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10-16-2002, 04:12 PM
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Cam gear Bronze Thrust Ring
I have a sbc 383 stroker engine that I was in the process of breaking in when I discovered the bronze thrust ring behing the cam gear was worn to just a few thousandth's left with only about 1500 miles on the break in.
I am running a roller cam with gear drive. Does anyone have information on what could possibly cause the cam to have so much back pressure on the thrust ring to cause it to wear out with so few miles on it? I am going to replace the bronze ring with a Torrinton bearing but am at a loss as to what is going on. Any help appreciated Rex 
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10-16-2002, 04:39 PM
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do you have a cam button? may be to tight to the cover or a short water pump is pushing the cover back changing the clearance.
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10-16-2002, 04:41 PM
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do you have a thrust button on the front of the cam? are you using a high volume high pressure pump? both can cause such wear if not properly set up, if its the pump you will also wear your cam and distrib gear. for heavens sake get rid of that gear drive, i know they sound good but if you ever go to cam grinder or other high perf seminars you will learn that they are by far the worst cam drive systems around. all the crank harmonics get transferred to the valve train causing all kinds of greif.
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10-16-2002, 05:03 PM
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The cam button to cover clearences are within spec's and there is not any sign of wear on the distributor gear to indicate the "high volume" oil pump is producing excesive load on the cam. I have always used this type oil pump and never had a problem like this before.
Yea I do like the whine of a gear drive but was not aware of any problems assosiated with them. Have you ever heard of one causing this type of problem? How can you set an oil pump up wrong? Rex
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10-16-2002, 05:26 PM
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OK,I went out in the garage and checked my short water pump clearences with the timing chain cover and it is realy close. I have a new "high volume" water pump that gives me about an 1/8 th inch more clearence than the old one that was on there so if thats the problem its resolved.
I"ll check the cam button clearence with some putty with the old pump bolted back on to see. However the bronze thrust ring wore down about 60 thousandth's and I'm not sure the water pump could have moved the cover that far back,I"ll do some further checking on it. Thanks For the help Rex
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10-16-2002, 06:18 PM
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you probably found the problem, as for the pump i've seen people put washers in the relief spring bore to "improve pressure", springs shimmed solid (blows the filter right off the block when cold) housings " blueprinted" to a +.002 gear protrusion, and pickup tubes welded with enough heat to send up a moon rocket, been doin motor buildin since back in 65.you think youve seen it all, then in comes the next guy
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10-17-2002, 12:29 AM
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Your hardened steel cam gear (spur or helical?) requires a radial Torrington thrust bearing not a brass shim. Excessive wear occurs because the two are not good wearing pairs at the loads imposed by gear drives and high volume pumps. Switch to the bearing and you won't have any more problems. Most drive manufacturers recommend this mod, particularly helical drives. High pressure valve springs exaserbate the problem by pulling the cam rearward due to lifter offset. When you install the bearing make sure you have correct clearance or have the gear machined on the running face, the best way is to machine the block but since it's assembled it's too late now. Either method works equally well if done properly.
__________________
Outlawed tunes from outlawed pipes
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10-17-2002, 04:42 PM
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OK, I installed the water pump and my cam button clearences were still within spec's.
I heard a story today from a Pontiac guy and he said he remembered reading an article a few years back where they found that when useing roller cams if the lifter bores were out of alignment it would cause the rollers to put excessive force on the cam forcing it forward or backward. He felt this could be the problem. Surely if this were true I would have heard about it before now. Any body else hear anything like this? Anyway I guess I'll just machine my cam gear to correct tollerences for the Torrington bearing and hope for the best. I want to thank all who responded to my problem, it was much appreciated and what this sight is all about. Rex
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10-17-2002, 05:40 PM
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that story only applies to flat tappet cams, which are ground on a very slight taper to keep the lifters rotating.
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10-18-2002, 02:14 PM
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Ok how about the dist to oil pump clearance, may be bottoming out the the oil pump and making the cam pull back?, Have your heads and block been cut?
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10-22-2002, 06:57 PM
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I think roy is on to something, you should check the wear pattern on bronze gear, if the dist is too low the bronze gear will try to climb the cam gear thus pulling the cam to the back of the block, nothing else should pull the cam back as long as there is ample clearance of cam walk..
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