SOHC.co.uk Forums > CB750
Oil pressure issue / motor rebuild
MrDavo:
Trigger, you have a pm.
Photo taken this morning with my beautiful assistants, Big Leigh on the left can single handedly lift an H-D 1200 motor into a car boot, so handy to have around. We each wrote a guess for the 'motor in' date on the garage wall. We expected a lot off faff after watching those clowns on the telly doing it, but it all came out suprisingly quickly and easily. 'Prior preparation prevents piss poor performance' as they told me when I was firing steam locos for a hobby.
We didn't resort to lifing the bike off the engine, because we couldn't be bothered taking off (and putting back on again) the wheels, and possibly the indicators, but did it the old fashioned way.
Eddie is an engineer, and will be providing calibrated micrometers, borrowed from work, and an ultrasonic bath for the carbs. It also did a lovely job on our coffeee machine's filter 8) .
MrDavo:
Well I got the head off. Number 3 exhaust pipe has always been a little bit straw coloured, but I thought I'd fixed any air leak when I tightened up the inlet rubbers. Obviously not. I need to look at that carb - partly blocked main jet or fuel feed passage? Any other suggestions? The tappet gaps were right, btw.
The head gasket delaminated as it came off, while all looked clean and new in there, I think it was all put together a long time ago. The bores and pistons all look good so far, no visible wear.
The big PITA at this stage is that the barrel is reluctant to come unstuck. There doesn't look to be any jointing compound, but I'm nervous about using force. Tapping with a rubber hammer hasn't worked, I gave up and came in after a while. Any good suggestions?
MrDavo:
Futtocks! After going in the garage last night to strip my engine I have
!) Broken my workmate - off to B&Q soon to buy a real wood plank top, not the cr*p fibreboard it came with. It did say '100Kg weight limit', not sure what a CB750 motor weighs.
2) Wrestled with it on the floor and decided to invest in one of Trigger's engine stands.
3) Failed to get the barrels off. I may now wait until I can hold the motor securely, but I've tried the putting rope in the bore and the head back on (held with the 4 screws) and trying to turn it over trick. It didn't budge. I'm wondering whether to remove all the studs now. I've tried tapping with rubber mallet and wooden blocks, I'm scared of using extreme force though.
I also tried to buy an NP gasket set on eBay, but later the seller rang to say that the borrowers had been in the packet, so the order had to be cancelled. :(
AshimotoK0:
You can still strip the bottom end and get to the crank etc for inspection with barrels still on. I cant remember but there may be small recesses in the castings to get a pry tool in. Sounds like butchery I know but sometimes you will need to do it. Trigger/Bryan/Oddjob will know they are the pros's on here.
K2-K6:
I wouldn't take any of the barrel studs out unless you are replacing them, or need to for any other reason. You'll give yourself a big headache if you get into that.
You can try to gently, using a rubber block, or something similar, to tap the top of the barrels first forward and then backward to see if they will release from the gasket and dowels. It's not much but just enough to break the adhesion at the base. Right at the top level with the head gasket surface so you are in effect using the barrels themselves as a lever to rock them loose while not putting any up or down blows onto the fins as they will snap.
The studs should not ordinarily be holding anything as they are all waisted down their whole length and so generally have clearance for the barells.
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