Piston Rings 1958 model 30

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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Piston Rings 1958 model 30

Postby Ironhead » Sun Nov 08, 2009 7:22 pm

Hello All, Having just obtained a set of rings for my Hepolite pistons plus 30 thou. My mate who has been a mechanic at least 50 year, noticed the oil scraper ring is in two halves top and bottom,
He's never seen rings like this before,Has anybody any experience of these rings and are they OK,
Thanks Alex

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Piston Rings 1958 model 30

Postby Don Madden » Sun Nov 08, 2009 8:43 pm

Do they have castellated protrusions on on side? If so, they are the original type rings used on the twins. Scrape the edge of the rings across your finger & if one side feels sharper, the sharp edge goes down. On the castellated rings the sharp edge is on the same side as the lugs, so both are to fitted down to scrape the oil off the cylinder. Space the gaps on opposite sides of the piston.

Some scraper & top rings are also taper faced & the sharp edge always should be fitted down. Fitting them wrong will cause excess oil to be passed into the combustion chamber.

Cheers, Don.

Edited by - Don Madden on 08 Nov 2009 8:44:33 PM

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Piston Rings 1958 model 30

Postby rex.webb » Sun Nov 08, 2009 8:47 pm

Now wher did i see youg "Micky Mouse" ??
r w webb

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Piston Rings 1958 model 30

Postby Ironhead » Mon Nov 09, 2009 9:08 pm

Thanks for that Don you are spot on, we checked them today my mate understood exactly what you were saying I diden't I do now thanks.
My other question is on each packet it says leave a gap of 3thou. per inch for normal air cooled engines, more for racing engines but my workshop manuel says leave a gap of 6thou in total, 2thou per inch.
What do you suggest Don.
Thanks again Alex.

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Piston Rings 1958 model 30

Postby Don Madden » Tue Nov 10, 2009 1:55 am

The six thou for the oil rings & scraper is OK but use the 3 thou/in of bore for the top as it gets much hotter. A little too much gap will have little effect if the gaps are staggered, (no! not dipped in whiskey), but if too little the rings can shatter as the ends are pushed together.

There are different instructions for ring gap position & most work fine on water cooled engines but for my air cooled, I set the gaps at the pin end position staggering each as I go except the top ring which I put nearest the inlet valve to minimize distortion. The ends try to straighten out with heat.

You can carefully spread oi & scraper rings but it is best to roll the top ring into position by starting at one end & working the ring into the groove with minimum spreading.

Cheers, Don.

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