Super Tigre G-75 Piston/Ring Problems
 

I just got a used Super Tigre engine that was running great. It was very dirty so I decided to clean it. I competely dismantled and bathed it in antifreeze overnight. It's now almost new looking but i cannot get it to go back together. I know that it is a pinned ring setup. I can see the pin and I *believe* I marked the piston correctly so that its back in the correct place.... I did not take the ring off nor did I remove the piston head from its arm. I have the ring lined up with the pin when I attemp to insert it..I've been at this for hours but I cannot get the piston to go back into the sleeve. I have lots of lubrication involved and have even tried doing the opposite of what I did to take it off... which was to heat it up. After heating it up the sleeve slid in just like it slid out but when the piston slid up into the sleeve it was tight... too tight to turn things over... so I pulled it back out.... what am I doing wrong?????

When I look from the back of the engine, the piston has a marking on top that is at about 2 oclock... I THINK thats where it was at but now that I have been having so much trouble I just cannot be sure and there is nothing to be found online to show me for sure.


HEEELP!@

RE: Super Tigre G-75 Piston/Ring Problems
 

When it rains it pours. I tried to fit the piston into the sleeve outside of the engine just to see what the problem was and while I WAS able to get it in it was still too tight to work. That got me to thinking that maybe there was some gunk under the ring that was keeping it compressing all the way. So, as I took off the ring, it broke.. :(

Now what are my options? Can I just get a replacement ring and hope for the best or what???

RE: Super Tigre G-75 Piston/Ring Problems
 

Ok.. its all coming together now.... the ring has a NOTCH next to the break in the ring... does THAT go over that pin?

I was trying to make the OPENING in the ring come together over the pin...

RE: Super Tigre G-75 Piston/Ring Problems
 

The pin goes in the notch.

The second big thing to notice is, the pin is to keep the gap of the ring from coming past a port. So set the sleeve upright on the table and hold the piston/rod between your fingers above it. Hold the piston in the direction you assumed that it came from the engine.

Now to repeat myself, the gap of the ring must slide between the ports. So put the gap of the ring on the side of the pin that will place the ring gap between the boost and schnurle ports of the engine. You may have to turn the ring over to accomplish this?

Typically the pin goes to the left front corner and the gap in the ring goes to the right when looking down on the piston.

On the big end of the connecting rod, one side has a chamfer in the bearing hole and the other does not. The chamfer goes towards the crankshaft.

Often, there a rubbing marks on the side of the rod that goes towards the backplate on engines that have had an electric starter used on them.

I buy my rings from Frank Bowman.

Frank Bowman
1211 N. Allen
Farmington, NM 87401

[email protected]


Enjoy,

Jim

RE: Super Tigre G-75 Piston/Ring Problems
 

Will replacing the ring require me to break the engine in again???

RE: Super Tigre G-75 Piston/Ring Problems
 

yes;)

RE: Super Tigre G-75 Piston/Ring Problems
 

It will break in a little faster this time than when new.

RE: Super Tigre G-75 Piston/Ring Problems
 

[b]Demi:

Looking down at the top of the cylinder, with the crank shaft at the 12 oclock position, the pin in the ring groove should be about 7:30, the gap in the ring at 7.

Bill.

RE: Super Tigre G-75 Piston/Ring Problems
 

[b]ADENDUM:

Be sure to put the ring gap the right way from the pin - if installed at "Eight oclock" it will catch oin the boost port and break.

Bill.

RE: Super Tigre G-75 Piston/Ring Problems
 

Very helpfull response William. I should be getting the new ring on Tuesday. I'll give it a go using this knowledge. I'm hopefull that it will be a quick and easy rebuild.

RE: Super Tigre G-75 Piston/Ring Problems
 

[b]Demi:

Before you reassemble the engine wrap a bit of 600 grit around your right index finger, then stick it through the sleeve with plenty of light oil. Use the palm of your left hand to roll the sleeve on your finger, moving your finger in and out as you roll the sleeve. This in and out is to keep from making any purely circular cuts in the inner surface of the bore.

It doesn't take a lot, you may not see any difference in the appearance of the bore. If you see even a slight changer you have definitely done enough.

Wash the sleeve in hot soapy water, rinse thoroughly, dry and oil it.

I strongly recommend a fuel with at least 3% castor oil. Makes the ring (and the rest of the engine) last a lot longer. And gives a lot better protection to the bearings, Use a good after run oil as well.

When you restart the engine let it warm for 30-40 seconds, go to full throttle and immediately peak the mixture, then back to idle for 10-20 seconds. Full throttle again, then back to idle again.

Keep repeating this for about 90 seconds total, and the ring will be seated.

What you are doing is using the maximum combustiion pressure to force the ring against the wall at full throttle, then allowing it to rest and reoil with the idle time. Contrary to popular opinion, the ring will seat in less than 90 seconds of running time.

Note: While the ring will be seated it will not be totally "Broken In" yet. This is a matter of the ring gap. At the higher temperature of full throtle running the ring will expand, if the gap is too narrow the expansion of the ring will cause the gap to close, and the ring will bind.

After your initial run to seat the ring, restart and run the engine at full throttle for 30-45 seconds. If the rpm doesn't sag go back to idle for a moment, then go to full throttle for a little longer. When it will hold full throttle indefinitely the engine is once again ready for unlimited flight.

If at any time the engine rpm does fall off at full throttle bring it back to 4-5K rpm, richen the mixture a little bit, and give it 5 minutes or so, then recheck at peak rpm. Shouldn't take a lot.

Hope this helps.

Bill.

RE: Super Tigre G-75 Piston/Ring Problems
 

Bill,

Got any tips for putting the ring on the piston? I went to pick it up today and they told me it wouldn't be here till Friday now. I would hate to break the new one while putting it on.

RE: Super Tigre G-75 Piston/Ring Problems
 

[b]First double check my memory. Assemble the engine without the ring on the piston, after using your "Sharpie" marker to show the position of the ring pin. With the piston at the bottom of its stroke you will be able to see all the ports, the pin, as memory serves, will be fairly close to the edge of the boost port, the port across from the exhaust. Now looking at the ring you can see how to install the ring so gap will be on a solid part of the cylinder wall. I'm remembering the gap as being the way I said in the earlier post, but if putting it on that way would put the gap in a port then turn the ring over and install it the other way around.

Now with the piston out again, set the ring on top of the piston with its notch directly above the pin in the ring groove and the gap positioned in the way you have proven to be correct.Slide the ring slightly over the edge of the piston to where you can push the notched end down to the groove. Then carefully work the rest of the ring into the groove, stretching it a little as you can.

Before you put the piston back into the sleeve oil the ring liberally, being sure to get oil into the groove behind the ring. And you now know to put the ring notch over the pin, and not the ring gap. Haw.

Enjoy your engine.

Bill.

RE: Super Tigre G-75 Piston/Ring Problems
 

Wouldn't you know it. Friday comes and the ring arrives....in pieces. They assure me they'll try to have it sent overnight...on Monday, for a Tuesday delivery..for a 100% discount when it arrives.

RE: Super Tigre G-75 Piston/Ring Problems
 

[b]More fun and games with the USPS.

Bill.

RE: Super Tigre G-75 Piston/Ring Problems
 

The Super Tiger G75 ring replacement went as smooth as could be. I broke the engine back in on Saturday in the back yard and the idle is perfect again.

The airplane I put this engine in is a scratch built SPAD using my own plans. It's a [link=http://spadworld.net/forum/viewtopic.php?t=11027&start=60&postdays=0&postorde r=asc&highlight=]Coroplast Ultimate Biplane[/link].

Here is a video of the first flight with the G75: [link=http://www.washingtonlakes.com/Flight/Ultimate/CoroUltimateBipe-75.wmv]Video 1[/link]

Ok after all this with an older engine little or no compression?
Does this mean the cylinder is worn out?

After all what, we need some facts, but most likely only the ring is worn out.

In another thread he said he replaced the ring with a new OEM ring.

I replaced the ring with a new OEM ring compression is better?
Runs fair uses a lot of fuel, I have been through 3 tanks of fuel on the bench, not much change?

OEM ring replaced, still soft n compression, uses a lot of fuel?

Try running it right at the 2/4 stroke break to where it's running rich 2-stroke most of the time with the occasional miss. Do this for maybe 24oz of fuel. Let the engine cool down and flip the prop briskly through compression a few times. See if it improves. If it doesn't, try scuffing the bore with 400-600grit emery paper to make a cross hatch scratch pattern and re-break it in.

Back to to the questions I asked earlier - what did you do to prep the liner before installing the new ring and how have you been running it to seat the new ring?

Paper is too fine. I'd guess the cylinder didn't get roughed up enough so the ring isn't wearing in. I would use a rougher grit and scuff the liner again, then re-run it. 4-stroke rich for a minute or so, then take it to the 2/4 break where it runs mostly in rich 2-stroke mode with occasional miss and do this for 4 tanks. On that 4th tank I run mine so it's -just- lean enough to run a full two-stroke. Run two ranks that way. Then peak it out and run 800-1,000rpm rich of peak for awhile. Maybe a dozen flights. ST rings are fairly hard and take a long time to seat. Expecting stellar compression and perfect ring seal after 4 tanks (unless they were 16oz tanks) is very optimistic IMO.

Need help ring broke
 

Hey have g75 supertiger and the piston ring broke any replacement I can get and where