Honda CB750K5 Restoration by Royhall

[royhall]

Had a few guys email me about people who can repair the cases, many thanks for that. I do have a local guy who's successfully repaired them in the past for me. Usually it just knocks a lump out of the upper case, but this one is a heavy smash with cracks radiating out like a spiders web. The cracks run as far as the output shaft seal and involve both upper and lower cases. With the amount of welding required it is unlikely that the cases won't distort. I have decided to go with James's spare engine and part out the bits I don't need to help a bit with the cost. But the suggestions are most welcome.

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[Laverda Dave]

That's good news Roy and sounds like a plan is forming. Looking forward to seeing the photos of the actual damage as it will likely help others when looking for a 750 and the pitfalls involved.
Did the seller state the cases were damaged or was it just a case of 'Here's a barn find, non-runner, unchecked etc'?
Good to hear this won't be one of those projects that stalls at the first hurdle, good luck with it and the rebuild thread will be a good read.

[Trigger]

Had a few guys email me about people who can repair the cases, many thanks for that. I do have a local guy who's successfully repaired them in the past for me. Usually it just knocks a lump out of the upper case, but this one is a heavy smash with cracks radiating out like a spiders web. The cracks run as far as the output shaft seal and involve both upper and lower cases. With the amount of welding required it is unlikely that the cases won't distort. I have decided to go with James's spare engine and part out the bits I don't need to help a bit with the cost. But the suggestions are most welcome.

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To repair that much damage you have to bolt the cases down to a 28mm thick plate and do a little welding at a time, letting it cool down for an hour at a time. The last one i repaired that had a hole the size of my fist, took quite a few days. 

[royhall]

That's what we did last time and it worked out okay. This time I think I really need to change the casings as there are literally cracks everywhere and they are running into seal and bearing surfaces. As James has the bits available I may as well take the safest route. The guy must have been going for it when the chain snapped as it went with a real bang.

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[royhall]

That's good news Roy and sounds like a plan is forming. Looking forward to seeing the photos of the actual damage as it will likely help others when looking for a 750 and the pitfalls involved.
Did the seller state the cases were damaged or was it just a case of 'Here's a barn find, non-runner, unchecked etc'?
Good to hear this won't be one of those projects that stalls at the first hurdle, good luck with it and the rebuild thread will be a good read.

Thanks Dave. I actually asked the seller if he knew of a chain break as the chain was missing and the engine looked half out. But he said he didn't know and couldn't see without dismantling so I took a chance knowing it may be 50/50. Guess I just lost, but with James's parts were back on track. And don't forget it was dirt cheap.

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[royhall]

Having recovered from the setback of the crankcase break (thanks James) I have moved on with the strip down (Note: Strip down not teardown, this is not American Bubba ham fisted work. I hate those God awful Americanism's). Talking of God awful American, back to the bike. After the initial thoughts that it's not too bad, it is actually a bit of a mess. At some point in it's life it appears to have lived outside unprotected for an extended period. Nothing that can't be dealt with though so I will let the pictures tell the story.

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[royhall]

One ray of hope, I have sent the clocks off to Pete Horton who says they are not too bad so that's a nice surprise. I have dealt with all this mess many times before on my other bikes but I don't think it has been all together on the one project. It is going to require a lot of new parts as some are too far gone to recover, so I think the initial estimate of 7k including the bike itself has fallen by the wayside. More pictures on the horror of it all.

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[royhall]

Looking at the handlebar controls, the right hand side unit is actually broken on the casting so that will need replacing. I notice Silvers and Yamiya stock a remanufactured piece. Are they any good quality wise, and are they a good match for the originals. The left hand unit is intact but appears to be full of corrosion, but strangely, the controls still move okay although at this point I haven't had a multimeter on them. It may be repairable unless the pattern ones are good. Yamiya sell them as a pair at a not too bad price so I'm hoping you guys may have some good feedback on them. Alternatively, is there anyone out there that repairs these things at a reasonable cost.

The rims initially looked okay to re-chrome. Unfortunately they have very deep corrosion pits on the outer edges (not shown in the pictures) that I think will be far too deep to buff out. So that will be replacement DID rims required, fortunately they are available. The chain guard has damage behind the shock on top of where the indent should be. Looks like someone has fitted slightly wrong shockers at some point and at full travel they have been hitting the guard. I suspect the bike has been owned by some monster sized individual as the shocks are set to the hardest preload and the seat is squashed flat at the front. McDonalds anyone?

On stripping the front brake there was not a drop of fluid in there and everything is seized rock solid with both corrosion and the crystalised remains of the fluid. I think some new parts may be in order there as well. The wiring and electrical system is a total write off unfortunately requiring new harness and sub harnesses. Both water ingress and Bubbas attention with his Scotchloks and sticky tape for the multitude of extra lights and silly extra's have totalled the system.

I was going to replace the tank and side panels with Yamiya ready painted items, but on checking the tank it doesn't actually look too bad. So Friday next week were having a trip out to Preston to have the fuel tank and oil tank dipped and phosphated. I will decide when that's done on the fate of the tank but it does look solid. If that's the case it will be a good cost saving to get it repainted. It has had a bad custom job done at some point where they have filled the badge indents, hopefully its just filler as the dipping will take that out. The side panels have also been filled so they are scrap as dipping plastic ends in a soggy mess. It's a shame really as they are not broken.

The carbs look like they have been kicked around the car park along with loads of corrosion. They are seized solid. A replacement set is on it's way shortly (thanks again James) so hopefully a good set can be made out of the two.

More soon.

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[heli_madken]

Sorry to hear about the engine Roy it is a bit of a lottery I think buying blind from the US, will the new engine with a different serial number make the process of registration a little trickier?

The bike itself reminds me a lot of my 550 which had sat outside in Scotland unprotected for a few years. With the exception of the carbs and engine I think most things you would have planned to change anyway, even the engine would have got a good working over so in my view it isnt too bad.

To me it all adds to the challenge and immense satisfaction when you have completed a beautiful bike.

I bought handlebar switches from here - https://www.cb-four.com/cgi-bin/shop/ and found them to be quite good quality, havent had any problems at all with them

Looking forward to updates

[royhall]

Thanks for the tip Ken. I have had a ton of parts off CB-four.com over the years. They are another good source for parts and I especially like the fact that they list good used parts as well. Unfortunately on the switchgear issue they don't have the correct USA spec K5 pattern part switches, with the UK/European versions having the wrong markings. CMS have the correct ones but I am not sure of the quality. It would be nice if someone could recommend the CMS items as it would be an easy fix for a big problem.

[Oddjob]

The left hand switchgear Roy, are you intending to get the UK version with the flasher/horn or the US version with just horn?

I spotted this the other day https://www.ebay.co.uk/itm/224623350655?hash=item344c98537f:g:-wIAAOSwW4lhI5Eb Genuine switch, in decent condition, wires look good. That's if your going with the US version. Same seller has a lot of 750 stuff, take a look.

What's wrong with the right hand one, you said the casting looks broken but it just looks like it's missing a screw to me.

I do have some spare switchgear body parts so I might be able to help out. I'm also pretty good at refurbishing them.

[royhall]

The casting is actually damaged at the back. Your right that guy does have a pile of good stuff, will have a better look later. Thanks for that. I think for now I will go with the CMS repro units as they have been recommended. The guy says it's hard to tell them apart from OEM. A bold claim but I shall soon see, they may end up going straight on eBay but to be fair they aren't expensive. But I will keep you in mind if refurbishment is required.

[Oddjob]

Bottom or top casting Roy?

I have some spare castings so might just have the part you need.

[royhall]

The left hand switchgear Roy, are you intending to get the UK version with the flasher/horn or the US version with just horn?

I spotted this the other day https://www.ebay.co.uk/itm/224623350655?hash=item344c98537f:g:-wIAAOSwW4lhI5Eb Genuine switch, in decent condition, wires look good. That's if your going with the US version. Same seller has a lot of 750 stuff, take a look.

What's wrong with the right hand one, you said the casting looks broken but it just looks like it's missing a screw to me.

I do have some spare switchgear body parts so I might be able to help out. I'm also pretty good at refurbishing them.

Thanks for that. Next time in the garage I will get them off the handlebars and have a good look at them. Out of interest, how much would you charge me to restore the pair. PM me if you want. By the way, you don't happen to have a spare rear grab rail for a K5 do you?

[AshimotoK0]

I once bought an aftermarket  set of 750K0 switches from Yamiya only to discover that the UK ones were different, so I sold them on to a member here.
The quality was good though and if they had been correct for my UK  K0,  I certainly would have used them. Not sure they do the correct ones for the  USA K5 model though .. only seem to list K4 ......  James will probably know.

Re-anodizing old ones is very difficult & expensive. You can get good results by dunking old ones in strong caustic soda, which will bring the black anodizing off in seconds and leave you a lovely base finish for paint. Then prime with a thin coat of  black etch primer ( Clostermanns stuff is what I used) then coat with PJ1 satin back and bake at 150°C  for about 20 minutes. Then 'knock back' the finish with Solvol Autosol polish. If you do decide to refurbish some used ones and you are short of any small parts .. just ask and I may be able to help. I had a whole bunch of switch 'innards' re-plated a while back.

Hard to say for definite but I  reckon from the pics. that  your existing sitches should restore pretty good.