Radical Factory Honda 250r - Circa 1982

[troybilt]

I've been going back to some old old Dirtwheels mags and came across an interesting article on a Factory Honda 250r for Stadium cross... Dean Sundahls Atc. Anyway, here's what was interesting:

"...after the crankcases are matched, RPM (Racing Products for Motorcross in Toledo Ohio) cuts a small boost port into the front transfers. This allows the fuel/air charge to start its trip to the top a little sooner..."

Keep that in mind when you read this:

"The crankshaft receives RPM's unique "turbo" modification. The crank is full-circled, stuffed, and balanced. With this balancing, the 250r counterbalancer can be removed, allowing the engine to rev move freely because it has less weight to turn."

Next part is really interesting to me:

"Special "veining" is then cut into the outer circumference of the flywheels. This machining, when used with the small boost port (from above) cut into the cases, actually forces the charge into the transfer ports and up to the combustion chamber, giving the engine a sort of "two-stroke turbo" effect, as well as fully atomizing the fuel/air mix for better burn. This is the most expensive mod done by RPM, as well as, being an exclusive in the engine-building field." [by Staff of Dirt Wheels, Oct 1982, Dirt Wheels]

I thought that was interesting and never heard of it. Maybe its common knowledge, but I thought I'd share.

[bigmatt61]

Are we talking something like knurling a crank?

[hartwill]

I don't know what the Hell any of that means, but I want one. lol.... you said this place is in Toledo? I'm only an hour away from there. wonder if they are still in business?

[bigmatt61]

Now that I read that better, it does sound like your knurling the throws of the crank. I've had that on all my 250r race motors.

[woodsracer144]

what is knurling the crank???

[troybilt]

Originally posted by bigmatt61
Now that I read that better, it does sound like your knurling the throws of the crank. I've had that on all my 250r race motors.

Big Matt, depends on what knurling means. I wish I could show you all the pictures, but what they did was on the flywheels of the crank, machined very small "grooves" or what appears to be grooves on the entire circumference of the flywheels on both sides of the connecting rods. The "grooves" act like tiny squirrel cage fan blades (more or less) that when spun by the motor, create a positive air pressure, that forces the mixture back up the transfer ports. An easy way to think about is welding turbo compressor blades to the crank flywheel, and machining in a boost port into the cases for better pathway for the mixture. I've not seen this on anything since those 1982 motors back then. But if you could imagine there were no other competitive bikes other than the ATC250r, reminds me of nascar, where the cars are all even, so the motor gurus came up with all sorts of clever ways to gain an advantage. Very interesting times in the atv racing world back then.

[hondamancbr03]

They also called it "Turbo Cutting" the crank...This was thought to aid in the scavenging effect. No real numbers ever appeared on a dyno from it so it became a lost art.
Couple years back I split a motor apart for a friend and found such a creature, I took it my local crank guy who does all my true/welding of my cranks....He said it never really caught on because it would provide enough of an advantage to make it worth the cost.

[troybilt]

Originally posted by hondamancbr03
They also called it "Turbo Cutting" the crank...This was thought to aid in the scavenging effect. No real numbers ever appeared on a dyno from it so it became a lost art.
Couple years back I split a motor apart for a friend and found such a creature, I took it my local crank guy who does all my true/welding of my cranks....He said it never really caught on because it would provide enough of an advantage to make it worth the cost.

That's interesting, thanks for sharing. According to the article they thought it was the greatest thing since sliced bread... but you know how Dirt Wheels can be... not much has changed since 1982 for them... LOL!!

I wonder if a guy could expand on that thought? ... or if there is anything there to research?

[hondamancbr03]

The turbo cutting is the only time I’ve ever heard of anyone trying to improve the scavenging of the two stroke cycle....IMO scavenging is an area that can be improved and if ever done correctly should show some HP on the dyno or seat of the pants dyno. During the early 90's in when the really aggressive porting started to take place from companies like JD, and then stroker cranks came into the game for the Banshee riders and builders realized "Why waste time on improving scavenging when you can port big and stroke bigger"

I have access to one of the original JD builders here local, he was working for Jim back when they were doing all the R&D on Banshee's trying to make a name for the company. I have to contact him for some advice so I’ll throw the scavenging question his way and see what he says.

BTW.....The one item that caught my attention was a balanced stuffer crank (which I’m a fan of for mini's) and removing the balancer, that is something I would like to research.

[troybilt]

Originally posted by hondamancbr03
The turbo cutting is the only time I’ve ever heard of anyone trying to improve the scavenging of the two stroke cycle....IMO scavenging is an area that can be improved and if ever done correctly should show some HP on the dyno or seat of the pants dyno. During the early 90's in when the really aggressive porting started to take place from companies like JD, and then stroker cranks came into the game for the Banshee riders and builders realized "Why waste time on improving scavenging when you can port big and stroke bigger"

I have access to one of the original JD builders here local, he was working for Jim back when they were doing all the R&D on Banshee's trying to make a name for the company. I have to contact him for some advice so I’ll throw the scavenging question his way and see what he says.

BTW.....The one item that caught my attention was a balanced stuffer crank (which I’m a fan of for mini's) and removing the balancer, that is something I would like to research.

What is a "stuffer" crank just for my clarification? I think I knew but I'm not sure.

I'd love to do some R&D on this stuff, the possibilities are endless.

I like to study this stuff is there any books that you'all recommend? I'm getting a couple from amazon now. I took a couple classes in college on IC engines but it was pretty basic and discussed all power cycles. I want to hone in on the 2 stroke stuff.

[woodsracer144]

Just when I think i start to get a grasp on this stuff someone has to bring up another topic and then I'm totally lost again! Thanks Troy. nice move! now i have to spend hours surfin the web for it...

[wilkin250r]

Originally posted by troybilt
What is a "stuffer" crank just for my clarification? I think I knew but I'm not sure.

I'd love to do some R&D on this stuff, the possibilities are endless.

I like to study this stuff is there any books that you'all recommend? I'm getting a couple from amazon now. I took a couple classes in college on IC engines but it was pretty basic and discussed all power cycles. I want to hone in on the 2 stroke stuff.

I've seen several slightly different interpretations of stuffed cranks.

Crankshafts, by natural design, aren't perfectly round. They have more material at one end to balance the weight of the piston. You can see this on many 4-stroke crankshafts, they don't need to be stuffed because their crankcase isn't part of their intake track.

https://xcbobcom.accountsupport.com/shoppe/catalog/images/hr%204st%20crank.jpg

For a 2-stroke crank, however, this would cause severe turbulence in the crankcase, and if you analyze the crank position through it's stroke, you'd see that you would be effectively "trapping" air underneath the crank during the intake cycle.

A "stuffed" crank creates a hollow or filled with some type of material to make the crank perfectly round to correct this problem.

http://www.1dirracing.com/catalogs/prodthumb/t_16766.jpg

[hondamancbr03]

Originally posted by troybilt
What is a "stuffer" crank just for my clarification? I think I knew but I'm not sure.

I'd love to do some R&D on this stuff, the possibilities are endless.

With a stuffer crank a very little amount of material is removed (if any), just enough to balance the crank with the addition of the filler material, the plastic filler is added to reduce crank case volume, which ultimately is how you gain HP, The lower the crankcase volume the higher the case PSI is on the down stroke so when the intake port opens, you will get a stronger surge of fuel as well as a stronger pipe signal.

It gives you a better bottom and mid range power which is why i use them on my mini builds, those little pistons and strokes can use all the help they can get.

You can find stuffer cranks for Blasters everyday, but i haven't researched them for Honda or Banshee. Be careful when buying stuffed cranks, there are good and bad ones available and nothing worse than having the filler material fly out during full throttle!

I wish my bank acount would allow me to live the life of a two stroke R&D junky.

[troybilt]

Originally posted by woodsracer144
Just when I think i start to get a grasp on this stuff someone has to bring up another topic and then I'm totally lost again! Thanks Troy. nice move! now i have to spend hours surfin the web for it...

I know me too, I find and article or website with some interesting information and its just throws me for a loop.

So far from what I'm reading the old-schoolers, i.e. pre-1986/87 knew their crap on the 2 strokes... they knew just how to get every ounce of usuable power from these badboys. They forgot more about these these motors than I'll ever know reading books and studying on the internet.

[troybilt]

Originally posted by hondamancbr03
With a stuffer crank a very little amount of material is removed (if any), just enough to balance the crank with the addition of the filler material, the plastic filler is added to reduce crank case volume, which ultimately is how you gain HP, The lower the crankcase volume the higher the case PSI is on the down stroke so when the intake port opens, you will get a stronger surge of fuel as well as a stronger pipe signal.

It gives you a better bottom and mid range power which is why i use them on my mini builds, those little pistons and strokes can use all the help they can get.

You can find stuffer cranks for Blasters everyday, but i haven't researched them for Honda or Banshee. Be careful when buying stuffed cranks, there are good and bad ones available and nothing worse than having the filler material fly out during full throttle!

I wish my bank acount would allow me to live the life of a two stroke R&D junky.

So do they "stuff" the crankcase with material or the crank to reduce the volume?

[troybilt]

Here's the article, its not mine but I have the same issue at home:

http://airfoolers.com/?page_id=739

[hondamancbr03]

Originally posted by troybilt
So do they "stuff" the crankcase with material or the crank to reduce the volume?

They stuff the crank with plastic and then balance the crank...It's the same as the "cans" we have on our 250R cranks but they try and fill all the voids when using the plastic.

I attached a picture of a Blaster stuffer.....I'm looking for a stuffer for a 250R but haven't found anything yet.

[woodsracer144]

that stock crank shaft has 2 spots milled flat on it by the bearing for the connecting rod... i don't think that is right? is it?

[hondamancbr03]

Originally posted by woodsracer144
that stock crank shaft has 2 spots milled flat on it by the bearing for the connecting rod... i don't think that is right? is it?

Which picture?

[woodsracer144]

oh sorry its under that air foolers link. its on the 3rd page i think... theres 2 cranks sitting next to each other..

[hondamancbr03]

Originally posted by woodsracer144
oh sorry its under that air foolers link. its on the 3rd page i think... theres 2 cranks sitting next to each other..

The flywheel side looks odd to me.....It just may be a generic crank picture off Hot Rods website.

Look at the flywheel side lenght compared to the one above.

But i believe he was showing the picture to reference a crank with cans and a four stroke without.

[bigmatt61]

Example of a stock crank.

[bigmatt61]

Knurled crank. Sorry about the poor picture quality.

[quadrcr161]

ive heard of people adding the groves and even fins to the crank but never had any of my motors with those mods.

Im sure there is a very fine line between getting a gain or loosing HP doing something like this. im sure theres those who have mastered doing this though. Like a pump you have to have the right conditions on both sides to get the best efficiency or you can cause cavitation, vibration due to the added material or cause imbalance to the rotating assembly, none of those would be good things to have happen.

[wilkin250r]

Originally posted by woodsracer144
that stock crank shaft has 2 spots milled flat on it by the bearing for the connecting rod... i don't think that is right? is it?

Yeah, that's common on older cranks, I think it's a balancing issue. That area is in rotational phase with the piston, so cutting that off means the OPPOSITE side is off-balance. So the off-balance side counteracts the piston, when the piston moves down, the off-balance side is moving up.

[woodsracer144]

Originally posted by bigmatt61
Knurled crank. Sorry about the poor picture quality.

Wouldn't you want the lines to go one way and not two? I would think that the one direction would be best, Crank spins counter clock wise from flywheel side, so would you want the lines, if they would meet, to make an arrow pointing towards the front of the ATV? thus, forcing the air out and up? I feel as if the two direction thing would counter act each other and not be able to help.

I also thought the grooves would be much deeper then they really are.

[hondamancbr03]

Originally posted by woodsracer144
Wouldn't you want the lines to go one way and not two? I would think that the one direction would be best, Crank spins counter clock wise from flywheel side, so would you want the lines, if they would meet, to make an arrow pointing towards the front of the ATV? thus, forcing the air out and up? I feel as if the two direction thing would counter act each other and not be able to help.

I also thought the grooves would be much deeper then they really are.

There have been several attepts to help with the scavenging, the method i have come across was as you described with the cuts running across the crank.

Neither method made enough difference to warrant the cost and thus it became a lost art.

[2-330s]

i have seen a few cranks that were "turboed" trinity did them one was a 250r the other was a quad 500. both motors ran good but, i thought for flattrac quads they could've been faster. they had horizontal lines cut into them.

[woodsracer144]

I think we could dig this back up and a few of us test them...I have the ablity to get some fairly good deals on a dyno i think... so if you want to get something together...

second is that I think that there is lot that would effect the out come of those cuts
the dept, the angle of them, as well as how many and spacing of them.

You could get a cutter that would mount on a lathe that wouldn't take very long to get it set up.

any one have any other pics of that done to a crank shaft?

[hondamancbr03]

Originally posted by 2-330s
i have seen a few cranks that were "turboed" trinity did them one was a 250r the other was a quad 500. both motors ran good but, i thought for flattrac quads they could've been faster. they had horizontal lines cut into them.

Trinity tried to think outside the box for a while with cranks and their heads as well.....They still to this day turbo cut the head. I have a head on my bench that is an early moddel done by JD i believe when they were doing the R&D.
I'll take a picture and post when i get home.....It made me laugh when i seen it!

[bigmatt61]

I do not claim to understand alot about two stroke engines.
That being said I can tell you what I was told as to the reason this"diamond knurl" was added to the web of the crank. It helps "throw" any residual oil in the bottom of the case around, thus aiding in lubrication. Since the knurl is not pushed up enough to cause rotational issues or damage to the cases and was free, I didn't see a problem with trying it.
Since the posting of the info in the DW mag I can now also see how it might help atomize fuel and "pack" or "push" more thru the transfer ports.
It also explains why I was told it was a little known trick that few people remembered.
Now does it truly help "pack" more fuel, I don't know. I do know the lubrication thought behind it is right on. After sitting awhile I can go out and grab the rod and rotate the crank and it brings oil up every time.
As to why a knurl as opposed to a slot or groove, I'm guessing here, since your not removing material just moving it around you shouldn't have balance issues?

[hondamancbr03]

[i] I'm guessing here, since your not removing material just moving it around you shouldn't have balance issues? [/B]

It's not only a balance issue, it's a trueing issue as well....Most all cranks come balanced from the factory these days (not all), what they don't do is come in perfect condition as far as trueing goes. My last Hod Rod crank come out of the box and directly on the crank stand and was outside of the Yamaha (Banshee) specs for a trued crank.

If you start hammer knurl's all around the crank i can almost promise you it will push it out of true....The way you true a crank is with a soft brass hammer, a crank stand and dial caliper and spin and smack, spin and smack....Not pretty but that's how it's done. So you can imagine what smacking knurl's on the crank is going to do.

[bigmatt61]

Is it possible for the crank to be trued after being knurled?

[hondamancbr03]

Originally posted by bigmatt61
Is it possible for the crank to be trued after being knurled?

Sure is....Most machinist call it crushing or spreading depending on which way the crank needs to be moved.

[hondamancbr03]

Originally posted by hondamancbr03
I'll take a picture and post when i get home.....It made me laugh when i seen it!

Ok....As promised here's a picture for all to enjoy! This was WAY back in the R&D day's of JD. Trinity has perfected this method with CNC i believe.

[woodsracer144]

good point!

[mxduner]

With this balancing, the 250r counterbalancer can be removed tick tick... tick tick:cool:

[woodsracer144]

Originally posted by hondamancbr03
Ok....As promised here's a picture for all to enjoy! This was WAY back in the R&D day's of JD. Trinity has perfected this method with CNC i believe.

whats that do?

[250rPRIDE]

ya tom carlson TC made a power star head, even changable ones with differant cc's for differant compresstion and feuls, tom is one of the best builders around but i dont think it did much,

as for the cranks i have seen my good friend WASTE big money on a turbo cranks which had the big deep cut fins in it, and he also had a crank centrafused, it was weird with like holes drilled in it, he was a drag racer and had to keep in the 250cc class so they always were looking for little tricks ect.. but neither one of these were good for no more than mabe a tenth in 500ft, if that, he sent in new oem honda cranks to get this work done and in my eyes he ruined to good factory cranks. haa now hes back to stock.. take it for what you like, this is just what i seen from one person...

[hondamancbr03]

Originally posted by woodsracer144
whats that do?

In THEORY it was to create a funnel reaction that would focus the fule to the spark plug.....Notice how the cuts turn and angle to the plug. Trinity still does this I believe but they have perfected it by using the CNC or another type of non-human method.

This is a friends motor i'm building for him, i'm sure with this CUSTOM head he will fly right by me!:)

[Higgy87TRX425]

I've never heard of "Hammer Knurling". The knurling that I've done Has been on a Lathe with a knurling tool. The knurling tool is held in the tool holder at exactly the same angle as the piece to be knurled, then the tool is slowlly moved into position on the part thats being turned until the proper knurl is showing up on the part. As long as the preesure of the tool against the part remains the same I don't see how this could through your crank way outta wack! I imagine that it would stay pretty true. I've never seen anyone use a hammer when knurling! By the way, I'm a Machinist and I'm postive that the knurling that I saw on that crank in the photo was done on an engine lathe. And to answer that other guys question I don't see why you couldn't true a crank after it had been knurled, but if its already been trued I think it might be a waste of time. Anyway just my thoughts on the issue. Not that anyone asked me, but it is an interesting topic.

[hondamancbr03]

Originally posted by Higgy87TRX425
I've never heard of "Hammer Knurling". The knurling that I've done Has been on a Lathe with a knurling tool. The knurling tool is held in the tool holder at exactly the same angle as the piece to be knurled, then the tool is slowlly moved into position on the part thats being turned until the proper knurl is showing up on the part. As long as the preesure of the tool against the part remains the same I don't see how this could through your crank way outta wack! I imagine that it would stay pretty true. I've never seen anyone use a hammer when knurling! By the way, I'm a Machinist and I'm postive that the knurling that I saw on that crank in the photo was done on an engine lathe. And to answer that other guys question I don't see why you couldn't true a crank after it had been knurled, but if its already been trued I think it might be a waste of time. Anyway just my thoughts on the issue. Not that anyone asked me, but it is an interesting topic.

The crank work in the picture does not look like it was done by hand i will agree with that, i know for a fact that early days of turbo cutting or knurling was done by hand until tooling was developed. And as for the "Way outta wack" issue, i myself find trueing to be something that i don't wait until it's "why outta wack" before putting it on the crank stand to check. I look at trueing as important as balancing IMO.

And for my engine builds, if i found a machinist to knurl my crankI would without question have it checked for true. I have to ask, for the 5mins it takes to put the crank on the stand and spin it to check....Why not do it? Or why even suggest not doing it?

[1promodfan]

The crank thats in my 250R has been turbo'd cut. (thats what I was told it was called) Hank's engine builder up out of Virginia done his cranks like that. I didn't know what it was until someone told me about it. I was also told it helped create a type "turbulance" in the crank cases. I hope this helps on the topic.

[Higgy87TRX425]

I see nothing wrong with truing the crank after knurling it! I was thinking that since ur not using a hammer on it when knurling, it shouldn't be much if out of balance at all if you've already trued the crank. I do agree if it only takes you a short time why not check it. Better to take the time and do it right the first time. That hand done knurling you spoke of, scares me because I know that knurling tools have been around for years. It's the difference between precision measuing within thousanths on a Lathe which is very precise, and doing it by hand which would be real hard to measure precisely.

[hondamancbr03]

[i] I know that knurling tools have been around for years. It's the difference between precision measuing within thousanths on a Lathe which is very precise, and doing it by hand which would be real hard to measure precisely. [/B]

This took me about 2 mins to google on Knurling....The Machinist i use said in the early days they wouldn't knurl the entire lobe so it was just as easy to stamp it. Most machinist are known for being fanatics about tight tolerences so that's why i was a little surprised you would suggest not checking the crank after working on it.
Your tag says you live in the Portland area....Does the shop you work in do two stroke work? Boring, head work, case work? Always looking for another shop.


"The knurling tool itself is fixed into the lathe and cautiously directed to the turning piece with a tiny crank unlike the first knurling tools to be used where as a selection of three types of patterns (straight, angled and diamond) were available on high strength steel stamps to be used in small areas and most commonly flat surfaces. Since knurling is extremely a rough process, the machinist must use a liberal supply of machine oil on the rotating shaft. A knurling tool hardly ever makes a complete imprint the first time it is pressed against the shaft. Machinists usually make several passes with the knurling tool, allowing the individual cutters to make small bites into the metal."

[Higgy87TRX425]

Ur right we always check and recheck everything we do! My thoughts were about how much putting a knurl on a crank would change it, or throw it outta true. If ur were using a hammer on it then by all means recheck the truing. I was just saying that I don't see the truness of the cranck changing that much after knurling done on a Lathe. With a hammer and a stamp definately. I didn't mean not to check it my point was that I didn't think that knurling with a lathe would change the truness much it at all. There's never anything wrong with rechecking ur work. We all do it, probably more then we should. Sometimes it just gets a little fanatical like you said. Thats my point. No I don't work on 2-stroke engines at my job. I'm thinking about looking for a job in a shop that either builds motors or machines parts for bikes. I've been running a 2000w CNC Amada Laser for a while. I actually made sprokets for my dirtbike a while back on the laser. They turned out pretty good!! Living where I do we have alot of shops that build motors and produce aftermarket parts for bikes. Cascade, Direct Drive, Trinity, White Knuckel, Chozen Preformance just to name a few are all within driving distance to me So I'm thinking about changing jobs and doing some machine work for someone in the industry. You gotta love what you do if ur gonna do it for any length of time. I just don't wanna burn myself out!! If I combine my hobbies with my Employment I'll either love it or leave it! I just saw that you're from Oregon too. Where about?

[hondamancbr03]

I'm in the Portland area as well......After being on this forum for a while and seeing the names and some of the builders (LRD,LED,Cascade etc etc) that are mentioned and knowing that i am within walking distance of most all of them makes me appreciate our area.

You gotta love being able to look Arlen in the eyes as he provides you with a life time of information! or stand in the show room of Cascade and drool!

If I had a job working with any of those no one could stand perma grin stuck on my face!

[Higgy87TRX425]

Yeah I hear that, I think it might be hard to work if you're we're always checking out all the bikes and cheesing over all the badass parts that cost an arm and a leg!!

I know that good machinist are almost always in need. So I think that it would be best to build a repore with the shop you wanna work at and then try and get in. If you know your sh$$ then I'm sure that it will show, it always does one way or another.

We are pretty fortunate to live where we do. Like you were saying talk to a few of the guys on here and you realize that real quick!! God bless the Pacific Northwest. Great ridding and great builders that you gotta love!! Anyway man nice talkin to ya! Hit me up again or I'll bust into another one of your conversations, Ha Ha!! Later.