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Old 08-22-2013, 09:36 AM   #16
zig06
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Nice job!

I've been thinking about doing something similiar, like dropping a DRZ-250 motor (electric start) into a RM250 chassis that I already own.
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Old 08-22-2013, 11:11 AM   #17
Luke OP
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Originally Posted by operose View Post
Awesome. I have a warmed over Blaster with no paperwork and a 1972 Honda SL125 with a basketcase motor. Was planning on smashing the two together and you just cemented it. Way to go on this one.



That poor little bike isn't going to know what hit it.


Post pictures.
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Old 08-22-2013, 11:14 AM   #18
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Should be a nice woods bike. I'd love to update my old IT200 to YZ suspension and brakes. The IT motor is basically the same as a blaster.

I bet that'd be good. A front end swap should be pretty simple. Just a warning, the YZ suspension is pretty brutal in stock form. You might go for WR parts instead.
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Old 08-22-2013, 11:29 AM   #19
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How is the transmission gear spacing? Wide ratio or tight like a motocrosser?

Just my .02 (if it's worth that) but why not weld in new mounts for the front instead of cutting the case down?

Like others, I am liking the idea of a xr250 in a crf frame. If built as a custom with all legal bits on, it would be issued a new VIN as a street legal bike here in NM

The transmission is really wide. It's geared for about 50mph on the top, in theory should hit the rev limiter at 60. In 1st it will putt along right at 2mph without slipping the clutch.


I cut the case because it seemed like a good idea at the time. I think my reasoning was that I had already ruined the cases by drilling out the swingarm pivot hole, so if things didn't work out I wouldn't have also ruined the YZ frame.

In retrospect, I should have cut and replaced the mounts. That would also allow the motor to be lowered a bit at the front which would give some more room between the carb and the shock.
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Old 09-03-2013, 06:44 AM   #20
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The transmission is really wide. It's geared for about 50mph on the top, in theory should hit the rev limiter at 60. In 1st it will putt along right at 2mph without slipping the clutch.


I cut the case because it seemed like a good idea at the time. I think my reasoning was that I had already ruined the cases by drilling out the swingarm pivot hole, so if things didn't work out I wouldn't have also ruined the YZ frame.

In retrospect, I should have cut and replaced the mounts. That would also allow the motor to be lowered a bit at the front which would give some more room between the carb and the shock.
But you needed it done now, and cutting and welding was more time! (Or, at least, it sounded like more time and work when you were trying to fit the engine in there) :loll

Videos or it doesn't run
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Old 09-04-2013, 10:28 AM   #21
Luke OP
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But you needed it done now, and cutting and welding was more time! (Or, at least, it sounded like more time and work when you were trying to fit the engine in there) :loll

Videos or it doesn't run
Ok ok, I was going to take some video where the sound isn't awful, but here's what I've got.

wr200 on morel's maze from Luke Bennett on Vimeo.

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Old 09-05-2013, 04:46 PM   #22
Lutz
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I really like the direction you went with this bike. I've long been thinking about something along the same lines: a dead simple, air cooled two stroke in modern chassis. Only it could easily be made street legal where I live, so I'd want to do so. I'd totally forgotten about the blaster engine as a possibility, thanks for the reminder!

How badly did the stock fuel tank interfere with the cooling fins? Could it be made workable with a heat gun, or no way at all?

I may have missed it, but did you use the oil injection system or are you premixing?
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Old 09-05-2013, 09:48 PM   #23
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I really like the direction you went with this bike. I've long been thinking about something along the same lines: a dead simple, air cooled two stroke in modern chassis. Only it could easily be made street legal where I live, so I'd want to do so. I'd totally forgotten about the blaster engine as a possibility, thanks for the reminder!

How badly did the stock fuel tank interfere with the cooling fins? Could it be made workable with a heat gun, or no way at all?

I may have missed it, but did you use the oil injection system or are you premixing?

Thanks!

The blaster motor definitely isn't much of a street motor- it's pretty down on power. Good enough for trail linking, but not cruising. Great dirt motor though.

The yz tank wasn't even close to fitting. Probably more than an inch of interference, and it was at the petcock. The XR tank works, but I'd really like to built a custom tank.

Oil injection was blocked off by the PO, so it's running premix.
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Old 09-09-2013, 09:28 AM   #24
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Old 10-31-2013, 10:17 PM   #25
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just found this thread, my .02 (i've rode this bike) it is very fun to ride, super torquey and Luke built it in 9 days, a miracle when you consider the CB sled took him 9 months!
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Old 11-01-2013, 10:57 PM   #26
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It's way past time for an update. I've been riding it around a bunch, and it was working very well until it didn't. I pulled the motor apart and it was a mess inside so I did a full rebuild. It's almost back together now, Rick and I just put it back in the bike tonight.



Earlier, I re-did the intake. The carb was sitting crooked in the boot in order to clear the shock, so I made a wedge spacer to get the angle right.







This required making a new airbox-carb adapter.
















Most of the rebuild was just basic parts replacing. Here's an original bit. It's for holding the countershaft while tightening the clutch nut.




Part of the rebuild naturally turned into chasing moar powah. I watched a bunch of youtube videos on how to turn the combustion chamber from the original conical design to a hemispherical design with a useful squish band. So it was time to really abuse the Sherline.











The head came out to be a little over 20 CC , a which is a little on the conservative side. The guys really chasing power go for 18 or 19. They also change the port timing which lowers the compression a little.



Checking the squish clearance. The solder is put on the piston, then the head installed and the solder gets mashed. I got a minimum of 1.1mm, which is also a tiny bit on the conservative side. I have a few different thicknesses of base gaskets to adjust this without machining the head again. It turned out that using no base gasket at all gave the right clearance.

Compression turned out to be 160psi, which is right about what I was hoping for.
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Old 11-02-2013, 09:50 AM   #27
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I've been waiting for an update on this.

Have you bothered to calculate fuel mileage?

I'll be interested to hear how the engine mods work for you. Should be way more torquey. (Just to be sure...you know that varying base gasket thickness does change port timing, right?)

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Old 11-02-2013, 02:05 PM   #28
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I've been waiting for an update on this.

Have you bothered to calculate fuel mileage?

I'll be interested to hear how the engine mods work for you. Should be way more torquey. (Just to be sure...you know that varying base gasket thickness does change port timing, right?)

I haven't figured the mileage accurately, but when I first put it together it was getting around 25 miles to reserve, or about 12 mpg. After fixing the air intake and the jetting I've gone up to 50 miles on a ride and never hit reserve. So, better than 25mpg.

It's very rare that I ride more than 50 miles in a day in the woods, so it's plenty. It'll probably change with the new head.


I gather that lowering the cylinder will tend to move the torque to lower engine speeds, although not as effectively as changing each of the ports individually. I suspect that the new piston is a little lower than most, so the port timing may not have changed that much. At least, that's what I'm hoping.
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Old 11-02-2013, 02:13 PM   #29
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Oh, and I nerded out with a gps track from one of the rides on this bike. I'd say that this ride was pretty typical for the woods out here. Here's the amount of time spent at different speeds:



Which is why I'm not really interested in high power or top speed.
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Old 11-06-2013, 10:47 PM   #30
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Last little work of the rebuild, so I thought.


The handlebars always bugged me, the clutch and brake perches never sat right- they had to be clamped on the bend of the bar in order to be in the right position. So I made some bars. 7/8 stainless tube, cut and re-welded to get the right angle. Risers were added to get the position right. Nuts were welded in to the ends to hold the handguards.










Get it ready and go ride.






I'd love to show you all a video of the new awesomeness, but a few miles in to the break-in ride I got hung up on a root and flipped the bike. Landed perfectly on the handlebar, bending it way down and breaking my video camera.

But it didn't totally suck, the motor ran great. I'm really happy with what the rebuild and head work did. The top end feels about the same as before, but there's lots more torque at the bottom and midrange.

Oh, and the handlebar bent next to the clamp not at my weld. A small victory.
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