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Honda CB750K5 Restoration by Royhall
royhall:
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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Johnny4428:
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 4â€x 2†method. The best I seen was an engine hoist and home made C frame.
Laverda Dave:
Well done Roy, that's great progress and a transformation considering what you started with!
Trigger:
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 ;)
Lobo:
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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