Need Help Reassembling Skyhawk...

N

navifty

New Member
This is slightly embarrassing but I am a newb after all. I disassembled my 2-stroke motor (not sure what brand, seems standard) and now I can't get it back together. My terminology may be wrong so I posted a picture below, but basically I took off the head and cylinder case[?] and now the piston[?] won't fit back into the cylinder case because of these two black plastic rings that expanded. Anyone have any tips on getting the piston thing back into the cylinder? Forcing it was a no-go...

Picture of the piston[?] and the four mounts for the cylinder case[?] (not shown)
 
Don't try to force it! You will break your rings, (don't ask how I know). Look at the piston ring grooves carefully. You will see some little black pins inside the grooves. You have to position the ends of the piston rings with these little black pins, only then will the rings compress enough to allow you to slide the piston back in the jug.
 
navifty said:
two black plastic rings that expanded.
Picture of the piston[?] and the four mounts for the cylinder case[?] (not shown)
Click to expand...

The two "two black plastic rings" are the piston rings. These rings have a special way of going on. There are a alignment pin that the ends of the rings align up with.


You being totally inexperience of installing a piston here is the best way for you, in fact the best way I've found for these engines, as it helps in not breaking rings for a noob.

1) Remove the cylinder (which you have done).
2) Remove the piston (remove "C" clip retainer from ONE side)
3) Slide out piston wrist pin (only enough to remove piston from piston rod)
4) Remove piston from engine. (note as to where the front is, mark if you need to. There should be a arrow/mark on top of the piston. This will be aligned with the exhaust port)
5) Place cylinder on work area, upside down (piston skirts upward)
6) Place top ring as needed (aligned with piston alignment pin).
7) Set piston into the cylinder, the ring will contact the cylinder base, the piston base is beveled out.
8) With your fingers squeeze the ring into the piston. The cut away in the skirt helps accomplish this.
9) Tap on bottom of piston (do not force) and slide the first ring into the cylinder.
10) Repeat steps 8 and 9 for the bottom ring.
11) Cylinder and piston can now be installed over the studs.
12) Align piston on piston rod.
14) Insert the wrist pin.
15) Install "C" spring.
16) Tap cylinder in place.

Before I install the cylinder I use a gasket sealer on each side of the gasket. I like...

There is a dabber attached to the cap...I cut it off and use a small paint brush as the applicator. This bakes for a neater/cleaner application, as any excess will not be the easiest to remove.
 
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...oh, my, Al, that's completely the wrong way to put a cylinder together.

Remove the studs.
Grease the rings and piston with a thin layer of grease.
Align the rings with the pins.
Using 1/2" square sticks(pros have a fork shaped tool that does the same thing)place them under the piston in a front to rear direction. These prevent the piston from moving away from the cylinder.
Using your fingers compress the rings 1 at at time while rocking the cylinder fore and aft. This works the cylinder down over the rings.

Replace the gasket and studs, torque the nuts down to proper specs.

You can find video on youtube showing what I've described. It isn't all that hard but I've been doing it that way for years. I raced go-karts and rebuilt my McCullough, Yamaha KT100's and my 250 cc Suzuki powered kart the same way.

http://www.youtube.com/watch?v=DeoSJdc6kwA

This isn't the best example but it covers what you need to do to get it assembeled. Just be careful, those rings snap easily(don't ask how I know :p )
 
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Dave... who are you to say I'm wrong and your way is ONLY the right way. Do it your way, I'll do it mine. But here are two options and both will work. Find it kind of senseless to remove the studs. Oh and in 50 years I've NEVER broken a ring accidentally...I have broken one and used it to clean out the ring grove. So I guess you have broken one...if so that speaks for your instillation method/instructions.
 
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This is a very easy way I found to compress the rings and get the piston into the cylinder. Make sure the rings are in the correct position before tightening to wire ty. It doesn't need to be super tight. Once everything is ready, just push the cylinder down, and the piston will easily slid up in the cylinder. Be sure to apply grease to the cylinder wall and piston first. Don't forget to lube the wrist pin too.

picture.php
 
And this is exactly why I am against the advice to a new builder to disassemble their engines for cleaning/inspection. If you've taken them apart, have a firm grasp of the inner workings of an internal combustion engine and its parts, then go for it. But telling a new guy to tear his new engine apart is a disservice.

Tom
 
Al.Fisherman said:
Dave... who are you to say I'm wrong and your way is ONLY the right way. Do it your way, I'll do it mine. But here are two options and both will work. Find it kind of senseless to remove the studs. Oh and in 50 years I've NEVER broken a ring accidentally...I have broken one and used it to clean out the ring grove. So I guess you have broken one...if so that speaks for your instillation method/instructions.
Click to expand...

I have never seen it done your way in 40 years of rebuilding two strokes, never. And that ring I broke is the ONLY one I've ever broke.

Go to youtube, see if you can find ANYONE that rebuilds a two stroke your way. Maybe it's an Alabama thing, what do I know? I'll snail mail you a cookie if you can ;)
 
I don't use "grease" I use the same oil I mix with the fuel; in my case Opti-2, and lubricate the cylinder, piston and the rings. Align the ring gaps with the alignment pins in the grooves and compress the rings, one at a time, with my fingers. I do not remove the cylinder studs, there's no need for that, and use a light touch. As was stated, the rings will break easily if man-handled.

Get the piston started in the bore and slide it up until you feel resistance then compress the rings a little more making sure the gaps and alignment pins stay aligned then apply more pressure. The piston will slip into the cylinder up to the next ring. Repeat the process and the second ring will slide in.

If you've never done this process before it can be frustrating but don't get upset and force anything. You can break the piston rings and/or scratch the cylinder walls. Do that and you'll be ordering parts.
Tom
 
Does it matter what I use to grease the piston and wrist pin? I currently have on-hand synthetic wet chain lubricant and polyurea bike component lubricant... is there a special high-heat grease?

Edit: Thanks 2door, just saw your response
 
Just lube it with the 2 stroke oil you mix with the gas.

The internal engine parts will be lubed once it's started with the gas/oil mixture that is drawn in from the carburetor.

No need to apply grease to the piston, rings, or wrist pin and bearing.
A coating of 2 stroke oil is all it will need.
TiM
 
Thanks guys, the pins were the ticket, those things are TINY and I just didn't see them.

And 2door, everyone starts somewhere. I seek to learn and I'm willing to complicate matters in the process. All help is appreciated.
 
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