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My recent acquisition ; an '81 R100RT has some very corroded header pipes especially at the joins with the balance pipes, front and rear. I am wondering if I replace them, should I go with front and rear balance pipes or just the front, will it make a big difference? I have seen inconclusive debates elsewhere on the internet as to the actual function of the rear balance pipe : mid range power, noise reduction or just to make it more difficult to remove and replace.

I cut my rear balance pipe out. Still goes like the clappers.
Staintune are the ticket if you can afford $700 for stainless. They will make single or dual crossover headers.

The second balance pipe was introduced primarily to tailor the power curve. The main measurable effect was to bring the peak output down a few hundred RPM (in fact within the red line). The effect on the rideability of the bike is difficult to assess because there were so many small changes around that time including the change in the clutch/flywheel which definitely affected the subjective feel of the power curve even if it didn't affect the power output of the motor. I think you'll see little subjective difference from fitting twin balance pipe headers. Getting away from power issues, the twin crossovers certainly make the headers more difficult to fit and, more especially, to remove. I suppose really, it depends how 'stock' you want to keep your bike... and how often you feel the need to pull the headers.

Rob

my R75/6s only came with 1 cross over pipe, have ran well for 40+ years do I need 2

richard t wrote: ↑Thu Dec 19, 2019 4:47 pm my R75/6s only came with 1 cross over pipe, have ran well for 40+ years do I need 2

No... the 75/6 was designed with one and runs perfectly well like that.

Rob

I actually had to cut the two decaying cross over pipes to remove the headers from the engine. The headers themselves are pretty rusty but may be useful some time in future. A bloke on Gumtree sold me a single cross over set from an R90. I'm still waiting for them to arrive from Western Australia.

dirtsurfer wrote: ↑Thu Jan 09, 2020 5:58 pm I actually had to cut the two decaying cross over pipes to remove the headers from the engine. The headers themselves are pretty rusty but may be useful some time in future. A bloke on Gumtree sold me a single cross over set from an R90. I'm still waiting for them to arrive from Western Australia.

Pretty sure that you should have no problem fitting them... I believe the 1981 1000cc engine has 38mm headers the same as the R90s. Some of the early 1000cc motors have 40mm headers which could make it a bit tricky.

Rob