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HelicopterEngines Plugs Mufflers Fuel › YS piston damaged
06-02-2004 01:16 AM  13 years agoPost 1
scoobynewbie

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Nashville, Tn

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I think I screwed up. I recently replaced the bearings in my YS80. After a few tanks, engine made some noise and died. Pulled engine out and found ring is broken away at gap and piston is broken out above ring gap. I could see the ring gap through the exhaust port before I pulled it out. That's not the right place for the gap is it? (The gap of the ring was at the pin in the groove.) I think when I re-installed the piston and rod I rotated it 180 degrees. I noticed when I rotated it the other way, the ring gap would never encounter a port in the liner. Anyone got a decent piston and ring for a YS80? Also, the liner looks ok but will new ring seat ok in old liner?

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06-02-2004 04:55 AM  13 years agoPost 2
jetsurgeon

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Raleigh, NC

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Scooby,

Let’s get this engine orientation out of the way first.

Look at the engine as from on top of the head (where the glow plug would mount), with the crankshaft threads pointing away from you (12 O’clock) and the back plate should be pointing toward you (6 O’clock). This will set our engine orientation, for alignment below.

The sleeve (cylinder) is indexed by a small pin on top of the engine case. This alignment pin would be at about the 11 O’clock position, if you’re looking at the engine as I first described above.

On the piston, there is another small indexing pin installed in the piston ring area. This pin keeps the ring from turning around the piston as it goes up and down in the sleeve.

When you install the piston into the sleeve, you want the ring index pin to be at your 7 O’clock position. When you verify this with the sleeve, you will notice the ring pin index on the piston doesn’t “ride” / go over any of the ports within the sleeve. This is the correct alignment of the piston within the sleeve.

Now most folks don’t know this, or forget, and they get the piston installed 180 degrees backwards on the crankshaft. Meaning the piston ring index pin is now at the 1 O’clock position within the sleeve. When you look at the ports on the sleeve at the 1 O’clock position, you’ll see that YES the piston ring index does overlap 1 or more port openings on the sleeve. This is a disaster waiting to happen.

Usually what happens is exactly what you described above. When the piston goes back down within the sleeve, the ends of the piston ring expand (because piston is installed 180 degrees out) into the port. Now when the piston is on it’s “UP” stroke, the ends of the ring can’t get compresses back towards the piston center, so the port just breaks the ring (sometimes in many pieces) and sometimes the little section of the piston above where the ring mounts is also broken off.

At the least, a new Piston & Ring will be needed, but the sleeve may also need replaced if it’s scored.

Hope this helps. Yes I know it sucks, but think of it this way, you’ll never make this mistake again. Will you?

Blue Skies,

Jeff

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06-02-2004 01:36 PM  13 years agoPost 3
scoobynewbie

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Nashville, Tn

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Thanks for the clarification. Thats exactly what I did. Your right, i'll never do that again!

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06-06-2004 05:35 AM  13 years agoPost 4
Scrub

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Antioch, CA

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Great info Jeff, I'm in the process of replacing the piston, ring and liner in a used engine and found the piston to be installed incorrectly as you described (180 deg. rotated).

Is there a 'trick' to installing the sleeve? I'm having a hard time getting the sleeve over the ring once the piston is in the block.

Thanks,
Scrub

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06-06-2004 06:25 AM  13 years agoPost 5
jetsurgeon

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Raleigh, NC

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Scrub,

As for a “trick” to get the piston started into the sleeve as the sleeve is inserted into the engine case. No tricks I know of……. just pay attention to detail and take your time.

You will want to make sure the piston ring is positioned properly within the piston grove, meaning the ends of the ring will definitely seat on the piston ring index pin, as it’s inserted into the sleeve.

Another note: I’ve seen YS engines which some sleeves just fall out of the engine case, while others won’t budge one bit. If you have one of these little stubborn tight fitting sleeves, you’ll need to heat the engine case up with a torch, to make it expand just enough to slide in the sleeve. Doesn’t take allot of heat, meaning DON’T get the case anywhere cherry red…. Got it? Wear some sort of thick gloves (flame retardant if possible) so you don’t burn yourself while handling the hot case.

This is how I replace the Sleeve, Piston, Ring, and Bearings on a YS. Your findings may differ…

1. Place both of the new front and rear bearings into the freezer.

2. Remove engine from machine.

3. Remove glow plug and head.

4. Remove back plate.

5. Insert a delrin crankshaft lock into the engine, where the back plate was, in order to hold the crankshaft while you unscrew the fan hub nut.

6. Remove fan assembly, nut, and crankshaft lock.

7. Heat engine case (around the head area - fins) to ease removal of the sleeve.

8. Pull up on sleeve to remove from engine case. If you have difficulties, either heat the case up some more, or insert a plastic tooth brush into the engine back plate area, and push up on the edge of the sleeve (NOT THE PISTON).

9. Remove piston & connecting rod from crankshaft.

10. Remove crankshaft from engine.

11. Remove the pump / regulator, and carb assemblies from the engine.

12. Heat engine case with a torch on the outside of the case, where the rear engine bearing is located.

13. Gently smack the engine, on its back plate area, onto a wadded up towel. The rear bearing will fall out. Note: The bearing is going to pretty damn hot, so don’t catch the towel on fire, with the bearing sitting on it.

14. Heat up the front engine case around the front bearing area.

15. Insert a wooden dowel into the engine from the back plate area, to push out the front bearings. Note: You may need to gently tap the dowel with a hammer to get the bearing to pop out.

16. Clean the engine case with alcohol and a rag or compressed air. Make sure it’s really clean!

17. Find a ¼, 3/8, or 1/2 in drive socket, which is just a few thousandths smaller in diameter than the front & rear bearings. Also get a socket extension to fit into the socket that’s about 6 inches long, and a hammer.

18. Go get the bearings from the freezer.

19. Heat up the engine case where the front bearing goes.

20. Place front bearing onto engine case, align up the socket on the outer race of the bearing, and gently tap the socket extension with a hammer, that’s plugged into the socket, to seat the bearing down into the case. (Yes it’s a very tight close tolerance fit).

21. Heat up the case on the outside where the rear bearing will go.

22. Insert the rear bearing into the back of the engine case, and then insert the socket with the extension to push / tap / drive the rear bearing into the case. (Remember get a socket that’s just a few thousands smaller in diameter of the rear bearing, and this socket must only touch the outer race of the bearing when installing).

23. Make sure both bearings are fully seated into the bearing areas.

24. Insert crankshaft into engine.

25. Paying attention to the piston index pin direction, attach the piston & connecting rod to the crankshaft journal (pin should be in the 7 O’clock position from above posts).

26. Make sure the piston ring is positioned properly around the piston ring grove, so it will compress.

27. Put the piston at BDC (Bottom Dead Center) on the crankshaft.

28. Heat engine case around the cooling fins to ease in sleeve installation.

29. Insert the sleeve into the case, but be careful, don’t jam it all the way down onto the piston. If you have the case hot enough, the sleeve will be super easy to install and twist around within the case.

30. Push down on the sleeve until you can align up the piston at the bottom of the sleeve. (You may have to reach down within the sleeve with your finger to reposition “center” the piston within the sleeve area.

31. Gently push down and twist back and forth on the sleeve to get the piston & ring started within the sleeve.

32. Push the sleeve completely down into the engine case; remember the sleeve index pin at the 11 O’clock position.

33. Place a drop or two of triflow oil on the top of the piston and spin the crankshaft with your fingers, the piston will now go up and down within the sleeve. (Two drops really go along way)!

34. Install the engine head with head shim, and torque bolts down evenly. I use blue loc-tite on the threads.

35. Install your crankshaft lock back into the engine, and install the fan assembly, tightening the engine crankshaft nut.

36. Remove crankshaft lock tool.

37. Install back plate onto the engine case, torque bolts down evenly. I also use blue loc-tite here as well.

38. Install carburetor and pump / diaphragm housing.

39. Done.

While you in there, I would also replace any gaskets which are torn or in bad shape, along with a new diaphragm within the regulator assembly.

Once you've done this a time or two, you can get all of this done (minus removing the engine from the machine) in about 20 minutes.

Good Luck, hope this helps!

All the best,

Jeff

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06-06-2004 06:51 AM  13 years agoPost 6
Scrub

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Antioch, CA

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Wow, that's a lot of typing. Thanks this help a great deal.

Scrub

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06-06-2004 07:27 AM  13 years agoPost 7
jetsurgeon

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Raleigh, NC

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No problem. Good luck on your engine assembly.

Jeff

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04-26-2005 01:39 AM  12 years agoPost 8
RotorheadBob

rrApprentice

Wash DC Metro Area

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Toaster oven instead of a torch,,.

Great instructions for the YS engine...

I have one of the hard-to-remove sleeves. I don't have a torch and want some idea of how hot to warm the engine in my toaster oven (now just for engine work, no more toast in this guy!).

What's the fire hazard for the heat to make the sleeve ready to drop out? I'm concerned about my table top and any towels that get used.

Thanks.

Rob

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04-26-2005 05:59 AM  12 years agoPost 9
nabi

rrApprentice

Holmdel, NJ (central)

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I've replaced rear engine bearings in YS 91 engines.
(no front bearings yet ...)

put engine in the oven (or toaster oven I guess) for ~15 minutes
at about 350 degrees.

wear some oven gloves first, then take engine out and tap it
down onto a wooden board or something similar, the rear
rearing will just drop out.

once the rear bearing is out, you can also get the liner out
as well.

I had no need to freeze the new bearings before putting them in.

cheers,
nabi.

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04-26-2005 12:45 PM  12 years agoPost 10
airdodger

rrElite Veteran

Johnston USA

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That was a detailed list,whew. A heat gun will get the engine warm enough to remove the liner. Don't forget to check the ring end gap. Put a mark on the piston top where the ring pin is and look through a port on the way down to see that the ring stayed in place. I don't freeze the bearings never found it helped and the possibility of introducing moisture on the bearing was a concern. I put the rear bearing on the crankshaft and install, this way the front bearing is used as a guide, will drop right in. The crankshaft should rotate very free if you spin it between your fingers, if not remove and do over. Don't use any petroleum based products in a YS. I would also not use Teflon lube in a new ring install, just my opinion. Chris

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04-26-2005 01:42 PM  12 years agoPost 11
mrNoodles

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Borlänge, Sweden

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Heat gun works very well. Just dont forget to wear gloves.

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04-26-2005 09:54 PM  12 years agoPost 12
RotorheadBob

rrApprentice

Wash DC Metro Area

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Nabi, et al

Guys,

Thanks for the info.

Nabi,

You in the class again? I'm currently scheduled in the second one. See ya soon!

Rob

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04-27-2005 01:29 AM  12 years agoPost 13
nabi

rrApprentice

Holmdel, NJ (central)

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Rob,

yup, I'm in the second class.
looking forward to seeing everyone again .... :-)

nabi.

ps thankyou for putting up the guys ....

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HelicopterEngines Plugs Mufflers Fuel › YS piston damaged
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