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Old 12-14-2004, 10:15 AM
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BBC cam gear problem

I'm at the end of my rope!

I have a 454 that eats mild flat tappet cams during the "20 minute break in" procedure. So after 3 chewed up cams, I installed a mild street roller which fixed the cam/lifter wear. But then the teeth on the distributor gear wears to a sharp edge and the metal from the gear clogs the lifters.

I tried the comp cam roller which doesn't require a bronze gear and that didn't work any better. Then I tried a Lunati cam with a bronze distributor gear and the gear wore out the same and it even wore up into the distributor shaft which made a huge end-play in the distributor.

I tried both low volume and high volume oil pumps. I made sure the distributor wasn't being pushed into the oil pump shaft.

I have been fighting with this engine for a three years now and I hate to quit.

The block is currently at a local race machine shop right now. I'm had the lifter bore alignment checked. They say about 1/2 the bores are out pretty bad and they can fix them with bushings. But that doesn't help the cam gear problem.

Any ideas?

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Old 12-14-2004, 12:12 PM
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Yes the main issue with BBC`s (mostly just the 454 blocks) is the lifter bore alignment... It can cause all kinds of issues but mainly flat cams from break-in to 5K miles down the road... You might now also have the cam bores checked for alignment...? The cam may turn freely when installed but may still be in a bind...?

Keep us informed as to the progress please...
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Old 12-14-2004, 01:49 PM
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gears

My first thought would be that the cam is walking foward and causing excessive clearance at the distributor gear....

What arrangement are you running to stop cam walk??

What did you set the cam end play at with each cam???

What typ of timing chain cover are you running????

Look close at the cams and the lifters and see what the tracking looks like



Keith
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Old 12-14-2004, 02:55 PM
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Thanks for your replies!

I did measure the cam end-play when I installed the roller. I don't remember the number I used but it was something like 0.010". I do know that I used a value recommended by the manufacturer. However, you guys are making me think about excessive end play could be causing the gear wear. I'm using a stock timing chain. But I tig welded a 0.050" feeler gage on the inside to correct the endplay. I have a roller bearing on back of the timing chain gear and a roller cam button on the front. The stock timing chain cover seems pretty strong but maybe that is the problem???

The wear seems to reduce the thickness of all teeth from the base of the tooth to the tip. Plus the bronze gear gets eaten up at the distributor shim/gear contact point. The shim will wear into the bronze gear 0.050 or 0.060" and the excessive endplay makes the rotor to cap gap so big the engine starts to miss. Not the mention all the metal particles clogging up the lifters. That is when I tried screwing the shim to the gear. I made a "horse shoe'd" bronze gear. That stopped the "up and down" wear and really slowed down the gear "sharpening" but it still wears out after 5K miles.

After pulling off the intake few times to un-clog the lifters, I found that compressed air blown down the push rod allowed oil to flow start flowing again out the pushrod. I know that sounds bad but beats taking off the intake every month!
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Old 12-14-2004, 03:07 PM
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I`ll say this, since I hate to see any rodder spend a ton of money and the problem still exists. When the engine ate the second cam, then it was time to stop and take it to a machine shop, if there is no good reason that`s visible with the naked eye that it should be doing this, then part of the machinists job is to find the problem. Surely, the engine wasn`t doing this when it was released, otherwise it would have been replaced by chevy under warrenty. Swapping to a roller cam would solve the wear issue, but as you`ve learned on your own, it lead into another problem that is likely related to the first problem, I hate it that it`s caused you so much grief, as I`ve been there before, and it taught me the lesson, if the problem still exists and there seems to be no good reason, to the machine shop it goes since I don`t have money to waste and that money could have been used on something else. good luck on your project.
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