OS engine

[tealc]

OS engine problem resulted in the engine stopping while in flight. I have not opened the engine yet to see the damage but since I know that I will be doing a rebuild I was was wondering what Boca bearings I should put on order? What have you guys ordered in the past? I am running an OS SX hyper 50.

If you are wondering, I took the another club members 2 cents and applied it to my heli. This went against my gut feeling and leaned the engine a little to much which resulted in the engine going into shut down before I could get the heli on the ground. This was my highest and farthest auto I had to do. Don't know the total damage but I broke one of the grip links, the frame, and landing gear. All the head parts seem ok and will check tomorrow in greater detail. Tail was not damaged at all. I am amazed that I did not do more damage as I ran out of head speed thirty feet or more up. But I did get it back over the landing area and away from all the trees on the tree farm till I pulled to much collective, thus killing the remaining head speed.

As the wife stated after watching it fall from the sky, "You should have gone with what you know not what someone suggested. Stick with your gut next time."

Todd

[flyingquisinart]

It can never hurt to get a rear bearing for sure. The Boca Web Site has them cross referenced to most popular engines. Check your fuel lines and tank bung for leaks just in case you have an underlying problem that was made worse by leaning out the carb. Sorry about your heli, those frames don't break easily!

Sent from my LG-P509 using Tapatalk 2

[dharwood]

While I was in there, I would replace the rear bearing. I have used BOCA standard steel as well as SS in mine. The SS should hold up better as far as corrosion is concerned.

Hopefully the liner is not damaged. If it is good, you are only likely out a ring and piston.

Good luck!

Dale

[The Dude II]

Might try Paul at RCbearings.com.

BOCA is good...but $$$$$$$$$$ proud.


That said...you may have just got it to seize from heat. Have you tried spinning it via hand..then starter?

Of coarse, if you heard a "POW" and abrupt engine stop...may need those parts!!!

[tealc]

Pulled all the gear off the broken frames. Once the engine was out she spun very easy. I did hear a pop right before she quit. So, I am still planning on pulling the engine apart just to inspect (what I saw through the exhaust port is a coffee colored piston). Might do it tonight if I get to it. Been pouring "table top epoxy" on my newly constructed build bench. The wife wants her kitchen table back. Todd

[tealc]

So, here is the piston and liner. I am thinking replacement because of the drag marks on both indicating that they were rubbing together. The bearings have a very small rough feel so those are going for sure. I could use Gus's and other suggestions on the piston and liner.

[jbeech]

Piston/sleeve plus rear bearing should get you going again. Remember, you'll be breaking in a brand new engine once these are installed. Here's the link to the white paper I wrote vice the OS 50SX engine, which goes into enough detail to effet the repair (if you need it).

OS Max 50SX-H White Paper: http://www.audacitymodels.com/Images...X-H-screen.pdf

These engines are sensitive to being run too lean because they have a ring (instead of being ABC design) and thus, will give their all until the ring gives up the ghost and you get what you have on your hands. The reality is a few clicks leaner will seem to give more power until it doesn't Hopefully you've learned what too lean 'sounds' like and while it's unfotunate, this nevertheless ends up being a learning moment for you.

My only advice from all this is as follows . . . is it ever happens again, and it can by merely taking off without the pressure line attached to the muffler, shoot the auto immediately. This will likely save the engine. Moreover, if you botch the auto attempt while the engine is idling you can always flip the switch and gain back a little altitude before damaging the engine and thus, making another attempt to shoot it again.

Finally, if I may be so bold as to suggest, this may be the impetus to force you to practice shooting autos until you get comfortable. It usually only takes a tank or two worth of fuel and in fact, you may find yourself addicted for a while because they're an exhilirating maneuver to perform, especially when done to perfection.

In closing, I'm glad the damage was relatively light. Also, if you decide to upgrade to a P6 frame set, now's the time. Remember to purchase the new removeable bearing block, which is mounted above the engine where the old style P50 frame set features a molding-in bearing support. Of course, we have both frame sets in stock so it's really macht nichts.

Side Frames, P6: http://www.audacitymodels.com/Produc...3/Default.aspx
Bearing Block, Split, P6: http://www.audacitymodels.com/Produc...8/Default.aspx

[tealc]

Thanks JB. I found that "white paper" page on your website and was very helpful in pulling the engine apart. If fact I used it to make sure is was "doing it right." Yet, lesson learned. Go with what I know and have been running verses doing what someone else says who has never flown the OS 50sx hyper. I had been practicing autos prior to this but never from the height and orientation when I first heard the problem starting. So what this means is that once the rebuild is complete and engine is "broke in," I will spend a tank or two just shooting autos. By the way should I pick up a new ring. How does one tell when the ring has given up the ghost.
Todd

[jbeech]

I'd replace the ring - no question - because the one in that engine doesn't owe you anything!

With respect to replacing the sleeve, that's a trickier question because often a light honing with 600-grit and light machine oil, or better still, 000 or 000-steel wool and kerosene will result in a better surface. E.g. one ready to seat a new ring.

The kicker in making the decision is to first ensure there are no grooves already scored into the sleeve's surface by the event that led to failure. Deeper that is than those, which you're creating by the honing process. If there are, then get a new sleeve too. FWIW, I prefer 000-steel wool and kerosene with larger displacement engines and 0000-steel wool for smaller engines with the crossover being in the range we're dealing with here so use what's handy as either will do fine.

As for technique. I use my forefinger to apply pressure using an in-out/rotating-back-and-forth motion (same-same as with 600-grit emory cloth and light oil). The idea is to have a surface, which will bed with the ring to make a nice seal with the end result being a nicely crosshatched surface, which is perfect for the break-in process.

Also, whatever you do, don't opt for a brake cylinder hone because it's too easy to make things worse. A ball-hone would be a better choice but they're pricey and special ordered for a specific diameter. Last thing, very often you don't need to 'do' anything with the sleeve other than check the end gap before installing the ring (place it at the top of the stroke, square it up, then measure with feeler guage followed by installation), no honing necessary. It's all a matter of condition, if the sleeve is scratched deeply, replace it, otherwise go for it.

Last thing, based on the pictures you submitted I suspect you're in for piston, ring, and sleeve.

I hope this helps.

[tealc]

At the request of Gus here are some more pics. Thanks JB, Gus and others.

[The Dude II]

heads looks good!

per JB

Last thing, based on the pictures you submitted I suspect you're in for piston, ring, and sleeve.

Bearings while you're at it.

[tealc]

Thanks, Gus. I will get the parts ordered. Bearings were done already. Todd