Author Topic: pistons AJS  (Read 5438 times)

Offline mark2

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pistons AJS
« on: April 24, 2014, 11:04:19 AM »
has anyone used one of these and was it ok , I have bought one and measured it , its 18 tho oval , this seams a bit high to me
http://www.ebay.co.uk/itm/331062239006?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Offline rogerwilko

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Re: pistons AJS
« Reply #1 on: April 24, 2014, 11:49:42 PM »
Most pistons are cam ground. So the diameter from front to back is bigger than the sides. With JP pistons use 4 thou clearance or it will nip up. There are long rod and short rods with AMC singles. By the position of the gudgeon pin on the ebay one it is a short rod piston.

Offline CaptonZap

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Re: pistons AJS
« Reply #2 on: April 25, 2014, 01:35:30 AM »
has anyone used one of these and was it ok , I have bought one and measured it , its 18 tho oval , this seams a bit high to me
http://www.ebay.co.uk/itm/331062239006?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

It isn't as high as these. http://www.motosport.com/dirtbike/Athena-Big-Bore-Piston    :o
As long as you have enough clearance on the widest dimension, you are good to go.

Offline mark2

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Re: pistons AJS
« Reply #3 on: April 25, 2014, 09:33:31 AM »
I have taken the piston and barrel to the engineering company I use (since the 1960s and have always had good service) , and they are not happy with the shape of the piston , and have ask if it could be a bad ground one , I have contacted JP but so far they have not sent the technical spec . they will boar to suit no problem but have recommended not to use it ,

Offline rogerwilko

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Re: pistons AJS
« Reply #4 on: April 26, 2014, 12:19:56 AM »
I think you're being over cautious. JP have been in business a long time. Just use it. Look at the piston aformentioned

Offline CaptonZap

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Re: pistons AJS
« Reply #5 on: April 26, 2014, 01:25:52 AM »
As a point of reference, VW Bug engine pistons, with a 3.3** diameter, have a .016 in difference in skirt diameter. Air cooled, iron sleeve, aluminum piston, pretty much the same technology.
Does your machine shop want to sell you the "correct" piston?

CZ

Offline mark2

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Re: pistons AJS
« Reply #6 on: April 26, 2014, 08:17:47 AM »
you could be right I will wait for the spec from JP , the only piston (new AE) I can compare it to is for a 500 Ariel , this measures 7 tho oval which is more what I would expect/like

Offline mark2

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Re: pistons AJS
« Reply #7 on: April 29, 2014, 10:53:41 AM »
got the spec from JP , 18 to 20 tho is correct , so will have board , see what it sounds like