Are we talking about the same thing ? I drilled a small hole in the bottom of the "V" on the idler gear to get extra oil to the idler shaft. Did not think about any oil "escaping". Just oil the shaft.
Do not think it matters. Show me all the engines that were put together in the late 80s, installed in the early 90s and driven, raced in 2 classes, 14 races a year just about every year since 2000 and still is running great with 50+ lbs at a hot(fast) idle ?
Might be overthinking it. Not that is a bad thing, just does not matter in the end.

I'll take the advice of a legendary USAC Sprint Car engine builder whose engines won TWO national championships.....How many miles do you really think were acquired in all those races? After all, a drag race engine operates for mere SECONDS at a time.

That's what I have already done too. I figured any oil getting to the shaft would exit at the top and bottom through the small amount of clearance the gear has on the shaft.

Do you guys decrease the check ball down one size? I have seen several get hung.. reducing the size reduces the risk of jamming open..Or maybe just hone the hole a tad..

I haven't reduced the size of the check ball. Just whatever came with the pump. I did clean out the cavity and ensure it seals. I used an inspection light to check for light passing by the ball when its on the seat.

I'm not trying to be inflammatory, just asking as I am trying to think how the drain hole will remain a drain hole.
As the gears come around and mesh together it will force a small amount of oil into the hole. This oil will be forced out, either through the additional hole drilled 180 from the feed hole or through the top and bottom at the shaft bore. Then again when the next hole in the gear comes around ( theoretically the drain hole) the same thing happens. Oil is forced in and out. Wouldn't it be beneficial to only have 1 hole to force the oil to flush the shaft and out the top and bottom. ?
That was my thinking when I drilled the feed hole at the middle point of the gear height.

Hey Scott,
I like to use a grey scotchbrite wheel to deburr the gears completely and also the cover.

Oil has three purposes in an engine: lubrication, cooling and cleaning. Oil that does NOT drain back is holding contamination (i.e., carbon, metal, fuel, etc.) that needs to be filtered out. The idler shaft and gear in an oil pump are no different. The oil that is redirected into the idler shaft needs a port by which it can be circulated through the oiling system for filtration. It is as simple as that....

Again, it is not possible to drill any holes 180 apart on a Melling Pontiac idler gear. Not happening. At any rate it is just a theory. How do you know the oil flow see,s one hole as incoming and one exiting. Maybe they are both intakes holes and the oil exits out the top and bottom of the gears ? No real way of telling, its just someones idea.
I bet when I pull my pump the idler shaft is perfect. I will post it.

"How do you know the oil flow see,s one hole as incoming and one exiting. Maybe they are both intakes holes and the oil exits out the top and bottom of the gears ?"

I would bet this is what happens

You two do what you want to. I’m just a retired ASE Master engine machinist and engine builder. What could I possibly know(profound sarcasm)?

Don’t get me started on all the errors in this statement. I HAVE drilled supply and drain hole in Melling oil pump idler impellers that are 180 degrees apart for DECADES. Do what you want to; it’s your engine, but I sure as hell do NOT want to see the crying when something goes to s$&t....

Wow dude, no reason to get your panties all bunched up. In not questioning your skills or knowledge. Just asking questions and giving my opinions.
So you don't feel the drain or flushing out oil will adaquately flush from the top and bottom of the shaft bore?

Don't wear panties, but it's YOUR engine; do what you want.....I've said all I intend to say on the subject. The average clearance on the idler gear shaft is .0015 to .002. How much oil do you assume will drain out of that clearance while it's being "whipped" at a few thousand RPMs?

Isn't the oil pump immersed in oil?


:confused:

I would love to see some pics of this mod. Pictures always speak a thousand words and could clear the air a little.

I will try and get a picture in the next day or so. I have not fully assembled the pump yet as I am waiting for the bottom plate. I just need to make a trip to my shop.

Related ?

Anti-gall/ anti-cavitation dimples in bottom of both gears. Pictured here.....


https://butlerperformance.com/images/F193770497.jpg





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Since I have ran Pontiacs for more than 35 years, street raced and raced at the track and never blown a head gasket, spun a rod bearing much less blown up a engine, I think I am good.

I know its a small thing, does not mean a lot. But how are you going to drill holes 180 deg apart on a idler gear unless you drill through the "tip" of a gear. I am assuming you drill the holes at the bottom of the Vs. Look at the pic of this idler gear on this Melling Pontiac 60lb pump. What is that 150-160 deg V to V. So the balance will always be out, you are removing weight unevenly.
I
The oil is getting crammed into the hole when the 2 gears mesh. How can there be any positive in- out flow of oil ? I just think if you drill 2 holes oil is getting crammed into both of them and there is no "flow" between the 2 because the hole you think of as a exit hole is getting oil shoved in it every time it makes a revolution in a millisecond.

It works because of the high and low pressure areas in the pump cavity. Not trying to get involved in the arguement, but you asked... Pump theory isn't particular to Pontiacs, or even combustion engines.