The Stovebolt Site Forums The Shop Area Engine Shop cam gear...aluminum vs. phenolic?

Considering a new aluminum cam gear because the phenolic one has been on the truck for...who knows how many miles?? Seems prudent to change to aluminum before the old one breaks.

Two questions:
1. Just how durable is the phenolic? Have heard a few instances of them breaking, but don't know how likely it is for a high mileage engine.
2. How much louder is the aluminum? These old trucks are already pretty loud by modern standards. If it's noticeable above all the regular noise, maybe should stay with phenolic.

Gonna pull engine to adjust bearings, install new main seal, and paint the firewall, so now would be the time.

I thought phenolic was only used on cars, not trucks?

I've seen several phenolic timing gears with teeth broken off. That stops the engine in its tracks, and if an intake valve happens to be fully open when the cam stops, there can be piston to valve contact. I don't recall ever seeing an aluminum gear lose a tooth, and finding one with enough tooth wear to need replacement is pretty rare. There's also a steel cam gear that's made for Mercruiser marine engines that appears to be a direct swap for a stovebolt cam gear. I've got one in the shop that I intend to do a comparison with an aluminum gear to see if all the dimensions are the same.
Jerry

I have used many aluminum cam gears, and as long as you put a dial indicator on it, and make sure it is running true, it will be almost silent.

That's my understanding as well, and is evidence someone had worked on the engine before I got it in 1982.

Pre68 Dave And if it's not running true,how do you adjust it ?? Hadn't even thought about mine,saw it when I turned in fresh bearings is quite as far as I know. Bought one I think for 5$ at a garage sale was new.

Skooter 50 years ago worked with an old mechanic who ran a garage on a busy hi-way. If people came in with broke-down Chevies he would ask if the wipers flew up when it quit,if they said yes he would say welp timing gears are out of it !! I would use the aluminum one,lot safer for your valves,also when the cam stops I think it can get killed by a rod bolt there are some flats on the cam to clear the rods. Just noticed it on a new cam I bought.

all my trucks have the fiber gears, 216 and 235 engines between 1949-1953
i just replaced one earlier this year, the fiber gear in my 53 GMC 1 Ton failed, i grabbed a slightly worn fiber gear from a partially disassembled 216 i had handy and put it all back together and it runs better than ever,
this engine spun a lot when the fiber gear failed on the highway at 40mph
the 235 and 216 are non-intrusion engines, the valves will clear the piston in any position, something out of the ordinary would have to happen to crash a valve
the cam shaft also cleared all rotating parts when it was stopped with crank spinning, i did pull mine out to inspect but it was fine and went back in with it's new old gear.
-s

I used a short piece of pipe, slightly larger than the cam snout, against the gear. I would then tap on the high side. It doesn’t take much to correct the runout.
Make sure the retaining plate still has the correct clearance when done.

I'll put up with more noise if it means the gear won't come apart.

Guess the next question would be...does the cam or crank have to be removed to change the gears?
And if it's been running phenolic cam gear for the last 45 years, must the crank gear also be changed? There should be little wear to the metal cam gear if it's spent much of its life meshed to phenolic teeth, correct?

I don't know of any way to replace the gear without removing the cam. Removing the camshaft is actually the biggest part of the job though. I replaced my cam gear not long ago. I used aluminum, only because my old one was fiber, and it was loose on it's hub. The aluminum gear does not have a seperate hub, and I assumed that might make it more reliable. I'm no expert though.

I did not change the crank gear when I repaired mine
Yeah the cam does have to come out now that I recall because the cam gear is pressed on and you need to be able to press old one off and new one on that’s right
The crank can stay in motor
Distributor and fuel pump need to come off to allow camshaft to come out.
-s

One of the reasons they get wiped out is the oil passage gets clogged and the gears starve for oil. While you have it apart make sure the oil passage is open. The older 207's had a nozzle that sprayed oil on the gear teeth, I'm not sure how the 216/235's do it, but I'm sure they do somehow!

Mike B

I recall seeing an oiling feature in the 235 when I had it apart
The gears are meant to get a small dribble of oil in a proper working engine
The oil drains to pan at the bottom there are explicit return holes as well -s

clipped a zoomed in photo, with markup:
A - a small tube extending out over the crank gear
B - you can see clear into the pan area(pan removed in photo) this is oil return

The 216's have the same cam gear oiler as the pic that 2ManyTrucks posted. It gets oil from the pressurized oil gallery along the side of the block.

Would never suspect a failure like the one in your pic. Broken teeth, yes. Maybe someone in the past had hammered the outer edge and weakened it or something. Or perhaps the axial load on angled gears can do that over time, as opposed to straight cut gears.
Yeah, I'm leaning toward aluminum. Just trying to get past "if it ain't broke don't fix it" mindset that has served very well with this truck!

I have messed with a bunch of Model A engines years ago and only saw one that had a fiber gear that was loose from it's hub. The fiber gear in my '51 I assume has been in place since 1953 and was in good shape when I had the cam out to replace gaskets on the front support. I think either fiber or aluminum would work well for years.

The fibre gear gave up on my 69 chev pickup .it had a 72 engine from a Pontiac in it (250 )six that was in 1990 so it was 18 years to give you a idea of durability.

Back when these engines were daily drivers, it was common practice to swap a stripped cam gear without removing the camshaft. Break the fiber gear off with a big pry bar, and split the metal hub over the woodruff key with a hammer and chisel. Then use an air powered hammer to drive the new gear on after heating it in an oil bath or CAREFULLY heat just the hub with a torch if the replacement gear was the fiber type. Aluminum gears virtually never failed, but they could be removed by drilling and tapping a couple of puller screw holes in the old gear. The more careful guys would remove the fuel pump and have a helper pry forward on the camshaft through the fuel pump hole to avoid damaging the thrust plate while installing the new gear. Someone who couldn't replace a timing gear before lunchtime probably wouldn't have a job the next day!
Jerry

The one on my 41 broke in two and ruined a vale in the process several years ago.
Swapped to aluminum with the cam in place (as Jerry said) and never looked back.
Pretty much everything on the car is louder than that cam gear, never noticed any difference.

Frank