What seals the oil pump to the block on a flathead?
 

Obviously, there is a cutout that appears to be a place to put an o-ring on it. I don't have an o-ring in my rebuild kit. I don't remember a gasket under the mounting surface. Only one bolt holding it in place would also not be ideal to seal with a gasket.

So, is there an o-ring that seals the pump to the block?

Re: What seals the oil pump to the block on a flathead?
 

No. The only thing that seals it is the fit between the block and pump housing.

Re: What seals the oil pump to the block on a flathead?
 

No seal there that I am aware of....not necessary. On the later pumps there is a small gasket that goes between the pick up tube flange and the oil pump body.

Re: What seals the oil pump to the block on a flathead?
 

No O ring or gasket. If it leaks, it just goes back to the pan. The whole thing is strange. There is no pressure lube to the back cam journal. It just gets a spray/mist coming out of the top of the oil pump. The idler gear also gets the same oil and throws it on the cam gear and then it goes to the cam. The fuel pump push rod has no pressure either.

Re: What seals the oil pump to the block on a flathead?
 

As stated above there are no seals or gaskets between block and pump. This can be source of pressure loss with aftermarket pumps. However, if you have ever tried to remove a well used Ford pump you understand the fitment is rather tight and will not leak excessively.

I have welded and machined o-ring grooves to get a better seal on a test engine oil pump but the results were disappointing from a gauge observation viewpoint. Initially I thought the Melling pump allowed too much clearance but I was not able to quantify any improvements with the modifications.

Re: What seals the oil pump to the block on a flathead?
 

All depends on which vintage engine you are talking about.

Re: What seals the oil pump to the block on a flathead?
 

Try not to over think the Flathead, there's not much you can do to improve it. Designed in the late 20 and produced in the early 30's, it was a "State of the art" engine winning several awards for designed. In 21 years of production the basic design never changed. And the sound has never been duplicated by any other engine, something nobody can improve apron

Re: What seals the oil pump to the block on a flathead?
 

I have only owned one flathead and burned sludge is what sealed my oil pump to the block. I almost never got it removed.

Re: What seals the oil pump to the block on a flathead?
 

I could never get my oil pump off my block. on my model B 4 banger engine. .When I dropped the pan, It hung there glued to the block by 80 years of whatever. I tried to remove it but didn't want to break it. I was able to clean the screen on the oil pump with 100s of worthless 1980s baseball cards..the only thing they were ever good for.