Hi all,

sorry to bother you again but I have another question regards the gap I need to create for the piston rings.

Russell Motors had a look into their book and told me the following measurements

Compression rings 0.030"-0.035" = 0,762-0,889mm
Oil ring 0.008" =0,2032mm

I am really surprised that I need such a big gap on the compression rings. I am used to have 0.3mm max on older bikes. Do I really need more than double that??

Would be interesting what your bikes are equipped with.

Thanks
Phillip

email (option): phillip.thaler@gmx.at

Hi Phillip...I'm no Norton man but that does seem a lot. The M20 has .008" for all the rings..and its pretty much the same thing. No doubt a Norton owner will comment soon . I don't know of any other British motorcycle engine that runs gaps that large..and I've had a few...Ian

email (option): ian@wright52.plus.com

Edgar Franks says 0.020" for compression and 0.008 for oil control. However, later in the section headed 'Racing', he states 'Top - 0.030" - 0.035", 2nd 0.025" - 0.030" and oil 0.006"

It may well be that he was referring to the camshaft engines as the side valves were no longer being raced by that time.

Interesting, so a bit similar to what I have got from Russel.
But still I think thats to much. Of course to tight may lead to a stuck piston.
An old mane once told me (worked on Manx) I should go for
0.025mm top ring
0.02mm 2nd ring
0.02-0.028mm oil ring (at least this is similar to Rusell and Franks)

???????


Phillip

email (option): phillip.thaler@gmx.at

The WD 'Maintenance Manual and Instruction Book' states:

"The ring gap should be :

Compression ring ... .030" - .035"
Scraper ... .008"

Check gap with feeler gauge. If the gap is not large enough, it can be enlarged with a file."

It seems they were concerned about the risk of no gap but too large was not seen as a problem.

'Radco' states that at least .003" per inch of cylinder bore should be present, with rings needing replacement if 0.10" per inch is reached. The Norton bore is 3" so it sounds as if they were set up worn-out !

It is a bit of an Edwardian engine but on the other hand, was using Wellworthy or Hepolite pistons and rings so no doubts about the quality there.

My 16H rings haven't got a straight cut gap but angled so the gap is about 45 degrees, so althought the gap is quite large, the ring ends overlapped.

email (option): horror@blueyonder.co.uk

I have a freshly rebored cylinder, 40 thou over, NOS rings out of the box, slid down the bore with a piston give me exactly .008 scraper and .030 compression. Wether a coincidence I dont know, but I was impressed that they read exactly as the shop manual dictates. As Horror states, they're bevel cut, I wonder if this can affect things as far as gap size, it certainly does make them more difficult to meassure than square cut rings.

I've always run mine as the book says 30 thou compression, 8 thou scraper. Never had any problems. Incidentely my book ( The Maintenance Manual and Instruction Book) says 30 thou. No mention of 30 to 35.