Dolmar and Stihl Pistons - I need help.

[Four Paws]

Guys, I need some info on the following. I am once again trying to source a replacement for a discontinued piston. The piston is 49mm with a 12mm wristpin. So far, the pistons I have found to be the correct diameter are from a Dolmar 120, and Stihl models 042, 039/390, TS350/360. Here is where you guys come into play. I need more info on the pistons I listed above, or any other saws that use a 49mm piston and 12mm pin!! Any measurements you guys could provide me with - like skirt width, overall heighth, compression heighth and ESPECIALLY pin diameter would be appreciated. Photos would be excellent as well. Feel free to reply here, PM me, or send me an email.

Thanks in advance, Josh

 

[DOLMARatOs]

Rent watch then buy the movie "World's Fastest Indian". Burt Munro used to hand cast his pistons using a blow torch and old chvy and ford pistons. Then turn them down by hand on a lathe.

http://www.worldsfastestindian.com.au/#

 

[Scooterbum]

And how about him making his cylinders out of cast iron sewer pipe with aluminum sleeves on the outside with fins cut in them for cooling.
The man is a legend!!

 

[Four Paws]

Well, I am back on this project again, and haven't had much luck getting the measurements I need.

If anyone with a 120S Dolmar, Stihl 042, 039/390 or TS350/360 cutoff saw, could provide me with some measurements, or mail me a burnt up piston (I'll pay postage) so I can measure it, I would be thankful.

The measurements I need are as follows:

Skirt Width
Pin Diameter
Overall height of piston
Height from bottom of skirt to center of pin

Thanks, Josh

 

[Lakeside53]

I'll dig around at work Monday - should have a bunch of old TS360 pistons somewhere..


Rbtree has a Dolmar 120 with a scored piston.

 

[Four Paws]

I'll dig around at work Monday - should have a bunch of old TS360 pistons somewhere..


Rbtree has a Dolmar 120 with a scored piston.

Thanks - just the kind of help I was looking for. I'll have to drop Rbtree a line!

 

[Lakeside53]

You could turn down a 50mm piston...

 

[04ultra]

I have a 120si piston......




.

 

[Jacob J.]

The Stihl 042 piston won't work for you-13mm wrist pin.

The TS-350/360 is a rather tall piston, if this is a custom Shindaiwa project you're working on I'm guessing that the 350/360 piston would require extensive machining in order to fit.

Your best bet would most likely be the Dolmar piston. I think the 120si piston was around 16mm from the top of the wrist pin to the crown.

 

[drmiller100]

if you found one with the wrong size wristpin, could you change the wristpin and wristpin bearing to something else to make it work?????

 

[Jacob J.]

Nope. Unless you want to weld up the wrist pin boss and CNC machine it back down the correct size, but you'll most likely ruin the piston anyways at that point.

 

[Goicoechea]

What are you building??

 

[Four Paws]

The Stihl 042 piston won't work for you-13mm wrist pin.

The TS-350/360 is a rather tall piston, if this is a custom Shindaiwa project you're working on I'm guessing that the 350/360 piston would require extensive machining in order to fit.

Your best bet would most likely be the Dolmar piston. I think the 120si piston was around 16mm from the top of the wrist pin to the crown.

Thanks for the info on the 042 piston - we'll cross that off the list.

The TS-350/360 piston will work great if it is really tall - just what I am looking for. The saw I am working on is a custom Shindaiwa, stock apearing saw. The factory piston has a WIDE skirt (38mm) but not much height. I would like a taller piston with a longer skirt - bump compression and allow for more radical port timing with the longer skirt.

Ultra sent me some measurements from the 120 Dolmar piston - looking good so far. Skirt is only 33.8mm wide. It is about 1.5mm taller than the stock piston though.

 

[Jacob J.]

One thing to keep in mind about the TS-350/360 piston, it's a slab sided piston because the bottom of the transfers feed directly from the case. I know quite a few of the Shindaiwa cylinders have deep enough transfers that they can be made to direct feed.

I don't the skirts were all that wide on the 350/360 piston.