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post #1 of 3 (permalink) Old 12-22-07, 09:25 PM Thread Starter
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460 ford

Have rebuilt 460 with RV cam HV oil pump. Put reman. dist. in it after 3000 miles it sheared pin in gear. Put another reman. in it did the same thing. Put a new Pro Form dist. from NAPA in it and ran less than 1500 miles and the top part of the dist. were the rotor sits came loose from the shaft. What is going on? Is it the pump , oil pump shaft , cam or bad luck? Thanks
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post #2 of 3 (permalink) Old 12-26-07, 03:08 PM
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cool Re: 460 ford

Originally Posted by RHein
Put reman. dist. in it after 3000 miles it sheared pin in gear. Put another reman. in it did the same thing. what is going on? Is it the pump , oil pump shaft , cam or bad luck? Thanks
The problem is none of the above.

If you are shearing pins in your Ford dizzy, it is MUCH more likely due to improper distributor thrust clearance than anything else in the world. Not likely thick oil, oil pump loading, etc. like many people seem to think, meaning that while lesser pumps or thinner oil may alleviate the problem, the culprit of the problem probably has not been addressed (but should be).

There is a distributor shaft end play spec of .020" and an installed clearance spec of less than .010" between the bottom of the dizzy gear and the block's dizzy gear thrust boss (the pad that the dizzy gear rides on once the distributor is installed). Few people understand Ford's reasoning behind the obscure specification and therefore dismiss it.

The reason for these spec is because as the distributor is turned by the cam gear, it is thrust downward against the dizzy's thrust boss in the block. If the shaft end play and boss clearance are out of spec (too much boss clearance/not enough end play), the dizzy gear does not ride on the boss but instead is floating in mid air all the while being thrust downward by the turning of the gear.

Eventually, the dizzy gear roll pin shears downward because the spec's were not set by properly measuring/installing the dizzy gear and/or shimming the underside of the dizzy gear to take up the slack between the boss and gear. Here is the spec, please read:

To say that the Ford engines randomly shear pins rotationally is a fallacy which is assumed by those that are not familiar with the detailed workings and necessary specifications of these engines. Their fix is usually to drill oversize and put in a bigger pin though the gear. The joke about such an approach is that this is a band-aid fix that may or may not end the pin shearing, because more than likely the root of the problem has not been corrected.

Here is a picture of the dizzy gear thrust boss in the block:

If you look in the mirror's reflection in the above photo, you will see just the lightest wear (from the bottom of the dizzy gear) against the top of the boss. This is exactly how the wear pattern should look. If you have more wear, the block gets chewed up; if you have NO wear, the gear is floating and you are shearing pins.


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post #3 of 3 (permalink) Old 01-03-08, 03:25 PM
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Re: 460 ford

here here paul. the ammount of morons that think this prob is caused by thick oil or hi vol pumps is amazing! i have seen a couple of dizzys with socket head cap screws ground down to clear holding the gear on the dizzy shaft!! or the usual answer is "ah those bloody ford engines, ya cant put thick oil in em or they shit em selves" !! the aussie falcon six is prone to the same prob due a dizzy machining inaccuracy, the ones with a dodgey dizzy body chew out the dizzy gear and bush and of course, people blame the oil! or the oil pump! its a crazy world!!

Craig Johnston.
Ford, Performance & Vintage engine specialist.
email- cjperformance@lizzy.com.au
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