Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models Building a KR engine for racing

Building a KR engine for racing

Post Tue Oct 26, 2010 9:59 am

Posts: 13
Ive decided I have way to much time and money.
Then again I've never been married and have no kids.
I bought a set of kr cases and have decided to build an engine for vintage
I've build a couple of Duck single for racing in Europe and realize that
the vintage racing there is serious and lots of modern tech goes into the
"vintage racing"
Looking at the kr I realize there are alot of items not available or
things that could be improved.
(I've got my own machine shop and an friend who is a cracker machinist)
I realize that my major problem will be cylinders.
From what I can see the K an KR cylinders are about the same on the outside
I realize the porting and valves are much different.
A client has a 3d laser scanner and will let me use it to measure up some parts
From there to autocad to set it up for the shrink factor and then casting
There are much better alloys to use than the cast cylinders orginally used.
(a set of cast aluminium cylinder? no thats going to far)
We will modify the casing for some superblend bearing and
figure our crank from what we have from there.
Any and all advice comments appreciated.
I already know I'm not a purist thank you (gr)

Post Tue Oct 26, 2010 11:09 am

Last edited by panic on Sun Nov 28, 2010 12:10 pm, edited 2 times in total.

Post Tue Oct 26, 2010 11:31 am

Posts: 13
Most of the G50s and the Manxs run "repo" cases let alone barrels
If your running crtt as a 425 or so there is no choice but to make your own
Replica's are good...
Most of the Binells and MV's running are "repros"
A couple of cylinders aint gonna bother anyone.
I am looking at shorter rods, a couple of choices there
The iron head xr had short rods as does the current xr
getting a set of short rods made I don't thing will be all the difficult,
I would not mind running the new larger crank pin from the current xr

Post Tue Oct 26, 2010 11:49 am

Posts: 13
Had one more thought about "non standard" ever see what the HD team did to
the iron heads to get them to breath right.. orginal? Short rods?
and thoses were orginal cylinders? well they may have looked like them at some time
the vintage people know there was never standard race bike, as long as it Looks period
and not to out ragious they seem to let it go. (I;ve always wondered if the Factory ever
ran any of the aluminium head for the ironhead xr?) They dropped valve seats as I've
heard but some of the more modern alloys may make it feasible.
jut a thought

Post Wed Oct 27, 2010 1:00 am

Posts: 591
Location: Crewe, Great Britain

Hi, Proudhon

1st thing, there's so much heat distortion going on when a side valve runs that I don't think alloy cylinders could cope...

Alloy Xr only went to superblend bearings cause they were reving past 9000 rpms... You'd be well pleased if your KR can run reliably for any lenght of time past 7000 rpm... These bearings have a lot more drag and will rob some of your hard earned bhp... And what's the point in having a bottom end good for 100,000 hassle free miles in a racer?

A few guys did try short rods in KRs in the late 60s, it it was that good, more would have done it... None won any dirt track or Daytona, that's for sure!!! Nothing to do with power, it looks like it played havoc with the peculiar H-D oiling system, and too much oil retained rob more bhp...

The last factory iron XR did run and were the guinea pigs for the alloyXR short rod, just cut the cylinders a lot. They breathed better than the std sprtster due to much smaller ports and valves, that's a set of unmachined ones:


A few sets of alloy heads were cast by the factory in the mid 60s for the XLR 900 from the std cast iron XLR patterns, not much luck there, there not enough meat all round to keep anything in check...

Gotta go to work, see ya all later...


Post Wed Oct 27, 2010 8:11 am

Posts: 13
Thank you

I would probably use the newer bearings to be sure everything lined up right
And the short rods would alow me to use a larger crank pin
All of which is overkill but I'll have to do alot of the machining anyway so
if I lose a bit of HP well so be it.
The alloy cylinders were a bit of a joke. But they would be alot easier to cast.
or even run billet through a cnc. I can't think of any aluminium barreled sidevalve
but by the time alloy barrels came most everyone was ohv anyway..

On the xlr alloy heads I did hear they dropped valves. Some of the Duck single folks
in europe have changed the valve angle and flattened out the dome... if that were done
there would be alot more meat there and with the modern alloys maybe...
Just daydreaming.
I;ve sent the cases out to have them measured up and to x ray (helps to have a radiologist at a
client...) onward.

Post Wed Oct 27, 2010 9:23 am

Last edited by panic on Sun Nov 21, 2010 12:30 pm, edited 1 time in total.

Post Wed Oct 27, 2010 10:28 am

Posts: 976
Location: Markt Einersheim, Germany

Not meaning to butt in,

Patrick you have a email from me.


Post Wed Oct 27, 2010 10:53 am

Posts: 13
The later xr rods were adaptable to a larger crankpin with smaller rollers. if the parts are there why not.
I said the kr barrel as an alloy were a joke... Now you have me interested..
You are most probably right (as always) but I'm going to research the material aspect anyway (gr)
just for a laugh
Yes iron or a alloy of iron steel or whatever will most probaby be the only thing that will work
it worked for along time. why reinvent the wheel. but whynot look?

Post Wed Oct 27, 2010 11:25 am

Posts: 591
Location: Crewe, Great Britain

Hi again,

Several points here...

Cast iron, probably the best material for a piston to run against...

Not modern enough??? Well they don't use it so much these days in bikes or cars NOT cause it's obsolete, just because they all want to make a profit... Cast iron is both dear to buy, cause it comes from proper ore, not endlessly recycled sihte, and dear to cast, it can only be done by knowledgeable and expensive foundries. You can't die cast it so you can't make thousands of the little buggers in a day so nobody's using it these days...

KR, XLR, iron XR and alloy XR ALL use the same crank rollers and pin diameter, but obviously slightly different rod or pin design... Still, even in the heyday of the KR, not all tuners likes the big rods, rollers and pin, some were quite smart in using the std KH or Sporty rods, pin and rollers, probably 1/2 a pony to be gained there from less friction... Remember, for racing, small, low drag etc is beautiful and the only way to go!!!

But short rod on a KR also means cutting the front of the timing cover cause the exhaust port is now way down, so has to have a vertical magneto, "à la XLCH", a crime in me eyes!!!

Alloy cylinders!!! They had enough problems with the K type alloy heads!!! They keep on cracking day after day unless major rework/relieving is done to them!!!


Post Wed Oct 27, 2010 1:42 pm

Posts: 13
I thought the pin size changed around 85
Didn't Mr. Storz have them made... then the Factory picked them up
maybe Im wrong
my KR cases the genrator mount is I have to deal with what I have.
Dr -** of the **** xray dept has prounced the patient crack and flaw free.
(how he knows about the cracks I''l have to find out)
Funny aside though My Brother broke his heal last week and was going
in for surgery... I guess they needed a couple of extra pictures before they cut him.
I didn't see it but Dad says him lugging in the cases with his wheelchair was hilarious.
your Medical dollars at work

Post Wed Oct 27, 2010 1:44 pm

Last edited by panic on Sun Nov 21, 2010 12:31 pm, edited 1 time in total.

Post Wed Oct 27, 2010 5:00 pm

Posts: 591
Location: Crewe, Great Britain

Hi panic,

From the photos I've seen of the Branch KR short rod, looks like the flange was shortened, a bit like when guys used to fit KH cyls on K and keep it 750cc/45ci... Manifold had no nuts, just clamps as Sportsters.
Probably use W type pistons as well.
From the height of the valve covers, this was still not enough lowering, so I can only guess that he cut the cylinders in half just under the bottom of the valve seats, turned off whatever was required, sleeved them and welded them back together...
The cylinder nuts look special as well...

A lot of work!!!

Girdler tells us Len Andres built one as well, but never seen any evidence of that KR, it could not have been for Brad and what I see of Lasher or Rayborn rides in the mid 60s looks like std KRs...


Post Thu Oct 28, 2010 8:45 am

Posts: 13
I can't tell you how much I appreciate you taking time
with my wacky ideas.
You are wonderful human being.
And I don't believe a word
of what your
ex wife
or all 3 say about you (gr)
really thanks so much

Post Thu Oct 28, 2010 11:43 am

Posts: 591
Location: Crewe, Great Britain

And I don't believe a word of what your wife ex wife girlfriend or all 3 say about you

:D :D My wife if a lot more than just OK, so I can't imagine where you might have heard this!!!

I do have wacky ideas as well from time to time, only time will tell if they were really bad or managed to see the light of day, you never know...

Still, it's also good to know where some of the pitfalls gonna be and deal with them!!!

Branch did it all these years ago and the bike still exists today... The only little worry I have is that he's the only one to have done it.

By the way, that engine was shoe horned into a slighly moded CRTT ( :o :o :o ) for Daytona 67, fairing from a 175cc Ossa Spanish bike ( :o :o :o ) and loaned to Gordon Jennings of Cycle magazine fame. Qualified just OK; 16th at 129.720mph, fastest was Fred Nix's factory KRTT at 140.823mph. He started the race but broke a wrist pin in the early stages.

panic: the big port and small engine made very lazy gas speed in a range that needed more power, and increasing piston motion near TDC would help

Real dilema here... All seem to agree the K valves are way to big to get any decent airflow in the manifold, but I'm pretty sure that if you reduce the sizes, the filling will suffer... H-D side valve tuning philosophy seems to be "forget about anything you've learned by racing an OHV, it won't work here"!!!


Post Thu Oct 28, 2010 5:10 pm

Posts: 13
He put it into a CRTT frame!!!.. I just went out and looked at one of my sprint frames.
I'd love to see how he did that!!!
I remember people doing strange things to Duck single frames (Yamaha ta250 ect)
Lookin at a sprinty motor is rather long though....Just not very tall.
It would be a cheap and easy way to set up a road racer though...
I'vegot some extra spint frames to play with..
I'll take a look.

Post Thu Oct 28, 2010 5:42 pm

Posts: 13
found the picture of the Branch 67 short rod
it was in american racer 1940 1980..........interesting

The short strokes were tried but never really had the developement time and money
of the other engines.. It didn't work right away and it seems to me every looked for another
answer. Untill the alloy xr anyway

Post Thu Oct 28, 2010 6:06 pm

Posts: 141
Location: USA
All this talk about speed makes me somewhat delirious,while on the subject I have seriously been considering a supercharger on the next WL/k Model.Any thoughts or comments.To be honest I am really overwhelmed at the choice of superchargers to pick from.Thanks for thoughts. :D :D

Post Fri Oct 29, 2010 1:31 am

Posts: 591
Location: Crewe, Great Britain

Proudhon: The short strokes were tried but never really had the developement time and money
of the other engines..

Looks obvious isnt it!!!

But, not as mentionned in Wright's book, OB might not have been that opposed to the short stroke.

OB and Branch had a very close relationship and in the end, it could be that Branch was doing sort of back door enginneerind research for OB on that one... Don't forget OB was under extreme pressure in the mid to late 60s to find A LOT more BHP out of the flatheads, the Triumph were by then a major threat, Nixon wasn't hanging about!!!

Couls be they found something drastically wrong in there, or needed loads of cash, or the rest of the program, twin carbs, fairings did work so well they shelved the short stroke temporarely for later attention which never came since the OHV became the rule a while later...

Celticdodge, superchargers !!!...,8744.0.html


Post Fri Oct 29, 2010 10:18 am

Last edited by panic on Sun Nov 21, 2010 12:32 pm, edited 1 time in total.


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