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Honda CB750K5 Restoration by Royhall
royhall:
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.
taysidedragon:
Looking good Roy. As good as new. 👍
Laverda Dave:
Great progress Roy. Keep the reports and photos coming.
royhall:
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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royhall:
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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