Adding ring locator pins to a piston without them

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Yotaismygame

Juiced Saws #GetJuiced
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I’m working on a saw right now that does not have locator pins. Crazy!? Yes! I would like to do more work to the exhaust port like remove the ring support that goes right through the middle of the port. But I’m worried with there being no way of holding the rings in one spot if the ring end found its way into this bigger exhaust port it’ll snag.

This saw uses two thin rings. I could either use just the top ring and place a pin in the middle of the intake or use both and place them between the exhaust and transfers.

I’ll bring @drf255 into this because I’ve seen him talk about re-locating pins.

Thanks
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A long time ago a guy posted here how he did something similar - He drilled the hole for pin and sized it as an interference fit and used a section from a high-quality drill bit as the pin. I think his piston used a 1.5mm thick ring though - your
application might be a lot tougher as the ring lands are so narrow.
 
I don’t remember where I read it but Drf255 mentioned adding pins from the top and tig welding the hole shut after inserting the pin. I have some small roller bearings I think will work great as pins.
 
Haven’t personally done it. Mike Lee had told me that pinning from the top was easiest. Tig bead on top of that is tricky, as it’s easy to melt the edge of the crown.

It‘s tough to do it right. In addition, most slugs have a cast in boss under the crown to add extra meat to hold the pin.

I bought micro taps and screws in hopes to add a threaded pin inset, akin to threaded studs vs. pressed in a cylinder head. Never got around to trying it, was always afraid to ruin a build with one.
 
Given the application, thin rings and all...it might be better to leave that section, maybe contour it down alot and play with the port size some...

Sent from my LM-G820 using Tapatalk
 
I've also used the 'piece of drill/undersized hole' method and it's worked out fine so far.
I'd be looking to do a blind hole and as Al mentioned, make sure there's enough meat to work with there.

One thing to be mindful of is that it's difficult to drill a 'half of a hole' in the land and is prone to making a wallowed out mess of things.
To make things easier you can fit a temporary piece of (preferably similar strength) aluminum in the ring groove and drill on the seam...

Some saws also have the pins centered in the groove and seem to do ok with that.
I could see doing an oversized pin and putting flats on either side of the the groove, then the ring ends would somewhat sit over the resulting shoulders and capture it from being able to walk out...
 
I've also used the 'piece of drill/undersized hole' method and it's worked out fine so far.
I'd be looking to do a blind hole and as Al mentioned, make sure there's enough meat to work with there.

One thing to be mindful of is that it's difficult to drill a 'half of a hole' in the land and is prone to making a wallowed out mess of things.
To make things easier you can fit a temporary piece of (preferably similar strength) aluminum in the ring groove and drill on the seam...

Some saws also have the pins centered in the groove and seem to do ok with that.
I could see doing an oversized pin and putting flats on either side of the the groove, then the ring ends would somewhat sit over the resulting shoulders and capture it from being able to walk out...

Bill, you can use one of those diamond bits a tad smaller than the drill bit against the step prior. This then gives you a clean unrestricted place to drill.
 
Remember the piston swells when in use so its best to make the fit very tight, drill the hole undersized, heat the piston up to 300F and pack the pin in dry ice, drive it in when ready and it should stay in place when in use.

I dont think the piston swells to the point it would be a concern. The interference is well greater than this.
 
Since the pin is halfway into the ring groove a plunge cut with a milling cutter would align the location for the new pin hole. It will give you a flat spot to drill into.

Note, time takes its toll on the pins that holds the piston ring from turning. I’ve seen these pins wear into there holes in the piston. With a lot of time on a two stroke this should be checked before it scores the cylinder wall.
 
Since the pin is halfway into the ring groove a plunge cut with a milling cutter would align the location for the new pin hole. It will give you a flat spot to drill into.


Sure, if you happen to have an end mill very close to the size of the pin, unlikely in my case as I don’t have (or ever even heard of) an ‘end mill index’ that matches sizes to my drill index’s. Could of course be done with cnc...
I’d prefer the pin to be supported over as much area as possible, including the ring land, so I don’t want to just clearance it.
 
What does it take to use a 52mm 064 piston in a 51.4mm 372XPW cylinder?
 
Well, with a lathe couldn’t you turn it down if the piston pin is in the same location and the pin to crown height and piston skirt dimensions are the same?
 
Well, with a lathe couldn’t you turn it down if the piston pin is in the same location and the pin to crown height and piston skirt dimensions are the same?
Sure, but then what about the ring? You would have to cut the ring groove deeper. Better question is why? The 51.4mm piston works just fine and that whole setup ports well.
 
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