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Discussion Starter · #1 ·
I tore down a sbc with gear drive like this:
https://www.summitracing.com/parts/cca-4100


I found a bronze wear ring behind the cam gear. It wasn't centered on the cam/gear though, it was dangling a little and had an off-center wear pattern on it. It's because the cam bottoms out in the back before pinching the bronze wear ring so it moves around. So it isn't needed right? Or does that mean I need a thicker one?
 

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If the cam bottoms out against the rear cam bore core plug before the cam gear pinches the thrust washer up between the gear and the front face of the block, then the rear plug was installed too deep.
Assembler or installer error right there.
The rear cam bore core plug should be installed just deep enough that the outer edge of the plug matches the inner edge of the chamfer on the rear face of the cam bearing bore hole in the block. I have seen guys mistakenly drive the plug in until it hits either the rear of the cam bearing or the bearing land in the block...that's too deep.

The cam should never be able to touch the rear core plug. Check the rear cam bearing, the cam pressed against the core plug is very likely to have rubbed metal grit off the plug as the engine ran and tore up the rear cam bearing surface. Closely examine the rear most 4 lifters and the distributor drive gear on the cam for grit damage too if you plan to reuse the cam.
Also check the cam button to cover clearance, with it running with the cam too far forward the button was either shimmed real short or cut shorter, or the cover may have been cut for clearance....make sure it is correctly clearanced when you reassemble.

I'd be a bit leery of re-using a flat tappet cam if it was broken-in and run off alignment with the lifter bores like that, being pushed forward by the rear plug.

Goes without saying, the current rear plug must be driven out and correctly replaced with a new plug at the correct depth. Probably a new rear cam bearing too, depending on how it looks to you.

Just a note, when you install a cam, always make sure it can be pushed back into the block farther than it needs to be, and that installing the timing gear pulls it back forward to it's correct position....that way you know you've got clearance at the back end of it.

A second note, toss that POS floating gear drive in the trash or swap meet sale pile and get yourself a decent double roller chain set. ;)
 

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I second on throwing the gear drive in the trash. I almost a motor to one of those. It was installed correct and I had an aluminum timing cover that I had clearance for the floating gears and well the floating gears decided over time to keep floating and want to push out and kept digging into my cover to the point that one day i was driving and I noticed at higher speeds my engine would go way up then way down in response in power and I thought what the heck.

I parked it and did not take it out and needed to check my timing. My Father was there and he went to turn my fan to rotate the engine a little and he noticed a big lag before things would catch up back and forth while turning it and said somethings wrong and the timing cover needs pulled to see what is going on. I went ahead and tore it all apart and when I took my cover off very easily without disturbing the gear drive I took the cover off and the floater gears were hardly on then they just fell right out. The cover was junk and I had to get a new one and ever since then I have always just used a good double roller chain and be done with it.
 

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Discussion Starter · #5 ·
Thanks for your good answers. I put the replacement cam in and found that it sticks out even further than the one I removed. You can see the gap in the pic.


Took it back out and found that it's .03" longer than the original and that 30 thou is enough to keep the timing cover from going on. The cover bumps so hard on the cam button that it bulges the cover out.



Can I remove the bronze ring and shorten the cam button to a little end play and call it good?


If not, can I remove material from the back of the cam to get proper insert depth?
Or can I pound the plug back out a little ?




The seller said "chains stretch" when I asked him about the noisy gear drive. I just want to get this thing moving again as quick and cheap as possible to see if it's any good.
 

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Thanks for your good answers. I put the replacement cam in and found that it sticks out even further than the one I removed. You can see the gap in the pic.


Took it back out and found that it's .03" longer than the original and that 30 thou is enough to keep the timing cover from going on. The cover bumps so hard on the cam button that it bulges the cover out.



Can I remove the bronze ring and shorten the cam button to a little end play and call it good?


If not, can I remove material from the back of the cam to get proper insert depth?
Or can I pound the plug back out a little ?




The seller said "chains stretch" when I asked him about the noisy gear drive. I just want to get this thing moving again as quick and cheap as possible to see if it's any good.
The cam bottoming out on the rear plug that has been driven in too far is your sole problem, and the thing you need to fix.....any other way of doing things is just being a hack.
Removing material from the last cam bearing journal is going to be tough, cam is hardened so it would have to be ground off, If you are so inclined, hack away but beware getting it too hot and changing the temper as that could lead to cracking.

You may be able to use the old cam as a driver to push the plug back a bit, but you risk either creating an oil leak or even worse yet a too loose fit on the plug, which can then be pushed out by oil pressure. If the plug gets pushed out, you'll lose all the oil in the engine and into the bellhousing area in a matter of just 30 seconds.

You know what needs to be done to fix it right and reliably...you either need to pull the trans to access the plug and replace it correctly, or pull the engine for the same reason.

Only you can decide if cutting a corner is going to be worth the risk of fixing it again, or having to fix an even bigger problem caused by a cheap fix.
 

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Discussion Starter · #8 ·
I'm fine with going to a double roller chain.



The cam on the left is the old one, .03" shorter than the new one. But both are just a little too long for the gear drive and bronze bushing to ride the face of the block. So the cam tunnel plug must have been installed a little deep.



Seems that what matters here is that cam lobes are centered under lifters, that cam and crank gears are flush with each other, and that I can grind the cam button to clear the inside of the timing gear cover ~.01"....right? IF so, best case, I can just pull the crank gear forward 1/8" to get flush with the cam gear, and shorten the cam button. Enh?
 

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I'm fine with going to a double roller chain.



The cam on the left is the old one, .03" shorter than the new one. But both are just a little too long for the gear drive and bronze bushing to ride the face of the block. So the cam tunnel plug must have been installed a little deep.



Seems that what matters here is that cam lobes are centered under lifters, that cam and crank gears are flush with each other, and that I can grind the cam button to clear the inside of the timing gear cover ~.01"....right? IF so, best case, I can just pull the crank gear forward 1/8" to get flush with the cam gear, and shorten the cam button. Enh?
So your going to let the cam continue to rub metal filings off the rear plug, have the cam sit too far forward in the block to correctly align with the lifters, have the cam gear rear thrust face not even up against the block, and then pull the crank gear forward just to get the chain to align....then hope it's fit under the cover and not rub the gear or the chain on the inside of the front cover after you butcher the cam button short enough to cram the cover to the front of the block.
Something I forgot earlier is also distributor gear mesh is going to be screwed up to by the forward placement, so examine that close.

Okay, good luck with that mess.....

Chain and gear, or gear drive both end up the same thickness, so neither gains more clearance to the cover.

I'd take the chance of driving the plug back a hair before I hacked away like that....then keep an eye on the oil pressure gauge and maybe you'll get lucky and it all stays in place.
Or take a cut-off blade in a 4-1/2" grinder and a trickle from a water hose to cool things as you cut, and slice 1/16" off the rear cam journal and then deburr it up nice.
 

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Discussion Starter · #10 ·
I thought so too but I see no evidence or reason to think metal is being shaved off the plug. It's shiny and the back of the cam has a slightly shiny spot. Whether the cam rides on the plug or the face of the block seems like it might not matter...as long as there's no shavings. And it's probably getting decent oil from the cam bearing right next to it.



Anyway, just looking at all the options. I agree that ideally the plug is corrected. But risk of a leak or worse can be avoided by one of these workarounds. I'll probably turn or grind the back end of the cam off a little.
 

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Discussion Starter · #13 ·
It runs ok, I guess we'll see how well and for how long. I can feel the vibration from the gear drive in the motor though and that's no good. At least now I know the motor is decent and can go from here. I just didn't want to spend too much to find that out. Thanks for all your input! See the startup video..

 

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I'll cross my fingers for you, hopefully you don't have a problem with that rear plug ;)

You had me worried for a minute you were going to start it up with a new cam and let it idle.....:sweat: LOL Was watching the vid just hoping you knew what to do. :mwink:
 
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