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[slowmo]

Hmm.... after you have chiseled off the carbon around the ring grooves, you may want to check if the fore and aft oil ring groove has been squeezed down to pinch the ring.

If that is the case, you might want to consider a new piston and if so, measure the bore just to be sure it is not oversize (or close to limit).

From what I have gleaned, the OEM piston is rather weak due to the large cutouts for the oil ring an has been known to fail.

Faced a similar dilemma with my 65 and went for a new piston etc splurging out uncharacteristicaly in a moment of madness on a forged piston. I suspect that the OEM at half the price would do if on a budget (unless you are an out and out throttle bender).

As there are enough things to worry about with these fossils, I felt I couldnt cope with the extra lingering doubt!

[Mark M]

Look at the pictures guys, this is a 1950s Redditch 350 not an Indian engine. Blowby is fairly even, all things considered. Measure bore to piston clearance carefully before making a decision about re-ringing or a rebore. REgards, Mark

[papasmurf]

The blow by does not look even to me by a very long way.

[stefaand]

Sorry yes, should have been more specific. It is a 1955 350 bullet, and it's all original.
I hope you are wrong, papasmurf! I Havn't managed to take the bottom end apart because I can't get the magdyno off without the proper tool (everything is relaly tight on this bike) I will propbably buy a heating gun soon, maybe that will get it off. I have taken a peek trough the oil sump bolt hole, and theres a nice mountain of oily sludge in there. This has been my worry all along, that the accumulated latent maintenance of mr I-will-weld-the-swingarm-nuts-to-the-frame-using-all-the-weld-I-can-find, as well as the mileage it did without an oil change, probably offroading.
The big end has no vertical or horizontal play, but a bit lateral play, but I've come to understand that this is not excessive (according to a youtube video on an indian 350) and I havn't found any other indication of damage on the bike. Quite stupidly, I did not check to see if the piston rings were seated at the correct angle, and they may have twisted a bit.
I will try to meet with my Honda guru and measure the bore and piston and clearance with him, I hope soon.
is 22000 miles really time for a new piston and bore? it seems early, considering the light wear on all other parts.

[Mark M]

Stefaand, speculation about mileage is a distraction, measurement and close examination is the way forward. The magdyno pinion needs a special puller but you can make this with a centre drilled cycle thread bolt, I can check the size if it's easier to make one than get the correct tool? Given the amount of work you've done (and probably expect to do!) this is a tool you might want to own! REgards, Mark

[stefaand]

You are absolutely right, Mark.
That would be very helpfull indeed. My first tool-fab at the same time..We have a small Lathe here but I have no idea how to work it, and our pillar drill isn't true. I read somewhere that a 50's-60's triumph pinion extracter would be the same, and I know a 50's triumph guru, but far away as usual.
To be honest, Mark, I was really hoping, quite naively, on finding a perfect machine underneath all the dirt. I guess I havn't really been fooled too hard yet though, knock on wood!

Thank you for your help!

[PeteF]

I agree with Mark, mileage is just a number.
BUT
It looks like basic maintenance has been neglected (don't know for how long of course) so 22,000 miles could easily be new piston time. The piston and bore need measuring properly as you intend to do. If it measures OK and is undamaged then it's good to go with rings and hone. You also need to get all the sluge out of the engine and you'll probably find more in the oil tank.
A bit of lateral play on the con rod is OK as long as you can detect NO play vertically.
When looking at mileage figures you have to realise that the engineering in 1955 was nothing like modern standards. A Honda it ain't!

[Norm]

Going on what it looks like, split the cases and clean all the sludge out, I have found sludge an inch deep in some motors I have pulled down. Then it depends on what you use plan is, are you planning on riding it around or just restore it and trailer it to events etc. This controls the level of restoration you need to achieve, if you are doing this on a buget

[simon]

The mag cog removal tool is very easy to make if you have someone around who can do the most basic tool making. I have one on my desk at work that I made for a bike I used to own. It's either a 9/16 or a 1/2 (memory is fading) probably 1/2" with a 26tpi thread on it with a 1/4" or thereabouts bolt threaded through the middle. Happy to post a picture if you need a visual. If it were me I'd slap a new set of rings in it and drive it carefully. A bit of racing space might cause it to clatter a bit but it has the look of something that needs to be put back together. Let's face it it's never going to be a racing machine and there is something rather nice about an old original machine going nicely. My tuppence worth anyway.

[papasmurf]

PERSONALLY I would not bung another set of rings on that piston until I had checked the width and depth of the grooves all of the way around, and the maximum gap between the piston and the bore.
One side of that piston look totally fubared to me due to the height of the cag stuck to it.

I can't believe the service limit for difference between the bore and piston is 0.3mm or 12 thou in old money. If you clean the piston up and check if the gap is anything like that, personally I would bin it.
(I can't believe the from new bore piston/bore gap is 0.08-0.1 mm either.)Seem s bit large by modern standards.)