Who has had their engine pipes off a big six?

[genphreak]

Engine pipe hardware question that I've been trying to work it out for a while to no avail.

On my M30 the engine pipes have no sealing rings. The tops of the engine pipes -where they connect to the manifolds- are flared and these flares mate to machined surfaces on the manifold output flanges. There are 2 pairs of stainless studs in the manifolds that stick out a good 50mm to allow a bracket to go on each pipe which is then secured by a compression spring and nut on each side of it.

I guess the springs help to manage movement if the pipe is forced is forced yet always bring the surfaces back to square with the right pressure on them to reseal.

Some engine pipes I have seen have flexible joints in them also. I believe many other M30 engined e34s have seal rings instead of bare machined surfaces. Does nayone know why various cars are different?

Mine is RHD, but I believe this is not the only factor.

Many thanks, Nick


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Here is the bit I am talking about, I expected it to have seal rings, not mate straight up bare and use a pair of springs to load the surfaces.

[Rustam]

Engine pipe hardware question that I've been trying to work it out for a while to no avail.

On my M30 the engine pipes have no sealing rings. The tops of the engine pipes -where they connect to the manifolds- are flared and these flares mate to machined surfaces on the manifold output flanges. There are 2 pairs of stainless studs in the manifolds that stick out a good 50mm to allow a bracket to go on each pipe which is then secured by a compression spring and nut on each side of it.

I guess the springs help to manage movement if the pipe is forced is forced yet always bring the surfaces back to square with the right pressure on them to reseal.

Some engine pipes I have seen have flexible joints in them also. I believe many other M30 engined e34s have seal rings instead of bare machined surfaces. Does nayone know why various cars are different?

Mine is RHD, but I believe this is not the only factor.

Many thanks, Nick


000000====))====CATS=========RESONATOR===MUFFLER=

^

Here is the bit I am talking about, I expected it to have seal rings, not mate straight up bare and use a pair of springs to load the surfaces.

I disconnected the pipes a few times. My car too did not have the rings as I expected. The springs are used to provide flexible connection in order to keep contact while the engine is allowed to move sideways a bit. The ends of manifolds and the pipes are spherical - for the purpose of providing ability to move while avoiding leaks.
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P.S. I tried to contact you regarding AFM procedure - please take a look at the replies in that thread. Your inbox was full.

[rob101]

they probably changed the design to have the sealing rings to allow them to increase the tolerances. i am wondering what the deal is with the spring. can't really say because i haven't seen what type of nut is on it or how stiff the spring is.
actually just out of interest
how long is the stud? it says here 87 or 95 mm
which might suggest that'd get pretty elongated underheat.
how thick at the flanges each? and the spring is not inbetween the flanges is it?

[genphreak]

they probably changed the design to have the sealing rings to allow them to increase the tolerances. i am wondering what the deal is with the spring. can't really say because i haven't seen what type of nut is on it or how stiff the spring is.
actually just out of interest
how long is the stud? it says here 87 or 95 mm
which might suggest that'd get pretty elongated underheat.
how thick at the flanges each? and the spring is not inbetween the flanges is it?

Rob the studs are awesome SS, they still look new after 17 years. and are 10" as the exhaust flies from the closest exhaust port. They cost a bit from BMW, so check twice before buying them. For the price of 20 studs in Aus, you could ship a set of extractors from the US or get half way to a turbo if you were up to making your own manifold. The nuts are 12mm M8 or so, appear like copper, but are not- or maybe they are some special harder copper/zinc/mix type alloy. They are the same ones as used on the exhaust side of the head (12) and to bolt up the cats (4 more) - that makes up about 20 on a car at like $1.20-$2 each from the Au stealer.

The 4 springs on the other hand are stainless also, also very good quality. If monkeys tighten them to far, time and heat relaxes them and they shorten under the compression, that is the only way they will need replacement.

[joshua43214]

It is very common for cars to not use gaskets or sealing rings at the downpipe to manifold junction. Every manufacturer has has its own method of dealing with engine movement, flex, and expansion. The flex pipe has a shorter lifespan but is cheap to make. The ball and socket type seems to last the longest but it is more expensive to manufacture. Adding a sealing ring to the junction would only shorten the lifespan of the joint, and since it is not needed, they are normaly left out. I like to coat the flared end of things with some high temp copper antiseize, this not only helps the pipe seat easier under spring load, but will help prevent any groaning or squeaking that this type of joint sometimes has.

The nuts are made from a copper alloy and should be replaced each time they are removed, but in practice can be re-used sometimes. They require very little torque to hold. If you can't find BMW nuts, you can use the VW type nuts, or double nut. Either way, never overtighten the nut onto the stud and never use steel crimp or nylon lock nuts.

[Rustam]

Either way, never overtighten the nut onto the stud and never use steel crimp or nylon lock nuts.

Can you please tell why Josh?

[joshua43214]

The nylocks will melt and not hold, the steel crimp nuts are meant for hardened studs in a better environment,such as machinery. They really have no aplication on cars and will often permantly bond themselves to exhaust studs to the point where even heating with a torch will leave a threadless stud. The stainless ones may work ok, but stainless tends to get grabby on even the smallest bur and may cause even more trouble.

If the proper nut is installed, they will seldom seize onto the stud and can usualy be spun right off with a 3/8" ratchet with a sharp snap to break it free.

[Rustam]

The nylocks will melt and not hold, the steel crimp nuts are meant for hardened studs in a better environment,such as machinery. They really have no aplication on cars and will often permantly bond themselves to exhaust studs to the point where even heating with a torch will leave a threadless stud. The stainless ones may work ok, but stainless tends to get grabby on even the smallest bur and may cause even more trouble.

If the proper nut is installed, they will seldom seize onto the stud and can usualy be spun right off with a 3/8" ratchet with a sharp snap to break it free.

Thank you.

[genphreak]

The nuts are made from a copper alloy and should be replaced each time they are removed, but in practice can be re-used sometimes. They require very little torque to hold. If you can't find BMW nuts, you can use the VW type nuts, or double nut. Either way, never overtighten the nut onto the stud and never use steel crimp or nylon lock nuts.

Awesome explanation Joshua, thank you for enlightening me so. Now I know why these nuts came loose- I had put a used one on and obviously this is a bad idea. I guess anti-seize is not necesary on new nuts either-perhaps that is why 2 came loose. But then again, it could be the springs- 2 of mine are deformed so are not doing their job anymore. When I took it to the shop to replace the exhaust they did them on so tight they deformed the springs and ran the nuts up the unthreaded section of the bolt, partially stripping the nuts. I replaced with new nuts but not new springs, they are bloody expensive from the Oz stealers.

Has anyone some spares?? They look ike this (pic is not my car btw, its that E30 with the M70); it shows the studs really well at the top of the pic.

[rob101]

mate i wish i had SS studs on the m50 manifolds
one bloody bastard nut got stuck and stripped a stud so i had to pull the manifold off.
a very interesting setup, i must say i am only familar with 2 flanges sandwiching a gasket myself for the manifold to front pipe joint. (ie M50 and CBR 610 cc engine with a custom manifold (FSAE car))
the expense of manifacture as has been pointed out (because of tolerances) i think is the reason why you see the rings and gaskets on other e34s.
PS after 14 years my studs looked like shite,
just goes to show they didn't make the m50s etc. like the m30 (idol of bmw engine engineering)