'48 Cub Project: Question on Bore size

Sat Oct 09, 2004 9:29 pm

Well, I'm out in the shop working on the block. It had stuck pistons in it, so I thought I'd just run a hone up and down a few times before using my dial bore gauge to see what size the block is, along with how much taper. I figured it would be a bit oblong and worn, but here's what's got me confused.

The specifications in the manual says the bore is 2 5/8", which would be 2.625". However, up or down, high or low, the highest measurement I get is 2.6225", and as low as 2.619".

So, what IS the bore supposed to be? There is some taper, and a few pits that I figured to require +.010" over bore, but I need to know what bore the new pistons would require. Is it 2.625".....or something else?


Sat Oct 09, 2004 10:26 pm

Frank. The Cylinder bore specs are 2.625 +.002 -.000. Don't know how you got a measurement of 2.619?? How did you set your dial bore? With mics? Did you calibrate everything? Did you measure over rust or burrs? The specs for the pistons are 2.623 +.0004 -.000. What do they measure?

The specs also call for re-boring IF the out-of-round or the taper up & down exceed .005. Standard rings come at the standard 2.625, and also +.020 and +.040 for oversize cylinders.

Hope this helps.............

Sat Oct 09, 2004 10:50 pm

Where is a good place to get oversize rings??

Sat Oct 09, 2004 11:01 pm

l0 wrote:Where is a good place to get oversize rings??

Your local Case / HI dealer should have them. P/N539354-R1. Also, Carter & Gruenewald ( 1-608-455-2411) or "Joe's Farmall Parts" (1-814-226-6214) have them. Probably many other places............

Note: Just checked my TC 37F Parts Manual.... It lists 539354-R1 as standard (2.625). 539355-R1 as +.020, 539356-R1 as +.030 and 539357-R1 as +.040. I'm not sure about the o'size p/n's availability (especially the +.030) as I have only purchased the standard size.

Hope this helps.

Sun Oct 10, 2004 9:34 am

I'm dead certain that my bore gauge is within a tenth or two. I have both a 2" and 3" standard, then I checked my mike and set it to 2.600" , then used the mike to set the bore gauge to zero.

All I can figure is that the bore has some raised metal from the rings or corrosion, but it's pretty consistent on measurements. I guess I'll hone it some more and then check some more. I only was able to salvage two pistons, but I'll measure them next. It's still a mystery to me. This engine must not have had much wear before it was parked.

Sun Oct 10, 2004 10:12 am


I'm sure you are familiar with taking the measurements, but have you considered using a telescoping gauge so you can use the same mike you use on the pistons? I find that repeatability can be very good with the telescoping gauges by dragging them over center one time so they find the exact diameter.

Just another way to confirm the numbers you found.

Sun Oct 10, 2004 10:33 am

Well, DUH!

For years I had a dial bore gauge which had a linkage for direct measurement. You know plus was bigger and minus was smaller. HOWEVER, did you know that on this gague, when the dial goes CCW, the bore is getting larger?!? Go figure!?!

So, moving from +.025" to +.020 means the bore is increasing. The measurements are such that there is from .003", to in pitted areas, upto .006". Now I'm going to measure all the cylindricity to determine if .010 overbore will get it. I'm begininning to think that I'll need to go .020" to be certain to get any and all pits. Anyway, it costs the same to go .020" as it does .010"

Sorry for the wolf crying. I just had a brain fart.

George: I can use this gage as a telescope gauge, by taking a reading and then turning the mike in until it reads the same. That's how I figured out what I was doing wrong. :oops:

Sun Oct 10, 2004 10:48 am


I have the exact same situtation, I first measured with a "shop" telescoping gage and a dial caliper, got the same confusing reading, so I cleaned a little bit and remeasured with a gage from my machine shop and a calibrated micrometer, got the same range of measurements. The block I am working shows no signs wear at all so I figured it must have been a slightly undersized new factory short block that fell victim to a bad head gasket.