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Author Topic: Honda 650 single  (Read 2093 times)

Offline unclerob

  • Posts: 166
Honda 650 single
« on: Jun 09, 2018, 14:57:22 »
Hello all, I've been posting over in the UK section about a project I've been slowly working on for the last couple of years, the idea was to build a sort of 60's single cylinder race bike replica using parts from the Honda RFVC singles. Have been slowly refining the design and have just started on the 8th one which I'm building for a friend....so thought I'd start a thread here on it...
A few pics of completed ones to start with...

Offline The Limey

  • Posts: 407
  • Evil English Villain
Re: Honda 650 single
« Reply #1 on: Jun 09, 2018, 16:03:33 »
Oh yeah!  Tell us about the build, the spec, everything!!!  ;D
I was born a rocker.  I'll die a rocker.  And I'm proud of it.

Offline unclerob

  • Posts: 166
Re: Honda 650 single
« Reply #2 on: Jun 11, 2018, 14:17:47 »
Yes, am going to....starting with the frame! This is the 8th one I've made and each has had a bit of modification to improve it, now fairly happy with the design. Its made from 11/4 CDS tube, 18g wall, the first couple I made pretty much freehand but then made a jig so it goes together pretty easily now.... the biggest problem I was having was distortion at the headstock where 5 tubes join to it....even getting the joints as tight as I could and being careful with the welding sequence it still moved. After they are done I was having them checked and straightened at a frame alignment place but never liked the thought of how much stress was being put into that area. Then hit on the idea of making the bend in the diagonals a bit different so that there was a small gap between them and the top rails and leaving the joint unwelded while it was straightened....so that the bend altered slightly as the headstock was twisted....then welding in gusset plates afterward to lock it all together...
« Last Edit: Jun 11, 2018, 18:16:34 by unclerob »

Online beachcomber

  • DTT SUPPORTER
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  • Posts: 3940
  • TJ - Beachcomber
Re: Honda 650 single
« Reply #3 on: Jun 11, 2018, 16:23:42 »
Perfection ..............................  8)
"if at first you don't succeed, you've already been a failure once"

" we're not going back to the sixties - we never left "

"yep, nostalgia ain't what it used to be"

"I used to be indecisive - now I'm not so sure"

Offline The Limey

  • Posts: 407
  • Evil English Villain
Re: Honda 650 single
« Reply #4 on: Jun 11, 2018, 17:14:12 »
Absolutely wonderful.  How are you registering them,nor are they purely track machines?
I was born a rocker.  I'll die a rocker.  And I'm proud of it.

Re: Honda 650 single
« Reply #5 on: Jun 11, 2018, 17:29:53 »
very nice!
"Remember when Goldwings were sexy? Me neither" -- Comet Tavern bathroom, Seattle.

Offline unclerob

  • Posts: 166
Re: Honda 650 single
« Reply #6 on: Jun 11, 2018, 18:15:16 »
Thanks! As for registration, unluckily I killed my lathe boring out some bar to make the headstock so had to use the ones from the original frames.....! Probably best to say no more other than this one which is for a friend and another I'm doing after are all getting the boring stuff like indicators, mirrors and such like and one or the other will be having an IVA....

Offline unclerob

  • Posts: 166
Re: Honda 650 single
« Reply #7 on: Jun 11, 2018, 18:40:16 »
And while I'm here a bit more about the frame design....the original one from the SLR and FX 650 just has the swingarm supported in the middle with the outer ends of the pivot bolt supported by the footrest plates. I've changed that so the main support is from 2 pairs of plates spaced apart 10mm either side which are then welded to the diagonals running directly up to the headstock. These plates also take the lower rear engine mount which is a long stud with spacers either side of the crankcase....these can be made to an exact length so as to get the chain line spot on.
At first I'd made the 2 front engine mounts..to the head and the downtube as part of the frame....have now changed that to seperate bolt on mounts....I make them deliberately a bit too short and then when the motor goes in I bolt the 2 rear ones up tight and shim the front ones to about a 2mm gap before doing the bolts up. Puts a little bit of tension into the structure and hopefully adds a bit of extra strength....thats my theory anyway! What it definitely does do is make everything easier to make....hard to weld it all in place and expect engine mounting bolts to line up exactly....

Offline cardinal

  • Posts: 58
Re: Honda 650 single
« Reply #8 on: Jun 12, 2018, 13:18:31 »
As a former bicycle frame builder I love seeing the frame fabrication pics and the jigs! Pardon my ignorance, but why are there two exhaust pipes if this is a single? (not familiar with that engine at all)

Offline unclerob

  • Posts: 166
Re: Honda 650 single
« Reply #9 on: Jun 12, 2018, 14:02:25 »
Its a 4 valve single and each port has its own pipe....some versions had 2 carbs as well! Also the valves are arranged radially instead of being paralell to each other....makes for a very complicated follower set up....and probably not really worth all the trouble Mr. Honda went to!