cylinder wear

[mycall]

The specs say .004 clearance between cylinder and piston in an ace 100. Is that on .002 on each side or .008 overall? And where is the best measuring points for wear and taper in the cylinder? Above the ports or down to the base also?

[thrownchain]

That's the difference in outside piston diameter, and inside cylinder diameter. Measure both and there should be. 004 difference.

[thrownchain]

90 degrees from the wrist pin, the cylinder in several spots top to bottom.

[mycall]

Thanks for the info. Does anyone know the Dia. of a stock ace 100 piston. In inches if you could.

[---]

Specifications are all posted on the Strictly Hodaka website under each models schematics. 100's were 50mm. Metric conversion is available on the Internet. Just Google metric conversion. Keep in mind that manufacturing tolerances grouped new pistons by variance, so they were not necessarily precisely 50mm anyway. Thats why each piston is fit to the bore, or rather, each bore is fit to the piston being installed, depending on actual dimension of that piston.

Most folks will use a feeler gauge to determine fit, and they are generally marked in inches. So 0.004" is the clearance no matter what the actual dimension of piston and bore, and no matter what oversize the bore may be.

[thrownchain]

I don't find the feeler gauge method as accurate is it should be, find someone who can do the measuring, it pays to be that accurate.

[ossa95d]

I agree with Dan. When measuring the bore and the piston the same measuring tool should be used. If a telescopic feeler gauge is used to determine the bore, the same micrometer can be used to measure the piston and the telescopic feeler gauge. That is the most accurate way to determine the difference between the two. We do this when boring a cylinder so we can finish sneaking up on the proper piston clearance with a hone.

[---]

And I disagree. First of all, there is a range of clearances that will work that is far broader than any variation attributable to the use of a feeler, the piston isn't round to start with, you can't be sure you have measured the piston skirt in the same exact spot as it would go in the cylinder, and telescopic gauges are technical tools for machinists, not field gauges. Accuracy is not called for here to the nearest ten thousandth of an inch. Instead, a person needs to learn their own tools and use them consistently. I let machinists use bore gauges. Then I use feelers to verify their work in pass/fail mode, have done so for fifty years, and I don't worry about it because long ago I learned how to use the tools I have, including bore gauges. You can spend all day measuring telescopic inside gauges, and rechecking, and rechecking. Or, you can lightly lube the piston and cylinder, slip the piston in right side around, and check skirt clearance top, middle and bottom in about thirty seconds.

My guess here is that the OP is not setting up an engine for a land speed attempt. A common feeler gauge is more than adequate.

[ossa95d]

Greg,
I have been thinking about this and will acquiesce to your position. Hodakas are perfect for owners to work on themselves and very few owners would have a set of machinist's telescopic gauges in their toolbox. A quick check with a feeler gauge will allow the owner to discern whether the piston is close to being within spec or not. Just because I am anal about certain things doesn't make it right for every person or application. I will continue to use the method I spoke of when boring cylinders. Thanks for setting me straight.

[taber hodaka]

I like the man or persons that bore it to be on the mark, spot on for what I requested the bore and fit to be. At the shop we always used a feeler gauge, checked at the top and bottom of the stroke and when fitting rings checked end gap at the top and bottom where the ring would be when the piston is down. easier to check with a narrower gauge.-------------Clarence

[Kels]

I think people may be forgetting that the piston is NOT a perfect cylinder. It is cam ground and is tapered from the top to the bottom.. So depending where you take your measurement with respect to the piston position will dictate your clearance..

MOST pistons are round at least to the skirt cutaways.. Some a tad higher, some lower..

Measuring clearances at any position above the wrist pin will lead to a larger measurement value.

Feeler gauges are not so accurate.. since you have to accommodate for rocking and other geometry.

In my opinion, the only way to get a true measurement is to use a bore gauge to measure the bore (the bore should be round from top to bottom) and then use a micrometer (not a caliper) to measure the piston at the lower skirt. Subtract the 2 numbers and that will be the clearance.

[---]

I am not sure but we are all saying the same thing even though we don't think so.

For the machinist doing the bore job to use a feeler gauge would be silly. I would expect a machinist to use precision gauges. But once it is bored and presented for reconstruction, checking with a bore gauge is decidedly overkill, and just what would it prove anyway? Would you reject a bore job because it was over-cooked by a half a thousandth? I think I already mentioned that pistons aren't round to start with and most folks who have been paying attention would already know that they are not. The point was, however, that because they are cam ground, just exactly where you take your measurements dictates results. What if you measure a little to the left or a little higher or whatever from where the machinist measured? How many measurements do you take? Do you average results, or keep measuring until you come up with the same answer more than once? You would be chasing phantom numbers that would make no difference whatever in suitability for use.

As for feelers, if you really want to limit error, take your favorite feeler and trim it down to a millimeter wide, but if you do, use it with care because it will be a bit brittle. Myself, I don't worry about it. What I want to know is whether the clearance is 0.002" or 0.005". For this, a feeler is fast and reliable. Besides, I don't do bore work and haven't for forty years. It takes practice and expensive equipment, which I don't have. Telescopic gauges and micrometers I do have because they came with the lathe I inherited, but I don't use them on motorcycles.