Installing New Piston

[pdqford]

Hi everyone. Great list!

I'm planning on replacing the piston on a 056 AV Magnum II (and I haven't located a manual yet).

Background:

The old piston broke the skirt off one side. It broke at the lower ring land. The owner said he mixed up five gallons of fuel, dumping the oil in and not thoroughly mixing the oil and gas. Saw ran a few minutes and locked up. Tight! I'm guessing (I'm new to saw internals) the piston started to seize on the upward stroke at the lower ring under load and the momentum of the crank weights and rod pushed the piston up and caused the skirt to be pulled off the piston. I can't find any marks in the bore and it appears to be chrome plated.

My Questions:

1. Installing a new piston, pin, and rings - I'm assuming that the bore should be honed to assist the new rings in seating, but is this true for a chrome bore?

2. Does the piston have to be installed with a particular orientation? Like, is the wrist pin location in the piston offset?

3. I see the old rings had the numbers on them facing the top of the piston. But do the ring gaps need to be placed in a particular location?

Thanks in advance for any and all replies . . . . . . .

 

[blsnelling]

Hi everyone. Great list!

I'm planning on replacing the piston on a 056 AV Magnum II (and I haven't located a manual yet).

Background:

The old piston broke the skirt off one side. It broke at the lower ring land. The owner said he mixed up five gallons of fuel, dumping the oil in and not thoroughly mixing the oil and gas. Saw ran a few minutes and locked up. Tight! I'm guessing (I'm new to saw internals) the piston started to seize on the upward stroke at the lower ring under load and the momentum of the crank weights and rod pushed the piston up and caused the skirt to be pulled off the piston. I can't find any marks in the bore and it appears to be chrome plated.

My Questions:

1. Installing a new piston, pin, and rings - I'm assuming that the bore should be honed to assist the new rings in seating, but is this true for a chrome bore?

2. Does the piston have to be installed with a particular orientation? Like, is the wrist pin location in the piston offset?

3. I see the old rings had the numbers on them facing the top of the piston. But do the ring gaps need to be placed in a particular location?

Thanks in advance for any and all replies . . . . . . .

1. If the cylinder is truely clean with no aluminum transfer, there is no need to hone the cylinder. The cylinder is NiSi coated and is exceptionally hard. If possible, use a OEM Mahle piston, even a clean used one is fine.

2. The piston has an arrow on the crown that alwasy points toward the exhaust port. The ring end gap locating pins will always end up on the intake side.

3. As above, there are ring gap locating pins in the ring groove. The ends of the rings are notched to fit and will only fit right side up.

 

[pioneerguy600]

Hi everyone. Great list!

I'm planning on replacing the piston on a 056 AV Magnum II (and I haven't located a manual yet).

Background:

The old piston broke the skirt off one side. It broke at the lower ring land. The owner said he mixed up five gallons of fuel, dumping the oil in and not thoroughly mixing the oil and gas. Saw ran a few minutes and locked up. Tight! I'm guessing (I'm new to saw internals) the piston started to seize on the upward stroke at the lower ring under load and the momentum of the crank weights and rod pushed the piston up and caused the skirt to be pulled off the piston. I can't find any marks in the bore and it appears to be chrome plated.

My Questions:

1. Installing a new piston, pin, and rings - I'm assuming that the bore should be honed to assist the new rings in seating, but is this true for a chrome bore?

2. Does the piston have to be installed with a particular orientation? Like, is the wrist pin location in the piston offset?

3. I see the old rings had the numbers on them facing the top of the piston. But do the ring gaps need to be placed in a particular location?

Thanks in advance for any and all replies . . . . . . .

The piston should have an arrow stamped in the top and it points toward the exhaust port, the rings can go in with the numbers facing up and the ring ends would have to be orientated to ride between the intake and exhaust ports. Most new pistons have locating pins in the ring grooves but on the older ones that did not the ring ends were placed so that they were offset from each other and in a position so that they would not catch in a port.
Pioneerguy600

 

[Mad Professor]

The piston should have an arrow stamped in the top and it points toward the exhaust port, the rings can go in with the numbers facing up and the ring ends would have to be orientated to ride between the intake and exhaust ports. Most new pistons have locating pins in the ring grooves but on the older ones that did not the ring ends were placed so that they were offset from each other and in a position so that they would not catch in a port.
Pioneerguy600

???? I've rebulit all sorts of two strokes and NEVER saw a piston without ring locating pins??

 

[pdqford]

3. As above, there are ring gap locating pins in the ring groove. The ends of the rings are notched to fit and will only fit right side up.

Ah-haaa. Now I see what those little black pins are for, and they won't let me put the rings in upside down, either.

Thanks for the quick replies.

(Brad wins - took him only 6 minutes to reply

 

[blsnelling]

Ah-haaa. Now I see what those little black pins are for, and they won't let me put the rings in upside down, either.

Thanks for the quick replies.

(Brad wins - took him only 6 minutes to reply

Someone's got to fill in for Andy!

 

[pioneerguy600]

???? I've rebulit all sorts of two strokes and NEVER saw a piston without ring locating pins??

Try Pioneer 600 series and 1948 Titan and IEL chainsaws, no locating pins there, plenty of others also. LOL
PIONEERGUY600

 

[Justsaws]

???? I've rebulit all sorts of two strokes and NEVER saw a piston without ring locating pins??

Got to go old school.

 

[pdqford]

When I install the new piston and rings, should I coat the piston and rings with a film of motor oil? Two-cycle oil? or leave 'em dry?

 

[harrygrey382]

even a clean used one is fine.

as long as it isn't worn (read shiny) - you need to be able to see the machining marks. Otherwise they'll be too much spit-back

When I install the new piston and rings, should I coat the piston and rings with a film of motor oil? Two-cycle oil? or leave 'em dry?

2-stroke oil. Although I think I may have used 30W oil due to convenienceopcorn:

 

[pdqford]

Need more coaching

F-i-n-a-l-l-y found a NOS piston for the 056 Magnum II, but what is the trick to get that !@#$%^ piston pin lock into the groove? Does it take a special tool, or three hands?

 

[stihl only]

Need more coaching

F-i-n-a-l-l-y found a NOS piston for the 056 Magnum II, but what is the trick to get that !@#$%^ piston pin lock into the groove? Does it take a special tool, or three hands?

If you have three hands, you won't need the special tool! It takes practice and patience. There is a special tool but it's pretty expensive to buy if you are only going to use it once.

Start with the gap of the clip at the top of the piston, start one side in, and slowly work it around. I don't know any better way to describe it that that.

You can use a small pocket screwdriver th assist you be be use care not to scratch anything up with it.

Is the piston factory, or aftermarket?

 

[harrygrey382]

Need more coaching

F-i-n-a-l-l-y found a NOS piston for the 056 Magnum II, but what is the trick to get that !@#$%^ piston pin lock into the groove? Does it take a special tool, or three hands?

never had a problem with long nosed pliars - just make sure you're working in a space where if it pings off you can find it...

 

[pdqford]

Start with the gap of the clip at the top of the piston, start one side in, and slowly work it around.

Okay. Guess I gotta just practice my patience. Thanks.

Is the piston factory, or aftermarket?

Looks factory. The piston came in a Stihl box with part # 1115 030 2003.
Cost?
.
.
.
.
$129 and change! :censored:

 

[pdqford]

never had a problem with long nosed pliars - just make sure you're working in a space where if it pings off you can find it...

I hear ya, Harry. That went through my mind when I realized how much tension that little bugger has.

But then I set it down to go look for a smaller screw drive and my needle nose pliers. Senior moment later (read twenty minutes) I found where I laid it down.

 

[harrygrey382]

I hear ya, Harry. That went through my mind when I realized how much tension that little bugger has.

But then I set it down to go look for a smaller screw drive and my needle nose pliers. Senior moment later (read twenty minutes) I found where I laid it down.

LOL, I like that - senior moment... I have them, and I'm guessing I'm on the junior side! They work fine, just gotta watch the pinging.

 

[stihl only]

Sorry, I don't always comprehend what I read I guess!! You stated NOS and I knew it wasn't nitrous!

The reason that I asked is that I had an issue with aftermarket clips not fitting in the fancy tool because they were made a little too long. A few file strokes and all was well. They were also made of a larger wire stock and were a MUCH tougher fight that any of the genuine ones I've ever dealt with!

Well, the tool I have isn't factory but I built it just for these PITA aftermarket clips. I can easily walk the genuine ones in with common tools.

 

[Taxmantoo]

just make sure you're working in a space where if it pings off you can find it...

That's why Ziploc makes those two gallon clear baggies.

 

[harrygrey382]

That's why Ziploc makes those two gallon clear baggies.

now that is news! Could often do with one - another fun one is the very small circlips on carb control rods. But admitting you may need one and so setting it up may be antoher matter...

 

[drmiller100]

on the wrist pin keeper, if you put a screwdriver or 1/4 inch socket extension through the center hole and through the wrist pin, the C clip can fly off...