Willard's vintage Hotsaw Builds

[Billy Currie]

A stroked crankshaft would make up the difference in piston height.

 

[Willard]

A stroked crankshaft would make up the difference in piston height.

Yep I was thinking the same too Billy.
I'm going to look into the early YZ250 and RM250 68mm and bigger pistons and then possibly stroke it later on.
I'm good for 69mm bore if not 70mm with my sleeved cylinder.
If everything works out good and then diaster strikes there's always Millennium Technologies with their nikisel plating to save the cylinder.

 

[Willard]

For now I will put the 66.75 mm cylinder and new piston on so my saw has a base motor.
Then I'll know later on when I put the big bore P/C on what to expect for performance gains.

 

[Bigmac]

A stroked crankshaft would make up the difference in piston height.

The height would be good but the port timing would be way to much, stroking a stock cylinder 4mm is about the max depending on the stock timing, like an 01 250 is pushing the timing with a 2mill stroker, the 4mill trx is about the max, and you don’t touch the roofs of the transfers

 

[Willard]

Yeah but the difference in my '83 from the trx is 3 mm. Still too much?

 

[Bigmac]

If the ring stops were Not in the way, then you could mill off 3 mm off the base of your cylinder and probably run the TRX piston, even if you were stroking it you would need to mill 3 mm off the base to run the TRX piston. You could stroke it with your current 83 style piston

 

[Willard]

The TRX ring stops are 4mm closer to each other then the '83 piston's so ring ends wouldn't be anywhere near the transfer ports.

 

[Bigmac]

The issue can be the ring hanging into the center intake boost port and catching in the big open intake port. The benefit of machining off 3 mm off the cylinder base and installing a trx piston would be crank case compression would go up and it would want to rev harder. I think that’s what Honda did with the 84, they tightened the cylinder base mounts and made the cylinder more compact along with lowering the overall cylinder height by moving the pin up in the piston, it would significantly change the crankcase compression

 

[Willard]

Yes in1984 along with the narrower full circle crank and crankcase to also boost bottom end compression.
Would be quite the undertaking with readjustment to the ports when lowering the '83 cylinder.

I'll have to take a look at the '83 through the intake manifold when I get the P/C and crank installed in the crankcase.
My tracking # says the crank with top end pin & bearing was out on delivery locally 8:40am . Still nothing yet 11 hours later.

For a future search will definitely look into the RM and YZ pistons from the 1980 to 1983 era.
Like you said auxiliary exhaust ports would be a cool venture in the 68mm plus cylinder too and get the spare crank stroked.

 

[Bigmac]

Yes in1984 along with the narrower full circle crank and crankcase to also boost bottom end compression.
Would be quite the undertaking with readjustment to the ports when lowering the '83 cylinder.

I'll have to take a look at the '83 through the intake manifold when I get the P/C and crank installed in the crankcase.
My tracking # says the crank with top end pin & bearing was out on delivery locally 8:40am . Still nothing yet 11 hours later.

For a future search will definitely look into the RM and YZ pistons from the 1980 to 1983 era.
Like you said auxiliary exhaust ports would be a cool venture in the 68mm plus cylinder too and get the spare crank stroked.

I’m not sure what you mean readjusting the ports?

 

[Willard]

I’m not sure what you mean readjusting the ports?

Yes correct 3mm lower piston and 3mm lowered cylinder porting would be the same.
I was also thinking readjusting ports after boring cylinder 3mm + oversize. Would boost bottom to mid range power but hurting top end.

The more I look into Millennium Technologies plating iron sleeves the more I like the idea of a 70mm bore if possible. I'm not looking at a application for hours long endurance runs on a track or dunes....

 

[Willard]

Well look what showed up.
Needs a good bath but tolerance wise it's in really nice shape .
Tight clean rod with no wear marks or stain in small end , safely within big end side clearance spec.
Pin and bearings look good on both ends.
Will setup dial indicator on it tomorrow to see how true it is.
Was a little concerned about how it was packed with a hole worn through its box. May have loosened up one of the stuffer plates. But I think I can tighten up the 2 pin rivets that hold it tight.

Last crank came the same way too.

 

[Bigmac]

There are several thing that happen when you increase the bore with out port work, the ports usually drop because all the roofs have an angle, that is usually why big bore run worse than stock not ported. Plus the ports are smaller to feed everything the same. I would just port set up squish and do everything we talked about. If you want more I would update to the newer platform and run the trx big bore cylinder, an 85-91 bottom end and trx big bore will be the cheaper route to bigger power. Sleeving and plating will cost you close to what a big bore cylinder with new piston and head, and has decent power, once you plate port and rechamber the head, your probably looking at spending $1500-2k for led or bdt to set up you 83 cylinder with a big bore, an esr ceo 81mm bore cylinder is only $1100 right now, I payed $730 for my 78mm bore cylinder With head and dome piston and econo port.

 

[Bigmac]

Well look what showed up.
Needs a good bath but tolerance wise it's in really nice shape .
Tight clean rod with no wear marks or stain in small end , safely within big end side clearance spec.
Pin and bearings look good on both ends.
Will setup dial indicator on it tomorrow to see how true it is.
Was a little concerned about how it was packed with a hole worn through its box. May have loosened up one of the stuffer plates. But I think I can tighten up the 2 pin rivets that hold it tight.

Last crank came the same way too.
View attachment 219574 View attachment 219575

Looks nice! Clean!

 

[Willard]

Thanks, it's nice to see I got lots of options!
Like I said before I'm looking at a 10 year competition run with these saws.
It's going to be a great ride.

 

[Bigmac]

That’s a long run! And fun! I have worked on different platforms and found the more options the better! I know I am biased to the trx, but it is because of the options, the banshee is a great platform in the twin cylinder world as well

There are over 10 different cylinders that fit the trx pattern, lots of aftermarket support plus you can get an off the shelf hot saw pipe. There is no other single single cylinder 250cc plus with this much support and tuning experience. I like your 83, but I wouldn’t worry about big bore and stroking, to me the cost outweighs the gain. In the trx oem cylinder, most feel the 69mm bore runs better than the 72mm even after porting, again this is oem. In the pro-x big bore, at 76 bore x 76 stroke is considered by many to be the peak preformer in that cylinder, more bore adds torque down low but but not hp in the rpms, the esr cylinder seams to breath well enough for 390cc performance up to the low 70ish hp. Pumas can get in the 80hp level
Short of the long if you need more it’s available in the trx/cr platform

 

[Willard]

I'm a birthday boy today. When I said I want to race my saws for 10 years I'll be 72 then.

So the run out on the new '83 crank is within spec according to the service manual. And it's almost 2 oz lighter then the '82 crank I bought last year.

The NOS 66.75mm Wiseco piston and rings came in today along with OEM crank seals and 7 head studs.
Ring end gap is .013" perfect for a air cooled engine like mine will be.
This 66.75 cylinder bore is in excellent condition, no scratches and no out of round what so ever . Just needs a good deglaze hone and it's good to go.
I can make the exhaust ports wide with the smooth piston side profile.
Should I bother drilling the 2 oil holes for the bridge?
I don't see any need for my short runs in the wood.

 

[Willard]

So exhaust bridge oil holes drilled in the piston it will be. Thanks again Nathan

My 4 Stihl 084 bar studs came in today so now I have to quit working on the CR250R and back to making the YZ125 look like a chainsaw. The Honda will get 2 of the studs too.

So I got two excellent condition top ends for the Honda (Also the YZ125).

Too early to decide whether the CR250 68mm or 66.75mm P/C will be the spare. Just need new rings for the 68mm piston.
When the time comes to deglaze these cylinders YZ included, I have to decide whether to use a ball hone or a Wiseco brush hone . I'm thinking 300 grit and will the brush hone put in a good 45° crosshatch?

Got the 68mm P/C mounted on the cases here. TDC the crown sticks over the deck and the crown edge is not far below it with 1.15mm (.045") clearance to top of deck.

BDC port floors to edge of piston to deck.
Ex 73.25mm
Transfers 73.15mm
Boost intake (no floor) 73.05mm

Port ceiling edges to deck not precisely as I want.
Ex 43mm
Transfers and intake boost 59mm.

 

[Bigmac]

So exhaust bridge oil holes drilled in the piston it will be. Thanks again Nathan

My 4 Stihl 084 bar studs came in today so now I have to quit working on the CR250R and back to making the YZ125 look like a chainsaw. The Honda will get 2 of the studs too.

So I got two excellent condition top ends for the Honda (Also the YZ125).

Too early to decide whether the CR250 68mm or 66.75mm P/C will be the spare. Just need new rings for the 68mm piston.
When the time comes to deglaze these cylinders YZ included, I have to decide whether to use a ball hone or a Wiseco brush hone . I'm thinking 300 grit and will the brush hone put in a good 45° crosshatch?

Got the 68mm P/C mounted on the cases here. TDC the crown sticks over the deck and the crown edge is not far below it with 1.15mm (.045") clearance to top of deck.

BDC port floors to edge of piston to deck.
Ex 73.25mm
Transfers 73.15mm
Boost intake (no floor) 73.05mm

Port ceiling edges to deck not precisely as I want.
Ex 43mm
Transfers and intake boost 59mm.

View attachment 219913 View attachment 219914 View attachment 219915

Did you put a base gasket in? Just for numbers is why I am asking

 

[Willard]

Yes the old base gasket was stuck to the cylinder so already compressed and a light snug torque on 2 studs across from each other. No rings on the piston but was sitting nice and square when measuring.

So if I took .045" off the top of the cylinder the edge of the piston will be flush.

I'm liking that 68mm cylinder, it looks trick with that raw aluminum color.
I got a sandblasting cabinet on the end of my side bench. Might just cleanup the black paint off the cases too. Then buff everything up to a mirror polish.