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Ring Gap
- Thread starter timtune
- Start date
Closer to 3" so my .012" gap is good.
Am I right in thinking a minimum gap is critical?
Too much ring gap leads to high leakdown/blowby and the associated consequences and it may burn some oil, but it'll still be a runner unless extremely excessive. Not enough ring gap can lead to ring seizure, scored cylinder walls and pistons, etc ... way way worse. You are in a good range.
Yup. A friend rebuilt a racing outboard and assumed you just put the new parts in as they came. Screaming RPM's suddenly went silent. A bit of work with a file fixed things.
I also recall something about the wrist pin retainer clips being positioned in a way that minimized float.
TK4
Well-known member
Always put the gap vertically up or down. the story goes that at high RPM the clips could flutter and fall out of the piston.
I don't know whether that's true or just a fable, but why take the chance ?
The wrist pin retainer goes in so the ends of the retainer are not in the "cut out". The retainer is a spring and it bounces around in there.
If the end of the retainer is in the cutout, the end of the retainer can jam or catch against the cut out, twist and fall out.
If you put the retainer clip ends at 3 or 9 o'clock, you put the weakest axis of the circle in the axis it will receive the most force, the forces are at 6 and 12... so if the circle spring with a piece missing (shaped like a C) is taking it's maximum load in the axis where the piece is missing, making the "C" collapse, making the C into an o of smaller diameter... and it falls out. If you put the opening at 6 or 12, the forces are going into that clip on it's strongest axis and it is less likely to collapse... it gets a larger diameter when it distorts.
... not something that effects 99% of cases, BUT is just good practice.
Big bore, high revving motors use "bobbins" and do away with retainer clips. The bigger the retaining clip, the more likely it is to fail. Big ol motors use a "C" clip. That ain't fallin out
A heavier wrist pin will minimize how much the pin moves around, but is a performance drain. A light pin moves around a LOT and can get into trouble.
I have no idea what "minimized float" is or means. The rod has to float on one end and be located in the bore on the other end.A floating pin has to float and a rigid pin has to remain rigid. The rod has to be located by something. If you have retaining clips you have a floating pin. If you have to heat the rod and press the pin in, you don't.
if you have a floating small end, the rod is located by the big end.
A rigid pin locates the rod on the small end and floats on the crank.
If the end of the retainer is in the cutout, the end of the retainer can jam or catch against the cut out, twist and fall out.
If you put the retainer clip ends at 3 or 9 o'clock, you put the weakest axis of the circle in the axis it will receive the most force, the forces are at 6 and 12... so if the circle spring with a piece missing (shaped like a C) is taking it's maximum load in the axis where the piece is missing, making the "C" collapse, making the C into an o of smaller diameter... and it falls out. If you put the opening at 6 or 12, the forces are going into that clip on it's strongest axis and it is less likely to collapse... it gets a larger diameter when it distorts.
... not something that effects 99% of cases, BUT is just good practice.
Big bore, high revving motors use "bobbins" and do away with retainer clips. The bigger the retaining clip, the more likely it is to fail. Big ol motors use a "C" clip. That ain't fallin out
A heavier wrist pin will minimize how much the pin moves around, but is a performance drain. A light pin moves around a LOT and can get into trouble.
I have no idea what "minimized float" is or means. The rod has to float on one end and be located in the bore on the other end.A floating pin has to float and a rigid pin has to remain rigid. The rod has to be located by something. If you have retaining clips you have a floating pin. If you have to heat the rod and press the pin in, you don't.
if you have a floating small end, the rod is located by the big end.
A rigid pin locates the rod on the small end and floats on the crank.
I'd check those numbers if I were you. 0.004"/inch of bore
TK4
Well-known member
Ring end gap or piston clearance ?
I was thinking of you ( @bittz ) when I ordered the new wrist pin circlips (under $5 for all 8) today for my 750 single cam. Pretty sure I've put a couple together using the old ones I took out.
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