Modified K engine

Hi everyone,

I am interested in trying some modifications to a set of mismatched, somewhat beat up K cases that I have lying around. The transmission area is damaged, and I am toying with the idea of cutting away the entire area and working towards a separate transmission set-up. I would then look to build up the rest of the bike with various parts I have collected over time.

The purpose of the exercise would simply be to utilize some cheap old parts, whilst learning more about these old engines in the process and having fun!

I know this has been done before, and I was wondering if anyone might be able to share some simple pointers, things to watch for, or even pictures? I am particularly interested in learning the best way to perform the cutting operation, and then in discussion of alternative transmission options for the early twin-tomahawk frame (also open to mods). This would include modern sportbike options if applicable.

Thanks and regards,

Simon

I took a closer look at the cases last night, and it would appear that the main concern when cutting would be to take care around the oil galleries where they run through the cases near the oil pump. I am guessing that these would need to be threaded and fittings mounted at the lower rear of the RHS case, rather than their current locations at the upper RHS.

I am also guessing that it would be better to leave a raised "web" of metal as reinforcement where the cases extend back to the transmisison, rather than cutting them off completely flush. I will also have to give thought to treatment of the rear motor mounts and primary before cutting.

Cheers,

Simon

Board member Tim The Grim has done this before to his KHK. Do a search through the members list for him. I believe he's in El Paso, TX. Formerly NJ. G

Thankyou, I have sent him a PM.

Hi Guys,
Hope you all had a fine Thanksgiving. I am pleased that greybeard52 brought up my name and hope I can be of some help.

I will try to get out to my shop tomorrow and get some new pics of the cases. They are mostly apart at this time so
I can hopefully show some details.

I had the luxury of also having a set of cases that had thrown a rod, so I cannibalized them as well to
use the mount bosses. I had a top notch guy do my aluminum welding and then had the cases line lapped and decked
by a guy with decades of H-D motor building experience.
Due to substantial preheat and professional care by the welder there was a minimum of distortion and they cleaned up without a problem.

I built a pillar shaped like an upside down " T " to serve as a center mount between the engine and trans. It mounts to the frame on a joining member I machined to mate the single down tube forend I built to the stock K frame center section tubes.

My oil line set up used brass tubing and permanent Loctite in the cases with some soldered on hose fittings.

Heck ! We've got 4 inches of snow here in El Paso with another 3 or 4 on the way. A real rarity and I'm not going anywhere tonight so I guess I'll head out back now.

Tim

Great stuff Tim, I'm looking forward to seeing the pics. I also have a couple of extra donor cases to cut up as required, so a close up of this area would be appreciated.

Thanks and regards,

Simon

Hi, Simon,

This is from a 1970 Sportster engine I've cut, K cases are similar. Oil inlet is at the back of the oil pump, the brass fitting on the cases is the return line:





Patrick

Way back in the '70's Sonny Raslowsky, The World's Fastest Pollock, grafted a 120" Shovelhead engine onto a Sportster transmission and squeezed it into the XLCH chassis. That was one fast bike, his daily street ride.

Here's my stuff.
1st post of a series to save time.

2nd post of Tim Stuff

More tomorrow evening.
ImageShack got weird and I'm tired.
But at least you got some of it

Bye for now.

Tim

That's great guys!

Patrick, I suspected you might have tried something like this in the past! Tell me, do you recommend leaving any more of the primary lip intact, and any of the cast lugs/bolt holes aft of the primary chain adjuster? At the moment I'm looking at following the line of the cases proper, but leaving the primary chain bolt holes intact - aiming for as much symmetry as possible.

Tim, valiant effort on the pics thankyou! I see what you mean about actually using the cases proper from one set, and the transmission portion from the other. I'm still in the daydreaming phase, however I am thinking of perhaps going with either a big twin transmission, or some other standalone transmission for this. I saw a picture recently where someone had grafted a sportster clutch onto a big twin set up, and wonder if it might have been for a similar application. Something like a pre-war Norton upright transmission would look great, but pricey. I guess there are the usual A10 choices available too.

I guess it will also ultimately depend on frame choices and final decision on primary set up, but in my wildest fancy it would even be interesting to cast or fabricate a housing for a cassette type transmission from something like a Yamaha TZ or TZR250. I can get my hands on these readily in Japan, but have absolutely no concept yet of what it would take to mount something like this up to the K, nor whether it is practical.

So far I have a spare set of beat up KH cylinders, and some nice KH cams and flywheels that might also be interesting to throw at this motor while I'm at it with the grinding and cutting (need to relieve the cases for these), though I will have to see what comes up first in terms of project priorities.

It's kind of getting tempting to cut off the generator boss as well...

Hi Simon,

My cut down Sportster: not finished by a long way... The idea is to have a primary belt there and a 2 speed drag box, but for the road, hence getting rid of primary casting bits, engine will be much lower than gearbox, these bits would have be in the way.

As for fixing, the rear new bolt holes have the same width and alignment as the front ones, easier then to get engine plates made. That involved some welding hence the shoe mounts are gone...

I'm toying with the idea to have a big empty frame tube to replace the gene, small engine plate on the left welded on it and bolt the engine to that tube on the right using the timing cover bolt patern... End product to look something like this, 30's style:





Rear rigid end between brake and drive sprocket:



Patrick

always interesting to see some serious engineering .... and this definitely qualifies

Patrick, is your proposed 2-speed drag box like a track racing ( long-track ) one? I have a Jawa one on one of my grasstrack bikes, and it just has a single-action change, ie a spring-loaded lever which you set to 1st gear and pull a trigger on the bars for a clutchless change under power, very brutal thing but fine for its application, but I can't imagine what use that would be be on a road bike - or have I missed something?

Hi 45 Brit,

I'm actually lusting after a Bewley one, the sprint one that has wider gears. Like the Jawa one, it can be moded to be all foot shift from the exploded drgs I've seen. A friend has one in an ESO Grass tracker but he won't bulge... but I'm patient!!!...

Patrick

Hi Patrick.. you would certainly need to be patient, waiting for someone to part with a Bewley box. The Jawa one is a rough old thing by comparison, but it does the job. I have one in a 500cc 2-valve Jawa and it shakes the whole bike when it changes!

I don't see why you couldn't change it to a footshift if that was what you wanted to do, but I don't see the point. You end up with a 2-speed box with no neutral and an external positive stop, or alternatively no positive stop. Why not look for a Norton box and blank off 1st gear and remove the kickstart? Lots of grass bikes are like that and it's very useful. You can get all kinds of modern clutches for them, the vintage motocrossers use them a lot as well.

Yeah, 45 Brit, but I'm a real sucker for punishment!!! I'm the guy that ran twin Tillotson on my KHK in the past...

The only other box I would consider, got to look real vintage, would be an old 3 speed Sturmey-Archer...

Patrick

[Pa]

You ran twin carbs on your KHK Patrick ? My bone stock single carb KHK scared the hell out of me many times ! Pa

Yep, Pa,

But now it's just a set of twin Linkert DC (one nearly "std", the rear one, one reversed/moded, the front one...) Last outing, mid-October, 350 miles at speeds you don't want to know, not missed a beat...:



Patrick

[Pa]

Sweet !!!!!!!!!!!