How well do you like your KX250F/K5 conversion

[sandblaster]

Instead of using a huge U shaped piece of aluminum on the frame to mount to the bracket how about just a simple wedge sort of like this?

I had considered that exact design but when it came to strength I feel the way I am doing it is the strongest.
Here is what I had come up with:



The huge aluminum block started as  2" x 1 3/8" x 1 1/4"
After a few minutes of machine time it does not weigh very much 

[sandblaster]

This is a 2006 kx 250f frame that was done by Jerry and the ims 3 gal tank fits with no problem hope this will help.

http://s1296.beta.photobucket.com/user/SHLEPY500/media/IMG_0783.jpg.html#/user/SHLEPY500/media/IMG_0786.jpg.html?&_suid=135493337071907457251697957659

Thanks!
It's kind of hard to tell what view that is but I think it is using the stock location of the 250F frame.
I originally was going to do something similar to that and I might still.
If one head mount is good, 2 might be better  

[SS109]

I had considered that exact design but when it came to strength I feel the way I am doing it is the strongest.

My concern was not weight but of strength. Just not as much welding on the main downtube. Basically the single block only affects one side of the downtube whereas the larger block affects three sides as you would be welding all the way to each side. Eh, just me over thinking stuff as usual!

I do agree that two head mounts might be the way to go. My bike won't be seeing any big air as it will be a desert/hare scramble bike but I don't want to chance cracked/broken rails. I know I plan to use the head mount like is SHLEPY's pic but might add the front mount as well. Of course, I will using a KDX250 engine and not a KX500 so there should be a little more room to work with. I would do the front like what I suggested in my other post but with the front bracket like this (sorry I butchered your pic!) to make engine R&R easier...

[sandblaster]

No problem on the pic   that is what thread is all about, R&D.
There are tons of good ways and bad ways to do this.
I would never have attempted anything like this before reading all the good info on this site.
The more ideas expressed the better chance of getting the best combo.

[sandblaster]

Because a few people had problems breaking their frame rails I wanted to be sure I understood where the transfer of energy was taking place at.
Here is a rough diagram of where the mounting points are in relation to the frame.



As you can see, when coming down hard on a jump the force is transferred in a radial motion pivoting on the 17mm swing arm pivot pin.
So, the rear head stay must be in line as much as possible with the direction of the force to prevent the engine from rotating forward and putting the cradle under tension.
Having the front mount on the head helps to stop any force that is trying to be transferred to the frame rails.
On further review I believe that if I remove the gas tank I can remove the engine without having to remove the front head stay.
Although when I get further into this I will test that theory  
Here is some pics of the different views.
Nothing is welded yet but you get the idea:









That's my story and I'm sticking to it for now  

[SS109]

I like that! Should work great at supporting the engines weight.

[sandblaster]

Time will tell.
Once this is done I will put my sponsored rider on it and let him do a few practice days on it.
With the kind of air he pulls off that will certainly show whether or not this is a good idea.
Then I will abuse it with hours of trail riding and perhaps a few trips to the dunes.
If it holds up to all that, I'll know this was a good decision 

[sandblaster]

I finally got the engine mounts done.
It's amazing how long this stuff takes when you don't have the proper tools
The front and lower mounts came out exactly as I planned in that they would be exactly the same size as each other.
Yeah, I got lucky 
The top mounts are completely different as you would expect.
The only change was on the lower left side of the engine there is a protuberance that requires the mount to be slightly machined for clearance.
It's all good as I was able to make them all the same, drill them, and then machine one of them to fit.

[sandblaster]

Experimenting with bolting the engine mounts on.
Talk about chatter  





Got it welded and then assembled:





Then I put a torque wrench on it.
Set it for 30lb and started putting pressure on it.
I was never able to get the wrench to click and I started pulling the bolt through  
Better to find out now on a test piece then drill out my frame and have it ruined.
I think I will try to use a cap screw.
It will stick out slightly but it will be much stronger as I won't have to counter sink the hole.

[SS109]

Yes, better to find out now! Thanks for sharing what you are doing and please keep us posted!

[Motorrad]

The bolt you pictured is stainless..  Big NO NO in load bearing use

[alward25]

The bolt you pictured is stainless..  Big NO NO in load bearing use

Funny you should mention that.  Guess how many load bearing stainless bolts we use on the MH-60T Jayhawk?  Almost all of them, or Titanium like the wrist pin I made was out of a Ti upper pitch control rod bolt for the main rotor head.  The main rotor blades are also held on with 8 3/4" diameter stainless bolts.  That is some decent load bearing.  Four 280 lb rotor blades being swing at 260 rpm by almost 4000 hp.  I have to take a cold shower just thinking about it.  But, aircraft grade is different too

I always enjoy our talks

Alex

[Larry Wiechman]

 A helicopter is several thousand parts flying in close formation for a short period of time.


 Back to motor mounts. Socket head cap screws or hex bolts (grade 12.9) and thick, hardened washers will help spread the clamping force. Button head screws suck, no matter what material they're made of.

[alward25]

They are a big ceiling fan, when the fan stops, the pilot really sweats

I like a 12 pt flanged head myself.

 A helicopter is several thousand parts flying in close formation for a short period of time.


 Back to motor mounts. Socket head cap screws or hex bolts (grade 12.9) and thick, hardened washers will help spread the clamping force. Button head screws suck, no matter what material they're made of.

[sandblaster]

Thanks for all the info guys.
Helicopters are really cool but I don't plan on that much air time  
I'm just trying to figure out a clean way to attach the motor mounts to the frame without welding.
And, I won't be using SS.
That was a quick and easy pic for representation that  I borrowed from a Google search.
Any suggestions besides having a big bolt sticking out of my frame rails?

12 pt flanged head?