Removing Two stroke piston ring index pins?

[Quickv4]

On our Aermacchi SS250, we have run into the dilimma with having to machine down the top groove of the piston about .020 to accomodate the OEM rings (we have a aftermarket or later piston).

If it was a normal 4 stroke piston, you would think, " just throw it on a lathe and machine it down, simple as that!"


Problem being, this two stroke has indexing pins (one in each groove) to keep the rings in a certain position. The pins appear to be pressed in the groove, and they would have to be removed so then one could machine the groove down.

Any help would be appreciated

[Laromonster]

Is the groove wide enough to get some needle nose vise grips on the pins?
If not you might want to grind them off with a dremel cut off wheel.

But then the remains might fall out later....




Try yanking them first

[Quickv4]

That is an option, just filing them out, but then what one replace them with

[cagiva549]

I would not touch the pins , they are criticle to the life of the engine . I have seen the totaled engine that is a result of the pins coming out . I had a rash of pins come out on some small engines I deal with several years ago , the rings rotate till the ends break off in the ports then destroy the bore and the piston . Make every attempt to replace the pistons with new or good used . SEYA

[barryadam]

I don't think the OP was going to eliminate the pins. He just needs to remove them to machine the ring groove.

They are pressed in. The best way to remove them with minimal damage is to heat the piston (alum expands more/faster than the steel pin) to about 350 degrees F and tap sharply on a wood block with a cut-out in it. The pin might fall out. If not, gently use some needle nose pliers.

[Quickv4]

Thanks Barry, I think the above poster misunderstood me.

I was almost guessing it would be a "heat and pull" kind of thing. I just didnt want to alter the alloy or heat treatment of the AL alloy, in case there was some other super uber-duber trick to getting it out.


I do have a junk piston I will try it on before I attempt it using the lone remaining good one. I also have an Infared heat gun, which should make it easier

[showkey]

One other problem or concern pistons are not "round" most are cam ground egg shaped longer in the thrust direction shorter across the piston pin this is more pronounced at the skirt and can vary...........

[Quickv4]

I do realize this, but I have a very hard time believeing they used a weird ellipse-turning lathe to make the ring grooves.

[xtop20A]

if you have to, set them up in the vertical mill and drill them out,if you end up with a larger pin-hole then machine a stepped pin for a press fit

[azcagiva]

Another option is to get a hold of a ring manufacturer. I have had total seal make some rings for my ducati. They might have a ring that will fit that piston without having to machine anything.

-John

[ixion]

In some cases (though all the cases I know of are old Briddish stuff), the holes for the pins go right through the piston. So you can poke them out from the inside. can't usually get a drift in, but you can lever with a bent punch.

[showkey]

Originally Posted by Quickv4

I do realize this, but I have a very hard time believeing they used a weird ellipse-turning lathe to make the ring grooves.

Talked to real good friend that worked for a piston manufacturer, at the top the piston they are near round or all most perfect round and the oval part section on most pistons is at the pin and below. So that is not a real problem .

He stated a bigger concern is the ring grooves on most pistons are not straight but cut on a angle of any where from one to three degrees. The grooves are cut in a single pass with a perfectly ground tool to the exact width. The pistons are chucked on the inside on machined bosses and there is a lathe point on the top of the piston during the process and that point is cut off later.

That ring groove angle is not easy to measure or check, and if not correct ring sealing, wear, friction and breakage can be the result.
Also rings and grooves can be "keystone" on some engines but more easy to ID.

His comment was find rings that fit the groove and grind the ends to fit the diameter.

Good luck

[C Squared]

Just FYI

A buddy machined some ring grooves for a Toyota mini truck to do what you are (mostly) This was over ten years ago and the truck is still going strong.
However, not a daily. And not a 2T
I'd just buy a piston/Cyl. combo and install it. There are a lot of NOS things available for this engine.

[Quickv4]

Hey Cory

I checked with both Moto Italia and Charleston Cycle, both of them do not have the standard bore anymore ( the factory had a color-code system, going from blue-pink-green-brown, etc) Th cylinder is a "blue". This is a chrome bore, so it isnt like one can just have the cylinder bored out as with a sleeved 2strk. Both my father and I are looking on Ebay for a NOS blue piston, no luck so far

If worse comes to worse, we can get the next oversize (which is still availible), and have US Chrome do a Nikasil job. But, its a bit $$$$.

Still going to try pulling one of the pins out on our junk pistons, to see how easy it could be.

WWGICD

What would the Guys in Cuba Do? (Think of the Harlistas)

[anonny]

If i was in your shoes I dont think I could ever sleep again knowing I removed and reinstalled that pin, my luck loosening it would be the doom of the piston, cylinder, rings and beyond.

Is there no way to source a matching set