Instructions for tearing down a gas engine
10-11-2011, 07:48 AM
#1
Thread Starter
My Feedback: (22)
Join Date: May 2008
Location: Lawrenceburg,
IN
Posts: 477
Likes: 0
Received 0 Likes
on
0 Posts
Instructions for tearing down a gas engine
I need to replace the bearings in an SPE engine. Is there any step by step or videos instructions around for disassembling this or similar gas engines? I checked youtube but only saw glow engines repair.
10-11-2011, 01:54 PM
#2
RE: Instructions for tearing down a gas engine
2-stroke gas engines aren't that complicated. If you can tear down a glow engine, you can also do a gasser. If you CAN'T tear down a glow engine - then send your gas engine to a professional.
Biggest concern IMHO is putting the piston and ring assembly back into the cylinder WHEN IT'S CLOCKED TO THE CORRECT POSITION. The cylinder has transfer ports and holes all over inside. The pistons rings are pinned so they ride in one of the spots where there is a continuous cylinder wall from the top of the stroke to the bottom - no transfer ports or exhaust holes.
The piston ring should ride up and down in the cylinder on part of the smooth wall. Typically you will have transfer ports at the following clock positions: 12 - 9 - 6 o'clock
Typical exhaust port is at the 3 o'clock position
You have solid cylinder wall at 10 - 2 - 4 - 8 o'clock positions
The piston will be pinned so the ring rides at one of the 10 - 2 - 4 - 8 o'clock positions - this keeps it compressed and doesn't allow it to open up into a port.
When you reassemble, make sure you feed the piston/ring up into the cylinder IN THE CORRECT POSITION
If you don't, that ring will find one of those transfer ports and then it will open up. The ring is under tension when you squeeze it down and slip it up into the cylinder. It's trying to expand. If it finds a transfer port or an exhaust port - it WILL expand. Now you're friggin' STUCK!! If it opens up into the exhaust port you can maybe manage to push and massage it back into the ring grooves in the piston and then shove it all the way up into the cylinder. But if it opens up into one of those transfer ports - you're HOSED. It's stuck and you have no way to squeeze it back into the ring grooves in the piston. Motors junk.
Make darn sure you got that piston clocked into the correct position before you stick it back up into the cylinder. Hey!! Call me an idiot - learned that little bit of information hard way.
See diagrams. Notice how the piston pin is always going to be located so the ring gap rides on a SOLID cylinder wall from BDC through TDC on the stroke.
Line it up before you shove it up in there. If that ring opens up into a transfer port you're hosed.
Next area of concern..... air leaks.
Seal it up when you put it back together. Buy or make NEW gaskets. Use a sealant. Air leaks cause lean runs. Lean runs cause dead sticks. Dead sticks cause dead planes.
Next area is the bolt and torque:
I use a tiny drop of blue or red loctite on the cylinder and case bolts. Keep in mind the case and cylinder are probably aluminum. The bolts are steel. Which one do you think will strip out first? The case or the bolt?
Snug them up to just a snerch past finger tight.
Now give each one about 1/4 or 1/3 turn. Now QUIT. Thats good enough. You don't have to monkey knuckle the bolts. That just leads to more problems.
Let it sit for 3 or 4 days and give the loctite and gasket sealant time to cure before you fly it.
Biggest concern IMHO is putting the piston and ring assembly back into the cylinder WHEN IT'S CLOCKED TO THE CORRECT POSITION. The cylinder has transfer ports and holes all over inside. The pistons rings are pinned so they ride in one of the spots where there is a continuous cylinder wall from the top of the stroke to the bottom - no transfer ports or exhaust holes.
The piston ring should ride up and down in the cylinder on part of the smooth wall. Typically you will have transfer ports at the following clock positions: 12 - 9 - 6 o'clock
Typical exhaust port is at the 3 o'clock position
You have solid cylinder wall at 10 - 2 - 4 - 8 o'clock positions
The piston will be pinned so the ring rides at one of the 10 - 2 - 4 - 8 o'clock positions - this keeps it compressed and doesn't allow it to open up into a port.
When you reassemble, make sure you feed the piston/ring up into the cylinder IN THE CORRECT POSITION
If you don't, that ring will find one of those transfer ports and then it will open up. The ring is under tension when you squeeze it down and slip it up into the cylinder. It's trying to expand. If it finds a transfer port or an exhaust port - it WILL expand. Now you're friggin' STUCK!! If it opens up into the exhaust port you can maybe manage to push and massage it back into the ring grooves in the piston and then shove it all the way up into the cylinder. But if it opens up into one of those transfer ports - you're HOSED. It's stuck and you have no way to squeeze it back into the ring grooves in the piston. Motors junk.
Make darn sure you got that piston clocked into the correct position before you stick it back up into the cylinder. Hey!! Call me an idiot - learned that little bit of information hard way.
See diagrams. Notice how the piston pin is always going to be located so the ring gap rides on a SOLID cylinder wall from BDC through TDC on the stroke.
Line it up before you shove it up in there. If that ring opens up into a transfer port you're hosed.
Next area of concern..... air leaks.
Seal it up when you put it back together. Buy or make NEW gaskets. Use a sealant. Air leaks cause lean runs. Lean runs cause dead sticks. Dead sticks cause dead planes.
Next area is the bolt and torque:
I use a tiny drop of blue or red loctite on the cylinder and case bolts. Keep in mind the case and cylinder are probably aluminum. The bolts are steel. Which one do you think will strip out first? The case or the bolt?
Snug them up to just a snerch past finger tight.
Now give each one about 1/4 or 1/3 turn. Now QUIT. Thats good enough. You don't have to monkey knuckle the bolts. That just leads to more problems.
Let it sit for 3 or 4 days and give the loctite and gasket sealant time to cure before you fly it.
10-11-2011, 02:35 PM
#3
Thread Starter
My Feedback: (22)
Join Date: May 2008
Location: Lawrenceburg,
IN
Posts: 477
Likes: 0
Received 0 Likes
on
0 Posts
RE: Instructions for tearing down a gas engine
Ok, thanks for the info. I've put bearings into glow 2-strokes but these gassers look different. I figured out how to remove the cylinder and the piston, now I need to separate the front and back case to get the bearings out, but first I need to figure out how to get the prop adapter out and then the crank shaft. Looks like I will need a gear puller. I've been reading what I can find and it looks like some folks use some type of glue when replacing the bearings to keep them from spinning in the cylinder races, is this necessary? DG
Update, I finally figured out how to separate the case. How do you get the bearing seals out without messing them up? They are discontinued from the motor mfg. DG
Anyone want to comment on my questions?
Update, I finally figured out how to separate the case. How do you get the bearing seals out without messing them up? They are discontinued from the motor mfg. DG
Anyone want to comment on my questions?
