Willard's vintage Hotsaw Builds

[Willard]

Nathan, here's a nice one to bolt onto my Mikuni SBN.
Just needs a screen.
These jetski carbs air filter are called flame arrestors.

 

[Bigmac]

Nathan, here's a nice one to bolt onto my Mikuni SBN.
Just needs a screen.
These jetski carbs air filter are called flame arrestors.
View attachment 207910

Looks nice, must have a screen built in? Thats what I would consider a flame arrestor, is it stainless steel? For flow a screen on top is what you want, not at the base.

 

[Deets066]

Wide weave screen would be fine. But I wouldn’t put any type of filter on it.

 

[Bigmac]

Are you going to add a decomp to the head, or have a larger starting wheel?

 

[Willard]

Nathan, here's a nice one to bolt onto my Mikuni SBN.
Just needs a screen.
These jetski carbs air filter are called flame arrestors.
View attachment 207910

I forgot to post the air filter with the velocity stack pic

 

[Willard]

Are you going to add a decomp to the head, or have a larger starting wheel?

Will install two 3120XP decompression valves on the head. One on each side of the spark plug.

 

[Willard]

Have been having a hard time getting focused on the YZ125 rebuild so decided to put the CR250 away in a bin out of site, along with the YZ125' old bits and pieces.
Multi tasking is not my thing, may be a good thing for the project.

 

[Willard]

For the first time ever I started using Ebay a little over a month ago and already found the main foundation pieces for the CR250R.

You'll never know what you might find on Ebay,
I ordered this yesterday for the little YZ125.
12T .404 .063 Sandvik harvester sprocket. Not being a .080 sprocket it will run my Oregon 50AL .050 chassis with 46RST HT cutters alot better.

Also ordered this 73mm x 30mm chunk of GR5 titanium for $20 out of Israel of all places.
Now to find a competent machinist who can make it into a hub adapter for the sprocket and rope spool......

 

[Willard]

Still cutting stencils and templates, got sidetracked with a couple of emergency residential tree removals. Finger crossed tree gear can now stay in storage till spring.
Final verdict is both powerheads will be horizontal with carbs tilted back 20°/25°.
Honda CR250R 1981-1987 service manual arrived, great reference with good thorough instructions.
But the break in procedures are confusing, it says when new or after a engine rebuild it requires 5 to 10 hours of running with less then 1/3 throttle.
My YZ125 service manual says after first 15 minutes running less then half throttle remove cylinder and check piston. Sand down any high spots on piston. Run another 15 with intermittent WOT through all the gears. Bike is ready to race.

Now I see my YZ125 has a thin little single piston ring and the CR250 has 2 thicker ones so I can see the Honda will take alot longer to break in.
But for running a hotsaw it would take me 10 years to break it in.

Any thoughts on using ceramic bearings and a single ring piston on the CR250?
Are there special rings for racing with quick break in with a cast iron sleeve?

 

[Bigmac]

Still cutting stencils and templates, got sidetracked with a couple of emergency residential tree removals. Finger crossed tree gear can now stay in storage till spring.
Final verdict is both powerheads will be horizontal with carbs tilted back 20°/25°.
Honda CR250R 1981-1987 service manual arrived, great reference with good thorough instructions.
But the break in procedures are confusing, it says when new or after a engine rebuild it requires 5 to 10 hours of running with less then 1/3 throttle.
My YZ125 service manual says after first 15 minutes running less then half throttle remove cylinder and check piston. Sand down any high spots on piston. Run another 15 with intermittent WOT through all the gears. Bike is ready to race.

Now I see my YZ125 has a thin little single piston ring and the CR250 has 2 thicker ones so I can see the Honda will take alot longer to break in.
But for running a hotsaw it would take me 10 years to break it in.

Any thoughts on using ceramic bearings and a single ring piston on the CR250?
Are there special rings for racing with quick break in with a cast iron sleeve?
View attachment 208854

There are a couple of considerations, like cylinder prep and clearances. I highly recommend torque plate bore and hone, with the design of the cr it’s less critical but I still recommend it, on my builds I now consider it a must do, the stud pull once torqued can warp the bore and create high spots. Second is piston clearance and piston material, it will depend on the forged oft cast for clearance, and I would probably bump up the clearance because it’s going to be air cooled and will expand faster. The old brake in guidelines were for cast pistons in a tight bore, so extra care is needed to make sure a high spot doesn’t take out a piston. In your case I would hear cycle it several times and then warm it up good and increase the rpms no load into some piss revs, then after all that I would make some cuts with it tuned extra rich in the top rpm, maybe 2000 rpm lower than normal, basically pig rich, but full throttle. Let it cool down then warm it up really good again then make another few cuts tuned a little leaner but still way rich after a gradual ramp up, break in you should be ready to go!

 

[Willard]

Thanks Nathan, I appreciate the advice.
When I first broke in the YZ125 back in the day I hooked up a garden hose to the cylinder and trickled water through it. Had a heat gauge setup in the head, kept temperature at around 160F and cut wood under load, advice from Bill Krause Racing.
Did this at the wood pile in the backyard for most of the afternoon. Had lots of wood cookies to burn that winter.

 

[Bigmac]

That’s a good idea too, you could even rig up an electric pump setup to get some extended run time under load. My 363 broke in, in about an hour, I rode it pretty hard too, just not extended wide open under load, it was a little reluctant to over rev until about an hour, cast liner, My banshee, with Nikasil bore is read to go after about 15 minutes! Lol

I haven’t done ceramic bearings, have talked to a few builder and they said not worth it, most of them are not correctly rated for this application, so if heard. The single ring is an option, it funny that only the 125’s got them and anything bigger didn’t, I have seen some testing and at higher compression the dual rings can hold more power and last longer, and the single is better for rpm, but not power, kind of a trade off. Maybe the larger bore dose not like the single ring

 

[Willard]

It appears the CR250R got single rings starting around 1984, it was an option. I can see a 350 big bore with that big piston would probably need 2 rings.
32:1 and under seals compression good.My YZ125 is rated Yamalube 24:1
Lots of pages of good technical information in the manual's air cooled CR250R section.
That cylinder bore warp from stud torque was that iron sleeve or nickisel ?

 

[Bigmac]

Cylinder warp happens with all of them, but the factory uses a torque plate when preparing the Nikasil bores, that’s why they last so well. Once I switched to torque plates for prep, I have had a noticeable difference in longevity and consistent preformance, the cr500’s are really bad for it, the last build I did the guy broke it in one the hill racing, and it preformed flawlessly. I can see stud lines inn the bore of 500’s with out a torque plate after only a few hours run time, and I know it’s an issue on the esr/pro-x cylinders, I torque plate jones my brand new cylinder and it was shocking how much warp was in it, and there was still a tiny spot that was a low spot.
The manufacturers experiment of the quite a bit in the mid and early 80s with two-stroke design, I take what lasted as far as design as things that worked, not that they got everything right! 02-07 Honda, what a mess! Lol the 92-01 cr’s the last gen Kx and latest yz 250’s are all really similar.
I run 32-1 in the gas Honda and 20-1 on the alky banshee, I have seen several Dyno showing that going all the way to 20 to 1 will gain horse power!

 

[Willard]

Nathan is that you running a trading post forum for vintage CR Elsinore parts?
With the parts I bought for this project the left over pieces I don't need could definitely be traded to someone who needs them .

Have been following a ThumperTalk thread of Arizona native SlowDinoDog's 1983 CR250R restoration and vintage track racing progress.
I've read the thread 3 times over already, lots of cool info of these early bikes.
I don't dare chime in on the thread with my own '83 Cr250r project, I'd probably be treated as a outcast for abusing a fine engine design.

Plugging away here I wouldn't be where I am if it wasn't for my family. Lots of fun stuff being involved with sport tournaments and school projects with the kids.

 

[Bigmac]

Nathan is that you running a trading post forum for vintage CR Elsinore parts?
With the parts I bought for this project the left over pieces I don't need could definitely be traded to someone who needs them .

Have been following a ThumperTalk thread of Arizona native SlowDinoDog's 1983 CR250R restoration and vintage track racing progress.
I've read the thread 3 times over already, lots of cool info of these early bikes.
I don't dare chime in on the thread with my own '83 Cr250r project, I'd probably be treated as a outcast for abusing a fine engine design.

Plugging away here I wouldn't be where I am if it wasn't for my family. Lots of fun stuff being involved with sport tournaments and school projects with the kids.

No it’s not me. Glad your plugging away, it fun to do research. I think that’s the funnest part of most projects for me. We I redid the Camaro, I was all over the internet, so much fun and you learn a lot!
Ya some of the purest would give you hell the majority would dig it! Especially since the cases were damaged!

 

[Willard]

No it’s not me. Glad your plugging away, it fun to do research. I think that’s the funnest part of most projects for me. We I redid the Camaro, I was all over the internet, so much fun and you learn a lot!
Ya some of the purest would give you hell the majority would dig it! Especially since the cases were damaged!

Yes I'm doing the MX industry a service by help recycling those damaged cases!!

Had a little hiccup in the project for the couple of days. Living here in a small remote city with
only 2 hardware store doesn't help.
Was making templates last week with a piece of semi clear fluorescent lighting plexiglass I bought for $20. I didn't want to spent $50US on a clear acrylic sheet. Ended up buying the clear sheet this morning.

In my idle time I was trying to measure up both engines cylinders bore and piston clearances.
My mic is not big enough and my caliper's readings are jumping all over the place from temperature change handling it.
So I have to go out and make friends with the local machinist. Services will be needed.

 

[Bigmac]

Was think of your project when I was working my 01 cr250, with a 330 cylinder
Hope things are going well!

 

[Willard]

Everything is going good Nathan. Not much to show yet but I can say cutting 5mm carbon fiber is a PITA. Tough and messy.

That 330 cylinder is a work of art.
ESR is selling their complete 310 kits for under $700US with billet head. Too bad they don't have the same 4 hole base pattern as mine.

A 72mm 1985-1986 ATC/TRX piston would fit nicely in mine with a new sleeve rebore bringing my '83 up to 310 I believe.
I understand LED likes to bore out the old sleeve and do work to the cylinder port areas before installing and porting the new sleeve.
Since the 1970s bikesaw builders were punching 250 engines out to 300+ cc. So it's only practical to still do that today.
I've been watching YouTube videos of guys ripping around with their vintage 1983 CR250R bikes and they Rip!!
Don't think I even need 310cc, ..Lol

The premier Stihl Timbersports is changing. The European's can't make the h.p we're making over here in North America so they dropped the log size diameter. Now the big Rotax saws that dominated for the last decade or more are getting beat by the Honda bikesaws.
European's now got their rotary Wankel saws ripping too setting world records.
Any smaller wood the 125's will be winning.

Been looking at a full circle Hotrods 4006 ATC/TRX crankshaft for my semi full circle 1983 engine. The 1984 CR250R also shares the 4006 so I see.
From my research seals bearings will fit up. 4006 PTO side splined stub is exact same as mine, plus the longer 28mm mag stub at the seal point will also fit mine.
Only thing I'm not sure about is the 4006 the same width between the '83 crankcase main bearings. I measured 70mm.
Sent a message to Hotrods and one of their suppliers, heard nothing back yet.
But for a 9000-10k rpm engine is the better crankcase compression pressure worth it?

 

[Bigmac]

Been doing some research, I think the 85 bottom end is the most trx friendly, I looks like 83-84-85 were one year motors the 86 -91 had some common parts but could be wildly different too, the 87-88 cases cylinders were different.

that crank won’t work in the 83, it could be made to work in the later cases but need machine work, with the esr 330, the 92-01 cases are and excellent platform and ignitions from 97-01 are excellent, and a bolt on