The Stovebolt Site Forums The Shop Area Engine Shop 250/292 fiber/aluminum timing gear questions

I recently bought a low mile 250 to go in my C-10 to replace the very tired 230. I'm a little worried about the timing gear now, though. The 230 I'm sure has an aluminum cam gear and howls loudly above 1,200 or so; I ran the 250 today and couldn't hear the timing gear at all. I didn't have any exhaust hooked up, but if it was anywhere near as loud as the 230 I should have very easily heard it. It should be a '71 truck block, is there any easy way to tell if it has fiber gear?

How loud are the aluminum timing gears normally? I have never heard another six that howls like my 230 in all the youtube clips of them I've seen, so I figure the gears are horribly mismatched or something in that one. What's the normal sound level like? Can you tell the fiber and aluminum cam gears apart by ear?

I'm also probably going to look at a 292 for my C-30 soon to replace the sludged up 195/283 and would like to know if it has the fiber gear or not before I put it in the truck, ideally before I buy it. I think the fiber gears seem to be problematic in truck use, say over 3,000? I will probably cruise at 2,500 most of the time, but (rarely) could potentially run 3,000-3,300 on the highway or if I have to hit third loaded on a hill, and don't want to shear all the teeth off a fiber gear and crash the valvetrain.

The aluminum gears are no more noisy then fiber, at least the ones I have heard. I also think its age not rpm thats hard on them. A stock camshaft will be easy on them, radical cams with big lift will for sure be hard on one.

Joe

If care is used when installing a aluminum gear, to make sure it has minimum run-out, they are very quiet.

I concur. Many (most I'd guess) of us have replaced the OE fibre gears with aluminum ones and rarely does anyone complain of noise. I don't hear it often from the many 6's I've heard. Gear noise is generally a fitment problem.

The 292 comes with aluminum timing gear.

With all due respect, are you sure it's the timing gear? Could it be a water pump or generator bearing?

Mark

Or a glazed fan belt.

Mark

GM would not have used fiber gears if there was threat of shearing the teeth off. Age is what hurts them. Remove the fan belt and install a muffler, then recheck it.

Joe

That's what I kind of figured. I now think I can see the gear through a hole bored into the pushrod galley, though. http://remanufactured.com/images/67-77%20250%20longblock.jpg I'll pull the side cover tomorrow and, God willing, should be looking at aluminum helical gear teeth.


The 250 has no issues, runs beautifully, and is still very "tight" with good compression, and no built up sludge or mechanical noises. That's why I asked about the gear; I don't want to have a stupid fiber gear in it that may kill it. There's a thread right now below this one where a guy made a slightly higher than normal shift and sheared the teeth off a fiber gear in a 235, and that doesn't help ease my fear of the fiber gears. I know a lot of miles have undoubtedly been run with them, but they are certainly the weak link in a six that is otherwise seemingly unkillable, IMO.

As to the 230, the alternator and waterpump bearings are fine, it's not the input shaft bearing in the trans, and it's not the fan belt squealing; the timing gears are the only thing left I can think of that could howl like that. It's always done it, and I've never really cared much about it. The differential carrier in that truck spun a bearing at one point and tore up the ring and pinion, and at 50MPH that's howling so loudly it really drowns out anything else. It's a super high mileage truck/engine that's seen more than its fair share of use and abuse. Here's a picture of the engine under the valve cover: http://s1067.photobucket.com/user/6...&_suid=13646931500540847220999615781 The picture after it in that album is the valve cover itself. It's well due for a rebuild.

Also, happy Easter everyone!

Even with the engine out of the truck, is a pretty big job changing out the gears. The harmonic balancer is a press fit and requires a tool to remove it. It also requires heat and or a press to install. The cam gear is also a press fit. They are tough to get off sometimes and the retainer plate is behind the gear and is easily damaged if you are not careful. To install a gear, the cam needs to be cold and the gear really hot ( 250 + degrees). This will let you get it together with out a big hammer. Just pressing them on cold will ruin the gear, it needs to expand and then squeeze back tight to the shaft.

Joe

I'm a machinist and do engine work, changing the gear won't be any problem for me. I'd just rather leave the engine alone and spend that time rebuilding something else if I can help it. Hopefully it already has the good gear in it, fingers crossed!

Took the cover off today, aluminum gear in the good 250.

I have noticed no difference in noise level with fiber, or aluminum gears. I don't know why, but GM used fiber gears in many of their engines for many years and they were never much good. They were always failiing. But it had the quiet roll royce lack of sound for the price of a chevrolet, at least for a while.