741 Scout Cylinder Bore Question

[JTR249]

I measured my cylinders 93346 and 93345 today and see that each are close, though still not standard 2 1/2" as listed in the 741 manual.
My question is, am I seeing normal wear or is this an example of an oversize bore? If so--how much? Is it +.030 since that is the approximate difference as standard bore is 2.50" for a 741?
I measured each cylinder with a digital micrometer and saw cylinder 93346 is 2.857" and cylinder 93345 is 2.866". I took the standard bore and subtracted it from my digital readings.
With a standard tape measure the distance is 2 and 7/16" bore.
-JR

[T. Cotten]

A digital micrometer, JTR, is great..

Are you using it with telescoping boregauge, so you can measure for taper, out-of-round, and other signs of wear, throughout the bore?

My 741 cylinder experience is minimal, but I observed unusual wear at the bottom of cylinders, where there are no fins, as if somehow the walls were too thick.

I would encourage a healthy over-bore; It would probably be more fun to ride as well.

....Cotten
PS: I lied, I hate digitals.

[RichO]

Problems on Indian cylinders are healthy over bores come closer to the valve seats and cracking can happen.

[tfburke3]

Problems on Indian cylinders are healthy over bores come closer to the valve seats and cracking can happen.

Sometimes true but not for a 741. 2 3/4 "jr scout piston will fit in with no valve seat problems and was a common upgrade over stock 2.5"
I considered this for my 741 since I aquired nos std jr scout pistons which were more available than oversize stock bore.The problem .
I think,is if you look at the 741 manifold , carb and valves they are really small,like lawnmower size,so I dont know if there would be much gain.
Tom

[JTR249]

Interesting points from each of you. I only know that my digital micrometer is a digital micrometer. I have never heard of a telescoping boreguage, though I think I understand the concept.

Could I try different sized pistons to see which type comes closest? Would that help narrow the possibilities?
The difference between the linear measurement of the standard bore and the actual measurement in linear method is 1/16" difference--if my math is correct.
Taking readings from these tools is not easy when you don't know what you get in used parts.

Thank you both.
-JR

[Jerry Wieland]

Interesting points from each of you. I only know that my digital micrometer is a digital micrometer. I have never heard of a telescoping boreguage, though I think I understand the concept.

Could I try different sized pistons to see which type comes closest? Would that help narrow the possibilities?
The difference between the linear measurement of the standard bore and the actual measurement in linear method is 1/16" difference--if my math is correct.
Taking readings from these tools is not easy when you don't know what you get in used parts.

Thank you both.
-JR

Not the best way. You really need to measure to get an idea of taper. Jerry

[JTR249]

Thanks, Jerry. I'll go back to the books.
-JR

[T. Cotten]

Interesting points from each of you. I only know that my digital micrometer is a digital micrometer. I have never heard of a telescoping boreguage,...

A telescoping gauge is tedious to use, JR,.

s-l1600.jpg

Because you have to set it to length in the bore, and then measure with your micrometer, at many places in the bore, to determine wear, taper, or concentricity problems.

A dial boregauge is far quicker and more accurate.

s-l400.jpg

....Cotten

[JTR249]

Thanks, Cotten. I will see what I can find.
-JR