Husaberg/KTM hybrid engine

Bergini said:

.5mm is very little.......i think you might be able to pull that one off just fine......on my chain it would only out 6-7 clicks and had 15 clicks or so to be maxxed out, i have heard of new chains coming in and being longer than the original which could pose a problem. in fact i though some of the chains were so long in comparison they were almost maxxed out at new......maybe thing to research for you, when i did my rebuild i left the old chain in for this reason, the older dark link regina timing chains were a great chain i have been told.......just do you research on which ones are the best

Click to expand...

I just caught your thread on your timing chain issue. If I remember correctly, my engine has a base gasket (it's been a while since I took it apart) and the answer may just be to remove the gasket and test fit with a new timing chain hoping that it won't be too loose.

Needless to say, this engine will go together several times before it actually runs.

So, 2 months have gone by and still the crank has not been machined. My machinist friend has been working 50 to 60 hour weeks and has no time for my project. Plus, whenever he is available, I take every opportunity to get him out riding for the sake of his sanity - jobless alcoholic brother living with him, working too much, etc.

However, I had another idea yesterday that might help the cam chain/tensioner situation. I also have a KTM 250 SX-F that's suffering an oil leak at the cam chain tensioner and, in an effort to understand everything that might cause a leak, I was looking at a schematic of the engine. Many newer engines, including this 250 KTM engine, have plastic chain guides (blades) on both the tensioner side and the side opposite the tensioner. Then I thought that, maybe I should just use an original Husaberg 95mm piston (instead of the KTM piston which has a .5mm higher compression height but valve cutouts that don't apear to match the Husaberg valve spacing). Then machine a full 1mm off of the height of the cylinder in order to match the 1mm shorter rod length and, if the chain is too loose for the tensioner to compensate, I can somehow mount a plastic chain guide blade to the cylinder on the side opposite the tensioner.

Going to take another look at the cylinder and cases for a suitable location to mount the additional chain guide.

Ok, so it took a few more months than I had anticipated (the machine shop got REALLY busy and Rodger was working 60 hour weeks) but the crank machining is finally done. Results:

As a reminder of where I stand, the KTM 525 rod is only 1 mm shorter than the Husaberg 600 rod so it was chosen as the candidate for this despite the fact that it rides on a 35mm crank pin (vs the 30mm pin of the 600) and the rod big end is 3.91mm wider. So, the crank machining involved opening the rod pin bore to fit the KTM pin and creating a countersink that accommodates the wider KTM rod.

Now for a little math to see if I've weakened the press fit by creating this counterbore. The crank is about 21.2mm thick in the area of the rod pin. I say "about" because there's a step towards the outside diameter of the crank that increases the crank thickness. Going to ignore this for the time being.

With the stock rod pin being 30mm in diameter, the amount of surface area in the press fit is 2*pi*r*h=1998 square mm of press fit per crank half.

With the KTM rod and the counterbore, the same calculation yields 2116 square mm of press fit per crank half.

Keeping my fingers crossed...

More updates soon once the crank gets pressed and trued (and welded if necessary).

Tom

Very slow progress...but progress, nonetheless. Here's a KTM 525 rod, KTM crank pin, and a KTM 525 piston mocked up in a Husaberg bottom end with a FC600 crank (machined to fit the KTM pin).





The press fit on the crank is a little on the light side so I'm definitely going to have it welded.

Near as I can tell, without torquing the head bolts down onto the cylinder with some sort of torque plate that allows access to measure the squish height (maybe I'll use some spacers), the piston is about .030" or .76mm below the deck. I expect that will give me a very low compression ratio. Trying to decide if I care for this engine which is basically just a prototype to prove the concept. If it runs at all, I'll be happy.

You bet I'm still at it. Turns out the original rod from this engine is actually in great shape. Going to keep it for the other 600 engine I have that needs work. Getting ideas for that one now. Maybe bore it to 97mm and use a high compression RFS piston that's machined a tad for just the right squish height...but I digress.

Yes, I'm still moving along on this project very...VERY slowly. I received my Iwis cam chain from Taffy over a month ago and finally had a minute to mock it all up. I was hoping that the chain would be tighter so I could mill some height off of the cylinder and get my squish band back to the clearance it should be. Well, counting the clicks on the tensioner...and I'm using 14 of the 16 clicks! The engine had no base gasket when I took it apart so that's the way I've mocked it up. And before anyone tells me to put a base gasket in it to space it up, since I'm running the KTM RFS rod and piston, I'm already .5mm farther down in the hole at top dead center than stock. A base gasket will make this worse.

So, is a cam chain like a drive chain where you really should change both sprockets at the same time as the chain? They definitely appear to have significant wear. I'm assuming that a KTM cam sprocket will fit and I think I've seen them in steel. What about the crank sprocket? Maybe with all three brand new (2 sprockets and a chain), I'll be back on track.

I also looked at the tensioner blade and it's got minimal wear. Not that this would fix the problem. You can only tension the chain so much before it starts contacting the cylinder.

Anyone have some wisdom for me?

Thanks for the tips Bushie!

Another option I've been looking into for overcoming the 1mm shorter KTM rod is a KTM 565cc piston that has a 24.5mm compression height (Wossner P/N 8583DA). Only problem is this piston is for a 100mm bore. I know this is a common modification to fit a 100mm piston in the KTM but does anyone know how difficult it would be to make the early Husaberg bore 100mm? I like the idea of a 660cc gen 1 Husaberg engine especially with the larger 35mm KTM big end bearing and pin.

I can't imagine that it would be too difficult because I have a KTM 525 cylinder sitting on my bench and, with the exception of the second coolant fitting on the KTM piece, they're almost identical.