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CB250Rs Rebuild

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MRA464:
Thanks all for the 3rd wire info and all your advice.
Do let me know if my posts get too boring.

So my first real issues, I had a stripped out the frame and I was left with a seized centre stand tube and more of a worry the engine with a seized lower rear bolt, all others were free and left loose.
Try as I might I could not remove the stand, so I concentrated on the engine mount bolt.

It was the typical steel corroding in aluminium with added salt and general road dirt.

I tried the usual methods, lubrication, heat, force, time, more lubrication etc not to no avail. Fortunately for me after several attempts I managed to get the unthreaded part of the bolt to move,
So I again tried to get the bolt undone but all I was doing was causing it to twist.
A new plan was undertaken, lucky for me the engine case is two lobs rather than being completely enclosed. This gave me access to the bolt so with a dremel and small cutoff wheel I managed to cut most of my way through the bolt with out touching the case. Now the bolt was weak, so I just sheared it off using a socket on the head, happy days one side off.
I now cut through the protruding threaded side as close to the frame as I dare, ready for it to be drilled out.
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Carefully I centred a drill and drilled enough of the bolt away to allow me to remove the engine with no damage. I then continued to drill the bolt and eventually with a drift it came loose and popped out, Result.
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The center stand was cut out of the frame and will be modified or replaced in a later post.
Now I could strip the engine to see if I had a good one.
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Oil looked like caramel sauce, fingers crossed, as it was running.

MRA464:
So now the engine was out I could take a look at its internals.
I had read in various posts that the threads easily stripped, so I had allowed the bolts to soak with oil overnight before attempting the disassembly.
Luck was on my side and they all came out easily with no issues ,moment of truth off came the cam cover.
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All looked good to me, but I am happy for your comments please. The rocker pads were clean with no pitting or damage the close up photos just show the wear lines in the surface and makes them look worst than they do visually.
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The bearing surfaces looked good again with no damage. So next to be removed was the cam chain, never stripped one of these so out with the manual, after some hassle I eventually manged to pull up the cam chain tensioned and pinned it in place. I had measured the tensioner are at approx. 7/8mm so I may change the cam chain on rebuild along with the balancer chain as advised by you kind gentlemen.
Cam sprocket was removed and out with the cam shaft, again it looked ok, bearing surfaces were good and the lobs showed some wear, closer examination with the camera showed some small imperfections, are these acceptable?
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At this point it was time to check the next know issue with these bikes, cracked head.

MRA464:
The only issue I had removing the head was trying to undo the top sunken 14mm headed bolts, after breaking a 1/4 drive socket, I managed to find an old 3/8 drive socket that I could fit inside the recess and after some force it came loose and all was good, no breakages or damage threads.
The head was eased off and I turned it over to see what I had, HAPPY DAYS all looked good no obvious cracks. Even looked like a good combustion colour
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Now had it had a rebore?
The piston looked ok with no apparent slop although it looked oily. On cleaning I could see no marking so I assume it is original.
The bore was also very good with no steps or scoring, so it looks like I have been lucky and picked up a usable engine. ( hoping your comments don't dash this hope.)

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I will carry out the engine work New piston /Rings, Cam chain, Balancer Chain and a general good clean as part of the rebuild.
It needs the output shaft seal changing as well, not sure if this can be done from the outside or if it needs the cases split.
I will also change all the other external oil seals as I go whilst I am in the mood.

So lets get started on the rebuilding of this little classic. Lots of parts to order and find.
 

K2-K6:
As you note, it's not quite the same looking at a photo compared to having the parts in front of you.

But the cam and rocker faces show considerable wear, the right side cam profile in particular looks like its been running with no clearance as the wear is complete round the base circle.  Also the oil has not been able to protect the surfaces as it should either through age or fuel dilution.  There's characteristic and noticeable "pickup" from the two metal surfaces being unsupported by oil film which has given the wear marks experienced.

It's not completely trashed itself,  but more hanging on with grim determination.

Laverda Dave:
I agree with Nigel, the cam looks like it's begining to break up on the lobe.
These cams are made from chilled iron, replacements are virtually non-existant and very expensive if and when you can find one. The rockers also look as though they have started to pick up due to dirty or lack of oil.
I would send both the cam and the rockers to Newman Cams in Kent, they will advise if the cam can be saved. They will weld new pads to the rockers and grind them to match. Your biggest problem though wil be getting the rocker arms out of the head. The rocker shaft is held in the head by a dowl, they are an absolute pig to get out, they will break if you do what they Haynes manual tells you to do, grind a notch in the dowl and use a screwdriver to attempt to lever them out! I found someone who spark eroded mine out called Peter Lovell Developments, he's in the midlands. He may do yours, he may not as he said mine were a real pig. He only did mine becuase another company gave me his number! He does have a website though. You can still get the dowls from Honda.
What are the cam bearings looking like in the head, if you can feel any groves with your thumb nail that's not good news either.
As for a replacement piston, see if you can get a genuine Honda piston and rings if you can, they are available sometimes. I had to use a brand called IMD, no problems at all (second time round!). Make sure you only get it rebored by someone who sticks to the Honda specifications, I learnt the very hard way what happens when so-called experts do what they think is right and not what Mr Honda designed!

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