MAYBE I jumped the gun ordering rings before taking measurements, but I just thought the engine is such low mileage and shows virtually no wear elsewhere , that I thought I could just get by with deglazing the cylinders and throwing new rings in.
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As you say....perhaps a gun was jumped, but with such low mileage, you might get lucky on this one (and my guess is that you will Bob).
 
I have found several spots ,elsewhere on the bike , that the guy used silicone for all sorts of purposes. Trying to seal up the intake manifolds, and various places where a fastening nut had apparently vibrated off, he would replace the nut without a lock washer and just smear silicone all over it to hold it in place. Haha! It worked, they were still there 46 years later!
 
....as I said.....
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IT WAS ALL GOING SO WELL............UNTIL IT WASN’T. :unsure:

ENGINE TEARDOWN

The first thing I did today was to remove the cam chain tensioner to facilitate removal of the cam.
Then I pushed the cam bearings out the sides so the cam could drop down and I could ease the cam chain off of the gear and remove the cam.
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With the cam out, now I could remove the head. It was stuck pretty good, so using a small block of wood and a soft hammer I tapped upward, making sure I only did this on meaty sections of the head, you don’t want to break a fin!
The head was lifted off.
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And then the jugs,
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And now some detail shots. The cam chain tensioner and the front guide both look like brand new with no discernible wear. The front guide is amazing, not a mark on it and it feels absolutely tight on there. I have a new replacement coming from Mikes, but not sure if it’s worth putting it on.
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Teardown continued in next post. This ones getting pretty long.
 
ENGINE TEARDOWN CONTINUED

Here are a couple shots of the cam.
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Next up, remove the pistons. They are pretty hard to read, but I believe they are both stamped 963 on top.
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Everything has been going beautifully up to this point. Now let’s take a look at the bores. Hint, this is where things go sideways.
The right cylinder looks beautiful, clean and can still see faded cross hatching in there.
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Now let’s look at the left. Water has been in here, somehow, someway. I don’t know if it was condensation, or the good buddy I bought the bike from who owned the wrecking yard and loved his steam cleaner, but have a look.
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So here I am.
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In my eagerness to get things started, I jumped the gun. I was so confident given the look of everything I had seen to date and the bikes very low mileage that I ASSUMED that I could get away with just honing the cylinders.
Let that be a lesson to you all. Don’t buy parts before you look!
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All I needed to wait was one more day and I would’ve known the correct course of action, instead I now have standard size rings flying in from Japan as we speak and a flex hone that will likely not see any action. So my Cheap Bastard Rebuild is about to grow. I’m a little unsure what the next step is for me. Do I take my jugs to a machine shop to be looked at and measured? Do I order over size pistons and rings and then go to a machine shop?
This is new to me, I may be slow , but I’m learning. ( and still having fun)
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Pity they don't make the 706cc big bore kit for the 256 engines...........Dam, that pitting looks to be near or over the 4th oversize, (76mm). If you have to re-sleve buy larger and get a set of TX750 pistons. bolt straight on to your rods.......

Don't think you wrecking mate done that damage............there was a reason for all that gunk you found. Sorry for your bad luck man.
 
Been exploring some options.

1. Cruizenimage carries a first oversized piston and rings set. 75.5 mm, $102 delivered to me. As Skull pointed out, I believe it’s doubtful that would be large enough, and I couldn’t find anything larger on their site.

2. Mikes XS carries a second oversized piston and ring set, .5mm over , $194 for a set.

3. Mikes XS carries a replacement cylinder sleeve for $123 that could then be machined to accept my stock sized piston and rings. I’d have to pay a machine shop to R+R the cylinder liner and then machine it to size. While the shop had my jug to install and size the cylinder sleeve they could hone the cylinder that is in good shape , and I would keep my stock pistons and my new standard sized rings. ( that I already bought)

Note: I just realized that Cruizenimage calls their 75.5mm piston set First oversize , while Mikes XS calls their 75.5mm piston sets Second oversize. Weird!

Oh by the way, I went back out and looked at my cam gear. Not a crack! Phew! Just a whisker of grease.
 
Bob, I guess it's irrelevant but I wonder if it sat outside for a long time with no plug in that cylinder and rain did the damage about halfway down the cylinder til it hit the piston and rings? You can even see the rusted ring impressions there.
 
Yeah maybe, it’s weird, there was no rust anywhere on this bike. All the rubber was dry rotted but the bike looked like it had been living in a dry cave.
It’s a good thing we enjoy challenges huh? I’m going to have to do a hard search for a machine shop now. I sure wish I had a guy close by that was as good as your machinist!

I really need to verify that the replacement sleeve will indeed fit my bike. I have bought so much stuff that says it will fit, only to get it and be unable to use it.
 
There will alway be someone come along who can use it Bob. If you can't, post an ad in Classifieds.

I'd be happy to take it to Terry for for you, but shipping? :yikes:

You live in a pretty big town/area. Bet there's someone there. You just haven't been looking that's all.
 
Another option Bob... I know Daniel has a bunch of engine parts. A good machine shop could press a good sleeve out of a newer cylinder set and press it back into your 256 motor. If he has a real good sleeve.... you might get to use those standard rings yet....
 
...... as to what caused the pitting, I'm guessin' one of the valves was left open for years on end. I suspect you'll find out which one when you pull 'em. :(
 
... Take my jugs to a machinist, let them look at it and give me an informed opinion...

Ditto! Jugs like that would show up occasionally at the shop. First thing was to hone them, then take measurements, then guesstimate the pitting depths. If necessary, do a thin preliminary cleanup bore on the bad cylinder to see if it can be kept within piston/ring availability size. Can't do that at home...
 
...... as to what caused the pitting, I'm guessin' one of the valves was left open for years on end. I suspect you'll find out which one when you pull 'em
...and the bike was left on the side stand, outside, for a period of time? That might explain why only the left cylinder shows corrosion/condensation....
 
Piston (and ring) oversizes go in .25mm steps on this motor, so the .50mm offering from Cruzinimage is a 2nd oversize set. It's very common to have to skip over the 1st oversize and use the 2nd oversize in order to clean up all the wear or damage. Maybe that's why Cruzinimage doesn't sell the 1st oversize. I thought they also had 4th oversize (1.00mm) at one time.
 
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