Shay Exhaust Manifold

[jlakes85]

Hi All,

The plans call for a 1 piece exhaust manifold/header made out of brass bar. The exhaust ports are drilled 0.312 in the cylinder. I want to make sure I get the 6.022ish distance correct on the brass so I don't have to scrap a $50 piece. I'm thinking of using gage pins in the holes and then measuring with a caliper. Is this the most accurate way to measure this distance? Thanks.

-jlakes85

[Bill Shields]

is it the MOST ACCURATE? -> or is it accurate enough if done correctly?

It is difficult to say that using a caliper is the MOST ACCURATE way to do things.

properly done, measuring between pins with a caliper can give you the measurement you need.

you can also set the unit up on your mill, indicate the hole centers and measure the distance that way.

There are other ways, but these seem the most obvious.

[Soot n' Cinders]

I just made some brass flanges for mine and brazed them to some copper pipe. Not quite as space efficient as the brass bar but it seems to be working pretty well so far

[jlakes85]

Hi Bill,

Sounds good. Setting up on the mill is out as the engine unit is complete and running..I was thinking of countersinking the holes in the brass slightly to address being off a touch or two

[Bill Shields]

You have to also consider that the manifold is going to run at one temperature and the base of the engine at another, which will result in a (minor) change in hole centers as things get hot. I don't know how long this manifold is -> and maybe this growth will be unmeasurable, but my experience with industrial pipe fitting generally tends to stay away from rigid assemblies in a straight line that are subject to temperature changes.

Having some 'play' in the assembly will be a help.

[jlakes85]

Hi Bill,

The manifold piece will measure 1.5 wide 0.75 thick 7 inches long. The exhaust holes are about 6.022 apart

[Bill Shields]

if you guess that there will be a 150 degree F difference once the manifold is hot as compared to the bed of the engine, maybe you are going to see something on the order of 0.01" growth of the distance between holes.

Doesn't sound like a lot, but the constant side thrust on the bolts (maybe brass?) may result in a fracture over time.

[Harold_V]

Hi All,

The plans call for a 1 piece exhaust manifold/header made out of brass bar. The exhaust ports are drilled 0.312 in the cylinder. I want to make sure I get the 6.022ish distance correct on the brass so I don't have to scrap a $50 piece. I'm thinking of using gage pins in the holes and then measuring with a caliper. Is this the most accurate way to measure this distance? Thanks.

-jlakes85

If a measurement is critical, a caliper is not much better than a ruler. Calipers, by their design, are not highly precise measuring instruments, subject to all manner of error when being applied. For that reason, the dimension you hope to determine may or may not be accurate. If I isn't, you'll work to the wrong dimension.

If the piece in question can be placed on a surface plate, you can use a height gauge and DTI to determine the actual center distance of the bores in question. That will yield an accurate dimension.

H

[Bill Shields]

Hi Bill,

Sounds good. Setting up on the mill is out as the engine unit is complete and running..I was thinking of countersinking the holes in the brass slightly to address being off a touch or two

I like Harold's idea but I would guess that putting the loco on a surface plate is also out of the question