Willard's vintage Hotsaw Builds

[Willard]

So I found a NOS Wiseco forged 66.75mm piston kit. I'll get the engine setup with it later in the winter. Lots of 68mm kits out there or maybe go 69mm and make 269cc.
I will try the 66.75 piston without the bottom ring after run in and see if it makes any difference.

Here's my 66.75mm CR250R cylinder. No scratches only a little ring stain between the exhaust and transfer ports. Just needs a deglaze hone.
I checked the bore with different calipers and telescopic gauges many times over and it come out averaging 66.75mm.
So I'm good to go for now.

But checkout the exhaust and transfer ports. The cylinder is upside down and there is no chamfer on the edges what so ever.
There appears to be some bridge relief though.
Also look at the ring stain.

 

[Willard]

I did find a Wiseco 466 68mm piston with smooth sides around the pin bores (no cutouts).
Could send the P/C to BDT for reboring and hone fit. But I won't know the deck height until I get my P/C back unless he can figure that out and go ahead with the decking and head work?

 

[Bigmac]

I did find a Wiseco 466 68mm piston with smooth sides around the pin bores (no cutouts).
Could send the P/C to Carlos for reboring and hone fit. But I won't know the deck height until I get my P/C back unless he can figure that out and go ahead with the decking and head work?

What dose the 466 fit? Yes unfortunately you have to do some things in steps, but a local machinist could do a lot of that too. Have you talked to Carlos or Arlan yet?

 

[Willard]

What dose the 466 fit? Yes unfortunately you have to do some things in steps, but a local machinist could do a lot of that too. Have you talked to Carlos or Arlan yet?

The 466MO (466 P3 and P8) is a 1981-1983 Cr250r piston.
No I haven't heard back from LED probably busy with the ESR new dished dome big bore piston kit, their ironing out PValve issues with it. . Haven't called BDT yet.
I wasn't expecting to have my local machinist do the boring but I will talk to him on Monday if he has a torque plate.
I know my local Honda dealer sends their cylinders and cranks out to the big city (Winnipeg) for reconditioning, probably because cheaper rates down there.

Lots of Wiseco 66.75mm and 68mm 466 pistons out there for my '83 Honda ( not as many 66.75)
I found them both in the newer style cutout piston bore side profiles and the older non cutout smooth . I picked out both sizes in
non cutout as mentioned the cutout ones forward of the pin can cause transfer port charge short circuiting when the exhaust ports are widened.

 

[Willard]

How's this for 35 years of cleanliness for my little YZ125?
Yamalube R 24:1

 

[Willard]

Can't feel one scratch with my finger nail in the cylinder bore. Only streaks from wet wood chips and saw dust. Just needs a light deglaze hone.
Only ran a air filter on it for the 1st year.
Piston exhaust side looks clean.
Ring gap is 0.022" still within the 0.031" wear limit.
Back in 1983 I borrowed my Yamaha dealer's YZ125J shop manual and wrote the whole thing out relating to the engine by hand, Lol.

 

[Willard]

Been doing some more shopping on fleabay for the '83 CR250R.
Bought a good spare crankshaft and a NOS 66.75mm piston/rings.

Plus this 68mm cylinder and piston for a spare. Needs a new sleeve but price was right.

 

[Willard]

Just a little update here.
Had both saws setup good for a photo shoot and ended up ripping them all down and building new fuel/oil tanks with top handle supports. It was back to the drawing board and got away from the 0.125" aluminum tubing and building them piece by piece out of 0.188" aluminum sheet.
Kind of like building pipes from what I have seen others do.

 

[Willard]

Was a good skiing weekend but back to cutting paper.
Will be cutting 5052 H32 aluminum tomorrow.

 

[Willard]

Jigsaw table saw works perfect cutting 0.188" aluminum for the bikesaws.
Got 2 Sandvik Windsor harvester sprockets for the little YZ125 (12T-.404)
I'll use the .063 on the left, the other too big at .080.
Local machinist says no problem making a hub adapter and rope spool out of the titanium.

 

[Willard]

Nathan,
The 68mm P/C came in late last night. The crankshaft and top bearing with pin for the piston should be here today. From watching the tracking from Ohio they they were 30 minutes apart.

I don't see the cylinder needing re sleeving like the seller advised.
The scoring claimed is just a stain from the piston running off the exhaust bridge with no oil holes.
Can't feel anything on it with the sharp edge of my pocket knife. Only a very light scratch below the exhaust port.

The piston and rings looks like new. Ring to groove clearance is 0.003". Ring end gap in the cylinder is 0.022"
Some scoring on the bottom edge of the intake skirt.
No bridge oil holes.
Piston measures from intake side to exhaust side average approximate(cheap digital caliper)
67.65mm under the bottom ring.
67.80 middle
67.85 below pin.
Cylinder bore 67.95-67.99
68.05 at bridge.
I'll measure up the piston for you to see if a 69mm TRX piston will match.

 

[Willard]

Forgot to add. Someone took a bur and lightly scratched the surface of the intake ducts, boost ports and exhaust near the pipe flange. Transfer and exhaust ports in the bore were not touched.
Comparing it to my 66.75mm cylinder below.
Presently focused setting up the YZ125. Honda is waiting its turn on the shelf.

 

[Bigmac]

Nathan,
The 68mm P/C came in late last night. The crankshaft and top bearing with pin for the piston should be here today. From watching the tracking from Ohio they they were 30 minutes apart.

I don't see the cylinder needing re sleeving like the seller advised.
The scoring claimed is just a stain from the piston running off the exhaust bridge with no oil holes.
Can't feel anything on it with the sharp edge of my pocket knife. Only a light scratch below the transfers on the intake side.

The piston and rings looks like new. Ring to groove clearance is 0.003". Ring end gap in the cylinder is 0.022"
Some scoring on the bottom edge of the intake skirt.
No bridge oil holes.
Piston measures from intake side to exhaust side average approximate(cheap digital caliper)
67.65mm under the bottom ring.
67.80 middle
67.85 below pin.
Cylinder bore 67.95-67.99
68.05 at bridge.
I'll measure up the piston for you to see if a 69mm TRX piston will match.
View attachment 219159 View attachment 219160 View attachment 219161 View attachment 219162

Looks like you scored on that deal!! The bore looks great, piston has some skirt wear. It will be interesting to see the port timing.

 

[Willard]

Will see if the crankshaft with piston pin and bearing will show up tonight so I can get the piston setup.
New Wiseco 66.75 piston and rings are due to show up anytime also.

Are Wiseco pistons made smaller diameter then OEM Honda pistons?
My CR250R service manual shows cylinder bore specs are slightly over 66mm.
This 68 mm P/C with Wiseco piston and bore is under 68mm spec.

 

[Bigmac]

Will see if the crankshaft with piston pin and bearing will show up tonight so I can get the piston setup.
New Wiseco 66.75 piston and rings are due to show up anytime also.

Are Wiseco pistons made smaller diameter then OEM Honda pistons?
My CR250R service manual shows cylinder bore specs are slightly over 66mm.
This 68 mm P/C with Wiseco piston and bore is under 68mm spec.

Yes weisco’s are smaller than OEM, forged pistons swell more when hot, they usually size them for the same bore and make the piston the proper size for expansion

 

[Willard]

Thanks that what I figured seeing I once heard OEM cast pistons expand much less then forged.

I'm going to get a few measurements of the 446MO6800 piston and maybe we can figure out if a 526MO TRX piston are comparable.
I found this Chinese piston aftermarket companies blueprint for a CR250 piston. I reassure I wasn't interested in buying them Lol.

 

[Willard]

No crankshaft showed up tonight, will have to wait until Monday.
Here's my 1983 68 mm piston.
Forgot to measure ring pins location.
Hard to measure from the edge of the dome so I think 75.5 mm or so tall.

 

[Willard]

So the measurements in above drawing are good. It is 75.78mm tall.
Here's the piston ring pins measurement.
Last pic is the Chinese bore gauge I just modified this morning.
I was wondering why my cylinder bore measurements were all over the place.
I took a breaker point file to the edges of the 2 spring loaded tips and rounded them off a bit. Now the center area has a better contact to the cylinder bore.
I also noticed too much tension on the locking handle can throw out accuracy too.

 

[Bigmac]

Sorry for the slow reply, but it doesn’t look good fit the trx swap the pin to edge of crown is 3mm difference! Made a markup of the difference,
Every thing else is super close, but the ring stops are different too as 28mm

 

[Willard]

Sorry for the slow reply, but it doesn’t look good fit the trx swap the pin to edge of crown is 3mm difference! Made a markup of the difference,View attachment 219458
Every thing else is super close, but the ring stops are different too as 28mm

Thanks Nathan, it's good to get that out of the way!
I got a very strong feeling the early 1980's YZ250 big bore pistons that everyone used back in the day in their newer Hondas would match up.
Seeing my '83 piston's ring pins are 4 mm wider and the YZ250 pins had to be moved for the newer Honda cylinder's transfer ports plus the spacer plate at the cylinder base for the taller piston.

Easy enough for me to message a ebay seller to measure up his vintage YZ piston.