Removing the frame upper rails

[SumpMagnet]

I am seriously contemplating doing this mod inn order to make working on the CB750 project a little easier, and to facilitate building the motor in situ, as well as potentially having to go back in to work on areas like the cam carriers...which I will have to fit less 'shiny' ones than I would like to begin with.

I have been frankly struggling with the project, not from the desire to get it done, but rather from a string of health issues, and arthritis. Displaced meniscus....ligament issues, and I am now potentillay looking at surgery to try and resolve this stuff.

So, I want to consider the options.

Carpys do a kit ...$139 plus postage, VAT etc.
Gordon's Mod .... $189 plus ransom demands and postage. Website is a little hard to navigate, so would probably need to e-mail to resolve.

Are there any options I missed?

Is there ANY supplier in the UK ?

I have a welder to install, as my little MIG set probably isn;t up to the job. So I would just tack the bits in place, then get a better welder than me to do the final job.

[royhall]

Did the Carpys mod on my F2 but without paying the silly money for his 3 tube kit. Basically made it myself. Been in use for 10 years now with no problems. Will see if I can find the photo's over the weekend. May be awkward as I'm in hospital at the moment.

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[SumpMagnet]

thanks!

no rush...under the circumstances! Hope you are on the mend

[royhall]

Sorry don't have the photos here and I won't be getting home for at least 2 weeks.

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[SeanFD]

Looking at this and noting the absence of the triangle in the finished job, I was wondering why new tubes are required.

Would it not be possible just to cut and shorten the existing tubes, fit the ends in and put it back together with the triangle still in place?

[royhall]

Sorry only got three pictures of it fully assembled but here they are. Decided not to bother with the Carpy's part as the triangulation was missing. So I made my own system and it has worked very well over the 12 years since it was done. It was removed once about 5 years ago to fix an oil leak from the rocker box. It came apart and went back together great.

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[SumpMagnet]

Thanks for the pics Roy, thats really handy!

Are those just sleeves over the top of the stock tubes bolted through? It looks very neat...and if it has worked for the last 12 years, then I would say it works just fine!
I get what you are saying about the triangulation. Honda decided it wanted bracing there, and I guess they had some idea.

Reading the detail of the Carpys ad, it appears just chopping the frame rails out was something people were doing back in the day. I know a lot of 'custom' frames had single top tubes for that clean chopper look, so I guess there were owners who wanted the look and had no money for a custom frame and access to a hacksaw! If that was the case, then the tubes were just gone, so supplying some tube was easy to fix it.

[Skoti]

Sorry only got three pictures of it fully assembled but here they are. Decided not to bother with the Carpy's part as the triangulation was missing. So I made my own system and it has worked very well over the 12 years since it was done. It was removed once about 5 years ago to fix an oil leak from the rocker box. It came apart and went back together great.

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Hi Roy,

Looks a tidy job.

Does your frame modification use shoulder bolts or bolts with spacers?


I'd be concerned about over tightening the bolts and possibly deforming the frame tubes.


https://theboltholder.co.nz/view-product/m10-m8-60-skt-shoulder-bolt-12p9-bl

[royhall]

The sleeves were made out of stock mild steel tube the right internal diameter to slide over the painted frame tubes.

The bolts were drilled through for slight clearance on the front, but drilled and tapped in the back. The bolts were then screwed into the tubes and just gently nipped. Then a nylock nut was tightened onto the back of the bolt to secure it. That way there was no need for sleeves as there's no crushing force, plus the threaded part located the tubes perfectly.

It was done about 12 year's ago and not the slightest problem with it, and the bike has been used quite a lot. I took it apart about 5 years ago to fix a leaking rocker box gasket and it came apart okay. I did coat the insides of the sleeves with copperslip when I originally built it and that helped. Would have been an engine out job without the modification.

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[SumpMagnet]

Lovely!

I have already searched out some tube. The top rails on mine measured 25.5mm .... and I found some 28.5mm OD 1.5mm wall tube. That should be a nice fit.
Plus 1.5mm should take a thread OK at a fine pitch. Check on the grease. going to keep the moisture out and stop things corroding together. Then I'll order some nice stainless button heads and nylocs. Whole thing is probably going to cost me less than the handling fee for Royal Mail imports!

Torn between M8 or M6 for the bolts. M6 is probably OK as the loads are not really on the bolts. Thats all really on the sleeve.

Going to give this a go. Worst case...I am going to have to pay someone to weld it all back together!
But it looks simple enough.

Thanks again @royhall this has been a massive help