Willard's vintage Hotsaw Builds

[Bigmac]

https://www.cbc.ca/news/canada/manitoba/mystery-mountain-ski-thompson-1.5004567?_vfz=medium=sharebar

Saws are looking good, thous girls must have twisted you arm! That sounds like fun! Enjoy!

 

[Willard]

Merry Christmas everyone!!

Going to use 0.188 (3/16") 2"×4" 6061 T6 aluminum for the whole fuel /oil tanks seeing the sideplates welded to them will also be 3/16".
So that means the cap bungs will have to be welded on top. No big deal.
If I get anywhere near 60 hp with the Honda I want something strong enough to hang on to.

So decided on a 68mm single ring Wiseco piston in the CR250 right off the bat. So hoping either Carlos or Arlen will do the boring to size up and do something with the porting along with a fat hotsaw pipe....So there goes my budget right there , Lol.
Yes and CR500 main bearings.

 

[Willard]

Forgot to add this to my last post.
Look what the mailman brought today just in time for Christmas.

Beautiful CNC work of art.

 

[Willard]

Nathan, I'm showing 2 pistons here.
446MO 1983 Cr250r top and below a 526MO 1985-1986 ATC/TRX.
They both look the same to me besides a bit more lightening groove above the wrist pin.
1983-2001 Honda con rod kits are the same.
So I'm hoping I can run the ATC/TRX piston in my 1983 cr250r and have all the benefits like 69mm plus big bore, single ring and teflon coating they have.

 

[Willard]

To add here's Wiseco's 1985-'86 ATC/TRX 69mm piston (racer elite I believe).

 

[Steve]

Forgot to add this to my last post.
Look what the mailman brought today just in time for Christmas.

Beautiful CNC work of art.
View attachment 214723

Now thats a piece of beauty!

 

[Bigmac]

To add here's Wiseco's 1985-'86 ATC/TRX 69mm piston (racer elite I believe).
View attachment 215124

It dose look basically the same. There may be a minor difference other than the cut out, the smaller cutout is and advantage, you can wide the exhaust farther without short circuiting the transfers out the exhaust, I would go for it!

 

[Willard]

It dose look basically the same. There may be a minor difference other than the cut out, the smaller cutout is and advantage, you can wide the exhaust farther without short circuiting the transfers out the exhaust, I would go for it!

Thanks, I'll be looking further into it.
So those cutouts are not false bottomed then?
Here's pics both sides of the ATC/TRX piston . Each side is opposite of the wrist pin.
Is this piston wrapped in plastic?

 

[Bigmac]

Sorry if I didn’t communicate that very well, they do not go all the way through, here are some pics of a 68 1/2 bore piston
If you would like pictures of a specific angle or different measurements feel free to ask

 

[Willard]

Thanks Nathan I will when the time comes.
Interesting about the allowance for the wider exhaust port wings!

 

[Bigmac]

It’s a long history story in two stoke Mx history, but the factory’s works bikes got ahead of the curve on the sub-exhaust ports and added them with the old style piston in 82-83 and lost a bunch of power Kawasaki and Suzuki both tried failed and figured it out! Honda waited it out! I had a sweet 84 Kx cylinder in a tacate 3, it had sub-exhausts and probably one of the nicest port layouts of the day, huge reeds and the works, the down fall was ignition and air box, imho. The cr500 has the problem with pro-x piston, the side relief is huge, if your widen the exhaust port at all the transfers short circuit out the exhaust through the piston, weisco is better, but you really need to use the weisco 89-01 piston, it’s like the trx. I ran a piston once that had the oil holes drilled for the bridge in a 330 cylinder, and my cylinder was bridge-less, I couldn’t get enough fuel to it, could not believe how much fuel was going out 3 tiny holes, put the correct piston in, dropped 5 pilot jets 3 needle clip and pulled a bunch of main, I pay a lot or attention to those details a lot now!!

 

[Stihl working Hard]

Now thats a piece of beauty!

+2 there are some extremely talented people out there

 

[Willard]

It dose look basically the same. There may be a minor difference other than the cut out, the smaller cutout is and advantage, you can wide the exhaust farther without short circuiting the transfers out the exhaust, I would go for it!

Lots of good info here, thanks again!
So what is the purpose of these cut outs on the side of the piston. Cooling or aiding transfer port flow?
Are the shorter ones matched to the ATC/TRX transfers but might not match the 1981-1983 Cr250r transfers?

 

[Bigmac]

Lots of good info here, thanks again!
So what is the purpose of these cut outs on the side of the piston. Cooling or aiding transfer port flow?
Are the shorter ones matched to the ATC/TRX transfers but might not match the 1981-1983 Cr250r transfers?

I believe it’s mainly for weight, and a little for balance. The 97-01 piston has a smaller, more of a hole not the machines relief, and they went flat top, mainly for weight. Some say for a better burn, that’s another topic...lol

 

[Willard]

To add here's Wiseco's 1985-'86 ATC/TRX 69mm piston (racer elite I believe).
View attachment 215124

I'm still down at the in laws with my family, going home tomorrow so I have had lots of time to research pistons on my phone,Lol

So I think I have room for this 69mm piston as talked about earlier. But there are lots of 68-68.50mm available also.
Not alot of info on the net about these older 1985-'86 ATC/TRX pistons so I sent the ebay seller a message if his piston in the picture is the actual single ring armor guard piston he's selling.
I got a new LA sleeve for the '83 Cr250 cylinder in my plans also.

 

[Willard]

While down here in the big city I bought some more goodies for the work bench.
I bought all this for about $150 US at Princess Auto (think equivalent to Harbor Freight with you guys in the US)
Definitely not commercial grade stuff but all I need.

 

[Willard]

Back of the catalog.

 

[Bigmac]

I'm still down at the in laws with my family, going home tomorrow so I have had lots of time to research pistons on my phone,Lol

So I think I have room for this 69mm piston as talked about earlier. But there are lots of 68-68.50mm available also.
Not alot of info on the net about these older 1985-'86 ATC/TRX pistons so I sent the ebay seller a message if his piston in the picture is the actual single ring armor guard piston he's selling.
I got a new LA sleeve for the '83 Cr250 cylinder in my plans also.
View attachment 215370

I have never used one of the race or elite pistons, always use the standard weisco’s, some of the new standard pistons are coming with the Teflon coating. The 86 style piston, has kind of been the standard for all big bore pistons, and they don’t make anything other than that for the Honda, here is a pic of the standard weisco 68 1/2 next to the Esr 76 1/2 big board piston they do offer a 69.5 as well

 

[Willard]

Nice looking pistons and what a contrast in size difference.
Those ones they didn't bother with the side cutouts.

I figured the teflon coated skirts might be a good idea in a hotsaw where short WOT bursts are made with no liquid cooling.
Definitely a single ring should break in seating alot quicker.
From reading Swede Tech's info their race engines lose power on the dyno after 160° F.
Maybe I could epoxy a heat gauge in the head.

 

[Bigmac]

I wouldn’t worry to much about the heat, they do make a stick on heat gage, they are pretty cool. On alky, I try to keep the temp 140f it runs the best over 125. Its hard to hit 160, I had to put a small radiator to even get that hot,1/2 size. I have to make 4 or 5 full passes to hit 140 after warming up, its a struggle to get over 100 after 5 minutes of piss revs! But a heat gage is still a good tool, and can help make adjustments. I would probably set the piston clearance closer to air cooled tolerances.