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Old 09-05-2010, 05:14 PM
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Sloppy fitting oil pump?

While trial fitting a pan baffle that fits between the oil pump & rear main cap on a sbc, I noticed that the baffle was an easy fit on the cap, but a tight press on the pump as far as dowel holes are concerned. The dowels were already installed on the cap when I bought the block, and measure 0.246" dia.
They seem to be a tight fit in the cap. The dowels in the pump measure 0.251" dia.
I punched out the dowels in the pump, afraid to pull the dowels out of the cap, and pressing in the larger pump dowels for fear of cracking the cap with dowels that are .005" larger in dia.?
Then when I set the oil pump on the cap and its dowels there seems to be too much slop. I expected some, but it seems to be so much that the drive shaft between the distributor and pump is going to be too far off. I know the .005" smaller dowels are the reason, but I'm still afraid to press the larger dowels into the cap, not to forget that I might have to align hone the mains if I didn't crack the cap.
I have access to a lathe at work, and think that I might be able to make a couple of dowels with a step in dia. from .246" to .251" half way in its length(1/2").(I think this is my best option)
I also have access to a cheap mill, and maybe a .252" reamer to open up the holes in the cap(do not want to!)
I know the drive from the dist. to the pump isn't all that precise and has room for error, but I want it to be as close to centered as I can get it.
The pump is a Melling Select by the way.
Any ideas why the caps dowels are so small to start with? Any ideas as to what I should do?
Thanks for any and all inputs!
ssmonty

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Old 09-05-2010, 05:56 PM
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If it was me I'd ream the cap to .249" for the larger dowels since you have the mill, and press them in, it won't change the main bore any so don't worry about that. Easiest, quickest, simplest solution to the problem. Then ream the pump to .252" for a slip fit where it is supposed to be

The whole problem likely stems from Mellings poor quality control, the holes in the pump for the dowels should have been tight slip fit on the factory cap pins but looks like they got sloppy and didn't want to throw away a run of pumps with oversized holes so they pushed the easy button and threw in some dowel pins..."let the end user figure it all out and make it work".

Never seen a pump come with dowels pressed-in, the dowels stay in the cap normally.

On second thought, a smarter move might be to get a different pump that actually fits on the stock pins the way it is supposed to. Jeesh, Melling sure has gone in the crapper over the last few years.
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Old 09-06-2010, 08:34 AM
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Sorry,
I didn't post the pics that I thought I had in the original post.
ssmonty
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Old 09-06-2010, 09:33 AM
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Thanks for the reply Eric!
Now that you mention it, I do recall ordering another pump some time ago. I had ordered it because I was concerned about the quality of the one I had(Select). When re-attaching the pump cover after changing the spring, I had snapped off the head of one of the 4 allen socket head cap screws. I wasn't even turning it that hard, and besides, I would have thought that I would have stripped the allen head out of the bolt before snapping the bolt in two!!! So I ordered a Sealed Power pump(TRW I thought). When I received it I noticed a "M55" cast into the side. I suspected that it was really a Melling pump instead of the old TRW that I had used in the past. I had heard some bashing of the Melling M55 pumps for being cast thinner than they used to be, and subject to breaking. I decided that I would go ahead and use the Select pump, but swap out the fasteners for some ARP hardware. Well I paid probably $25 or more for the new hardware(pump cover metric as well as the bolt on pick up) making my total for pumps starting to add up to allot more than the $24 years ago for a good TRW pump. Then this dowel thing!
Well, actually I've got another concern. The bolt on pick-up that came with the Select pump doesn't have any adjustment. It's also got a gasket that I'm not to confident in. I wanted to use the pick-up that was specified for my Milodon pan, but the hole in the select pump is allot larger than stock. I'm going have to wait until I get things mocked up again to figure out what to do(make a sleeve and weld, cut and weld,etc)
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Old 09-06-2010, 10:16 AM
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Oh Yeah, I was going to ask something else. I know there isn't a gasket between the pump and rear main cap. Seems like there would be a small leak at the least. Now if I'm using an aluminum pan baffle that bolts between the pump and cap(4 sealing surfaces instead of 2), should I use some kind of sealer or something?
ssmonty
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Old 09-06-2010, 02:08 PM
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Quote:
Originally Posted by ssmonty
Oh Yeah, I was going to ask something else. I know there isn't a gasket between the pump and rear main cap. Seems like there would be a small leak at the least. Now if I'm using an aluminum pan baffle that bolts between the pump and cap(4 sealing surfaces instead of 2), should I use some kind of sealer or something?
ssmonty
There might be a tiny leak but it is inconsequential. The cap and pump bottom are machined flat and seal against each other pretty well, and the baffle will also act like a gasket and indent slightly(like aluminum or copper exhaust gaskets do). Don't use any sealer at this area
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