Ace Cylinder Dimensions

[viclioce]

OK. I got my micrometer and these are the figures for my Ace cylinder & a lightly used std piston.

Piston dimensions
Top across center = 49.91
At wrist pin =49.91 (perpendicular to pin)
At skirt = 49.75

Cylinder at top = 50.12 side to side
50.49 front to back
Bottom = 50.60 / 50.53 /50.63

So this means there’s a .21mm clearance for the piston w/o rings in it at the top of cylinder & I have a lower ring I can put on but not a top ring. A .21mm clearance equals 1/64” or .015625” of clearance, after checking the conversion.

So does this sound like demensions I can just buy std size rings for and still use? Does anyone want other dimensions? Let me know!

Also including a picture of the piston. Piston was free. It’s used but in good condition. Have a second std size used & a .020 over used as well which I haven’t cleaned yet. Thanks!

Next I’ll pull the top end off the Combat Wombat and provide dimensions for that piston/rings/cylinder combo as well.

Victor

[viclioce]

What? No info??? I was hoping someone would answer ........ Victor

[thrownchain]

If those numbers are correct, the clearances seem a little tight.

[Dale]

Victor, what tools are you using to make these measurements?

[taber hodaka]

victor whatever reading you get I would take the item to a machine shop and have it verified?? I only use a feeler gauge for ring end gap and also for clearance to cylinder. With probably 100 + /- rebuilds and have not had any problems. Clarence

[Bullfrog]

Reviewing your numbers reveals some questions.

1. At the top of the cylinder the fore-and-aft and side-to-side measurements differ by 50.49mm-50.12mm=.37mm(.014") -- So the bore is "ovaled" by .014" (which seems like a lot of "out-of-roundness") This seems to be an indication of pretty extreme wear.
2. The fore-and-aft measurements from the cylinder top and bottom are as follows 50.53mm-50.49mm=.04mm(.0015") At only 1 and a half thousandths of "taper" - this seems to be an indication of almost no wear. Hmmmmm . . .
3. The fore-and-aft measurements of the piston at the wrist pin and skirt seem to indicate a lot of wear. 49.91mm-49.75mm=.16mm(.006"). On a new piston, the skirt diameter fore-and-aft at the bottom of the skirt should be the largest OD found on the piston - though not by much. Example - a NOS piston in basement gave the following comparable numbers for fore-and-aft measurements at piston pin height (49.95mm) and bottom of skirt (49.99mm). A difference of .04mm(.0015"). So, on my new piston the skirt is larger by .0015" -- and on yours the piston skirt is smaller by .006" . . . that doesn't seem good.
4. Finally, the difference between the fore-and-aft dimensions of the piston skirt and the bottom of the cylinder is 50.53mm-49.75mm=.78mm(.031") - this seems to indicate a LOT of clearance. Most folks would recommend max. clearance of about .008", and your numbers indicate almost 4 times that much clearance.

Summary - I think your measurements need confirmation. It doesn't make any sense to have an egg shaped bore which has almost no taper from top to bottom. And at .031" clearance, old timers would be telling jokes about the piston traveling as far fore-and-aft as it does up-and-down.

NOTE: Everyone starts somewhere, but taking dependable, repeatable, accurate measurements down to the neighborhood of .025mm(.001") takes some considerable practice. Measuring technique is very important - ie, you must develop a "feel" for measuring perfectly perpendicular to the bore axis of the cylinder/piston AND you must develop a "feel" for the same tightness (every time) of the micrometer on the item. And let's not even go into the "feel" required to use ID gauges and then measuring them to get the bore dimensions. Sooo, since you are on your own . . . take the measurements again, and again, and again until you get the SAME measurements in the important places. You'll get that practice mentioned earlier . . . and you'll work your way "in" on the correct measurements. THEN, you can analyze what the numbers tell you.

Ed

[Joe Ormonde]

It`s Primitive Pete time! This is where the (Ring Test) comes into play. Put a Model 92 or 93 Ring in the cylinder butt end to the intake side. Start at the top. Do you see any light between the Cylinder and the ring? Move the ring to several places and look. Any light anywhere except for the end gap and it`s out of round. Measure the end gap at the same time. That will show taper. But you need NEW Rings for this test. Use a Feeler gauge for clearance. Simple things first! If it`s out of round the clearance doesn`t matter. Get it bored. Works for me! Joe.

[thrownchain]

Oops my bad, if it's at. 015, you're looking at a .020 oversize to clean it up as long as that is the biggest variance in measurement. ( brain lag). And if it is out of round, bore it.

[viclioce]

Try to answer the questions.

Dale. I bought a micrometer at HF and it’s a new digital read out.

Thrown, it’s .015 with no rings on the piston. I have a bottom ring but not a top. Trying to determine if I should buy std rings, or if I should send Cylinder to Hodaka Dave with the .020 piston and have him bore it.

Joe, if I put the lower ring back on, what should be my clearance range, if I measure with a feeler gauge between the ring & cylinder wall?

Ed. I did each measurement 3 times and they all came within .002 Of I each other, so the numbers given are a mean average.

Hope this provides more useful info. Victor

[thrownchain]

Rings or not doesn't change the numbers. You're looking at the difference in bore diameter to Piston diameter.

[viclioce]

OK. Here’s what I checked out.

I have a brand new set of NPR .020 over rings. I slipped the top ring into the bore and got a ring gap of .008 at the top edge of the cylinder AND at the top of the ring wear in the cylinder. You can see a change in color of the bore and it shows the top of where the piston rings stopped.
So I get a ring gap with a .020 new top piston ring, squared with the piston of .008.

At the bottom of the cylinder, where the cylinder is a full circle, just inside past the skirt, I get a ring gap of .018. So the difference between the top of ring reach and the bottom of the cylinder just inside the skirt edge is .010.

Discussed this with Dan Cook on the phone while working through this. So I’m going to clean up the .020 piston I have & put these new rings on it, & then take a few more measurements. It appears this cylinder is a .020 bore. If it was a std bore still, the .020 rings would have NO ring gap and would overlap where the ends come together. So fingers crossed. I’m getting to the bottom of it! Victor

[Dale]

Try to answer the questions.

Dale. I bought a micrometer at HF and it’s a new digital read out.
Hope this provides more useful info. Victor

Victor,
In regards to my question about what tools you have used, I am confused as to whether you have a digital micrometer or a digital caliper. If it is a micrometer then you can measure the piston but not the bore. If it is a caliper then all bets are off. It will get you rough ballpark figures only, especially if it is from Harbor Freight. Don't get me wrong, I have plenty of Harbor Freight tools but their calipers are flaky.

To accurately measure the bore you need a dial bore gauge and in conjunction with a good micrometer you can measure the piston and determine the difference between the two.

Don't worry about ring fitment until you have the bore and piston determined.

I have assembled many Hodaka motors and have accumulated all the necessary tools to do my own measurements. What I do with those measurements is to educate myself as to the condition of my motor so that I can make the best choice of my options. Then I get the parts to a Hodaka expert to do what they do.

I honestly feel like you have the cart way ahead of the horse here.
I hope this makes sense and helps you.
Dale

[Bullfrog]

Vic,

At the risk of repeating myself . . . slow down, you'll go faster. See photo for more information.

If you aren't using a telescoping gauge and calipers to obtain the bore diameter, I'm a bit stumped as to how you are coming up with the bore diameter. The photo shows what a telescoping gauge looks like. It takes practice to use one well. I'm sorry but I can't provide a treatise on how to use one. Note that if you are using a digital caliper (also shown in the photo) to obtain bore diameter - you will not get a useful measurement at the top of the cylinder since you will be measuring the original bore in the un-worn area above the ring travel. It will also be extremely difficult to take a dependable measurement at the bottom of the cylinder since it is virtually impossible to reliably position the caliper points without ANY tilt (relative to the bore center line) AND precisely on a true "diameter" line. (the telescoping bore gauges tend to automatically "find" a true diameter due to geometry . . . in skilled hands).

NOTE: The only reason I included the digital caliper in the photo is to discuss an instrument which should NOT be used to measure cylinder bore diameters. The one in the photo is re-certified for accuracy regularly for use in my aviation accessory business - but is not the right instrument for bore diameter measurements.

Please re-read the advice you have been given - more slowly this time (it will make things go faster when you take the time to understand the advice). No one has suggested putting a ring on the piston and using feeler gauges to measure clearance between the ring and the cylinder wall. Joe's advice on going "primitive" was pretty good . . . but takes an experienced "eye" when looking for light between the ring and cylinder wall. Feeler gauges are indeed a good "old school way" to check the piston-to-cylinder clearance. It is effective, quick and simple.

Ed

[Joe Ormonde]

A cylinder can visually look perfect and be a MESS! My favorite one is when the cylinder was bored offset . That`s when the center line of the boring bar and the center line of the cylinder were not lined up correctly. That`s what causes a cylinder to not slide down over the piston. You checked the piston and it fit perfectly. When you try to slide the cylinder down, it just wont go! Why? Because the center line of the rod and cylinder are no longer correct . So the side clearance between the rod and piston is lets say zero on one side and .020 on the other. Easy to see if the piston has holes or windows when the engine has been reed valved: not so easy if it`s piston port. Material has to be removed from the piston so that the rod is no longer side loaded. Then the cylinder slides down. Not a problem with the Wiseco pistons Paul Stannard was selling, but a big one with the Factory ART pistons. Joe.

[Al Harpster]

Ed has covered this topic very nicely.

My experience says follow his advice & you'll get the clear & complete picture of what you have.

And you'll learn quite a lot working this way.

I've got the micrometers, I've got a dial bore gage, I've even got the Lisle "rigid" cylinder hone. These are great tools to have but it takes time to get the hang of using them.

The .003 feeler gage sandwiched between the piston and cylinder became my preferred choice to decide if I'm Ok to go. Okay, maybe .002 if you dare. Maybe .005 if you just want to run it.

Ring end gaps? Its good to know that they aren't too small, but they never helped me evaluate cylinder condition. Maybe I'm missing something on that one.

[viclioce]

Closing this thread. I’ve got a .020 piston & .020 rings. The rings have a .08 ring gap in the areas of the cylinder they will reside. The piston with the rings mounted, fits snuggly inside the cylinder and moves up & down with no light leaks around the rings. I’m taking the cylinder, piston & rings to my local machine shop and let him tell me if it just needs a hone or if it needs anything else. Thanks for everyone’s input. Victor