Oil drive gear which one to get?

DeBordEngineMan

DeBordEngineMan

Senior Member
I am ordering a new oil drive gear tomorrow and I noticed in the parts houses catalogs there is a standard and an oversized gear I understand what the purpose is for the oversize but how can you tell if you need the standard or oversize if you can not see the meshing of the gears? Mine has a little play not much at the drive gear but at the distributor I have about 1/2 rotation at the cam a lot of this is a combination of wore out contacts at the upper and lower shafts and some at the gear buying all new parts just didn't know which gear to get I can not see the gear in the oil pump I guess without taking off the oil pan and removing the oil pump right? Any help would be appreciated, thanks RobertDeBord
 
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You can take out the drive gear without taking the pan off .The oil pump is secure in place,held in position by the bottom spring and lock screw at the lower side of the block. At first I would remove the distributer and the top drive shaft.The top drive shaft can easily be removed with a pair of needle nosed pliers,it lifts straight out.Engage a suitable long screwdriver in the top of the female drive coupling and you can judge how much actual play you have at the mesh between the drive gear and cam. There should be hardly any, its a kind of guesstimate.You might have a distributer with the aftermarket one piece shaft so you wont have the upper shaft to remove.I have found most lash is caused by slop in the shaft slots and wear in the female coupling ends, I would bet that is where most of your lash is. To take out the drive gear assembly take the valve chest cover off ,with the distributer and coupling shaft removed you can pull the securing spring out from the top and then lift out the drive gear assembly.I make sure I dont turn the engine between inspections so when I replace it the gears mesh where they were before and it is easy to slot into the oil pump . Lash at the distributer causes rough running as the timing is all over the shop as we say in England.Sounds loike you have way too much.Tell us how you get on.

John in cool partly cloudy England.
 
FWIW, I had play in the dist shaft, too much I thought. Bought a .004 over and still had play. Then bought a .010 over and still has play, which I still think is too much. I used as a sort of guide the lash in the cam gear/crank gear, just by feel because you cant measure the dist drive, and the dist is still significantly more than that. I would think that a stock cam, or reground stock cam, has more than .004 of wear and that oversize at least would be safe. But the other things mentioned above should be checked first and bushings. Maybe someone with drawings of cam and drive could see what the numbers work out to out of curiosity, but again, you cant measure it though I am sure experienced guys could come close by knowing how a certain clearance is susposed to feel. $.02
 
I agree with the thought...it's not the gears but rather the slop in the drive shafts driving the gears.
A two piece dist drive shaft is a must. Not a one piece shaft. This takes care of the bushing killing side pressure caused by a single shaft misalignment.
No sideways slop in either shaft. This indicates worn bushings. These bushings are replaceable.
Very little slop in the key and groove drive.
For this positive displacement type gear driven oil pump it's the volume of oil that counts, not the pressure.
Every rotation equals the same quantity of oil moved. More oil pumped is simply more rpms. More pressure is going to rob the engine of a small amount of hp.
Other slop can be found by looking at the gear, some say worm, that the camshaft drives. This can be easily taken apart by hand.
Remove the manifolds. Intake and exhaust.
Remove the oil return pipe.
Remove the valve cover. Distributor, and all dist drive shafts.
Use fingers to compress the spring and prise out the shaft. You'll see it mid-ships in the oil gallery and between two tappets and valve stems with it's machined [worm] gear.
This gear should not be worn paper thin and sharp at it's edges.
If it's worn you WILL see the problem. If you have a problem at all.
I'm betting bushing based on what you have said in past posts.

"Hold it closer to the phone so I can look at it." skip.
 
Thanks guys for all the posts, I ordered a new distributor and a new oil pump drive gear and shaft today will let you all know how it turns out! Thanks Robert DeBord
 
My friend wasn't oiling his distributor bushings, they got tight, the shaft in the distributer was hard to turn so it took out the drive gear teeth, the ones that were left on it were paper thin. I freed his bushings and put in another gear and once in a while ask him if he puts oil in the oiler. I'm sure the past owner didn't put a drop of oil in it. It probably didn't wear out overnight tho.
 
Visual inspection of the cam gear and oil pump drive gear is a start...

When rebuilding an engine, I study the condition of the cam gear teeth and the used oil pump drive gear teeth and often see the wear that causes the backlash or sloppy fit. As suggested in previous posts, the best way to determine the correct oil pump drive gear (standard, .004 over or .010) is to test fit them. This is okay if one has all the sizes on hand as I do but they are expensive to own if you only need the correct one. To avoid the purchase of more than one I suggest the following check: Remove the valve chamber cover and then remove the drive gear assembly. With a magnifying glass, study the teeth of the used gear. If the gear is worn, you will find the teeth thinner near the center of the gear. If the mid portion of the gear is within 70% of the width at the outer edges of the gear and the desired fit is close to acceptable tolerance, a standard gear will most likely be the right replacement choice. With the same 70% tooth width standard, if the slop is considerable, order the .004" gear. If the oil pump drive gear has greater than 70% tooth width at the center of the gear and the slop is still considerable, order the .010" as this would indicate the cam gear has considerable wear.
When rebuilding engines with re-ground cams I would estimate my use ratio of available oil pump drive gears is:
Re-install the used drive gear... less than 15% (some used gears show little wear)
Install new standard drive gear ...about 35%
Install new .004" oversize gear ...about 35%
Install new .010" oversize gear ...about 15%
With new cams the standard gear is almost always the best fit.
In my opinion, don't run them so tight they have no backlash. A little clearance is good.
Hope this helps!
Good Day!
Dave in MN
 
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