Exhaust Manifold attachment question

[Kidasters]

Last night before going to bed, I was browsing one of my favorite books - Mike Macartney's "BMW '02 Restoration Guide", and I stumbled across this:

"Use copper-coated nuts on exhaust manifold fittings. Nuts should be M8, but with the heads a 12 mm spanner size instead of the normal 13mm. The nuts that BMW now supply as replacements are not correct for the 02 exhaust manifold. If you use these nuts, you may think you have tightened the edge of the nut onto the exhaust manifold, but what you have actually done is tightened the edge of the nut onto the head." (p. 116 of the aforementioned book).

Now - if I read that, it doesn't make much sense to me - unless I think about it the other way around - if you use the bigger nuts, you'll wedge them up against the manifold instead of sucking the manifold flush to the head. Or is it?

So - If I ever get my new IE header in place, what should I use? I didn't want to use the nuts I pulled off, mostly because they look like hell and it would be great to replace them. Thoughts?

Thanks,

Ken

[Guest Anonymous]

somehow I doubt it matters for the reason you give - I bet there's room on the manifold for a 13 mm nut to fit - but there might not be as much room for the socket or wrench to fit, and it can be a bear to get them off. I'd use the 12mm copper with some anti-seize, if I were doing it.

[PeterVarga]

Proper exhaust manifold nuts have a built in anti-loosening feature. The skirt of the nut has metal parts that actually grab the stud and prevent backing out like a lockwasher They are typically 12mm and you actually need the room to get the standard box wrench around the backside of it....not enough room for a 'gear-wrench' and with all the ratcheting you need to do in that very cramped location it would be the perfect tool if it fit!

[RandyMolson]

The nuts are single-use items. They are relatively cheap from your BMW stealership or the OEM parts suppliers like Blunt or Mobile Tradition.

[Kidasters]

Thanks all. I bit the bullet and found some copper exhaust nuts (12 mm) on the web. Bought them today.

The parts train towards my house just keeps getting longer and longer.

Ken

[TobyB]

For the header on the race car,

(a custom floater Stahl)

I have had better luck with the 11mm nuts (also sold on Ebay)

for VW's. I only use them on a couple of

harder- to- access studs, but they work well.

What McCartney means is that the 13mm BMW nuts

tend to bind on the flanges of the manifold, and don't

bear squarely on the pad. Then they bend the stud, and

tend to either loosen, leak, or cause the stud to loosen.

t

[TobyB]

For the header on the race car,

(a custom floater Stahl)

I have had better luck with the 11mm nuts (also sold on Ebay)

for VW's. I only use them on a couple of

harder- to- access studs, but they work well.

What McCartney means is that the 13mm BMW nuts

tend to bind on the flanges of the manifold, and don't

bear squarely on the pad. Then they bend the stud, and

tend to either loosen, leak, or cause the stud to loosen.

t