I had to remove the right hand side to get the engine in but I'am less than happy with how all pieces seal against the rubber,I have gaps around the side sections and front apron.
The front gap is caused by the engine being to far back in the car,from what I can tell the NOS factory rubber mount is the cause,appears OP's not drilled the holes in the right place .moving the engine forward will improve the fit of the tin but not much
The PO claims these were made from modified 911 tins using original 6 ones as patterns,the workmanship is really good but the fit maybe not so.
I would appreciate if someone could show some pics of theirs or chuck me a link on this subject,thanks in advance.

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Sometimes you have to pull the seal over to the tin and "hook" it under the tins vertical flange.

Yes, you need to mak the rubber fit the tin.
I suspect it's th rubber at fault, not the tin.

Rich

Repro rubber,maybe thats the issue then,not really sure about that,can't see how any other type would close the gaps...just saying.

Mine doesn't fit very well either. Loose on the sides and the tin sits higher than the rubber 'hook" section

I know of two sixes (one a 3.6) that doesn't use cooling tin at all.

Yea but that's not going to help with cooling,I now feel that my stuffs not to bad if it fitted better the engine may not go in with it on ? still not sure.

Thanks appears that way with mine also.

Yes, agreed....that's a really "dumb" move to not use tins on an air cooled engine.
You will run it much hotter than the factory planned.
There is no radiator or water cooling to help.
Your sole source of cooling is the fresh cool air that comes from the top.
The tins keep the hot air underneath the engine from recirculating back into the inlet of the air cooling system.

Exactly,thats why I would like it better,problem may be if I get the tin fitting better the engine may be harder to install?
There not a lot of room to get past the trailing arm mounts as is,thats why I removed one piece to get the engine in.

How about a bead of 1/4" - 1/2" self adhesive weather stripping tape attached to the perimeter flange of the engine tin? Not as nice as perfectly fitting engine tin/rubber seals, but it may help without being too obvious.

This makes me wonder how tight the seal was on cars when originally delivered, or after a few years use, or after 40 years use.

I think you have said what may be the problem:

"The PO claims these were made from modified 911 tins using original 6 ones as patterns,the workmanship is really good but the fit maybe not so."

as per my thread "taken off original six ",this car was in the the OP's garage for a fair while and this car is the only original one in my country.
Yea I had some doubt but he is straight up after my last email to him.

maf914 your last comment makes me think,yep maybe a poor fit from the start,think there must be some owners of factory cars that may comment...well that's what I hope for.

As the first responses said, if all the parts are right the rubber perimeter seal should almost hook under the tins and form a very good barrier.
No tin ? the tin is not there for decoration.

I am a fabricator welder by trade and done many projects on 911 based projects but I don't believe For a second those were refabbed from a 911 sheet metal set way too different..