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<  Performance issues  ~  stock pistons/ piston rings question - what will fit?

fang
Posted: Tue Jun 13, 2006 2:48 pm Reply with quote
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Joined: 19 Oct 2005 Posts: 23 Location: Austin, Texas, USA
Axle, I have another question for you, Oh Mighty Manipulator of Molten Motorcycles....

I have a K7 motor that I am trying to freshen up a little with some top-end work. This is not a race motor, just an old one that will power a bike that will be regularly driven with my wife on the back. There was no compression when I took it apart, but now I see that there was a little rust around the piston rings from sitting. Nothing serious. So I intend to clean everything, lap the valves, hone out those cylinders and probably slip in a fresh st of rings because they little worn out too. (I think that end gap is supposed to be .014 to .016, and most of mine are about .018ish.)
So I was thinking about getting some one-over rings and filing the end gap so they fit with the stock pistons. Not perfect, but I am sure it will be just fine.

Here's my question: Do you know if earlier pistons' rings will fit this K7, or do I need '78-specific rings? It looks like I can get a set of "up to 1976 rings" for around $30, but I suspect they won't fit. Do you know? Do you have any suggestions?

Thanks mate!
Peace and grease.

-fang
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Satanic Mechanic
Posted: Sat Jun 24, 2006 9:00 pm Reply with quote
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Joined: 04 Sep 2005 Posts: 309 Location: Munich, Germany
Quote:
Do you know if earlier pistons' rings will fit this K7, or do I need '78-specific rings? It looks like I can get a set of "up to 1976 rings" for around $30, but I suspect they won't fit. Do you know? Do you have any suggestions?
A good question which took me some time to answer Confused

From the parts #, the '78 models (K7, K8 and F2, F3) share the same rings but these are different from the earlier models:

13011-392-004 Piston rings STD (K7, F2)
13011-300-024 Piston rings STD (K0-K6, F1)

13021-392-000 Piston rings .25 over (K7, F2)
13021-300-024 Piston rings .25 over (K0-K6, F1)

13031-392-000 Piston rings .5 over (K7, F2)
13031-300-024 Piston rings .5 over (K0-K6, F1)

13041-392-000 Piston rings .75 over (K7, F2)
13041-300-024 Piston rings .75 over (K0-K6, F1)

13051-392-000 Piston rings 1 over (K7, F2)
13051-300-024 Piston rings 1 over (K0-K6, F1)

All the best,
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