53KR in a Low Boy Frame

Racing K Models

Re: 53KR in a Low Boy Frame

Postby hayleyl » Tue Oct 27, 2020 6:30 pm

Hugoct is spot on - an XRTT chassis would be a massive improvement or perhaps fudge a 77-81 ironhead frame, much better geometry etc. Nice project. Good luck if your going to compete against Beau Beaton and Cam Donald. My money will be on the Vincents. Cheers Hayley.
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Re: 53KR in a Low Boy Frame

Postby DaveAus » Tue Oct 27, 2020 6:44 pm

Thanks for the feedback. So it looks like for vintage racing I'll need to lay my hands on another frame.

I know where there is a 56K frame, would that be a better option?
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Re: 53KR in a Low Boy Frame

Postby 44UL » Tue Oct 27, 2020 10:46 pm

Dave, i am no expert. but i have been told that it seems a lot of KR's were in a '53 K frame and i have a spare. My '62 KR came in an early sporty frame and i found a few '53s since then.
62 KR, 56 KH, 56 KHK, 53 K, 47 Servicar, 44 UL, 48 UL, 48 WL race bike(40 rwhp) 51 WR, 68 XLCH, 38 EL, 65 Topper,
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Re: 53KR in a Low Boy Frame

Postby hugoct » Wed Oct 28, 2020 3:13 pm

The first KR frame is the 52R frame.
The 52R frame was available through 1970 with 21 documented variations.
The 52R frame is proper for KRs from 1952 through 1957.
You would want one of the 54 -56 52R frames with the cut steering head pulled in or one of the 57 and later frames with the 57R steering head casting.
Beginning in 1958 the 52R frame was used on the Sportster XLRTT only.
The 52R frame is known as the heavy frame (32 lbs. unmolested).
The second KR frame was the 58R frame which was available through 1970 with the same changes for the 1958 through 1970 time period as the 52R frame.
The 58R frame is the proper frame for KRs from 1958 though 1969.
The 58R frame was known as the light frame (27 lbs. unmolested).
The only way to tell the 52R frame from a 58R frame built at the same time is to weigh them.
1966 we see the Widman hiboy-hi seat frame with 66R tank and seat.
1967 we see the hiboy-lowseat frame with the 67R tank and fairing with the 66R seat, the first version lowboy frame, and the second version lowboy frame.
1968-9 the Team runs the second version lowboy frame at the road races with Wixon tank, seat, and fairing.
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Re: 53KR in a Low Boy Frame

Postby 44UL » Fri Oct 30, 2020 11:34 am

Thanks for that frame break down! Wasn’t it true that KR’s could have been in non-R frames? Say for dirt TT/Scrambles where a chromoly tubed frame would be prone to breaking? This is the setup I’m doing for my ‘62 which i know did scrambles before later converted rigid to flattrack. Thanks for any additional info as this has been a head scratcher to sort out.
62 KR, 56 KH, 56 KHK, 53 K, 47 Servicar, 44 UL, 48 UL, 48 WL race bike(40 rwhp) 51 WR, 68 XLCH, 38 EL, 65 Topper,
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Re: 53KR in a Low Boy Frame

Postby hugoct » Fri Oct 30, 2020 12:56 pm

All KRs, KRTTs and Sportster XLRTTs were delivered in 52R or 58R frames.
One year in particular (1959) Harley recommended that those going to Daytona use a Sportster frame (-58) and suspension (fork crown-54A, stem and bracket-54A, fork slider tube assy -52, rear shock-59R) because of the sand on the beach and the clearance needed. The added rake probably helped stability in the deep sand. They only recommended this for Daytona on the beach no where else.
The 52R (heavy) frame as specified for the Sportster XLRTT was more than heavy enough for any type of competition.
If chrome moly tubing was an issue for scrambles explain the success of the Rickman Metisse frames ?
There would have been no benefit afforded by the Sportster frame on a scrambles track.
Last edited by hugoct on Fri Oct 30, 2020 9:49 pm, edited 1 time in total.
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Re: 53KR in a Low Boy Frame

Postby Ferrous_Head » Fri Oct 30, 2020 8:05 pm

If chrome moly tubing was an issue for scrambles explain the success of the Rickman Metisse frames ?


There could be any number of reasons for that. Lighter, less vibratory engines. Better design. Better construction. Thicker walled tubes.

Your not really comparing apples to apples there.

If you just substitute the same size tubes in a frame with chrome-mioly it's going to be lighter, but not stronger.

If lighter bikes automatically meany "better" bikes explain the Titanium BSA to me.

My own experience is that building frames from chro-mo is fine if you only use the bike for one season. Long term, the stuff breaks.

Please bear in mind I build racing sidecar frames, not solo's. We put a lot more stress on our frames.
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Re: 53KR in a Low Boy Frame

Postby DaveAus » Fri Oct 30, 2020 8:44 pm

Is there any way of running a drum brake with that XR swing arm?
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Re: 53KR in a Low Boy Frame

Postby hugoct » Fri Oct 30, 2020 9:20 pm

Comparing solos to sidecar chassis is comparing apples to apples?
I know of chrome moly Trackmaster, Champion, Redline, Starracer, C&J, Wood, Knight frames that were used for many seasons at the top level of the sport in the US.
Better tubing, better fabrication techniques, better welders?
I know of Trackmaster frames built for Gene Romero built out of .049 4130 that were raced at the top level for the better part of 5 years. No cracks.
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Re: 53KR in a Low Boy Frame

Postby hugoct » Fri Oct 30, 2020 9:52 pm

Dave you can run a Sportster rear brake with the XR swingarm. Gordon Campbell makes a beautiful replica of the KRTT rear brake with the bigger shoes and finned hub.
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