Hitchcocks Forum

Has anyone an idea what a problem will create the pattern of dark dots on the cylinder wall as shown in the picture ?
The piston and the rings do not show any marks or signs of wear.
First I thought of a too large gap between the ends of a piston ring and the gas blowing through, but there are three separate rings and their gaps were placed around the piston and not in line on the piston. But if the gas is blowing through I would expect more a dark line than single spots.
I will measure the gaps of the piston ring ends, but have not done yet.

This is an odd one!

Daft question, but has this engine ever been run?
The honing marks seem very clear and the barrel looks immaculate.
Those small round marks look like corrosion marks to me.
I cannot think of any defect that would place regular spots of discoloration on a barrel?
The marks left in a used barrel would almost always be vertical and ‘smeared’.

But I may be wrong and ignorant. (Correction I may be wrong - and am ignorant!!)

Looking again I can see vertical scoring on the barrel - so that explodes my theory!
But still those very regular spots of discoloration are a mystery to me if they are not corrosion.
But even if they are corrosion I can't understand how they may have been caused.

This can only be a defect in the cylinder liner..

The marks only appear in the section of the bore where the rings will have been moving against it, not the unmarked lower part of the bore.

Is that a steel or a cast-iron liner? I'm wondering if there's been some odd electrolytic reaction between the liner and the rings, but then why only in a limited linear pattern?

Rushour's suggestion, possibly some impurities in the iron if it's a casting, seems most likely.

A.

Harald, I hope that’s not your Classic 500.... stop opening it...


Surly the barrels aren’t spot welded! Surely they wouldn’t be designed that way!?



John

Press-fit liners in alloy muffs, aren't they?

A.

What marks on on the piston in that position?

Adrian wrote: ↑

Mon Sep 21, 2020 7:48 pm

Press-fit liners in alloy muffs, aren't they?

A.

I know they’re press fit, but was wondering if that’s the way they are made before pressing in. And if it is corrosion, it wouldn’t worry me unless the bike was left stood for months at a time, I’d alway expect a coat of oil on there from a normal running bike.. Can’t see it getting there from behind!....

Hi, are they indentations or just a discoloration. If you zoom in they lo ok like paw marks. Gremlins perchance??? Vince