Piston crown protrusion.

Hi Hans

as I understand it the piston is supposed to protrude a little beyond the sleeve, and the top of the piston is chamfered so it doesn't hit the top of the combustion chamber as it curves in. Yours does look like it protrudes a bit far but I haven't measured mine. If you fit a 16H piston the chamfer has to be quite significant.

Did the barrel come with the engine? Or was it ever modified? it is possible that it was machined so that the bike could run a BSA Gold Star piston, that increases the compression ratio considerably but the barrel needs to be machined to be a little shorter?

I think a spacer under the bottom of the barrel would be the best way to sort it, then you can run the head without a gasket if you like

dan

Hello Hans, this is a photo of my 55 es2 piston/barrel after i had a liner fitted and piston supplied the piston protrudes similar to yours but i dont have any measurement to compare as i have built the engine up it is a standard piston fitted. Baz

Hi Hans

You could also machine a bigger chamfer on the piston, there's plenty of thickness at the edge, but do what ever is easier, have you checked that it is actually hitting the head?

It's not uncommon for the valve springs to hit the rocker box, there's not much clearance and as the valve wears into its seat the clearance gets less. I've just had mine fixed by Mike Pemberton. He'll be able to tell you the length of the valves. Mine are rather cosily sat in the head on the engine at the moment so can't measure them!

Im not clear if the piston hit the chamber before you used the shim? The piston should extend above the top of the sleeve, that is why it is chamfered. No need to make it flush.

Dan

Glad you got it sorted, I thought about a gasket under the rocker box too, but sent my head to Mike P, he put a valve seat in one valve, the other was ok and fitted the later narrower springs and spring seats.

I think timing is 41.5 degrees fully advanced btdc but it's a complicated bit of trig to work it out!

Hi Dan

Don't like to go off topic, (Just had my m50 head sorted by M.P.....very impressed}...but how do you post pics like that, in the text as opposed to at the end?

Regards John O

How to convert piston travel to degrees of rotation:

http://www.dansmc.com/mc_software2.htm

Going off topic .... sorry! ... posting pics in the thread is fairly easy if you upload you pics to say photobucket ( other providers are available!) select the photo you want to include and copy the HTML link rather than the IMG link. Then come back to your post on Nortons Owners and type away, when you are ready to insert the picture click on HTML which is just above the box you are typing into. Make sure your cursor is at the end of the text and click paste on your computer, I'm using an iPad so just tap the screen. You can then click "update" then post comment and bob's your uncle!

Going back to timing I think I recall it being recommended that you set the timing a bit beyond say 42 degrees so you could adjust it as you ride. I'll check mine again soon but as I use it for trials and lanes I'm not running it at full throttle

Previously Michael Rettie wrote:

How to convert piston travel to degrees of rotation:

http://www.dansmc.com/mc_software2.htm

Thanks to Michael for this useful link -- n.b. that connecting rod length makes a difference

Surely the amount the piston moves changes through crank rotation?

Yes but it is not linear and is related to the length of the rod as that changes the effective angle the piston is to the big end. There are a few of these calculators around, once you get past a particular con rod length the effect is too small to notice, on short rods it is enough however.