Author Topic: Honda CB750K5 Restoration by Royhall  (Read 28053 times)

Offline Laverda Dave

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Re: Honda CB750K5 Restoration by Royhall
« Reply #180 on: May 07, 2022, 08:58:13 AM »
Good progress Roy. No matter how big your garage is it will never be big enough after the first year because you will fill it with more bikes!
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Oddjob

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Re: Honda CB750K5 Restoration by Royhall
« Reply #181 on: May 07, 2022, 01:50:26 PM »
Curious Roy as to why you chose to pick those tyre sizes. The front is stock but the rears gone bigger. Any reason? I'd have thought you'd have gone for a 3.60 to match a 4.00.

Asking because I kinda like the look of the Avon Road Riders and was checking on sizes for mine, I always go bigger than standard as that's how I raced the bike back in the day, so I decided on 100/90 front and 110/90 rear.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #182 on: May 07, 2022, 05:54:32 PM »
Well spotted Ken. Easy answer, I didn't order that size that's what they sent and I didn't notice until you pointed that out. That's why the wheel builder had to buy an inner tube as the one I sent was for a 3.60. Bugger, I hope it goes in the swingarm without hitting anything. I am doing a few stupid things like that these days, and I thought it looked a bit big. Thanks for pointing it out, may have to change the tyre. Am going now to check what I actually ordered. Bugger, Bugger, Bugger.


EDIT: It appears that the sizes I have gone for are OEM standard and it was the inner tube that was supplied wrongly. Tyres Honda CB750K1 / K2 / K3 / K6 (SOHC) 1970 to 1976 (bits4motorbikes.co.uk)   Thank heavens for that.
« Last Edit: May 07, 2022, 06:01:41 PM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline Oddjob

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Re: Honda CB750K5 Restoration by Royhall
« Reply #183 on: May 07, 2022, 06:12:50 PM »
Weird that Roy. Honda seemed to have a formula that the rear tyre was the next size up from the front tyre. Like the 500 was the same front 3.25 but the rear was a 3.50. Maybe the 750 was the exception in that it got a wider rear rim than the 500 so it suited a slightly wider tyre as a result.

Never noticed that before but at least you don't have to change the tyre, so that's good news.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #184 on: June 18, 2022, 11:36:52 AM »
Sorry for the delay. There has been a fair amount of progress on the bike, just no time to document it all on here. I'm still waiting for quite a few things to return like, chroming, paintwork, polishing, etc.

I am also still waiting for the promised exhaust system that I paid a £500 deposit on last November with Colin at Predator Motorsports. Colin reckons the exhausts were already made but he was struggling to find a route from Japan that was cheap enough as container prices had gone through the roof. I have asked him via email recently about it but the reply was simply "Nothing yet" which doesn't tell me much.

I have mainly been concentrating on the engine for now. I had the cases/barrels/head vapour blasted then gave them a really really good clean to remove any traces of blast media. My jetwasher has a small nozzle device that is really useful for the small drillings along with the assortment of bottle brushes. Then after masking up they got three coats of the usual Simonize SIMVHT31D (worryingly I now know that number without looking it up) then backed in the oven at 150 degrees for an hour.

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They came out looking really nice so am well pleased. Virtually as soon as the barrels were out of the oven I took them to the engineering shop for a rebore. Once again I am using the Cruzinimage piston kit as the quality is very good and the price is excellent. The engineer worked to each piston seperately and gave them a 0.001" clearance. This was after an extended debate about it being too tight and it will seize. In the end a gave him a signed note that that basically said it's not his fault if it seizes. Anyway, looks like he did a good job just hoping he really did it to 0.001".

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Am hoping to get into the garage this afternoon and finally get the engine lower half back together.
« Last Edit: June 18, 2022, 11:39:23 AM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #185 on: July 03, 2022, 09:00:55 AM »
As usual I didn't make it to the garage that afternoon as once again life intervened. But it did get done.

I was very careful to make sure everything was stored correctly so there would be no mistakes putting it back together. The usual piece of cardboard makes a good holder to ensure that the valves go back in the same place they were born into. Likewise plastic zip bags and a marker pen work very well for the other parts. I have bags in a range of sizes from tiny to huge, cheap off Amazon. Later I will demonstrate how easily this plan comes apart with a 63 year old head in charge of proceedings.

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I went right through the gearbox checking bearings and looking for damage and all appears good. The bearings in particular felt like new so that was a bonus. I decided to replace the bearing in the lower case as it requires knocking out and they are only cheap. Unfortunately I ordered the bearing for the opposite outrigger housing so had to reorder the next time I was getting parts. So since I had the parts, the secondary shaft had all new bearings. On checking the cush drive rubbers in the chainwheel they were still soft and pliable so they too were good to go. Again that was good news as they can be awkward to do. It was surprising they were good as all the other rubber components were rock hard. Everything checked in the lower case then reassembly was straight forwards.

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The upper case assembly also went well. I have replaced all the main and conrod shells, and when working out it turned out that every shell was a green. Being sceptical the even Honda could be so accurate I broke out the micrometers, and sure enough all green. With the shells and housing carefully cleaned they were fitted and given a coat of Graphogen.

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The rest of the top half was then dropped into place (that sounds like I threw it in) without problems. Remembering to check at this point that the timing seal and half ring bearing locators were all in place.  I have used all new primary and cam chains and also replaced the primary chain tensioner. The wheels on the old tensioner were as hard as steel.

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Next up will be mating the two halves. It's job stop at the minute as my tube of Threebond has gone chewy. Onto good old eBay and order some more. The courier likes bringing my parts as he is a classic fan with a Kawasaki Z1000 in the garage. He says he hopes I'm in when he comes so he can see the progress. What a nice friendly hobby, bloody expensive though. Next time.


Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline taysidedragon

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Re: Honda CB750K5 Restoration by Royhall
« Reply #186 on: July 03, 2022, 01:28:57 PM »
Looking good Roy. As good as new. 👍
Gareth

1977 CB400F
1965 T100SS

Offline Laverda Dave

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Re: Honda CB750K5 Restoration by Royhall
« Reply #187 on: July 03, 2022, 02:04:06 PM »
Great progress Roy. Keep the reports and photos coming.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #188 on: July 16, 2022, 08:40:45 AM »
A few days later the Threebond had arrived. I spread a very thin coating over every mating surface between the two halves, even when it looks like the area is inside the engine (oil may run down a bolt thread). After fitting the locating dowels and mating the two halves, the ten bolts holding the crank area were carefully torqued down in the correct sequence. I don't know if it's correct procedure or it's just me, but I usually do the sequence at 50% torque then again at 75% then finally to 100%.

At this point I check that everything turns as expected, then the rest of the case bolts inserted and torqued down. I check again at this point that everything moves as should. Whilst the engine is on it's back I checked the primary chain tensioner was in spec. Although it's a new Honda piece you never know if it's correct, fortunately it measured to be at the very start of it's tolerance so that was good.

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Now at this point I went on to fitting the oil pump that I refurbished earlier, unfortunately I got carried away and forgot to take pictures. When the pump was in I laid the engine on it's side with the oil hose connections at the top to prime the pump. It is not possible to just fill the pump as the anti wet-sump valve prevents the air being expelled so the oil can't get in. At this point I remove the valve and fill the port with my oil can until it starts to drip from the pump then refit the valve. I blank the hose connection ports with rubber bungs to prevent the oil spilling back out when the engine is laid on that side for putting into the frame. I then fit the sump plate and the engine stand and turn the engine the right way up. You can just see the rubber bungs in the picture.

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Up next was to fit the new plus 0.5mm Cruzinimage pistons. They come in the kit complete with gudgeon pins, clips, and piston rings. Compared with some Cruzinimage items they are very good quality. Before fitting the rings to the pistons each one is placed into it's respective bore and the gap checked with feeler gauges. All were okay. I usually stuff the crankcase openings around the conrods with rags to prevent a dropped pin locator clip dropping into the cases. The pistons are fitted with the little arrows pointing to the front of the engine. I move the rings around to try and get the ring gaps distributed evenly around the pistons.

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The next part can be one of the trickiest, fitting the barrels. I am using new camchain guides and tensioner as again the old ones were rock hard. I am still amazed that the cush drive rubbers were in such good condition when all the other rubber parts were rock hard.

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To assist in turning the engine I temporarily fitted the alternator rotor. After liberally coating everything in engine oil, I lifted the two centre pistons to TDC and placed wooden blocks under them. I don't bother using piston ring compressors, although I have some, as they are more faff than required. After fitting the tensioner parts not forgetting to thread the cam-chain through first, I lower the barrels gently onto the two pistons and, using fingers, gently massage the rings into the barrels. Once the two centre pistons are in I remove the wooden blocks and allow the pistons to fall gently whilst holding the barrels until they rest on the outer pistons. Again I gently massage the rings into place and then  push the barrels down onto the base gasket remembering to pull the tensioner forwards out of the way.

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« Last Edit: July 16, 2022, 10:01:22 AM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #189 on: July 16, 2022, 08:56:22 AM »
At this point anyone paying attention will recall my big problem. It is covered here on this thread   Mystery problem on 750 cams (sohc.co.uk)   After going over what happened to cause this problem (other than operator error) I realised the issue. When I remove the valves on stripdown I keep all the valves in a clearly marked piece of cardboard. At a point along the way I removed all the valves from the card and placed then in in the correct order on the bench for lapping in. Afterwards I put them back into the card but got them the wrong way round (not sure why I didn't just leave them in the card and lap them in one at a time). Then on building the head I just picked them out of the card and fitted them not noticing the problem, then the rest was history. Motto of the tale is double check everything. It is so easy to get excited about the progress and rush ahead resulting in mistakes. Lesson learned.

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And even stranger, I had actually taken a picture of the mistake and still failed to notice it.

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« Last Edit: July 16, 2022, 08:59:53 AM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline royhall

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Re: Honda CB750K5 Restoration by Royhall
« Reply #190 on: July 16, 2022, 09:31:54 AM »
The above mistake required me to strip the cams and head back off and re-do the valves. I took the chance to lap the valves again to ensure everything was still okay and no damage had happened. Trigger also suggested that I fit thicker o-rings to the oil feeds as the specified rings were too thin with an aftermarket gasket. On checking, that was correct. The standard ring is an 11*2.5mm item that was the same thickness as the gasket so would only just seal. I replaced those with 10*3mm to get a bit more compression. He also suggested removing the cam tower studs and sealing the threads with threadlock to prevent oil weeping through the threads. Really good advice that I would never have thought of.

So thanks Trigger. The full list of things Trigger says to check is on the thread mentioned earlier.  Mystery problem on 750 cams (sohc.co.uk)

I realise that the head gasket could have been reused but I decided to replace it anyway. I got a full NE gasket set from M&P for £52 so that was the cost of the mistake. The head went on second time around without problems. I use a length of coat hanger wire to keep the cam-chain from dropping down into the cases.

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The six rubber pucks should be fitted to cover the bolts beneath. I usually use some Threebond under the pucks to ensure a good seal. After cleaning and fitting the oil control valves with new o-rings then fitting the locating dowels I fitted the cam towers (don't forget to fit new o-rings to the blacking side of the towers). Carefully threading the cam chain sprocket over the cam, the camshaft was fitted from left to right, then after liberal use of the oil can and some Graphogen placed into the towers. The caps were fitted in their original places and everything torqued down.

With the crank set to 1:4 on the T mark the cam is rotated until the left hand ends scribed line is level on the tower with the cut out uppermost. The cam chain is then moved around the sprocket until the bolt holes line up the tightened into place.

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This time round the rockers slid in correctly and were all bolted down, again ensuring that they went back into their original positions. The tappet clearances were set whilst the rocker box was off as it's really easy to do at this point. The last on the list is to set the crank at 5 degrees from TDC and release the cam chain tensioner. After it springs forwards re-tighten the bolt and locking nut. Not forgetting to fit the speedo drive gear and new seal first, the rocker box was fitted in place and fastened down with all new screws as the engine came with a varied collection of mongrel fasteners.

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After suffering back problems last time I did a 750 engine, this time around I am going to leave off anything that can be fitted with the engine in the frame to reduce the weight. This includes the entire alternator and rotor assembly, starter motor and ring gear, all the gearchange assembly, all the clutch and baskets, and the points assembly. See I am learning. The engine is now ready to go into the frame. So children that will be tomorrows story, sleep tight.

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« Last Edit: July 16, 2022, 10:08:36 AM by royhall »
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

Offline Johnny4428

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Re: Honda CB750K5 Restoration by Royhall
« Reply #191 on: July 16, 2022, 10:23:48 AM »
Great to get to that stage again Roy! I’m sure she will breath better with valves in the right way 🫣 good luck with wrestling the engine into bike. If it’s bare fram no problem with engine on its side. With my bike built (second time round) I used the 4”x 2” method. The best I seen was an engine hoist and home made C frame.



1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1. Running resto,
1978 Honda CB550K3.
1999 ST1100 Pan European 50th Anniversary.
1975,1980,1984,1986 Honda C90’s
1973 Honda CB750K3

Offline Laverda Dave

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Re: Honda CB750K5 Restoration by Royhall
« Reply #192 on: July 16, 2022, 11:48:02 AM »
Well done Roy, that's great progress and a transformation considering what you started with!
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Trigger

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Re: Honda CB750K5 Restoration by Royhall
« Reply #193 on: July 16, 2022, 12:32:26 PM »
How are you going to do the fly wheel torque up with the top end on ? This should be done by putting a bar through the con rod small ends to lock the engine  ;)

Offline Lobo

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Re: Honda CB750K5 Restoration by Royhall
« Reply #194 on: July 16, 2022, 01:24:41 PM »
Beautiful job Roy, be sure to write up putting the engine into the frame as this is nearing for me. (I have a bare frame and intend the laying over method)

If you are using Part #3 (Guide overflow / top RHS’ish) pls give me a heads-up whether it fit it before or after the engine goes into the frame as it’s a relatively delicate bit of bracketry.

 

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