Here's my delimma (sp?). Got a new Melling HD oil pump. There are 2 gaskets in the box. One looks just like any other T4 oil pump gasket (Kinda square with a big round cut-out in the middle that the pump slides though and 4 small ones at the corners for the studs). The other was under the cover plate and is basically the same shape but has no big cut-out in the middle, only the small ones at the corners and is really thin, almost like parchment paper. Do I use the thin paper one under the cover?

Thanks

Jake doesn't use any. Just a thin layer of Loctite 518 under it and on the cover. You don't want a bunch in the oil pump. Also use it on all the through bolts and case fasteners. Great stuff! It anaerobic so it only sets up where there is no air which makes clean up easy cause it wipes off. It's kind of gooey so it will hold washers on while you're fishing for the nut.

Dave

In Jakes video he shows a gasket behind the pump and between the pump and the cover, both of them coated with Permatex 3H.

Allen

He doesn't do it that way anymore. I juat put mine together with the 518 and no leaks.

Dave

Here's my experience with a melling pump:

I did use the gasket, between the pump, and the cover. Use the thin one. I believe it is just .002 or .003 inch thick. It has to be very thin, as any extra space between the gears, and the cover will cause pressure loss. i believe the max total space is around .oo4 inch, and I try to go less. At a .004 inch max clearance, and a .002 gasket, that means the gears must be no more than .002 below the pump body.

i have found that the steel flat cover on my melling pump, even after lapping flat, did indeed bow up in the middle when the four cover bolts were torqued down. This is bad, as it creates a bigger gap between the gears and the cover (pressure loss). Stock VW Bug cover plates do not bow when torqued down. That is because the VW cover plates are stamped with lips on all four sides, that greatly prevent bowing.

I have proved this with a dail indicator on the middle of the plats as it is torqued down. The aftermarket plate with no edge strengthening bowed up in the middle several thousands of an inch when installed, the stock plate with the raised edges did not bow at all!!! This is very important. That bowing if not addressed pretty much neggates any lapping, and attention paid to gasket thickness and such.

Go buy a stock VW plate with the stiffened sides. You will need to grind or file a little off the engine case for clearance of the new plate. But it is the only way to assure good oil pressure. VW knew what they were doing with the raised edges on their pump covers, the raised edge makes them incredibly stiff to bowing

An other isssue is the aftermarket pumps sometime have the drive tang a tiny bit too long, so much so that you'd never notice it unless you look for it. Too long a tang will mean that the tang will be pressing on the cam gear, and will cause rapid wear. You can usually press the drive tang shaft a bit futher into the gear, to allow clearance, or grind a little off the end of the tang (grind slowly, and dip frequently in water so you do not over heat the tang, and cause it to lose it's hardness)

so in summary:

1. Get the VW specifications for the pump cover to gear cleanance (again off the top of my head about .004 inch max.) This clearance should include the thin gasket, so the .004 inch is with the gasket installed.

2. Lap flat using sand paper on a FLAT surface both the pump body, and cover. Lap the body with the gears installed, so that when you lap, the tops of the gears are dead even with the body (so if you install the cover without the gasket, there would be zero cleanance) Hence when you install the gasket, the gasket thickness will determine the cleanacne between pump cover, and the gears.

3. If you got a flat pump cover, with no raised endges, dump it, it is NO GOOD, uptain a staock VW Bug plate that has the raised edges. Lap it flat (it may not be flat even it new), and install it. you will need some minor cleancing on the cover / engine case to fit.

4. Besure to check the cleanace between the bottom of the gear drive tang, and the cam gear, the tang must NOT press against the cam gear, there MUST be clearance, and aftermarket (mellings) are know to be too long. To fix this, either drive the tang shaft further into the gear if there is room, else carefully, and cooley, grind a little off the end of the tang (not the driven sides ever, they are heat treated for wear resistance).


The oil pump, needs these items addressed to assure good oil pressure, and to prevent wear on the cam thrust.

If assembled without these "blueprinting" items addressed, you will likely have oil pressure lower than possible, which might be ok on a new engine, but as the engine wears it will really start to need that extra "lost " pressure if the pump was not correctly set up.

good luck, let us know if you have any more questions.

PS you will need a good straight edge, feeler gage, and a flat surface to check these things (and a caliper is handy to check drive tang depth)
A thick piece of plate glass can be used as a flat surface, but it should be thick, as glass will tend to bow. Best bet is a surface plate, or a good flat machine tool table.
It can take a bit of time to lap everything down, but the results are the best pump you can install.


dave

Thanks guys. Locktight 518. is it a FLAPS item?