Tools

I use a special tool to remove the exhaust header nut from the head. This is the BMW tool, (part # 83 30 0 401 758).

There are other sources for similar tools, for example Euro Motoelectrics has a tool.

Exhaust System Mounting Overview

The exhaust system is secured to the engine with a large threaded nut on the header pipe that threads into the exhaust port,

a bracket on the rear engine mount,

and by two Allan bolts into the underside of each muffler bracket at the rear bottom of the frame.

Remove Mufflers

I remove the mufflers from the header pipe by loosening the muffler clamp where the header pipe joins the muffler and then I remove the two Allan bolts on the underside of each muffler that secure the muffler to the frame muffler bracket.

I slide the muffler off the header pipe by rotating it back and forth while pulling it to the rear. An “L” shaped mounting bracket is bolted on to the bottom of the muffler. The bracket is secured to the frame muffler bracket by the two Allan bolts.

Unfortunately, the mufflers are rusty, and one of them has rusted through where it mounts to the header pipe.

Remove Header Pipes

This bike has a Brown side stand on the left side. Consequently the left header pipe clamp is relocated from the rear engine mount and moved forward to the front of the side stand bracket.

The header pipe clamp is secured to the hole in the Brown side stand bracket with it’s own bolt and thin faced shoulder nut. I remove the bolt and nut from the side stand bracket.

The header pipe clamps are bent so the tabs have an off-set to the inside. This allows them to mount flush to the frame, or in the case of a Brown side stand, flush to the side stand bracket as shown below.

The right side header pipe bracket is mounted on the rear engine stud, and I remove it.

There is an extra spacer between the frame and the inside of the bracket that I do not believe is stock.

Each of the exhaust header clamps is stamped with “R”ight or “L”eft as they fit on one side or the other.

Remove Exhaust Header Nut

I use a special BMW tool to remove the exhaust header nut. I insert the tool firmly between the fins of the nut being sure to seat the fins of the wrench as far into the fins of the nut as I can so I won’t break a fin on the nut as I remove it.

I lean on the exhaust nut tool and mine turns easily. But, if it won’t move easily, I use a small maul (2 to 5 Lb sledge hammer) and hit the end of the tool handle sharply. When it budges, I loosen the nut with the tool a bit more.

When the nut seems easy to turn with the tool I remove the tool and slowly turn the nut by hand until it comes loose.

WARNING:
The steel exhaust port threads in the head can be rusted and/or coated with carbon. Therefore, when removing the nut, you can gall the aluminum threads of the header nut and damage the threads in the exhaust port of the head. If you do that, it’s a bad day. 🙁

So, some caution is advised when removing the nut. You should be able to break the nut free with out too much force. If it’s not moving, try a small sledge (2-5 Lb) on the end of the tool’s handle to see it will break free. If it doesn’t seem to move after several sharp blows, assume the aluminum header nut is stuck on the exhaust port threads so applying more force will likely gall the threads. In that case read the following from Bob Fleischer’s site for methods to remove the nut and not damage the exhaust port threads.

–> Exhaust Pipe Finned Nuts

When you break the nut free with the wrench, slowly loosen it by hand. If at any time it starts to get hard to turn STOP. The aluminum threads are starting to gall. Tighten it a bit until it turns more easily. Heat the aluminum nut with a propane torch for a minute or two, and then try again. If it binds up again, see the above link for methods to remove the nut and not damage the exhaust port threads.

When the nut is off, I see the two metal rings that fit around the header pipe to seal it to the head. Their orientation is shown in the pictures below.

I leave the cross-over pipe in place and remove the exhaust header pipes from both cylinders. I use a rubber mallet to tap on the inside bend of the header pipe, alternating between sides, to coax them out of the exhaust ports in the heads.

NOTE:
I took the above staged picture to show how to use the rubber mallet to help move the header out of the head. It was a posed shot and I failed to remove the exhaust header nut as you should do BEFORE tapping on the inside curve of the header. So, remove that nut, then tap, but not so hard you dent the header pipe 🙂

My header pipes slide out of the exhaust ports in the heads after several taps alternating between the two header pipes and several wiggles of the headers as I pulled on them.

Header Pipe Seal Rings Orientation

Here is more detail about the exhaust header pipe sealing rings and their orientation on the pipe and inside the aluminum header nut.

The headers have quite a bit of rust.

I remove the cross-over pipe by removing the Allan pinch bolts and nuts at the bottom of the cross-over pipe. However, mine is missing one of the Allan bolts.

Header Pipe Diameter

There are two size header pipes on the RS bike, 38 mm and 40 mm. By 1983, all the header pipes are the smaller 38 mm size. But on the 1977 and 1978 RS bikes, you could have either size header pipe depending on if your engine was stock, or the “CFO” version. California, Florida and Oregon had state rules for emissions that caused BMW to use a smaller header, among other changes. Usually your engine block with be stamped with “CFO” near the VIN number stamp by the oil dip stick. But, it’s always possible some previous owner changed the heads on your bike and you may not have the header pipes you would expect.

As I expected, these pipes are 38 mm, and that is confirmed by the size stamped on the muffler clamp that is “40 mm”, or 2 mm larger than the header pipe diameter. If you wonder if your bike has the larger diameter header pipe, look at the clamps and if you see “42 mm” you have the larger diameter 40 mm headers.

NOTE:
By-the-way, all the RS heads through 1984 have 40 mm exhaust valves. Only the exhaust ports and header pipes differ in diameter.

Revisions

2019-11-22  Edits and typos.