Premier account).

Haven't investigated further, will take another look soon.

Any thoughts about symptoms and repairs? Broken or seized distributor gear/shaft is what first comes to mind.

Thank you for any inputs,

(Tried searching forum first; however couldn't narrow it down to this general subject).

ol 55,

Since your post is directly related to an engine issue, I have moved your post to the Engine Shop forum as the best place to get help in your problem.

Good luck and am sure others will reply back soon!

Dan

Could be a broken distributor gear, although that would be less common than a broken camshaft timing gear. Many of these were made of a fiber compound (for more quiet operation) and occasionally those will crack or lose teeth or otherwise go bad. When that happens, you'd get a timing change, maybe a backfire and your engine would stop running.

Thought about the fiber camshaft timing gear too. Will pull the valve cover today for inspection and to see if there is rocker arm/valves action when engine is turned over.

That fiber cam timing gear was installed 40+ years ago during engine rebuild.

Thank you,

I'm running one right now that is a bit over 40 years old. Good luck!

Here is the rub with a fiber gear letting go at speed. Depending on the position of the intake valves when the failure occurred, you may have had a valve, maybe more, hit the piston and bend. So if it turns out the gear let loose, make sure you do a compression test after you replace the gear. If no compression in one or more cylinders, you likely bent a valve and will have to pull the head and get it repaired.

A 235 has some flat spots between the camshaft lobes that are there to provide clearance for the sides of certain connecting rods. At certain points in the cam rotation it's possible to get contact between the connecting rods and the cam if it stops or gets out of time. The stroke on a 216 is short enough to keep the cam and rods from getting together.

Pull the fuel pump and use a bright light and an inspection mirror to see if the cam is turning.
Jerry

First heard that 235 is an interference engine. Wouldn't have guessed it.

Confirmed yesterday: Camshaft is not turning. Pulled the valve cover and turned engine over with starter, no action with rocker arms and valves.

The plan is to tow truck to shop this week for camshaft removal and timing gear replacement. Will opt for an aluminum timing gear if one is available. Will then address possibility of bent pushrods or valves once engine is reassembled.

Thanks for the Info and Tips so far.

PM or email me for a few tips and techniques on the timing gear change. The cam does not need to be removed. Back in the dark ages a timing gear change was about a 3-4 hour job for a good flat rate mechanic. It's not as simple as it sounds, but there are a few sneaky tricks that make it a lot easier and safer. I like to drill and tap the camshaft snout so a harmonic balancer installer can be used to press the new gear on- - - -it beats heating and/or hammering the new gear. You can check for bent valves before you do the gear change- - - -just back off the valve adjustments so both valves are closed and put a little air pressure into the spark plug holes. If you get a gush of air from the carburetor there's a bent intake on that cylinder. It's impossible to bend an exhaust valve by getting the cam out of time.
Jerry

Ol 55
The aluminum cam gear should be GM 3835473
That is the one I got when I built my 235 a few years ago.
There is one on E Pay right now.
Good luck.
Todd

Following up on this post and reporting a successful conclusion.

The cam & crank timing gear set was replaced with new gears on my 55 3100 First Series pickup.

History from three months ago: The fiber cam gear shredded while at driving 55 mph on the highway, which caused the engine to stop immediately. (125 mile tow!).

Radiator was pulled to access front of the engine. Crankshaft damper, timing cover and oil pan were removed. With camshaft remaining in the engine, the broken fiber cam gear was carefully chiseled apart and the steel center collar was split apart for removal. The old crank gear was removed with pullers.

A new steel crank gear and a new aluminum cam gear were installed, with timing marks lined up after cam gear was heated up for shrink fitting.

After reassembly, the engine started right up, although timing was very retarded with the new gears installed. The ignition timing was reset, and the engine runs great. Completed a 100 mile trip this past weekend.

Can say that a stock Chevy 6 cylinder 235 engine (no high-lift cam, no milled head, no modified valves/valve train) is not an interference engine. The engine runs the same as before. No knocks, rattles, pinging or signs of power loss.

Looking forward to more miles of smooth Stovebolt driving!

Thanks for the posted comments and advice.

The last time my 53 dump truck with original 235 destroyed its fiber cam gear it bent every intake pushrod but non of the exhaust ones
Which is strange because the previous time it did that I had your situation, no valve crashing
So I figured as you did that a 235 is not an interference type engine
When my cam gear failed it stripped a few teeth and the engine made several rotation out of timing at high rpm climbing a hill
Anyway I just put in straight push rods from a donor engine laying around and a new aluminum cam gear, the compression tested fine 115-125 lbs across the engine so it’s all tuned up and running well.

One concern on the late model 235 engines with the big cam bearings and the cast iron cam is clearance between the connecting rods and the camshaft. The cam has flat spots cast into it between the lobes so the rods don't hit the cam in normal operation. If the cam gets out of time there can be connecting rod/camshaft interference. Pistons and intake valves also run with a bare minimum of free space, so under some circumstances it might be possible for cam/piston contact with a badly out of time cam.
Jerry

Haven't heard of these specific instances, although as you say it's possible. In the words of a reputable vintage Chevy parts supplier in business for a long time when asked about whether the 235 is an interference engine: "No, there's enough room to sleep in there." (!)

Bent pushrods is another issue. Maybe valves floating at high RPM? Probably not caused by valves contacting pistons or catastrophic damage would likely occur.

Lots of theories! Many of you probably have practical examples to share.

Like the Sun test equipment motto they put on all their consoles for many years- - - -"We test- - - -not guess!" Anybody with a magnetic base dial indicator and a few brain cells to rub together can find out for sure.
Jerry

Not sure what procedure you are describing.

It's a procedure all competition engine builders use. On the "overlap" at the top of the exhaust stroke, put a dial indicator against the intake valve spring retainer and use a pry bar to push the valve down against the top of the piston. Start about 20-30 degrees of crankshaft rotation before the piston comes to the top and repeat the check every 5 degrees as the engine rolls over center. Record the readings. Then move the cam one tooth out of time in both directions and repeat the check. As the cam gets ahead of the crankshaft, there will be a MUCH closer relationship between the valve and the piston- - - -possibly a lockup situation. That kind of test is just "Engine Building 101" to anyone with anything more than "stock" engine assembly experience. I've been building round track race engines since the 1960s.
Jerry

Thanks for the detailed explanation. Interesting process!

Small block Chevy V8s also experience potential interference between a few camshaft lobes and connecting rods with certain crankshaft stroke situations and radical lift cams. Some H beam high performance rods are contoured to account for that possibility.