Cylinder Measurement/Tolerances
 

I am defining the process of measuring a cylinder. I understand the process of visual inspection for scratches and scuffs. I am trying to learn more about the measurement process.

I have Wayne's book. What is the difference between "nominal diameter" and "cylinder diameter"?

Wayne's book shows measurements at four different measurements. Two are at the top of the cylinder, just above the cooling fin (a cross pattern). And two are where the smooth part of the out cylinder wall start.

Using this information, what is considered a fail number?

Thanks for any help.

James

It is two measurements top and bottom at right angles. You are checking for taper, and out of round. Generally speaking, if you have 0.002" inch or more of either, the cylinder is worn out.

Correct...I Should edit it. There are four measurements.

The above is in inches? Are the measurements in Wayne's book not in Metric?

True, I am using inches. I am giving rounded off numbers. All of my old school measuring stuff is in inches. I made some notes in my Wayne's book converting to inches. IIRC the new specs are something like 0.0015" out. The wear limit is something like 0.002". If you are reusing rings, pistons and cylinders and are close to 0.002" taper or ovality, it would be time to make some decisions. Much over that and you would probably be wasting your time, if you wanted a motor that would not smoke and would last.

I would think an inexpensive bore gauge should work?

Nikasil when worn doesn't get a ridge like an iron cylinder, it gets wavy around the last 3/4" of the top stroke. It can also bellmouth (Fish mouth) the bore as well.
The Nikasil can "look" good and still have these issues.
My 3.0 cylinders were like this.

You don't need to spend a bank account on a bore gauge but you do need to ensure the dial indicator for the gauge is sufficient. You need one that measures 0.0001" increments, not the cheaper 0.0005" increment. Fowler makes a decent bore gauge kit but their included indicator gauge is only a 0.0005" unit. I bought a replacement 0.0001" indicator to "upgrade" my Fowler kits

In order to set the bore gauge you also need to have a decent micrometer (also 0.0001" resolution) because the inexpensive bore gauges are comparator style, not direct-reading.

I have been using the bore garage available from Eastwood for about 10 years now. That gauge, combined with a good micrometer set I bought on EBay, provides sufficiently accurate and repeatable measurement on cylinder and case bores. A great tool.

Thanks guys. I will look at them.