KTM Blaster going Universal motor mounts

[best]

A while back I got a weird vibe out of the Blaster, turns out middle motor mount was broken. Pulled the motor out to fix it and as I knew I had a cylinder scuff, I wanted to get it replated, so pulled it and sent the cylinder out for replate. Turnaround time is going to be longer than I figured on up here in the Great White North, so I start working on PLAN B. Drop another cylinder on the 250.

As it turns out, the older 300 cylinder would not fit on the 250 due to a huge deck height issue, maybe solvable with a special piston, but rather than get into that I figure I'll just swap in the whole running 300. Plan C.

Wrong. The 2003 SX 250 has different motor mounts. This is going to take a whole re-engineer, just like starting off fresh on a swap. Sheesh, way more work than I wanted to get into right now, especially with things going on with work, family, and other projects on the go, but it is the right way to do things. Get the 250 fixed up, make the Blaster accept any engine I have.

The 250 swap involved a cut down front mount and welded on mid mount:

After hard pounding on rocks this spring, the middle (bottom) motor mount failed where it was welded to the frame. Poor weld (MIG fluxcore), brittle weld, strain from a hard pound, what ever, it broke. I don't have a picture of the broken middle mount but here is a rad mount that broke also:

Simple tack on bits, they need more reinforcing around the frame to put less strain on the welds.

Turns out the pre-2003 KTM motors are longer to the front mount and needed to be angled up more. Using the stock swingarm pivot ment the motor mounted unacceptably high. I needed to mount the swingarm lower to get a good motor fit. Here is the start of the swingarm mounted 1.1" lower:

One plate tacked on, bar through the swingarm pivot to hold the motor and swingarm in place. Looks like everything is going to work. Here laying on the footpeg is the second plate cut to shape to be welded over the first:

So now I need to mock up the front motor mount. I use cardboard to figure out a shape and size. I will probably be using 1/8" aluminum for the front mount. In this picture there is a mock up for the bottom mount too, but haven't figured out how to bolt it to the frame yet:

It is going to be a few days before I get back at it, so looking for ideas and criticism. Have a look in the radiator picture above. the loose chain in that picture comes close to the frame so I worry it will hit when lowered 1.1". Here is another picture of the loose chain with suspension unloaded:

Might need a roller or wear strip. Lowered mount point will probably lower ride height slightly too. Ideas?

 

[Chuckie25]

I don't know about it lowering the full machines ride height but will for sure lower the middle of it. You'll prolly need to make you a skid plate so you don't smash the lower frame rail(s) into any large rocks. Also, your making the front motor mounts out of aluminum. Alum is a life limited material. All the vibrations, twists of the frame, jarring of the engine in rough terrain, etc will severly limit how long the mounts will last before cracking/failing. Also, how are you planning on securing the bottom (closest to the engine) part of the mount? A bolt through the frame or what?

 

[best]

I don't know about it lowering the full machines ride height but will for sure lower the middle of it. You'll prolly need to make you a skid plate so you don't smash the lower frame rail(s) into any large rocks. Also, your making the front motor mounts out of aluminum. Alum is a life limited material. All the vibrations, twists of the frame, jarring of the engine in rough terrain, etc will severly limit how long the mounts will last before cracking/failing. Also, how are you planning on securing the bottom (closest to the engine) part of the mount? A bolt through the frame or what?

I have been kind of agonizing these questions over in my head too.
Well, the 1.1" drop of the swingarm pivot with the LTZ shock will put the ride height pretty much back to stock. I'll have to ride it to see if I like it, and what problems or benefits it brings. Don't have much choice to get this 300 motor in at the right angle.

I have been using aluminum mounts for bikes and skidoo engines for a while now. It is a simple triangle, will be in a visible spot in case it fails, and saves me a pound off the front of the machine. Plus, I like the shine! I hear you and it will be something to watch. If it shows signs of fatigue, I'll replace it with steel.

Here is an aluminum head stay I made for my 300 bike, curved for more hand clearance around the plug:

Here is what I had for a bottom mount on the 250 engine:
Instead of the one plat in the center, I should have had top and bottom transverse pieces taking the torsion load.

Wish I had gotten pictures, but the tube had ripped on both sides of the pieces that attach to the motor, so that it ripped two 3/4" wide holes in the tubes. Bottom tack welds stayed intact, but too much pivoting stress in a small area. Welds held, Blaster frame tube is thin and failed. I think the welding makes the chrome moly brittle too.

This time I welded a plate across the top of the frame tubes, spreading out the stress and acting as a gusset for the frame corners. The interchangable mount will be a "U" shaped piece sitting on it and held by two bolts up from the bottom. No pictures yet, but it will be under the mount tab shown in this picture behind the head of the shifter:

 

[Chuckie25]

Ah ok then. After looking at your first set of pictures again I see where you're bolting it in at on the bottom. You run a head stay? That's a huuge no no for bikes that are being rode hard. You seen the damage caused by your frame twisting an all over bumps? Imagine if that tubing would not have failed. That load would have been transferred through the frame to the closest weak spot. And if your frame is as rugged as you want it to be, guess where that weak spot is: your head. As the frame twists and flexes it transfers that energy into the top of the head and can cause you to blow a head gasket or worse, crack the jug and rip a stud out. On our LT's that's the first thing we do because it has happened soo many times. Not trying to be a know it all, just passing along info. But you've prolly already thought of this and accounted for it haven't you?

And as far as your mounts/gussets go: I dont any problems occurring (yet) so long as you make sure to triangulate and disperse your weld over a larger area so the cromo doesn't get as weak. Maybe also look into oil bathing it? It's supposed to restrengthen the weld areas I believe.

 

[Chuckie25]

No head stay for quads at least. The frames of trikes and motorcycles can absorb and disperse the torque, vibrations, etc of hard riding differently than quads can. It's a whole speech about shock size relative to frame size/weight that Im sure you know lol

 

[best]

No head stay for quads at least. The frames of trikes and motorcycles can absorb and disperse the torque, vibrations, etc of hard riding differently than quads can. It's a whole speech about shock size relative to frame size/weight that Im sure you know lol

Yeah, I wondered that when I put my quad together. Frame is much less rigid. Even on a bike the head stay is made weak on purpose in case of a crash. Thanks for the input.

Steve

 

[Chuckie25]

No problem Mr. Steve. Hope I made some kind of coherent sense in all that rambling lol. My brain works too fast to hold a single thought for more than a few seconds. All i do is sit around and think bikes when I'm not working on bikes, designing expansion chambers, or porting cylinders (please don't ask me to do any work on your bike.. I don't trust myself enough to do work for anyone outside of my friends and family yet..). How's the swingarm bolt relocation coming?

 

[best]

Bad news.
With the older/longer/larger motor tipped up in the front, there is no room for the kick starter to swing.
I have been doing the mock up with a stripped case and just noticed this as I set the 300 in tonight.
I have toyed with tipping it forward for clearance or making some sort of extended kick starter adaptor, but don't like either idea.
At least I have a good middle mount for the 250 now, and my swingarm plates are well gusseted.

The kick start was close on the 250, I should have thought about this sooner...
This is the 250 during construction:

With the motor tipped bank, dropped or not, there was no room to swing the kickstarter.

 

[Chuckie25]

Notch that tube some to allow it to move. Then your 250 will be more comfortable when it's installed. Who do you send your cylinders too? I'm thinking of having my 270 and 500 nik'd so I never have to worry about wearing the cylinders out and having to resleeve

 

[best]

Notch that tube some to allow it to move. Then your 250 will be more comfortable when it's installed. Who do you send your cylinders too? I'm thinking of having my 270 and 500 nik'd so I never have to worry about wearing the cylinders out and having to resleeve

No, that picture is of my 2003 250 during construction. it works.
The 300 was tipped up to the degree I'd have to take a big cut out of this area.
Not that important to put the 300 into the quad, 250 works wonderful and cylinder is probably a week away.
I don't want to cut and weaken the frame that much.

Cylinder is at this shop here:

CVTech-AAB inc for cylinder and crankshaft rebuilding and replating in Quebec, Canada

Had them do crankshafts and YZ cylinders before, very pleased.
Still expensive, but their nikasil held up wonderfully, tougher than original Yamaha.
No charge for minor repairs to cylinder.

Often thought of plating hard to obtain steel cylinders that had gone beyond last bore size.
The said they can do it, but I never tried it.