SOHC.co.uk Forums > CB500/550
Top end refreshment
bomber:
Thanks Lester!
bomber:
--- Quote from: Oddjob on March 04, 2014, 09:56:42 PM ---I'd remove those bolts from the rocker cover. They should all have washers underneath to protect the alloy as they are tightened. Plus the nuts don't seem to be tight as one nut seems to be coming off. The clamps the nuts are attached to resemble the things you used to get on push bikes to secure the pedal arms to the cotter shaft that ran through the frame. They were called cotter pins and were basically just slanted pins with a threaded end. If you do remove them and remove the shafts they are securing make sure you note which rocker arm goes where, maybe a tag saying inlet number cyl.1 etc.
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Thanks for explanation, nuts were loose as I started to disassemble it and then took a picture.
You were spot on on the valve hitting piston! I was checking them today and all are straight except one and bingo thats same on which marked piston, I used metal ruler to check them and there is no way I could see it by eye.
So one valve to replace, does it mean valve guide needs replacing?
I measured pistons and cylinders with Vernier caliper, they all read 58.38mm only number 4 same one which has valve issue, read in direction front/back 58.44mm but left to right 58.38
It doesn't seems right as standard is 54.47-58.49, serviceable limit 58.35 does it mean that I should rebore for the 0.25 and use new pistons with new rings?
Also, all rings end gap are fine a part of the no4 which is 0.61mm and it should be replaced as limit is 0.7
bomber:
--- Quote from: Oddjob on March 05, 2014, 10:45:20 PM ---Put the valves in a drill and spin them up, if they aren't straight they will show a slight wobble, easy way to check them.
Check the end of the valve guide inside the inlet, see if you can spot any part of it missing, sometimes the valve bending breaks a small piece off. Other than that, get a new valve and see if it's a nice fit inside the old guide before thinking of replacing the guide, that will probably be beyond your talents at the moment.
TBH I never measured a piston unless I was looking to see if it had been bored and oversized. The best way to check for liner wear is the piston ring end gap, aside from a visual inspection of course, if it's all scored it's safe to assume it's gonna need a rebore. However to measure the liner wear you need a new set of rings, by one set of standard rings, use those to check each cylinder. If they all come back inside the limits then you can just re-ring the pistons. Position the new ring at 3 points in the liner, low edge, middle and top but not the very top as that doesn't get wear, about 10mm down from the top is fine. If the liners are very worn you can usually test them by using a finger nail and seeing if there is a lip right on the upper edge of the liner, as the piston rings don't go up the liner that far there will be a ridge on the liner right where the liner gets worn and where it doesn't, run your finger nail up the liner and you'll feel the ridge, if it's a big ridge then the liner is worn and a rebore is needed, a thin ridge you can barely feel with the nail usually means minimal wear and no rebore needed.
All that writing for something I could show you much better in a few seconds ::)
I strongly suspect the engine wasn't running when you bought it? I'm thinking that valve was stuck and as you turned the engine over it hit the piston, they usually bend much more than that if the engines running or you turning it over on the starter. I also strongly suspect you'll end up with a full engine out, you really need to clean that sand out of the bottom end and I suspect there will be additional stuff to replace on the bottom end, primary chain and dampers probably and camchain as well most likely.
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Thanks a lot for explanation.
You are right, bike was standing for over two years when I got it.
I will check that edge in liner tomorrow, to my untrained eye, liners look fine, there are dark patches but nothing I can feel on the finger.
Idea of taking engine of the frame worries me a lot, there is a strong chance that giving the work and family commitments I will not be able to have it back on the road before Christmas :'(
Thanks
Trigger:
Engine out is easy. Your half the way already. It does look as if it needs a good investigation. Once the sump is off you can check the primary chain. All these parts are not cheap. I have just finished a CB550 full rebuild.
tom400f:
--- Quote from: bomber on March 04, 2014, 10:39:42 PM ---Admittedly I'm way out of my depths...
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bomber - back in the day I discovered my 400F had its cam chain tensioner bolt broken off. I tried using a thread extractor (aka easy-out). Bad idea as I broke it off in the hole I had drilled.
I considered selling the bike and replacing it with a Suzuki GT380. Couldn't sell so I thought sod it - it's coming to pieces and I'll fix it properly.
I wasn't quite 19 and I had little more than a socket set, a Haynes and an old kitchen table in the garage. It was winter.
I didn't pull the rotor, I remember that, so the crank went back in with at least that seal not replaced. I *seem* to remember the Haynes manual saying the primary chain was never likely to need replacing (!) could be wrong about that one but I did replace the cam chain and tensioner mechanism. New rings too. Erm, coat-hanger method for the clutch basket.
Oh the bolt - got an engineering company to drill it out, machining a plug arrangement of some sort and tapping a new hole. It leaked a bit from there but hey-ho. Cost me 40 quid in 1979 to get that done. Bloody king's ransom but I learnt a lot...
Engine went back together and I felt it was so much better - clutch didn't snag anymore, kick start always engaged whereas before sometimes it would slip - don't really know why these things were better as no parts were replaced - no spare cash. Went like stink (as far as 400Fs ever do) and I rode it for miles and miles.
SOHCs are simple and easy to work on. Message: don't shy away from doing more than you think you are capable of. Take things easy, build confidence by careful progression. You will get a much better result that way. Good luck with it.
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