I'm replacing the header pipe on my '88 244 DL.

I have replaced the header pipe two times previously. Both times the manifold studs at the header pipe came out with the nuts. So I purchased new manifold studs from IPD but they turn out to be for the valve head not the head pipe.

I have found that whenever possible to replace nuts with stainless steel threaded together with anti-sieze. The SS nuts and bolts from the header pipe to cat came out nicely.

The manifold stud nuts took some wrestling to get off with PB Blaster and time. This time the studs did not come out.

I took the old nuts that secure the header pipe to exhaust manifold studs to the hardware store and they match 3/8-16 thread.
I buy SS 3/8-16 thread.

I get under the car and the new SS bolts will not thread onto the studs.

WTF?

I wire brush and wipe down with brake cleaner the studs. That does not help.
I find even the old nuts do not thread on easily but will thread on if I use a socket.
Is this wear and tear on the old studs AND nuts that have changed the profile of the threads?
Am I now committed to changing out the studs?

I went back to the hardware store and checked the original nuts on all the closest metric bolts and nada. The original nut still only threads onto the 3/8-16 bolt.
I double checked all the new SS nuts and they were the same 3/8-16 thread.

In addition, and this does not impact getting the new SS nuts threaded on but, staring at the studs I see the the threaded diameter gets smaller before it reaches the manifold flange.
No I am not seeing the blank knuckle stop.
It is as if the threads go from 3/8-16 down to something else.
Could that happen if someone tightened down with a coarse threaded nut over a fine threaded stud. Or is this OEM?
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1988 244 DL; B230F; LH-2.2; Manual 5-speed (M47)

i suggest you find flange-LESS nuts as they will give you more room for a socket since the nut is close to the weld on the header top to pipe

Noooooooooooooooooo!

Those are metric threads.

10mm x 1.5 is the correct metric thread.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502

you are having a problem because volvo threaded the manifold to accept 10mm x 1.5 tpi studs NOT 3/8 x 16


they are very close, the 3/8" bolt is about 0.019" smaller and the pitch's are very close so the 3/8 -16 bolt will thread in the 10mm x 1.5 but the 10 x 1.5 bolt will not fit the 3/8

you mixed them up in the past

You may have saved my bacon.

I need to go back to the hardware store and check everything all over again AND buy some 10mmx1.5 nuts.

Do you know if the manifold to header pipe stud is 10mm x 1.5 thread on both ends?

THANKS
--
1988 244 DL; B230F; LH-2.2; Manual 5-speed (M47)

Don't go to the Hardware Store.

Go to an AutoParts Store...a local parts store. Not AutoZone or wateever. Preferably a store with an machine shop next door or part of the operation.

They will have metric studs and selflocking nuts of the proper size.

Yes, the threads are the same at both ends. Try to get original Volvo nuts--or BMW nuts both of which are self locking and use a 15mm socket. At a hardware store you are likely to only have a choice of nuts which use a 17mm socket--maybe too large to get a good fit between stud and pipe. -- Dave

Dave,

I found exact match flange nuts at my local hardware. They were supposed to be one grade lower than grade 8 "automotive". No stainless steel available in that size.

If I am somehow struck with an abundance of motivation I'll check with the local BMW shop.

I bailed on attempting to replace the studs. The local dealer could only get them as a special order and I would then have to work on getting the old ones out anyway. My interest in replacing studs was because the studs had unscrewed from the manifold along with the nuts last time. I went the "ain't broke so don't fix it" route.




--
1988 244 DL; B230F; LH-2.2; Manual 5-speed (M47)

Around here, AutoZone sells self locking nuts in that size, grade 10.1