8N 1948 engine rebuild

tom.rockwell18 · Mar 5, 2017

I pulled the sleeves out of my 1948 8N. It had the thicker .090 sleeves. I kept the sleeves out and put in the V8 flat head pistons (.188 over). Now when the pistons come up they're
hitting the fire rings in the head gasket. I know they're clearing the head, it's just the head gasket.

If anyone knows a way around this problem that would be very helpful.
-Tom

showcrop · Mar 5, 2017

Sounds like the head gasket is strictly for a sleeved motor and that you will need to get one custom made.

Steve@Advance · Mar 5, 2017

If the gasket is hanging that far into the cylinder it will probably not seal properly and will soon fail even if the pistons didn't hit it.

You'll need the proper gasket.

Is this a common modification? If so, a gasket should be available. Any idea what the compression ratio will be?

Roger in Iowa · Mar 5, 2017

Possibly get a head gasket for a Mercury car. I think they had the same bore but without sleeves, but might not have been for those bored .090 over.

Roger in Iowa · Mar 5, 2017

What were the oversize pistons from? Head gasket from same should work??

Den N Ms · Mar 5, 2017

Tom,What did you do about the counter bore for the selves in the top of the block? You may have to put selves back in it.I don't think having that selves counter bore in the top of the block larger than the piston bore would be the best,nothing for the fire rings to seal against. It might also have sealing problems between the pistons and blow head gaskets faster than you could change them.Only other thing to do would be to have some steel rings machined to fill that counter bore cut with groves cut in the top of them for some stainless wire orings,and make a copper head gasket from some say .040 -.060 sheet stock.Best would be to put new available .090 selves and new pistons back in it.As the HP increase with the larger pistons you put in is minimal.

longcases · Mar 6, 2017

I had the same problem when I did that to my 2n. Most gasket manufactures have head and manifold gasket material in bulk. I bought a roll and made my own. Most parts houses wont know what you are talking about so go to a machine shop and ask there. Lay the old gasket on top and trace it over to the roll material and cut it out or sand which the material between some hard board and drill through, then use a tin snips to cut you cylinder size TO fit, did mine ten years ago and it is still running.

Indiana Ken · Mar 6, 2017

Tom,

I have been thinking of doing this so I am interested the solution you come up with - if you could post back please.

The gaskets from the V-8 will not fit the 8-N application. The V-8 has the center two exhaust ports running between those cylinders where as the 8-N does not. Sorry, I do not have a gasket supplier to suggest.

As a comment: The 8-N had a compression ratio rating of 6.5:1; reference operators manual, copy right 1950. Increasing the engine displacement by the 0.188" overbore will result in an increase to 7.2:1, assuming the same piston dome configuration and deck height. However, since your pistons extend above the block deck surface your compression will see an additional increase.

Mike M · Mar 7, 2017

The cylinder walls of those blocks are so thin I don't see how that could be a good idea to do ?

8N 1948 engine rebuild

tom.rockwell18

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showcrop

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Steve@Advance

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Roger in Iowa

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Roger in Iowa

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Den N Ms

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longcases

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Indiana Ken

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Mike M

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