Full Tilt CR250 Build - MXA Two Stroke Hall of Fame

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40 12/28/2015 5:21am
12/28/2015 5:21am
blackdiamond wrote:
This is what Varner's spec looks like on this bike. [img]https://p.vitalmx.com/photos/forums/2015/12/27/117073/s1200_20151224_134819_resized.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2015/12/27/117074/s1200_20151224_140319_resized.jpg[/img]
This is what Varner's spec looks like on this bike.





The Varner head is very similar to RB Designs. Expect it to run well. A dyno chart comparing your Varner engine with PR2 would be great.
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40 12/28/2015 5:25am
12/28/2015 5:25am
blackdiamond wrote:
I appreciate all the compliments fellas, I have a lot of blood sweat and tears in this one so I am glad all the 2 smoke...
I appreciate all the compliments fellas, I have a lot of blood sweat and tears in this one so I am glad all the 2 smoke die-hards dig the thread. It's too bad Honda couldn't just step up and keep developing the smokers so we could all just buy one like this off the showroom floor (or at lest something close to it)
Amen, brother
Reefer Sutherland 12/28/2015 5:28am
12/28/2015 5:28am
Awesome Johnson wrote:
Reefer, how was the watts built 02 cr in regards to low-mid-high end power. Was it gobs of power all around or mild to warp speed...
Reefer, how was the watts built 02 cr in regards to low-mid-high end power. Was it gobs of power all around or mild to warp speed type thing?

Black, I can't wait to see this finished but at the same time totally digging every post. I got a 2007 cr250 that is due for a tear down refresh and a lot of what I've seen so far will make its way on my bike. Thanks for this killer build thread!
It didn't make a lot of bottom. The power was all up top. I've never shifted less on a twostroke. It just kept pulling and never fell off. This was at Budds Creek too, up those hills.

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kiwifan
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kiwifan 12/28/2015 11:41am
12/28/2015 11:41am
some sick cylinder work there !!!! these sort of builds certainly get the juices flowing to getting a 2 stroke, now i know why the factory Hondas were real powerplants, there is obviously a lot of potential for meg hp in these motors...getting RV on this bike would be fun too, and being raced in the 2 stroke champs lol :-)
blackdiamond
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blackdiamond 12/28/2015 12:28pm
12/28/2015 12:28pm
bvm111 wrote:
You guys have me interested in the ignition, could it work on a 2006 KX250? I have a Tom Morgan tuned engine and it rips... But...
You guys have me interested in the ignition, could it work on a 2006 KX250? I have a Tom Morgan tuned engine and it rips... But I like the idea of trying new things as well, even though I really need to get my suspension set up better before I go looking for extra HP! Tongue
blackdiamond wrote:
I am almost certain it is not offered for that bike, they are only offered for the RM125, CR250 and CR500 to my knowledge. They don't...
I am almost certain it is not offered for that bike, they are only offered for the RM125, CR250 and CR500 to my knowledge. They don't really focus on MX but you could always try to get in touch with them at www.zeeltronic.com
Reefer Sutherland wrote:
They'll make it, but they won't have a basemap. And if you don't have an electronic powervalve it might not be worth it. You don't realize...
They'll make it, but they won't have a basemap. And if you don't have an electronic powervalve it might not be worth it. You don't realize how much that PV flutters until ol 'Borut' at Zeeltronic hooks you up. I found out about those guys through cars actually. They did a Skyline ignition that was popular. Didn't end up running it in mine (megasquirted it) but they know their shit and I kept them in mind.

I'm probably preaching to the Pope, but, are you aware that, if you were so inclined, you could run multiple ignition maps, (3) and in conjunction with the TPS sending unit, and engine rpm, the CDI can detect wheelspin, and then automatically revert to the more mild of the 3 ignition maps until the wheelspin stops, then revert back to aggressive map. It would be imperceivable to the rider, but it would hook up sooo well. Toss in programmable powervalve modulation and you have a traction controlled two stroke with a electric smooth powerband.

If you were inclined.
He got back to me this morning with 6 different power valve maps to try.
Mit12
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Mit12 12/28/2015 2:22pm
12/28/2015 2:22pm
Mit12 wrote:
I do not understand why they would have a flat spot on the out side of the head and the squish inside with a domed piston...
I do not understand why they would have a flat spot on the out side of the head and the squish inside with a domed piston. The picture of the Varner head is a way more conventional design. Yamaha did testing on heads and squish clearance. What they found is they will keep making more power when you tighten up the squish clearance all the way until the piston hits the head. Squish area, angle and radious all make a big difference in power and RPM. It all comes down to proper squish velocity for the RPM you are ported for.
slipdog wrote:
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend...
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend the new squish band into the dome and get volume(cc's) back after decking the cylinder
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
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slipdog 12/28/2015 2:37pm
12/28/2015 2:37pm
Mit12 wrote:
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston...
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
The Cr250 has a flat top piston.
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JW381 12/28/2015 3:34pm
12/28/2015 3:34pm
Sticky!!!
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RMRider1 12/28/2015 3:50pm
12/28/2015 3:50pm
Mit12 wrote:
I do not understand why they would have a flat spot on the out side of the head and the squish inside with a domed piston...
I do not understand why they would have a flat spot on the out side of the head and the squish inside with a domed piston. The picture of the Varner head is a way more conventional design. Yamaha did testing on heads and squish clearance. What they found is they will keep making more power when you tighten up the squish clearance all the way until the piston hits the head. Squish area, angle and radious all make a big difference in power and RPM. It all comes down to proper squish velocity for the RPM you are ported for.
slipdog wrote:
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend...
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend the new squish band into the dome and get volume(cc's) back after decking the cylinder
Mit12 wrote:
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston...
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The head was spec to run race gas, removing head volume is what is done to run pump gas....final squish measured at .055 from Gorr...Bike is extremely smooth with 0 abrupt hit...just a smooth manageable power delivery with head work and .03 shaved off cylinder base...
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Mr Happy 12/28/2015 4:19pm
12/28/2015 4:19pm
Bearuno wrote:
One of the best modification article series on the 03 - 07 CR250 was on the Two Stroke Motocross.com site. Very extensive, going as far as...
One of the best modification article series on the 03 - 07 CR250 was on the Two Stroke Motocross.com site. Very extensive, going as far as reinforcement welds in the crank cases to cover known weak areas. With the site it appears now dead and gone, I don't know how the series would be found.

Fair enough removing gears, if light weight is the goal. Though, you need to consider that the 3 spd Bike It / Cosworths Yamahas ( no idea on the KXfs, but I assume they might have tried the mega revs / minimal gears concept) were engines that revved to 16,500 rpm, and perhaps more. One Pom mag that regularly tested KTMs Works Bikes ( they tested Ferris's Bike It 3speed YZf that he did so well on, too) each season had, one year, the 250fs as having 4 gears - once again, engines that rev to the moon. A 2502T - not so much - most have peak power at between 8 and 9k. Yes, you can tune it for much higher power at higher revs, but it won't be much of an MX engine.

You can always carry a variety of sprockets and chains. Hell, in (many, many) years gone by, in OZ SX , teams / riders would sometimes run no gear lever, to avoid missed shifts/ impact / center punch shifts, on our tiny little AX style SX tracks of the era.

That ignition from one of the former Czech / Slovak countries? If it's the one I'm thinking of, they also do new powervalve motors, which, I've heard, are difficult to get, ex Honda.

The gen3 CR 250 frame is still my favourite Honda AF chassis.
These articles?
Part 9
Other parts
RMRider1
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RMRider1 12/28/2015 4:35pm
12/28/2015 4:35pm
Bearuno wrote:
One of the best modification article series on the 03 - 07 CR250 was on the Two Stroke Motocross.com site. Very extensive, going as far as...
One of the best modification article series on the 03 - 07 CR250 was on the Two Stroke Motocross.com site. Very extensive, going as far as reinforcement welds in the crank cases to cover known weak areas. With the site it appears now dead and gone, I don't know how the series would be found.

Fair enough removing gears, if light weight is the goal. Though, you need to consider that the 3 spd Bike It / Cosworths Yamahas ( no idea on the KXfs, but I assume they might have tried the mega revs / minimal gears concept) were engines that revved to 16,500 rpm, and perhaps more. One Pom mag that regularly tested KTMs Works Bikes ( they tested Ferris's Bike It 3speed YZf that he did so well on, too) each season had, one year, the 250fs as having 4 gears - once again, engines that rev to the moon. A 2502T - not so much - most have peak power at between 8 and 9k. Yes, you can tune it for much higher power at higher revs, but it won't be much of an MX engine.

You can always carry a variety of sprockets and chains. Hell, in (many, many) years gone by, in OZ SX , teams / riders would sometimes run no gear lever, to avoid missed shifts/ impact / center punch shifts, on our tiny little AX style SX tracks of the era.

That ignition from one of the former Czech / Slovak countries? If it's the one I'm thinking of, they also do new powervalve motors, which, I've heard, are difficult to get, ex Honda.

The gen3 CR 250 frame is still my favourite Honda AF chassis.
Mr Happy wrote:
These articles?
Part 9
Other parts
That's an older than '02 build...
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Mr Happy 12/28/2015 4:50pm
12/28/2015 4:50pm Edited Date/Time 12/28/2015 4:51pm
RMRider1 wrote:
That's an older than '02 build...
Fair enough, I've not owned either so have no idea. The last archived copy of the site is from Feb 2015 so if they were published after that date then it looks like they're gone.
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slipdog 12/28/2015 5:12pm
12/28/2015 5:12pm Edited Date/Time 12/28/2015 5:23pm
RMRider1 wrote:
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The...
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The head was spec to run race gas, removing head volume is what is done to run pump gas....final squish measured at .055 from Gorr...Bike is extremely smooth with 0 abrupt hit...just a smooth manageable power delivery with head work and .03 shaved off cylinder base...
Edit: Sorry RMRider, I just saw you had an '06 and I thought you were talking about an earlier flat top motor. I will assume you are correct as I don't know about the '06 set up
RMRider1
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RMRider1 12/28/2015 6:04pm
12/28/2015 6:04pm Edited Date/Time 12/28/2015 6:04pm
RMRider1 wrote:
That's an older than '02 build...
Mr Happy wrote:
Fair enough, I've not owned either so have no idea. The last archived copy of the site is from Feb 2015 so if they were published...
Fair enough, I've not owned either so have no idea. The last archived copy of the site is from Feb 2015 so if they were published after that date then it looks like they're gone.
Cool link though!
blackdiamond
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blackdiamond 12/28/2015 6:27pm
12/28/2015 6:27pm
Mit12 wrote:
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston...
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
slipdog wrote:
The Cr250 has a flat top piston.
The 2002-2004 are flat top, the 2005-2007 are domed if I remember correctly. Here are a few pics of the forged single ring Wossner piston we are going to run in this setup. Wossner offers this piston in 3 different sizes and in a single or double ring format.







Bearuno
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Bearuno 12/28/2015 8:20pm
12/28/2015 8:20pm
RMRider1 wrote:
That's an older than '02 build...
Mr Happy wrote:
Fair enough, I've not owned either so have no idea. The last archived copy of the site is from Feb 2015 so if they were published...
Fair enough, I've not owned either so have no idea. The last archived copy of the site is from Feb 2015 so if they were published after that date then it looks like they're gone.
As the others have said, no, not that one. It is the #15 bike pictured a fair few posts ago.

I don't think the articles were produced originally for the 2TMotocross site - they may have been transferred over from another site / FB, then added to?

2TMX had them up - they were certainly earlier than Feb 2015 (well, the '2010' pretty much gives the inception date of the project, but I'm pretty sure I didn't see it on 2TMX till much later than that) - but they seemed to disappear from the sites archives sometime before the site closed down. As I said, the engine cases had quite extensive weld reinforcements done, (as the article writer said) to serve as a preventative measure. I'd never heard case cracking problems were a common thing with the case reed engine, indeed, some pretty knowledgeable tuners I directed to the articles had not experienced such problems, but, they did not knock the reinforcement welds. They did say some sections near some bearing landings, were quite thin / worrying, especially if you were intent on going for the mid / high 50 HP mark.

It was a 'take' on the owners / tuners involved ideas of what could have been the sort of development of the 07s through to 2010, if Honda hadn't decided to stop 2t production by the 2007/08 year, at least a decade before.

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Joko
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Joko 12/28/2015 8:23pm
12/28/2015 8:23pm
zehn wrote:
Honda KYB SSS? Huh?
blackdiamond wrote:
Basically, the same basic fork that the Yamahas use currently (and the best performing IMO) but in the Honda version which was last spec'd on the...
Basically, the same basic fork that the Yamahas use currently (and the best performing IMO) but in the Honda version which was last spec'd on the 2012 CRF450.
Didn't the 2014 CRF250 have showa forks?
Mit12
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Mit12 12/28/2015 8:29pm
12/28/2015 8:29pm
slipdog wrote:
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend...
Assuming you're talking the Eric Gorr head, the flat spot on the outside is the squish band. The second cut is the angle he used blend the new squish band into the dome and get volume(cc's) back after decking the cylinder
Mit12 wrote:
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston...
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
RMRider1 wrote:
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The...
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The head was spec to run race gas, removing head volume is what is done to run pump gas....final squish measured at .055 from Gorr...Bike is extremely smooth with 0 abrupt hit...just a smooth manageable power delivery with head work and .03 shaved off cylinder base...
Ok I understand now. I thought the piston was domed not flat. I would imagine that the area that looks flat is probably 1 to 1 1/2 degrees tapered toward the center?
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burn1986 12/28/2015 8:55pm
12/28/2015 8:55pm Edited Date/Time 12/28/2015 8:56pm
That bike may be a little too powerful, lol. The 07 CR I had was a downright beast (I shouldn't have ever sold it) and I didn't have anything done to it, just a fresh piston and crank. This CR build is kind of making me sweat and water at the mouth. Smile
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FWYT 12/28/2015 9:17pm
12/28/2015 9:17pm
blackdiamond wrote:
The front caliper is a slightly modified Ride Engineering billet caliper with lightened pistons and the rear is a 2015 CRF 450 caliper that has been...
The front caliper is a slightly modified Ride Engineering billet caliper with lightened pistons and the rear is a 2015 CRF 450 caliper that has been machined to reduce the weight slightly and help with cooling. The rear brake piston has flutes machined into it like some of the braking systems frequently used on race cars and GP bikes. This mod greatly reduces the heat transfer from the brake pad to the piston by allowing it to vent. After the piston modification it was DLC coated for less friction and drag. All of the caliper pins, brake pad pins and bleed nipples are specialty parts from Racetech Titanium. The caliper pins are DLC coated as well for less friction.

The pics below show the calipers in various stages with these mods.















Sweet thread! It's giving me that warm fuzzy feeling!! Smile

Did you consider a four piston front caliper like the Magura or Brembo units?
blackdiamond
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blackdiamond 12/28/2015 9:22pm
12/28/2015 9:22pm
zehn wrote:
Honda KYB SSS? Huh?
blackdiamond wrote:
Basically, the same basic fork that the Yamahas use currently (and the best performing IMO) but in the Honda version which was last spec'd on the...
Basically, the same basic fork that the Yamahas use currently (and the best performing IMO) but in the Honda version which was last spec'd on the 2012 CRF450.
Joko wrote:
Didn't the 2014 CRF250 have showa forks?
Sorry about that you are exactly right, I meant to say 2012 CRF450
blackdiamond
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blackdiamond 12/28/2015 9:26pm
12/28/2015 9:26pm
blackdiamond wrote:
The front caliper is a slightly modified Ride Engineering billet caliper with lightened pistons and the rear is a 2015 CRF 450 caliper that has been...
The front caliper is a slightly modified Ride Engineering billet caliper with lightened pistons and the rear is a 2015 CRF 450 caliper that has been machined to reduce the weight slightly and help with cooling. The rear brake piston has flutes machined into it like some of the braking systems frequently used on race cars and GP bikes. This mod greatly reduces the heat transfer from the brake pad to the piston by allowing it to vent. After the piston modification it was DLC coated for less friction and drag. All of the caliper pins, brake pad pins and bleed nipples are specialty parts from Racetech Titanium. The caliper pins are DLC coated as well for less friction.

The pics below show the calipers in various stages with these mods.















FWYT wrote:
Sweet thread! It's giving me that warm fuzzy feeling!! Smile

Did you consider a four piston front caliper like the Magura or Brembo units?
I did look at possibly doing a Brembo SXS conversion but at $850 per end, there would have to be a major difference. I do hear they are incredible but this brake setup works pretty damn well so I am not sure its worth the extra cash?
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blackdiamond 12/28/2015 9:27pm
12/28/2015 9:27pm
Mit12 wrote:
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston...
I know that it is a squish band but what I do not understand is why it is flat. A flat squis with a domed piston creates trapped gasses at the edge of the piston. I would like to understand what the benifit to that design is?
RMRider1 wrote:
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The...
The angle on the squish band is more like 45'...I'm sure the design is to ignite the perimeter gasses trapped on the edges more efficiently. The head was spec to run race gas, removing head volume is what is done to run pump gas....final squish measured at .055 from Gorr...Bike is extremely smooth with 0 abrupt hit...just a smooth manageable power delivery with head work and .03 shaved off cylinder base...
Mit12 wrote:
Ok I understand now. I thought the piston was domed not flat. I would imagine that the area that looks flat is probably 1 to 1...
Ok I understand now. I thought the piston was domed not flat. I would imagine that the area that looks flat is probably 1 to 1 1/2 degrees tapered toward the center?
I can't speak for others but I know this one is flat.
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Arkmx 12/29/2015 12:21pm
12/29/2015 12:21pm
blackdiamond wrote:
Here are some pics of the cylinder work at various stages. [img]https://p.vitalmx.com/photos/forums/2015/12/28/117107/s1200_20151223_143209_resized.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2015/12/28/117108/s1200_20151223_143305_resized.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2015/12/28/117109/s1200_20151223_143328.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2015/12/28/117110/s1200_20151223_225943_resized.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2015/12/28/117111/s1200_20151223_230056_resized.jpg[/img]
Here are some pics of the cylinder work at various stages.











.

Terry does awesome work!

Enjoy!!
.
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blackdiamond 12/29/2015 1:29pm
12/29/2015 1:29pm
Here are the last of the pics taken during the engine assembly. Some cool shots of the exhaust port and the before and after of the intake manifold blending and matching.













1
Awesome Johnson 12/29/2015 4:20pm
12/29/2015 4:20pm
How about a couple pictures of the speedway bike you got in the background of the last pic. Speed way bikes are bad ass! Pretty sure I don't have the sack to rip one of them like you should.
blackdiamond
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blackdiamond 12/29/2015 10:54pm
12/29/2015 10:54pm
Awesome Johnson wrote:
How about a couple pictures of the speedway bike you got in the background of the last pic. Speed way bikes are bad ass! Pretty sure...
How about a couple pictures of the speedway bike you got in the background of the last pic. Speed way bikes are bad ass! Pretty sure I don't have the sack to rip one of them like you should.
That bike has a very special meaning, unfortunately it is not my bike and therefore not my story to tell.

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