I have one of these

http://www.osengines.com/history/osm...2-max-40rc.jpg

new in a box and have installed it on my old trainer. When I went to start it to begin the breakin, I found that the airbleed screw is missing. I have looked on the internet to see If I could find one, but have had no luck.

Will any scew work in this as long as it is threaded correctly, or does the tip have to be specially shaped?? I am new to air bleeds.

Is there supposed to be a spring over the screw to hold it in adjustment??

Anything else I should know about this motor??

Beagle, i´m almost sure that this screw is a metric 2.6 (M 2.6). You could try one from the carb of the OS LA line, almost sure that fit.
Good luck

Break-in can be accomplished without the airbleed screw in place. Break-in is accomplished at high throttle with the needle valve set very rich. Fuel should contained 20 to 25% castor oil for lubricant and 5 to 10% nitromethane. Forget throttling the engine during break-in. Just run it with the carb opened all the way opened. Castor oil fuel is important for this and other OS engines of the same era. a 10x6 or 10x5 propeller is perfect.

Depending upon the type of fuel being burned, we sometimes used to completely remove the low speed airbleed adjustment needle with this and other similar sized OS engines. They ran perfectly that way.

This type of engine requires the use of an idle bar equipped glow plug. Yes, there are a few non idle bar plugs that might work, but finding one that will could be expensive since you may have to go through quite a few before you "get lucky" and find the proper plug. No, it won't hurt anything if you run the wrong plug. It just won't throttle as well as it would with the proper plug. I used to use Fox R/C Long glow plugs (idle bar equipped) and received good performance from my OS Max .40 - H engines.

Good luck. I always did with my engines of this type.


Ed Cregger

The airbleed screw does have a spring on it to help to keep vibration from rotating it.

As for fuel. I would go to a minimum of 22-25% oil content in the fuel. The Max-H series had Meehanite pistons in a steel sleeve and unbushed conrods. Most commercial fuels are only 18% nowadays. Duke Fox used to recommend a 29% oil content for his .35 Stunt engines (same construction) which he still makes. He also still supplies the 29% fuel for us old toots with good old engines.

The H35 has a cast iron piston but the H40's are ringed. Either way I'd go along with 25% all castor preferably.

No special shape is necessary, just use a machine screw. You should have a spring or other contrivance to keep it in place.

MJD

Thanks for the input. I thought it would run wide open with out the screw as well, but I never was able to get it to fire once. Looks like I have some fiddling to do to get this going. I am running Wildcat Premium Extra fuel. It has 18% oil with an 80%synthetic, and 20%castor blend. I have had several people tell me that it will be fine as long as I keep it pretty rich.

Engines like this are very different than the engines of today. I would bump the oil up to at least 22% and 25% is even better. The older engines just need more oil to keep them alive. Just think of the tolerances, metalurgy and fuel available at the time they were designed. You can add extra oil to each tank of fuel if you don't want to do an entire gallon.

turbo

If has been sitting in a box for 20 years the ring might be stuck; look in the exhaust and look at the ring while changing directions; you should see it wiggle. It is one of OSs best engines and my first big engine so I like them. I would also start the engine at a lower throttle setting and then go to WOT. It needs an idle bar plug and castor and it should run for a looong time.

if i was you i would get a .40 la airbleed screw
or head down to ace hardware, bring the engine and try screws till you find one that fits. when you do just add a ball point pen spring or something similer to keep it in place
any screw is better than no screw.

I robbed a screw out of an OLD engine I had laying around and it fit the air bleed perfectly. I doctored up a gallon of fuel with 10oz of Klotz Beenol castor to bring the total oil content up to approx 25%. I began the breakin yesterday. WHAT A MESS!!! I set the needle valve as sloppy rich as I could get it and keep the engine running. I downloaded a manual somewhere for this motor and began following the breakin instructions. I would run the engine wide open for 2 minutes and then shut it down to cool for 2 minutes. I did this for 3 tanks of fuel, Approx 45 minutes (the manual called for 30 minutes). The engine barely got more than warm to the touch, and it was 95 degrees out.
The manual then instucted me to lean the engine untill it just broke into a 2 cycle run and follow the same procedure. During this time the motor would get very hot (too hot to keep my hand on for any period of time, but not hot enough to instantly burn) so I would allow it cool for much loger periods while I had a few flights with my other planes.

Question #1 is is it OK/Normal for the engine to get so hot?? I know the engine was getting plenty of oil as it was blowing it everywhere, I had a huge puddle on the table where i was doing this and it was running across the table and dripping on the ground. The entire fuselage of the plane was covered with oil dripping off all along the side and the wing. Honestly I have never seen so much oil in my life.

Question #2 When I was doing the second part of the breakin the tuning of the engine was very inconsistent. one time I would start it and it was in a slightly sloppy 2 cycle, shut it down to cool then restart and It would be 4 stroking like crazy and I would have to lean the needle to get it just into a sloppy2 cycle again. Shut it down to cool start it up and it would be screaming I would richen the needle back to a sloppy 2 cycle. Is this normal during a breakin for the needle to be so inconsistent. If not what else could it be???

Your engine temps sound to be fine although "too hot to hold your hand on for any length of time" is a bit vague . I'm in the process of running in an iron piston engine in a similar manner to what you've been doing. I gave it an hour running at between 6-7000 revs so a very rich 4 stroke with all castor fuel. Surprisingly the temp actually came down considerably during that hour as it ran in but this particular engine had an extremely tight "ABC type" pinch which slowly loosened. Head temp dropped from 146F to 115F at 7000 revs after an hour and then stabilised. So your "barely warm" is fine. I've now got to the stage where I'm taking it to the 4-2 break point to start building up some heat in the piston and this happens at 11,900 revs (with an 11x4 prop) where the head temp is 200F which gets uncomfortable to the hand very quickly . So your "very hot" sounds about right.

As for the change in tune when restarting, it could be a slight air leak from the needle valve (use a piece of fuel tubing to seal it) or possibly that it can't quite make up its mind if it wants to 2 stroke or 4 stroke so picks one or the other.

Thanks.
I will continue the breakin and make sure it stays pretty rich. I think once it is broken in a bit better it will even out. If not I will start looking for air leaks.