More on gear teeth wear.

Todd Hedges · #1 (**permalink**) 10-31-2002, 09:52 AM

I know there has been a lot of discussion on distrb. gear wear on several posts, but I have another problem with the steel gear wearing 95% to 100%(missing) of the teeth off on one side and barely touching the teeth on the other side. Basicly, if the gear were laying flat on a table, from 12:00 to 5:00 there is substancial wear and damage on the teeth, the rest is 15% to 20% wear.

I realize that there is a problem with the teeth wearing, but why more on one side?
Alginment is my first guess, bu what could be off?

The center line of the shaft in relation to the cam gear?

The intake hole to the center line of the block?

I am really concerned that this problem is going to show up again on the next gear, and I'm in the same place next year.

Back in Black · #2 (**permalink**) 10-31-2002, 10:04 AM

That perhaps the cam and distributor must be compatible/matched...maybe from the same source or at least recommended by the cam maker/dist maker as compatible...could it be relative hardness of each?

Homewrecker · #3 (**permalink**) 10-31-2002, 10:13 AM

Something new to look at. I have heard good reports about these. Summit now carries them for SBC. I don't know if they're available for your motor or not. Might be worth looking into.

http://www.engineeringtalk.com/news/vct/vct104.html

Mr.Fixit · #4 (**permalink**) 10-31-2002, 10:31 AM

Turn the oil pump drive shaft with a 5/16" socket on a long 1/4" drive extension. Does it require more force at a certain part of the rotation? Now push down some on the shaft while turning, does it bind a bit more now? I would venture the guess that your oil pump is harder to turn through a certain part of it's rotation. The dist gears that had to push it through that part have worn out. Assuming the dist shaft is straight, the gear was normal, and such.

rhino · #5 (**permalink**) 10-31-2002, 02:02 PM

Is the distributor shaft bent at the bottom ? It would not take much to cause uneven wear. Also the teeth on the gear mat not be cut square or concentrically to the bore of the gear.

rhino

Mr.Fixit · #6 (**permalink**) 10-31-2002, 02:27 PM

That pattern of wear is consistant with the oil pump being run under a strong preload from the distributor shaft. After you press the gear off, drop the dist back in, clamp it down, then turn it. It should rotate with only minimal resistance as you are turning the oil pump too. I bet it will have more than minimal resistance. Oil pump drive shaft is too long (or you could say the broached hex drive in the dist shaft isn't deep enough)

RICK LAKE · #7 (**permalink**) 11-04-2002, 07:22 AM

Todd Hedges HI. What distributor do you have? there are 3 types of gear material for dist. gears. Broze iron and steel. What cam shaft was installed? There are two differant size gears. .467 and .531. If you have the wrong gear it will shave the gears offon one side. Do you have a billet cam shaft or iron cam shaft? You need bronze with a billet shaft Call the engine builder and ask? Your cam shaft may be walking in the bearings and shaving the gear also. Let's do the basics first, check the cam and type of gear needed. Check the end play on your Distributor, there is a spec of about .35 to .50.CHECK with dist for end play number. You may have the right cam and wrong gear? Get back to us

Rick Lake

zipzip · #8 (**permalink**) 11-05-2002, 12:30 PM

Every gear has runout in it. This makes a "tight" section and "loose" section when run with another gear, although there should be backlash all the way around. If the oil pump shaft is "pushing" the gear up toward the distributor, it will take out the backlash between the distributor gear and the camshaft. This will greatly exaggerate the load generated in the "tight" section of the runout, thus causing your wear.

Remember the hardness requirements between camshaft and distributor gear if running roller cam made from higher alloy steel.

Sorry if I rambled, but I design gearing for a living...

Todd Hedges · #9 (**permalink**) 11-05-2002, 03:32 PM

thanks for all the info.
I just finished pulling the engine out yesterday.
I will be bringing the engine back to the builder that originally assembled the engine last spring. He seems very resonable about the whole ordeal so far. I will definately bring the information mentioned here with me.

At best, we're talking 6 months till the streets are swept clean again. They just sanded the roads last night due to ice.

Has anyone created a cobra bodied snowmobile yet??????

Wayne Maybury · #10 (**permalink**) 11-11-2002, 07:59 AM

I have put my Cobra away for the winter and last week I decide to pull the distributor since there has been so much talk about gear wear. I have a 351W with an MSD distributor, a Comp solid lifter cam, and a stock oil pump. The engine has 1500 miles on it.

Well sure enough, the gear had quite a bit of wear. Each tooth is evenly worn, top to bottom. There is no sign of wear on the bottom of the gear similar to what Andy Dunn found or uneven wear as described by Todd at the beginning of this thread. I haven't tried to turn the oil pump manually yet, but I will. I will also try to turn the oil pump using the distributor once the gear has been removed from the shaft.

I took the distributor to the engine builder on Friday and he simply shook his head. He couldn't believe it, another gear problem. He said that he rarely saw distributor gear problems until a year or two ago, now they are very common. He has contacted a couple of other engine builders and they are also seeing the same thing.

He took various measurments, turned the shaft, etc. He said that he cannot see anything out of the ordinary. He is going to replace the gear. The one thing that he did mention is that he will put a good amount of "cam break-in lub" on the distributor gear before it goes back into the engine.

Wayne

Todd Hedges · #11 (**permalink**) 11-11-2002, 09:56 AM

The builder who built my engine said that he has had many, many, many problems with the MSD gear on the 351's but never on the 428. I was the first.

He says there was a bad heat-treat process that was the cause from MSD. Better check it out.

His name is Joe and he works at Danbury Competition.
He is a good guy, doesn't talk much on the phone unless you keep the conversation going. Give him a try...
203 748-7356.

Good Luck.
My engine is back in his shop getting torn down.

Wayne Maybury · #12 (**permalink**) 11-11-2002, 11:45 AM

Thanks Todd, I'll check it out. This seems to make sense since my gear was evenly worn for no appearent reason.

Wayne