# DISTRIBUTOR GEARS & DIZZY INSTALLATION



## PontiacJim (Dec 29, 2012)

Did some research on distributor gears and this is the best I could put together using several internet sources to include the cam makers.

*Pic # 1* - In stock form, the only oil that lubricates the spinning cam and distributor gears gets there by the splash effect, but the distributor also has a drain hole from the lifter valley that lubricates it. Some Pontiac engine builders/assemblers will add the .030" drilled hole in the rear oil galley plug to help direct pressure feed oil onto the distributor/cam gears which is probably a good idea when you limit splash lubrication by using various windage trays, crank scrapers, or lifter bore restrictors, minimize the amount of oil going to the valvetrain/head, or use an 80 PSI oil pump.

The oil pump is driven off the distributor gear which means the resistance that the distributor gear applies to the cam gear also comes from spinning the oil pump shaft that turns the oil pump's gears. If you are running a high-volume oil pump, heavy weight oil (especaily on a cold motor), this can cause an increased pressure between the distributor gear and gear on the camshaft. Tight bearing tolerances that are used to increase oil control, and high rpm engines can also cause the oil pump to work harder and add to the extra resistance on the distributor gear. So it is important to know what tolerances are used in your engine if it is rebuilt and what oil the builder recommends - conventional oil or some form of synthetic oil.

*Pic #2 * TIP: Always replace the factory stock oil pump driveshaft with an aftermarket hardened one. The factory shaft may not hold up to thicker oils and/or higher pressure oil pumps. It is the "ears" on the end of the shaft that seemingly break. The factory shaft has protrusions, or nubs, on the shaft to keep the shaft from falling through the engine when just an oil pump is changed out. If you purchase an aftermarket shaft, they usually do not have these and no need for concern, they still, work. Use a reputable source to get your replacement. The measurement of the oil pump shaft measured by me shows to be 7 1/2" long with a diameter of 1/2".

*What type of gear for what type of cam?

1*. When using a flat-tappet camshaft in your Pontiac engine, you can use a cast iron distributor gear like factory (60PSI oil pumps used a cadmium plated gear), bronze gear, or composite gear. Some flat-tappet cams can be had with an optional parkerized heat treatment to help prevent lifter scuffing during break-in. The cam will come with a darker appearance throughout to include the cam's lobes. This also hardens the cam's distributor gear and requires the use of a melonized distributor gear.
*2*. When using a ductile iron roller cam, use the melonized steel gear or composite gear.
*3*. When using a billet steel roller cam, they can be made of different steels so it is important to use a matching gear suggested by the manufacturer. Options can include a melonized steel gear which provides long life, but it seems with a solid roller the bronze gear is to be used but the softer bronze gear should be changed more frequently due to its wear properties. Some billet steel cams will use a cast iron cam gear pressed onto them, so a matching cast distributor gear, melonized gear, or a composite gear could be used.

Melonized gears are a Nitrided Ductile Iron and not the same as steel or cast iron. Heat treated for durability, they have a slick surface, and are compatible with any type of cam and often used by the OEM for long life and generally used as the default gear on replacement distributors. A Composite gear is compatible with all camshafts but it is also just as susceptible to wear if used with high viscosity oil and high volume oil pumps. When installing a new cam, it is best to replace the distributor gear as the gear mates with the camshaft during engine break-in much like a new ring and pinion gear does.

When in doubt, always contact the cam manufacturer/seller and use their recommendations.

Be advised that you want to get a replacement gear that matches the distributor's shaft diameter. The standard GM shaft diameter is 0.491" while many aftermaket distributor's use the 0.500" shaft diameter. Competition Cams offers a composite gear for GM 0.491" distributors.

Often overlooked during assembly or when a distributor is changed out or upgraded, is the installed height of the distributor relative to the camshaft. The distributor's installed height is determined by the height of the intake's distributor mounting boss. This generally isn't a problem on Pontiac engines where the distributor shaft collar seats against the engine block and not the intake.

*Pic #3* TIP: *Cam End Play.* This tip applies to engine rebuilding moreso than an engine already running, and it can have and affect if you are going to install a new or rebuilt distributor. This is another tolerance often overlooked by an engine builder and the owner/assembler that can cause distributor gear wear, along with lobe wear, timing fluctuations, cam bolts coming loose, and rapid timing chain stretch.

If you have your distributor depth set correctly in a running engine and notice undue gear wear (not normal wear as can be found in a bronze gear) it could be because your camshaft is moving too much inside the block. A cam moves back and forth in the block and this movement should be checked at the front of the cam between the thrust plate and cam.

When installing your cam, you do not want the tolerance to be too tight nor too excessive from the factory specifications of .003" -.007" and no certainly no greater than .010" max. The cam thrust plate's thickness AND the step on the back side of the cam gear dictates the endplay the cam will have. The factory cam plates were .124" thick, but some of the new aftermarket plates can be thicker or thinner - some have been measured thicker at 0.131"-0.132" thick or thinner at .116". The cam sprocket has to fit correctly on the cam's snout and should be fully pulled thru the cam gear and protrude past the face of the cam gear when the bolt is tightened, not flush with it. If the timing gear is flush with cam snout when assembled with the eccentric, check to see that the eccentric is centered properly on the snout. Centered properly the gear is pushed onto the snout past flush when the bolt is tightened. If the eccentric is not located right during assembly, it could keep the nose of the cam from being fully pulled thru the cam gear and interfering with the cam gear step from fully seating, and allow too much end play.

The camshaft is pushed against the thrust plate by the distributor gear due to its helical cut gears and load from oil pump driveshaft. The cam plate's wear surface is lubricated by engine oil pressure. The rear cam plug is simply an oil seal only, and has nothing to do with cam end-play - so don't be fooled by those who say you don't have the rear cam plug depth correct. The cam should NEVER touch the rear plug or it will wear through it.

If your tolerances are not within spec, the first place to check would be the camshaft sprocket. Aftermarket cam sprockets are not always "factory" correct with regards to the step on the back of the cam gear - the thickness can be more or less than factory. Replacing it may be your first thing to do. Next might be to try a different thrust plate having a different thickness. Nitemare Performance sells a .121" plate that may work with a thicker cam gear. Other Pontiac performance suppliers also sell thrust plates and could advise you on their thickness.

*Back to installing the distributor and checking it for its' correct depth/gear tolerances*:

*Step 1*: Coat the distributor gear with white lithium grease to check the gear's wear pattern - this will be done in Step 3.
*Step 2*: Check this by installing the distributor in the engine without any gaskets and use the distributor hold down and snug it up. Remove the cap and rotor so you can reach the top plate for the main shaft where the advance weights connect. Grab the top plate with your hand to see if there is any up-and-down movement. If you can move the distributor shaft up and down between 0.010" and 0.030" then you should be fine - based also on the clearance between gear and distributor base.

You will find recommendations that the gap between the top of the gear and bottom of the distributor housing should be set to a clearance of .010" using shims. Pontiac distributor gears, being counter clockwise, pull the distributor down so the clearance is not as critical as a gear cut to push up on the distributor. Factory is around .060" and my '68 dist. measured .053", but if you must clearance the gear go with .015" for small cap distributors and the factory HEI seems to have more clearance and is said you want to shim it to get .040"-.045". The issue would be if you don't have any movement, it could be because the distributor gear is bottoming out on the oil pump's drive shaft (which is not likely). You may need to use a nylon shim under the distributor housing-and-block mating surface to raise it up the needed amount so it won't be bottomed out.

*Step 3*: Now you are ready to check the gear contact pattern by rotating the engine several revolutions. Pull out the distributor back out and the pattern left on the gear should place the wear in the center of the gear. If this looks good, put the gasket on the base of the distributor, your hold down clamp & bolt, and set your timing. If you do not have a good contact pattern, it could be the gear bottoming out into the oil pump's drive shaft (not likely, but possible when using aftermarket), or a matter of shimming either the distributor gear-to-housing at the base to move the gear down or shim under the distributor at the block to raise the gear up (always recheck your up/down distributor play and contact pattern), but an uneven pattern seen going around the gear may indicate a bent distributor main shaft or a bad/worn distributor bearing.

Stacking gaskets on top of each other to get the correct height is not a good solution over shims. Over time the gaskets will compress and the gear mesh problem will return and it could cause the distributor to get slightly angles and not be centered vertically on the gear and wear out the distributor & cam gear and your distributor.


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## armyadarkness (Dec 7, 2020)

Great info! When I did my cam, the retainer plate was on backwards, and Ive since seen two others with the same issue. Not sure why people think that oil groove should face the timing cover, but it's useless in that orientation.


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## the65gto (Oct 9, 2008)

Reminds me of a "nightmare" when I pulled the dizy out and the oil pump driveshaft hung in the bottom of the dizy. It dropped and disappeared into the engine. After about an hour, I used a magnet on a telescoping rod, found it and was able to retrieve it. Brewski's were in order.


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## armyadarkness (Dec 7, 2020)

the65gto said:


> Reminds me of a "nightmare" when I pulled the dizy out and the oil pump driveshaft hung in the bottom of the dizy. It dropped and disappeared into the engine. After about an hour, I used a magnet on a telescoping rod, found it and was able to retrieve it. Brewski's were in order.


I need a shot of Wild Turkey, just reading about it.


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## PontiacJim (Dec 29, 2012)

the65gto said:


> Reminds me of a "nightmare" when I pulled the dizy out and the oil pump driveshaft hung in the bottom of the dizy. It dropped and disappeared into the engine. After about an hour, I used a magnet on a telescoping rod, found it and was able to retrieve it. Brewski's were in order.


It happens. Had another member setting his in from the top and down it went. Took a bit of doing, but he did get it back out.


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