Thread: A log of my updates on my '32 Brookville highboy

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If you look at the coefficient of expansion for steel and assume a nominal ten foot length for the pipes the movement from a 50F ambient to nominal 180F exhaust temp (higher with CAT's) yields over 1/4" of growth. It's proportional to the change in temperature, so going from a frigid winter day to operating temps is going to be more. Bob, you's will be flexing that vertical mount, and the donut provides very little for isolation with the bolt coupling both rigid parts.

Originally Posted by rspears

If you look at the coefficient of expansion for steel and assume a nominal ten foot length for the pipes the movement from a 50F ambient to nominal 180F exhaust temp (higher with CAT's) yields over 1/4" of growth. It's proportional to the change in temperature, so going from a frigid winter day to operating temps is going to be more. Bob, you's will be flexing that vertical mount, and the donut provides very little for isolation with the bolt coupling both rigid parts.

Are you sure a 1/2"? The table I use, the expansion is given 10 to the negative 6th in inches. Coefficients of Linear Thermal Expansion

Aw, you edited it to 1/4". Mine is a 5' run, so maybe 1/8" for my set up.

Originally Posted by deckofficer

Aw, you edited it to 1/4". Mine is a 5' run, so maybe 1/8" for my set up.

Yeah, I had looked earlier and missed the first digit. 1/4" is not nearly as much of an issue as 1/2" or more. Vibration & noise are more of a concern, and given the other noises on one of these that's not such an issue either...

Originally Posted by rspears

Yeah, I had looked earlier and missed the first digit. 1/4" is not nearly as much of an issue as 1/2" or more. Vibration & noise are more of a concern, and given the other noises on one of these that's not such an issue either...

I agree with you to rubber insulate the mounting. Before I did I had some audible resonant droning at certain rpm.