I finished the rebuild on the 73-454. The distributor drops in ok, but requires 2 gaskets to take up the slack (adds about .125" or less) as it does not seat deep enough into the block, causing the timing to wander because you can not tighten down the collar to the manifold. I think it is the new oil pump drive shaft for the Melling HV pump that is slightly taller. The heads were milled .003" so I think that is not even a factor.

Does anyone have experience in determining how to measure the true distance from the top of the shaft to dist. collar so shims can be added? Ideas on any tool that is available is helpful.


[Modified by bigvette1, 7:53 AM 8/27/2003]

 

ONce in a blue moon I have seen this problem, but not on a BB chebby, just Pontiac engines of many moons ago....I usually took out one or more of the extra washers found under the gear end...I thought of them as shims for taking up sloppy clearances....maybe you got too many in there, or if NOT, then you have to use the extra gasket, not unheard of either....

GENE

 

Are you using an aftermarket intake manifold?

If so, I have run into this problem as well.
Adjusting the clearance between the lower gear and the housing (via shims) will not solve the problem because the cause is unrelated to the shaft end clearance. The problem is due to a shorter manifold height between the block rail and the distributor boss. There is a kit available which is supposed to address the problem (Mr Gasket) but it does not. So far, all I have been able to do is stack gaskets and/or manufacture a custom shim to take up the extra clearance between the bottom of the distributor mounting flange and the manifold.

I have come across the problem by simply changing manifolds without ever going near the oil pump and/or drive shaft, and with no head or block modifications. Some manifold/distributor combinations bolt right on, some do not. Luck of the draw.

I'm GUESSING there is a patent infringement issue with aftermarket manufacturers... if a product requires "significant" modifications to install, then the manufacturer does not owe GM any royalties. If the part is a direct bolt-on replacement part, then the manufacturer must pay GM a cut of the action for each part sold. To keep prices competetive, (for our benefit) aftermarket parts manufacturers will often design a part so that the target car or the part requires mods to install... therebye sidestepping the patent issues. Again... only a guess.

Tom

Edit... if you remove shaft shims to raise the shaft (and lower the housing), you will have too much shaft/gear end clearance. Excessive end clearance will cause your timing to wander because the relationship between the cam/distributor gears becomes "undefined" causing timing to be a "moving target".



[Modified by Tom454, 9:50 AM 8/27/2003]

 

Well put Tom. At least I am not the only one that has the problem. Thought I screwed something up and using extra gaskets seemed kind of like a Bubba fix, but it works until I can find the proper shims. Gear mesh is my real concern as the oil pump is driving quite well. Thanks.

Agree on the aftermarket theory.

 

Yeh, Tom got a good handle on the problem, I don't agree it's a patent thing though, but the aftermarket guys don't have any idea what GM's or anyone elses production allowances were/are.....and if you shave heads, intakes, or anything else, aftermarket gaskets even...youwilll have variations stacking up on you....some may be additive, some subtractive, but if you get into a situation they are all one war or another....well, you can be out of tolenance in one spot or another....welcome to mass production with more than one parts source.....been there seen that, done that....makes engineering staff tear their hair out.....

GENE

 

I'm always changing things so a few years ago I bought an Morroso oil pump shaft primer that is also a depth guage. I once had to drill another hole in the distrib shaft for the pin to set the correct gear mesh.

 

Great idea on the primer. I have one, just need to use it for that use. Drop it in, set the coller when it is seated in the oil pump shaft and measure it out. Thanks for the idea.