Manifold gaskets - early vs late - what's the diff

Just wondering what the difference is?

Getting ready for going to Memphis this weekend and have just discovered that the manifold gasket seems to have blown on my 77 right up front by air intake (I have stock everything with all emissions and original ZS carb).

Of course I have a spare gasket for my 72 but both Moss and VB list different part numbers for the gasket on the 75-80 assuming you've got the ZS and combo intake/exhaust manifold.

Obviously wondering why i couldn't just use the early gasket (Moss 296-410).

I'm guessing this may be caused by the pop, pop, pop I get on deceleration. It only happens when starting up from cold. Once warm it goes away except for an occasional pop. Any thoughts on the popping cause too rich or too lean? People have said lean but with the choke on that seemed odd (original water choke - idles at 1500/1600 until choke goes off).

Ideas & or info?

Thanks

Simon

I've wondered that too to the point that I compared the two and evidently I am real dense as the difference totally evaded me.

well, Chris...I'm glad to know that. because i couldn't see a difference either!

Since the ports in the head are in the same place....and the studs are in the same place...and the earlier manifolds are interchangeable...I can't imaging why on earth the gasket would have to be different.

BTW, I'm looking forward to meeting you this weekend! Look me up - I'll most likely be at the computer during registration and judging, or taking photos pretty much all weekend....

Well starting to look like I should have been out there pulling crap off all night instead of wondering what the difference is. I also noticed Moss had a High performance version and mentioned it for all A's & B's.

I guess I'll have a busy night tomorrow swapping it out so I can be up early on Friday for the convoy.

Simon

I was wondering if the material was different. There did seem to be maybe a small difference in the not important dimension between the ports but that could have been due to manufacturer difference.

That there tells you that whatever the diff is, it is not important.
The high performance version is what Sean Brown sends with his heads; a gasket of different than usual material that can be used well with headers as well as stock apps.

From what I have seen, the one for the later cars was metal faced (toward the manifolds). The earlier gasket used to be all gray in color with no metal facing. Now when ordering the early gasket, I always receive the later metal faced gasket. So from what I can tell, they are supplying the same gasket no matter which you order.

Well, there ya go! And Sean's special gasket is the whitish kinda cardboardish thing that allows for variation in fitment. A good idea.

My preference has always been the earlier gasket, without the metal facing. Anyone know where to find those?

What is BEck/Arnley providing these days?
Or, you could go with Sean's gasket which I think comes from Moss. It is not what you originally described though.
The Payen head sets do come with the corrugated foil on one side, but it seems that IIRC if you order just the manifold gasket from Moss, you get the grey on both sides gasket. Or you did some time not too far back.
Call and ask what they serve!

If you are dense then I am more than just dense...solid. Dense is better than transparent!!!

When talking about header gaskets, you are correct! :)

AHHHH I figured out the diff..... the later gasket is almost twice the price of the earlier one...lol

I have a gasket out of a 79 head set on my 67 engine, nothing has broken, leaked or fallen off yet so it seems to work. :)

To answer your question!

Yes, the popping may indeed be the gasket. Almost certainly if the popping is on overrun! It actually draws air into the exhaust which puts enough oxygen in to cause the unburnt fuel to ignite. A new gasket will solve it.

My guess on the difference in the gaskets (it is just a guess), is that the later gasket is the foil-faced one, designed to take the higher heat of a leaner running engine with a cat converter. The actual shape of the gaskets is the same.

Thanks to all for the input - I have my activity for tonight planned - packing will come after the manifold gasket replacement! ;) Who needs clean clothes at a car show anyway!

Thanks Eric for the popping input. It's been doing it for a while but I just put it down to it being on the choke since it then went away. We'll see if it's just been the gasket going slowly.

Hopefully see some of you in memphis and I'll report back to update the thread for searching purposes.

Simon

Well we seem to be back in business - thanks for the info/advice.

It took about 2 hours to get it all done and then I spent and hour dicking around with a busted hose from the front side cover to the carb. 30 mins getting 3/8 hose that was too small and then another 30 mins getting some 1/4 inc that worked :)

Quick test drive and everything seems to be fine. Still a little popping when warming up but slightly less I think. Tomorrow will tell for sure. But not blowing and indeed the top corner of the gasket was broken on the edge up by cylinder 1.

I'll update with some pics at some point but time to pack for Memphis now! TTFN

Simon

No worries Simon, we will be accompanied by the truck with the MG tow frame, you won't be stranded. :D

I spent the evening fitting cup holders getting ready for the trip.; :D

Just to close this out - a picture of the emerging broken gasket

And to compare the old gasket with the new. I couldn't see any difference - maybe what I had on there was the older style gasket anyway.

It worked either way.