Has anyone found pronounced ripples in their bores?
I lowered the pistons in my recently acquired 1973 750 Roadster (blown head gasket) to find a series of ripples about half way down the bore on one side. It measures about one inch wide by half inch high and seems deeper than new oversized pistons will allow. It's already on +30s and I don't think +60s will remove the damage.
Is this a Norton fault in the cylinder casting or just specific to my bike?
All ideas welcome

Has it been used without air filters?
I've seen that before.

Hobots post the other day had a ' Motorcycle Sport ' (magazine) download , saying theyed had one case of this .
Steve Wynn , Sports Motorcycles . Hailwoods Ducati afficianado , no less .

Tecnically you can get ' Ring Flutter ' , though youd assue worn lands in piston , or excess clearance there .
Assembly of rings to pistons dry may influance wear .Ordinarrily theyre Dripping Wet all over previous to ASSEMBLY .

Timing , Intake shock wave ( cam timing / intake length , COULD get the rings ' chattering ' on occasion .
So they went down the bore ( or up ? ) , in ' Steps ' , almost stop/start. Microscopically .

Id suspect thin whizz bang oil , 15 / 40 or something horrible .But dry assembly could well originate the condition .

I suppose youre going to say the rings are in perfect condition and the clearances to lands correct on dissasembly .

Could actually be chatter in the boreing bar .

The Norton was a museum display piece for about 8 years before I bought it.
It was brought up to running condition and looked superb.
It seems to have always had a standard air filter.
Because of the +30 pistons, I suspect a broken ring causing gouging as the piston was thrust up (or down) the bore.
Maybe another set of +30s was quickly substituted for damaged originals.
The looseness of some head bolts suggests a quick fix not rechecked.
I am hoping not to find further horror stories inside the crankcases.

Inspect engine cases with HI magnification and Bright Light, especially the factory stress risers at machined sharp corners of the though bolt flanges. Might be worth mag flux to fine cracks that may or may not let go in normal use but will if WOT hi rpm enjoyed much.

The best power plant I had in Peel Combat so far used knurled pistons to take up slack after re hone to take out grooves and oval wear on 0.40" over bore. Auto engine builder shops often has these air powered devices to do this. Knurls will wear down after a while but can't tell till looking in again, after 1000's miles of wild usage. Barrel is now on Trixie Combat with .040" new pistons/ring and light rehone. Didn't smoke till after 5000 miles on RH then guit to switch to LH so don't think its rings but head, till warms up full on highway. Could be both though as I discovered carb boots had slipped to let grit in 1000 miles worth.

Wonder if it is moisture/wet settled on top of piston while it has been one position for maybe 8 years.
Funny things air filters, all my older bikes never had them & never had any problem.

Problem is easily fixed.
Resleeved and new std pistons.
Since starting to play with Pommy motorcycles, I've never seen a distortion in a cylinder wall like this.
I've owned an ES2, an A50 Royal Star, an ex-police A65, a Thunderbird 650, 750 Roadster, XS 750E (still got that one) and the 73 Roadster with corrugated bore.
Will upload photos when I get them and figure how to do it.

2997v8 wrote:Problem is easily fixed.
Resleeved and new std pistons.
Since starting to play with Pommy motorcycles, I've never seen a distortion in a cylinder wall like this.
I've owned an ES2, an A50 Royal Star, an ex-police A65, a Thunderbird 650, 750 Roadster, XS 750E (still got that one) and the 73 Roadster with corrugated bore.
Will upload photos when I get them and figure how to do it.

Then you will have a set of std bores prone to cracking at the flange

How hard do you have to thrash a standard 750 to crack the barrels at the base?
I am not going racing although the stop light Grand Prix may be a little enticing.

It could go forever but due to the fact it will be seriously weakend it could break at any time, my experience with museums, collectors is they rarely do up the engines properly, they polish a turd.
Would be intrested to see what you are describing