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1972_911T 11-02-2005 03:44 AM

Piston Ring Gap Question
 
I have just been mesuring my piston ring gap, these are brand new rings. In the book it says the gap should be 0.2 - 0.4 with a 0.8 wear limit.

Is the 0.2 - 0.4 the factory measurements/tolerences when new? and thus with wear if you start off at the top end of this 0.4 you can go upto 1.2?

My ring gap measures about 3.8 so im at the top end of the scale I was just curious Y there is a range and then a wear limit ontop of this?

Steve

Rex Walter 11-02-2005 07:12 AM

1972_911T

A perfect cylinder with no wear will have a bore diameter of 84mm for a stock 2.4L engine. As your engine wears, the bore diameter will increase. The wear limit has to do with bore diameter you are allowed to increase your bore diameter up to 84.8 mm. The ring gap must remain within the tolerances given (0.2 to 0.4mm) regardless of bore diameter.

Rex

1972_911T 11-02-2005 07:33 AM

The wear limit in the book im reffering to is not the cylinder wear limit, its listed at the side of the piston ring gap as the ring gap wear limit as there is a different limit listed for each ring.

Rex Walter 11-02-2005 08:36 AM

1972_911T,

Take a look here, and see if this makes any more sense:

http://www.hastingsmfg.com/Service%20Tips/ring_gaps.htm

Hope this helps. - Rex

1972_911T 11-02-2005 09:16 AM

Still dosent answer my Q, what I dont get is Y there is a range and then a wear limit, Y isnt it just a range say 0.2 - 0.4 and this is what your rings should fall withing and if they dont either your rings or cylinder are excessively worn. But in the book it states a range and then a wear limt this made me wounder if the range was the factory tolerences I,e at factory when new they will all be between 0.2 - 0.4 then as then enigine wears its allowed to go 0.8 from this??

steve

Henry Schmidt 11-02-2005 10:29 AM

The starting limit or limit when new is large enough to cover the differences in stock new cylinders. Mahle has three or four difference sizes that fit into the 84 mm size category.

The cylinders will be marked 0-3 and although they (Mahle) seem to match pistons and cylinders well they only make one set of rings.

When we're building a performance engine we make the cylinder undersized , make the piston the match and fit the rings the the undersized cylinder. It's a lot of work but race/ performance engines always are.

1972_911T 11-02-2005 10:48 AM

So the stated ring gap size for my 3.2 0f 0.2 - 0.4 represents the differences in manufacturing of the pistons/cylinders when new and the wear of 0.8 is how much they can deviate from this during there operating lifes?

Thanks Steve

Henry Schmidt 11-02-2005 10:52 AM

Quote:

Originally posted by 1972_911T
So the stated ring gap size for my 3.2 0f 0.2 - 0.4 represents the differences in manufacturing of the pistons/cylinders when new and the wear of 0.8 is how much they can deviate from this during there operating lifes?

Thanks Steve

Yes


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