piston oversize

[thrownchain]

How much crossover is there between Ace 90 and Ace 100 pistons? I have a "50" marked piston which is considerably smaller than a ".040 " Ace 100 piston. Is the "50" an oversize 90 piston? I know I should measure it, but just as general rule.....

[taber hodaka]

I don't remember a 50 over hodaka piston for the Ace 90. I think it would be bigger than a stock Ace 100?? Time to not guess, but to measure. Is it a ART piston?? The ace 90 piston had a smaller wrist pin.------------Clarence

[Hydraulic Jack]

Assuming there is such a thing as a 0.050" oversized piston for the Ace 90, it would still be smaller than a stock Ace 100 piston, but not by much. Bore size is slightly more than piston size, of course, but bore size is easier to find listed. Ace 90 bore is 48mm, or 1.89". Add +50 (0.050") and you get 1.94".

Stock Ace 100 bore is 50mm, or 1.97". Since bore clearance on a two stroke of this vintage would arguably be around 0.003", you might say that a 50 thousandths over Ace 90 piston might just about fit a stock Ace 100" bore. But that's where the similarity would end I would think.

The wrist pins for each model are numbered differently, and I would not be surprised to find that Clarence is right about the 90 pin being smaller, so there woukd be zero crossover between the two pistons.

I don't think Hodaka offered a 50 over piston for the Ace 90, assuming the marking is a 50 in inches and not a .50 in millimeters, but there might have been an aftermarket maker who offered one that big. Bottom line is you have to measure the piston for diameter at the skirt, pin size, and crown height.

[viclioce]

Is the piston marked 50mm or is it just marked .050? Victor

[thrownchain]

After getting out the micrometers and doing some measuring, have figured out the "50" is actual size of the piston, not an oversize. It is a Ace 100 piston, and brand new. Will need rings and wrist pin clips and it's ready to go. Cylinder matches the piston. It is not an ART piston.

[Hydraulic Jack]

I don't think I have ever seen a piston marked with its actual size in millimeters or inches. Usually a stock piston has no markings at all, or might be marked +1 or +3 or whatever, depending on the batch tolerance range. Oversize marks are usually just the amount oversized, frequently in thousandths, as in "20". I can't recall ever seeing a piston for any engine marked in literal size, and the literal size for a 50mm stock piston is actually around 49.3mm. If it isn't an original ART piston it could be anything, maybe old Wiseco.

Photo just for curiosity sake?

[thrownchain]

I matched the 2 pistons I have up, wrist pins are the same, ring grooves line up, same height from pin to dome, same length. I could send a pic direct if you would like to see. Never took the time to learn how to post pics. Only visual difference is that the "50" piston has a slightly raised lip on the very outer edge of the piston top.

[MTrat]

In the same general vein; has anyone found or worked up a cross-over chart for 'Brand X' pistons or rings with Hodaka. It seems someone used Yamaha with modified wristpin or something. Any knowledge on this topic would be enlightening, and, heck, maybe even useful...

[Hydraulic Jack]

Posting pictures is a function of posting a message. When you type a message, at the bottom of the white message box are two buttons, one of which you already use (Submit). The other button is "Full Editor & Preview." Hit that button instead of submit. That lets you literally see what your post so far will look like, and gives you additional options.

The additional options are: 1) Save Draft; Preview; Submit....... and just below those three are:

Options, and Attachments.

Since posted photos are attachments, just like they are in email, hit the attachments tab. Now you will see an option for "Add Files." Hit that one. You are given three additional options: 1) take photo; 2) photo library, and 3) iCloud. Use whichever is appropriate for your photo needs. From there it is exactly like adding photos to email, that is, cruise your library, chose your photo, follow the prompts. Once you choose to attach, WAIT for the green time line to turn into a green check mark. What you are waiting for is the upload of your photo, which takes a moment.

Once you get the green check mark, you will be asked if you want to "place inline" or "delete". Your choice. If you choose place inline, it will put the photo file in your message wherever the cursor is in your message. You may also add a comment to the photo if you want but that is optional.

Sounds complex, but it isn't.

[thrownchain]

Test post

[Hydraulic Jack]

In the same general vein; has anyone found or worked up a cross-over chart for 'Brand X' pistons or rings with Hodaka. It seems someone used Yamaha with modified wristpin or something. Any knowledge on this topic would be enlightening, and, heck, maybe even useful...

If anyone has ever done something like that, I have not seen it. A forum member modified his 125 a couple of years back, but wouldn't offer details of the modification. It could have been a Yamaha piston was used, but whether that also required a modified rod or crank assembly, I don't know. I don't know of any straight across piston trades with any other two stroke engines.

Making a cross reference chart would require access to dimensions for pistons and wrist pins. Most manufacturers only tell you the bore and stroke, but that isn't anywhere near enough information to cross reference pistons. Then, too, ring stops would need to coincide with Hodaka port configurations, so it isn't a simple process. Perhaps that's why we haven't seen a chart...

[dirty_rat]

The only Yamaha piston that I know of that uses a piston pin of the same size as a Hodaka 100 (pin is 12mm thick) is a YSR 50. But in that case, the piston is way too small for a Hodaka cylinder, as it is a 50cc engine.

[thrownchain]

Pics, ,040 on the right. Rings on the "50" piston are thinner.

[thrownchain]

Also the "50" piston seems to be slightly heavier built.

[Hydraulic Jack]

Looks like a Wiseco forged piston. No idea what "50" represents. Intended for a 50mm bore is my best guess but have never seen one marked that way. Perhaps someone who has seen old school Wiseco pistons will know.

[thrownchain]

Did anyone make a 050 oversize for the Ace 100? Or are 040 and then 060 my only choices? I've got a cylinder that won't clean up at 040 but don't want to have to jump to 060 if I don't have to.

[olddogs]

Years ago I sorted through a stash of vintage aftermarket parts catalogs, attempting to build some cross reference material. I found some misc. front and rear sprockets, wrist pins, clutch/brake levers, various Wiseco rings, (for Hodaka Wiseco replacement pistons) and upper rod bearings for other brands that worked. The only pistons I found that crossed were the 250 Suzuki and either a Harley Rapidio or Baja, I cant remember which. Did not help much as the Harley pistons were more rare than the Hodaka. I did buy up some 250 Suzuki oversize pistons that I used to keep my T-dog going when I raced the Vintage Enduro circuit many moons ago.

[thrownchain]

Ok, more directly, did anyone make a 050 oversize for the Ace 100? I know Wiseco only goes in 020 increments, the big 4 went in increments of 025. By being resourceful you can get more rebuilds by using stock and after market pistons as needed. Did ART make a 050?

[dirty_rat]

I believe that the Wiseco pistons that Paul at Strictly Hodaka had made were made in .010, .020, .030, .040, .050, .060, .070 and .080 oversizes. I know he is out of some sizes, but his site still list a .050 over Ace piston (Wiseco). As for other companys going with 25 incriments in piston oversizes, that is .25 mm (equal to .010).

[dirty_rat]

Also, the Wiseco pistons often do have the size marked on the top, such as the above listed .050 oversize Ace 100 piston is marked with 51.25mm on the piston crown.