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Oil-pump Gears
Posted by: Frog ()
Date: June 18, 2017 08:28AM

In keeping with the habit I have of running into a problem every time I start a new phase of assembling my engine, this one has to do with the new oil-pump gear set I ordered from Clark's.

The gears provided were nice and shiny; brand new I suppose. I removed the original gears from the pump housing and installed the new ones lubing them with a bit of engine oil. First thing I noticed was that the gears would not mesh (were binding) without additional urging by the distributor shaft I bought for the purpose of turning the gears. I stopped at this point and measured the clearance between the gears and housing. That came out to the minimum of .002" as specified by the information supplied with the gear set. Gear backlash recommended is between .002" and .008". There was absolutely NO backlash clearance on any of the gears. Based on the definition of "backlash" in the next paragraph, it would not be wise for me to use these gears.

Backlash is the clearance between mating gear teeth to let the gears mesh without binding and to provide space for a film of lubricating oil between the teeth. This prevents overheating and tooth damage.

I reinstalled my original gear set and made some measurements. The clearance between gears and housing was at the specified minimum of .002". The backlash, though, came out to .012", well above the recommended maximum of .008".

For kicks and giggles, I left the original drive gear installed and replaced the other gear with the brand-new one. The clearance between the gears and housing remained at the specified minimum of .002" and the backlash was .007", which is within specs.

Shall I send the gear set back to Clark's and get another one, OR, use a combination of the original drive gear with the brand-new one?

BTW, the original gears had some surface rust on them and I removed that with some 600-grit sandpaper. All that's left are what appear to be black stains on the gear teeth.

I can only imagine what the responses will be on this one.

Thank you.

Frog

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Re: Oil-pump Gears
Posted by: BobV66Vair ()
Date: June 18, 2017 09:05AM

Call Clarks and discuss it. They will most likely send another set. They have been very good about dealing with any problems in their parts. They also may not have heard the problem so alerting them will help the next buyer.

Did you try using the new drive gear and your old small gear? Might be interesting to know if the drive gear has the same clearances as your old one. Please post results, this is interesting.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Oil-pump Gears
Posted by: Frog ()
Date: June 18, 2017 09:22AM

I'd thought about that, Bob.

I'm gonna go ahead and switch gears.

Thanks.

Frog

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Re: Oil-pump Gears
Posted by: Frog ()
Date: June 18, 2017 10:27AM

Here are the results:

First image is of both new gears. You can clearly see that there is no backlash between the meshed gears. Also, the green arrow represents the point where there is .002" clearance with the housing; red arrow, less than the minimum recommended clearance of .002". In fact, I couldn't fit the thinnest feeler blade (.0015") in there.

Next two images show the new drive gear with original other (idler??? terminology) gear. You can clearly see the backlash between the two meshed gears. BTW, the backlash clearance varied among the meshed gears. Some approached the high (.008") limit (one was over), all were more than the lower limit (002").

Frog

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