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Old 09-13-2013, 01:46 PM
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Excessive distributor gear wear?

Hello

So it's been a long while but i have another concern about the engine i was describing in this post:

Engine break-in paranoia

I continued the cam break-in, then drove the car for a few month, a little at a time, approximately 50 miles. I decided to change the oil and filter. The oil coming out was a little dirty, but nothing alarming. Then unfortunately my career took me away from home for a while, but I'm back home now and wanted to drive my car again. I put fresh gas in it and pulled the distributor because I wanted to make sure the oil pump was still primed. The distributor gear seems to have an awful lot of wear given the short time the engine has run.

I have attached some pics. What do yall think? One pic is a little fuzzy but I tried to circle in red something very concerning to me which is a shard of metal coming off one of the gears. This cam isn't anything fancy and shouldn't have required a special gear, but I'm thinking I don't want to put this back in the engine and i'm considering pulling the engine back out to check on the crank and bearings. From what I can see, the cam gear does not show this amount of wear.

Also these pics are pretty high res so you could download and zoom in to see more clearly, assuming this site doesn't process them on upload.
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Old 09-13-2013, 02:45 PM
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One possible thing is dist height check >>>

With a new gear installed that is the recommended one for the cam.

Check to ensure the dist is not bottoming out. Remove the cap and rotor with the dist installed, grab onto the rotor plate and make sue you can lift the shaft up and down a few thousands. If there is no travel then you need to shim up the dist base at the intake manifold with another spacer/gasket till you get a SMALL (.003-005) amount of play. This helps with cam and dist gear allignment & mesh.

2 more of my cents

TJ
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Old 09-13-2013, 03:02 PM
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I have not checked that clearance, I will clean the gear up and take a look at this. Thanks for your input.
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Old 09-13-2013, 03:48 PM
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Did you get a new distributor gear with the new cam? Is the cam a flat tappet? Is the gear made of iron?

Is this a high volume and/or high pressure oil pump?

There are two different types of distributor shims. One goes on the shaft on top of the gear to control shaft end play. I think from memory you want to be about .060-.090". And the other shims (like Custom10 pointed out) go between the intake manifold and the distributor to control how deep the gear engages the oil pump. The shims are cheap, and while you are checking this out, might as well do it right and pay attention to both areas.
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Old 09-13-2013, 04:09 PM
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I left off a lot of specifics, sorry about that. It's a Pontiac 455.

Quote:
Originally Posted by Silver Surfer View Post
Did you get a new distributor gear with the new cam? Is the cam a flat tappet? Is the gear made of iron?
I did not, I got a cam and and lifter set from my machine shop and the distributor is a new Pertronix HEI. The cam is from Howard's cams, flat tappet hydraulic cam. I'm assuming the gear on the cam is iron yes.

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Is this a high volume and/or high pressure oil pump?
Standard oil pump

Quote:
Originally Posted by Silver Surfer View Post
There are two different types of distributor shims. One goes on the shaft on top of the gear to control shaft end play. I think from memory you want to be about .060-.090". And the other shims (like Custom10 pointed out) go between the intake manifold and the distributor to control how deep the gear engages the oil pump. The shims are cheap, and while you are checking this out, might as well do it right and pay attention to both areas.
I'm definitely going to do some research and find out what the end play should be. I just sort of blindly threw the distro in and fired it up i hope I haven't hurt anything.
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Old 09-13-2013, 05:27 PM
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From what I can see in the picture they look alright to me. Both of my distributors where pulled after a couple hundred miles to check on them and for other reasons and they both had a wear pattern on them both where the gears meshed up together. Five years later they both still look the same and have done fine with no issues. I am running roller cams in both builds of mine. You will see a wear mark on them that is normal as they are rubbing parts. What is the best pattern to see that I could not tell you but both of mine show up in the middle area.
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Old 09-13-2013, 09:56 PM
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What kind of shape was the cam thrust plate in. Did you put in a new one when you changed cams? Excessive cam walking can also do this.
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Old 09-14-2013, 09:00 AM
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The one is a retrofit style and has a thrust button on the end and has a spot drilled into the cover to allow proper end thrust. My other 350 has a oem style roller setup so it just uses a thrust plate and there is no setting the cam as its just bolt up. All stuff was new when put together. Now both distributors show wear on the gear and like I said they have been fine for over five years and they look like shiny where they have a wear pattern. Many factors come in to play here such as how much has the block been decked as well as have the heads been milled more then .060 etc as that can effect how the distributor sits and how much space is between it and the intake were it sits. My block has been decked but only about .015 and heads milled less then .020 and I have checked everything to make sure the intake still lines up ok and it was just fine and the distributor sits on the intake just fine with out a bunch of play and gap. I don't know if others will disagree or not but my timing has been fine and never moved at all over the years and they look as good as new. I have seen other distributors from factory motors such as my brothers old 305 and his was original and it had the same wear pattern as mine had and even after 100,000 plus miles it still looked good but not as good as a low mileage one but you could tell it had a proper wear pattern on it.

Last edited by eric32; 09-14-2013 at 09:19 AM.
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Old 09-22-2013, 09:59 AM
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i'm sorry to say this but, yes, that's too much wera even for a 150k miles engine, the contact area should be just shiny and clean but not recessed or showing any kind of wear, once the "wearing" process has begun their life expectancy will be pretty short, i'm talking because of my experience with them.
I'm kinda obsessed by this problem because i went through it with an AMC 401 engine years ago i changed that engine in favor of a SB Chevy just to wake up from this nightmare but murphy's law had something to do even on my 350, than i thought was proof from this issue but is not.
My mistake was to leave the old dizzy gear with a new Edelbrock cam and a no sense high volume pump...i replaced cam and the whole distributor of course with a new gear, made a groove into its shaft to improve dizzy/cam gear lubrication, put a new stock oil pump,did a good set up included put it at the correct height and did a very good break in with the proper lubricant, that's it, nothing magic...

Back to your problem, i'm pretty sure you have to change both cam and dizzy gear but before to di that i would check if distributor shaft is bottoming down causing an excessive drag on the oil pump getting the distributor hard to turn, make also sure the oil pump itself is spinning nice and free,the distributor height isn't the direct responsable of the wear unless gears are woring close to the edge wich i think is almost impossible, however the contact pattern of the gear must be kinda in the middle of the height or close to that, you just need to get shims to put in underneath the distr. shaft neck or get and adjustable one from MSD.
You said your oil pump is stock, are you 100% positive about that? Just check on its casting, stock pump is Melling 55A, no HV or H something.

I also believe that there's sometime a very little balance keeping the gears wear under control, just make sure all the components you're using are matching together and do again a very good break in after the set up, put moly lube or a very good specific lube on the gears, i use to put moly instead other stuff because it's thick and will stay on for months, so you don't have to worry about fire up the engine if you cannot.

I'll write down all the things i know about this problem and hope you find a solution, the most likely causes of premature or excessive wear are:



-Distributor is bottoming down on the oil pump shaft causing excessive drag
-High volume and or pressure oil pump with stock or close to stock bearings clearances
-Non matching gears, example "steel roller cam with iron dizzy"
-Very thick oil and cold weather can lead the gearsto wear faster because of the huge load on them
-Camwalk
-Bad break in (so rare)

Said that, anything that creates more than normal load on the gears could be a problem.
keep me tuned!
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Old 09-22-2013, 12:27 PM
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Keep in mind that most all distributor gear/cam gear wear in any engine type is a result of improper tooth engagement or excessive cam thrust. This type of set-up is nothing more than a smaller scale version of a ring gear and pinion for your rear end. When proper backlash and tooth contact pattern are obtained, trouble free use will occur. High pressure oil pumps are used in virtually all brands of engines that people race and hot rod, and 99% of them don't eat up the distributor gears. The ones that have experienced issues because of High pressure pumps had other issues they weren't aware of that contributed to this. FYI, a cam using a thrust plate setup isn't a bolt it in and forget it type of assembly. You still have to check to see if the cam has excessive thrust with the components being used. And yes, you can adjust this if they have excessive amounts or even if they don't have enough. So if you were to install a new Richmond gear in your 12 bolt and just bolted it in and didn't set your pinion depth or backlash....what do you think would happen. If you just happen to have a 500 HP engine in your car, would you draw the incorrect conclusion of " Well hell, I guess Richmond Gears can't even handle 500 HP", not realizing that you overlooked critical errors in installing it. Most times just putting in a distributor isn't rocket science, but realize that it is a gear just like your ring gear and pinion and does require the same parameters of installation to allow it to function properly and trouble free. Take the time to check it, you'd be surprised how often parts are made incorrectly or had flaws that were overlooked during their QC process.
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Old 10-11-2013, 10:43 AM
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I see that the camshaft endplay should be between 3 and 7 thousandths.. What's the best way to check this exactly? Do I need to remove the timing gear?

Also how do I check the distributor shaft once its installed?
Thanks for all your input.
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Old 10-11-2013, 12:11 PM
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The cam endplay can be checked in the same manner as the crank thrust. You will need a dial indicator to mount to the front of the engine block. You can either pull and push against the gear(it needs to be installed, as it limits the rearward movement of the cam), or you can gently use a screwdriver to move it fore and aft.
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Old 10-11-2013, 12:59 PM
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Thanks, sounds easy enough. I have a decent magnetic base dial indicator so I'll be using that. What about the distributor shaft? again use a dial indicator to measure up and down movement?
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Old 10-11-2013, 04:47 PM
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Quote:
Originally Posted by CaptainCaveman View Post
Thanks, sounds easy enough. I have a decent magnetic base dial indicator so I'll be using that. What about the distributor shaft? again use a dial indicator to measure up and down movement?
You can check distributor end play with the distributor out using a feeler gauge. If i remember correctly, it should be .008" to .012", but you might research that to be sure. Anyway, measure the clearance between the bottom of the distributor and the gear, figure the shims that will be needed, then pull the gear and shim accordingly.

Bill
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Old 10-12-2013, 06:35 PM
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Sounds good, thanks everybody.
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