Willard's vintage Hotsaw Builds

[Bigmac]

But the CR500 and CR 250 six bolt hole reed valve gaskets do line up right?

No

cr250 and 500

 

[Willard]

On my phone tonight I clicked on Ebay and ordered the service repair manual . Too easy,Lol.

 

[Willard]

Cr v3’s and the esr cageView attachment 206916View attachment 206917 View attachment 206918You can see the cr cage is offset a little on the inlet

No

cr250 and 500View attachment 206935

Thank you sir, that is a wealth of good information.
From my internet researched theories a thicker intake manifold produces more engine torque at low to midrange rpm. There are spacers available to adjust the length of the intake. So I'm I'm thinking the thicker based ESR won't offer as much top end in a chainsaw race then the VForce.

The YZ manifold here I made in the early 1980's averages out to the thickness of the OEM curved rubber manifold. The aluminum intake was originally squared out to match the reed cage but JB'd it to match the cage insert I added later. I thought the insert was a gimmick and a few years later went back to the OEM rubber intake and made another adapter from a 42mm sled engine and a copper plumbing flange. Added the 42mm Tilly HD carb and the little YZ125 ran strong on the top end.
Yes JB worked great 36 years ago too.

From recently looking at the Honda CR250R factory parts list a reed cage insert was introduced around about 1986, so I guess it wasn't a gimmick.

 

[Willard]

So the YZ125 homemade aluminum manifold is out the window, is too heavy and thick. Will use the OEM reed cage with the Boyesen insert.
Have lots of carbon fiber so will make a 38mm bore manifold adapter with studs for the jet ski carb and blended to match the insert in the cage.
Couple pieces of 5mm thick CF glued together with JB weld should do the trick.

 

[Willard]

Have been following this (same year as mine) 1982 YZ125 factory works sand cast cylinder on ebay UK for a few years. Has nikisel coating and trick porting with the intake port bridges removed.
Needs special rings but the seller never got back to me.
After getting my '83 Cr250 cylinder I can see the "trick porting" of the times. So easy enough to do on the 125. Not sure yet about removing the CR's exhaust bridge.

 

[Bigmac]

I like your yz cylinder compared to the sand cast one for top end power, the sand cast one look like it would have a wider power band and probably roll on quicker.
I would look for a good local builder to get you set up, these older motors gain a lot from porting and setup like squish and better ignitions like your doing, it would not surprise me if the squish on the cr is .080-.100 and 01 is .060 and gains at .040 the older port numbers are usually pretty conservative as well, if you get a degree wheel on it you will know were you stand!

here is an old lrd pre led cylinder, you can see he widen the exhaust and added “wings” you could go a little farther in a drag application, and the bridge can be thinner. I cleaned up some of the transfers and intake
Here is one that I did, and isn’t done

 

[Bigmac]

Ok the reed spacer, two theories on that, so it increases the crankcase volume and that will lower crank case compression and full the ports with less pressure and add in low end and not support top end power. 2 is with a good top end pipe and porting, the scavenging effect of the pipe will gain with more crankcase volume and the pipe will take advantage of the extra fuel and air in the crankcase. On the trx we often run a cylinder spacer plate with the long rod and old piston, the cylinder spacer can range from .160-.250 and that’s the cylinder volume at the base gasket, it isn’t something that’s crazy noticeable, just an FYI.
On the carb side of the reeds the shorter is generally ideal for response, I am not sure if there is and ideal size, the cr used a super short carb boot and the trx is longer, I run the cr. The only thing I can maybe see is less reed spit back with a little longer intact side, but I bet the short is better for throttle response and even peak, but may cases some tuning differences

 

[Willard]

Thanks for posting all that Bigmac, I'm on the same page as you in thinking.
Degree wheel and a new magnetic stand dial indicator is on my shopping list. But I got to get a piston first.
Porting and final tune (never a final tune) will come but I got to get these motors outfitted with plywood template side plates before I start cutting carbon fiber.

Got company over this weekend so have to stay close to mama's apron strings. Can only escape to the shed for a half hour at a time.
It's only big enough for saws. 12'x8' with storage in the attic. 100amp service

 

[Deets066]

Ok the reed spacer, two theories on that, so it increases the crankcase volume and that will lower crank case compression and full the ports with less pressure and add in low end and not support top end power. 2 is with a good top end pipe and porting, the scavenging effect of the pipe will gain with more crankcase volume and the pipe will take advantage of the extra fuel and air in the crankcase. On the trx we often run a cylinder spacer plate with the long rod and old piston, the cylinder spacer can range from .160-.250 and that’s the cylinder volume at the base gasket, it isn’t something that’s crazy noticeable, just an FYI.
On the carb side of the reeds the shorter is generally ideal for response, I am not sure if there is and ideal size, the cr used a super short carb boot and the trx is longer, I run the cr. The only thing I can maybe see is less reed spit back with a little longer intact side, but I bet the short is better for throttle response and even peak, but may cases some tuning differences

Wonder if a boost bottle would do anything here. Probly not a saw that’s full throttle all the time.

 

[Bigmac]

Wonder if a boost bottle would do anything here. Probly not a saw that’s full throttle all the time.

Ya my experience with boost bottles are on twins, I noticed a better idle quality and 1-16 throttle difference, I haven’t tried it on a single. Theory wise it should help low end and reduce spit back, so that could be helpful is certain times, Like if you had a really small intake boot area or a really short air filter where the spit back could saturate the filter and caused an extreme rich condition, As a rule of thumb on reed valve motor, you need at least a minimum of 2 1/2 times your carb bell diameter to the back wall of your air filter and that’s a minimum

 

[Deets066]

Ya my experience with boost bottles are on twins, I noticed a better idle quality and 1-16 throttle difference, I haven’t tried it on a single. Theory wise it should help low end and reduce spit back, so that could be helpful is certain times, Like if you had a really small intake boot area or a really short air filter where the spit back could saturate the filter and caused an extreme rich condition, As a rule of thumb on reed valve motor, you need at least a minimum of 2 1/2 times your carb bell diameter to the back wall of your air filter and that’s a minimum

Yup, stores that atomized fuel. When you get back in the throttle it’s instant.

 

[Willard]

Have a good VeteransDay / Remberance Day everyone.

Just showing the breathing capability differences of the little '82 YZ125 on the left between the '83 CR250 on the right.
Now the CR250 intake has basically gone unchanged up to 2001.
The YZ needs the intake bridges removed and it will breathe alot better.
Last picture is a 2001 CR250R "B" cylinder I found listed on Ebay.
Count the head stud holes...7.
I'm very puzzled because the only 7 stud CR250 heads I know of are my 1983 and the 1984 models.
Anyone know anything about this B cylinder?

 

[Bigmac]

Have a good VeteransDay / Remberance Day everyone.

Just showing the breathing capability differences of the little '82 YZ125 on the left between the '83 CR250 on the right.
Now the CR250 intake has basically gone unchanged up to 2001.
The YZ needs the intake bridges removed and it will breathe alot better.
Last picture is a 2001 CR250R "B" cylinder I found listed on Ebay.
Count the head stud holes...7.
I'm very puzzled because the only 7 stud CR250 heads I know of are my 1983 and the 1984 models.
Anyone know anything about this B cylinder?
View attachment 207194 View attachment 207195

I would would say it’s a cr500 cylinder, more picks and I could probably tell

 

[Bigmac]

Can you measure the centers of cylinder base bolts? In the case, both directions, I am curious if the trx cylinder will fit

 

[Willard]

Yes I think you're right they mistakenly advertised a CR500 cylinder, bore looks huge too.

Do you mean measure my '83 Cr250 cylinder base stud holes?

 

[Willard]

I would would say it’s a cr500 cylinder, more picks and I could probably tell

Yup you're right, parts list shows 7 stud CR500 cylinder.

 

[Bigmac]

Yes I think you're right they mistakenly advertised a CR500 cylinder, bore looks huge too.

Do you mean measure my '83 Cr250 cylinder base stud holes?

Yes, measure your cylinder base stud spacing both directions

 

[Willard]

Yes, measure your cylinder base stud spacing both directions

Got it down on paper with metric steel ruler , approximate by eye (I do have a good eye for center on the cylinderbase)
Digital caliper on studs not accurate as some were off.

Also included my '83 crank dimensions.
If my 7 lb 8 oz crank is heavier and not as good then the newer cranks it's possible to put a newer crank in my crankcase. Main bearings and PTO seal are same from 1983 up. Webs might be bigger diameter on newer cranks.

 

[Bigmac]

Ok, thanks, have been curious! The trx is 100mm 100mm and 90mm on the exhaust the 92-01 is square at 100mm it must be the 85-91 cylinder that can swap

I did a quick weight on the 01 crank, it was 8 pounds 4 ounces, digital bathroom scale so it may not be perfect

 

[Bigmac]

And the crank is 60 mm between bearings and 185mm tip to tip everything else is the same