Question for engine builders

[GregT]

The piston pin rotates during operation, spinning against the clip. I find it hard to believe that clip does not rotate. Even the piston rings themselves rotate during operation.

Rings yes, as others have stated.
The ends of the piston pin are chamfered so that any end thrust on the pin will push the circlip harder into the groove. Given this and that the circlip ends are deliberately left sharp, i'd doubt if you'd see any rotation under normal use.
I've had properly installed circlips pop out - but it's taken a massive overrev to do it. Inertia will eventually overcome circlip preload in the groove.

[stetracer]

It is the change of piston direction
That causes the stress on the cir clip. At 10,000rpm your piston is going up and down 166 times a second. At 10 mph if you hit a brick wall with a 100 lbs it will have 10 times the force. That is why little kids were getting killed in little fender benders sitting in there mothers lap even though mom only weighed 100lbs at 10 mph she was crushing the baby with a 1000 lbs of force and it is even greater at higher speeds. So that little cir clip at 10,000rpm is fighting a lot of weight when placed in sideways

.

[stetracer]

So I don't have to worry about my ring gaps placement I can just line them all up on the exhaust side from now on as the are going to line up sometime while the motor is running anyway.
I guess I worry about to many little details

[storm 64]

Piston cir-clips? Teflon Buttons is the only thing I'll use...

[Mekanix]

I wasn't arguing

Me neither, I find this stuff really interesting.

Just to wonder how and why some things happen.

Piston cir-clips? Teflon Buttons is the only thing I'll use...

Never herd of that before.

[Jet-Lee]

Rings yes, as others have stated.
The ends of the piston pin are chamfered so that any end thrust on the pin will push the circlip harder into the groove. Given this and that the circlip ends are deliberately left sharp, i'd doubt if you'd see any rotation under normal use.
I've had properly installed circlips pop out - but it's taken a massive overrev to do it. Inertia will eventually overcome circlip preload in the groove.

Not all circlips have chamfered ends, though.

http://www.dansmc.com/circlips.jpg

It is the change of piston direction
That causes the stress on the cir clip. At 10,000rpm your piston is going up and down 166 times a second. At 10 mph if you hit a brick wall with a 100 lbs it will have 10 times the force. That is why little kids were getting killed in little fender benders sitting in there mothers lap even though mom only weighed 100lbs at 10 mph she was crushing the baby with a 1000 lbs of force and it is even greater at higher speeds. So that little cir clip at 10,000rpm is fighting a lot of weight when placed in sideways

Comparing body weight coming to a stop, to a few grams that does not experience instant stops, is reaching....far. Beyond that, your calculation is incorrect. 100lbs at 10mph coming to a stop (within 1ft of distance, a tiny crumple zone btw) would only generate 334 pounds of force.

http://hyperphysics.phy-astr.gsu.edu/hbase/carcr2.html#cc2

So I don't have to worry about my ring gaps placement I can just line them all up on the exhaust side from now on as the are going to line up sometime while the motor is running anyway.
I guess I worry about to many little details

Are you trying to be facetious, or does it come naturally? Line up your rings however you see fit. It's been stated by several here that they do indeed spin.

-EDIT-

Here's some math for you. Since RPM is irrelevant, it's piston speed that ultimately drives your engines upper rev limit, we're going to work with 4200fpm which is the common ceiling for a non-racing engine. Wrist pins are between 60 and 120 grams in weight. If you think a wrist pin circlip weighs more than 1g, show me proof.

So these are the numbers we're working with in a GS550 motor. 1g circlip at 4200fpm in 2.2inches. That gives us .914lbs of force...but that's actually halved because the mass being used is only half of the circlip, which gives us .457lbs of force acting on the circlip trying to compress it at each the top and bottom of the stroke.

I don't know what circlips you use, but mine take quite a bit more force to compress than that.

-EDIT-
Please note that a GS550 turning 10krpm is only seeing ~3666fpm piston speed, which lowers that force even more to ~.345lbs.

[GregT]

Not all circlips have chamfered ends, though.

Re read my post - i said piston pins have chamfered ends - to clarify, this is when using wire circlips.

Where did you get your figure of 5800fpm as a safe piston speed ? with the pistons available to us and the ring widths used, around 4200fpm is the practical maximum.

[Jet-Lee]

Re read my post - i said piston pins have chamfered ends - to clarify, this is when using wire circlips.

Given this and that the circlip ends are deliberately left sharp, i'd doubt if you'd see any rotation under normal use.

I read it correctly.

Where did you get your figure of 5800fpm as a safe piston speed ? with the pistons available to us and the ring widths used, around 4200fpm is the practical maximum.

Going back and re-reading, I don't know why I had 5800 in my head. you are correct at 4200fpm. I will edit my calcs to reflect that number.

-EDIT-

Here is where I grabbed the 5800fpm. I knew it sounded wrong (it's still early), but I didn't feel like going back to my Buell build thread to see what number I used for that. Now going back and looking, I was using 4200fpm seeing as I'm turning 8krpm on 3.125" stroke which is ~4150fpm on antiquated-engineering-based H-D components.

[stetracer]

Piston cir-clips? Teflon Buttons is the only thing I'll use...

I also us the buttons but some of the piston profiles won't let you use the buttons

[rapidray]

You guys over think TOO much stuff! The rings, pins & valve springs ALL rotate when the engine is running. You learn a LOT with a spintron & a high speed camera. I have used Teflon buttons & aluminum buttons in the past but prefer clips as the are lighter & I have NEVER had one come out. Clips don't compress so the orientation, as long as the clip opening isn't in the cut out of the pin bore, isn't an issue. Ray.

[gsrick]

We are taught at MMI that you rotate the rings by manufacturers specs. Some are 180 out from each others orientation and some are at 120. We are also taught that the rings do rotate and there is a possibility that the rings can line up now and then, but since it happens so remotely and with the inertia and rotation from other cylinders, that it doesn't effect the running of the engine. It happens so fast, like in milli seconds, and they don't stop and stay that way, there is no noticeable effect.

Wrist pin clips are the same, whatever the manufacturer says is the way we do it. They know best they pay a lot of money for their engineers to figure these things out.

Rick

[stetracer]

Me neither, I find this stuff really interesting.

Just to wonder how and why some things happen.



Never herd of that before.

These are Teflon buttons

[4cyl h2]

ray whats your technique for installing the clips? i worry about compressing them to much