Forum bmwbike.com

Has anyone done away with the crossover pipes on the /2 exhausts? If so are header pipes for the R69S available without the crossover outlets? It just seems that if the engine would run Ok without them, then exhaust fitting and even more so, removal, would be so easy.

Fitting and removal of the exhaust pipes is not hard if they fit properly. I have had a couple of stainless steel pipes that did not fit well and required force. On one in particular, the stubs for the crossover pipe were pointing downward a little. I don't think the stainless steel manufacturers have very good jigs.

The two Huggett chromed steel systems I bought in 2000 and 2004 fitted perfectly.

Good to see you at Founders Day Jon, sorry we didn't talk for longer.

I'm sure BMW would not add a complication (hence increase production costs) to their bikes without just cause. It is interesting to note, however, that all the plunger-frame models, including the R68, had no balance pipe fitted, yet they seem to run perfectly satisfactorily. Why do some "modern" post-'69 bikes have two balance pipes?

One can only guess, but I believe it might have something to do with softening the exhaust note. With no balance pipe the exhaust gasses are ejected one by one through a single silencer, giving quite a 'vintage' bark to the note. By utilising the second silencer the exhaust gasses from each cylinder have in effect double the internal exhaust system capacity, allowing only half the expansion into atmosphere through each silencer, and it is the expansion into atmosphere that makes the noise you hear.

You could say by comparason, listen to a BMW single, which is in effect half an R50. The trouble there is that the R26/27 silencer has been designed to meet the same noise legislation as the twins. If you were to fit a twin silencer on to a single I think you might notice an increase in exhaust noise compared with that of a twin.

I'm sure we would both appreciate other theories on the matter.

Gerry

Likewise nice to see you and the smart looking R50 of yours on the BMW stand, Gerry. Incidentally, I must have the oldest intact chrome R69S exhausts around-bought them from Frank Cox in 1980 and still on the bike. Mind you I have done a small mileage due to other probs on the bike which are now being resolved hopefully.

Gerry, I have some plunger twins including an R68 with balance pipes, the R68 parts book that I have shows balance pipe.
Your note that no plunger models had this has me interested to know if my bikes are fitted with wrong pipes.
I live in Australia, did we get different models here?? Hope to see reply.
Best regards Geoff in OZ.

I know that the R5-R71 prewar bikes all had crossover pipes.

Crossover pipes provide some "scavenging" (the exhaust pulse from one cylinder creates low pressure via the crossover in the other) which improves volumetric efficiency.

Best regards,

Bruce