I remember some discussion regarding bearings on this engines and some people recommending seals be left in place on rear bearings (which I did not agree with). Take a look at what Boca recommends in this newsletter:

http://www.bocabearings.com/newsletters/issue5.html

Nice site Chuck and A lot of helpful hints. I use BOCA but when you contact the people that built and designed the engines like OS and they tell you something else who should you listen to?? That's the problem I had with my last rebuild. I went with what BOCA said and left the bearings as they were then had to open the engine back up and remove A seal on the front bearing because the engine ran hot very fast from the front bearing. I still like BOCA and will use them but for A normal engine rebuild I will just stick with the cheaper OEM bearings I can pick up at my LHS. Without going back and reading all of this thread I think the deal was,Joes local Pattern Pros were telling him that the 1.20AX bearings only lasted A for A few gallons of fuel then he had to replace them with BOCAs. My thinking was he needed to find some better pattern pros and why/how would A pattern pilot be an engine guru, A lot of the pilots I know can't even tune an engine. It was just A thought. NOthing I ever brought up.

Yep. the reason I posted the site is because I thought I remembered someone saying that they were told to leave seals in place on the rear bearings which I thought was really odd and not necessarily good advice. This article also mentions that rear bearings should be open just as OS does it from the factory.

On another note, I just got back from our warbird event. Perfect weather.... high 40's to low 50's this morning with a fairly gentle breeze. A lot of very nice airplanes too. My Mustang didn't get done in time but it will be there next year.

I will be happy to update this thread with info on how well the new bearing works, and for how long. The info I got from the pattern forum was to get the sealed, stainless bearings, so I'm assuming the sealed ones you leave the seals on, but the shielded ones you remove the shields (for rear bearings).

Anyhow, I've flown the new AX for 2 days now, about 16 flights or so. The last flight had NO hesitation on throttle up, left a nice faint trail of smoke throughout the whole flight, and idled very, very nicely. Also, after flying the entire tank with lots of up lines, the engine returned cool enough to grasp and hold with no unbearable heat.

Awesome engine!

The article from Boca says to make sure the rear bearing is open on both sides (no shields, no seals which is the OEM way and I agree with it) and possibly leave one shield in place in certain situations (I'm suspect of this but I'll reserve judgment since I have no personal experience with it).

As for leaving front bearings sealed, I have seen people do it but I'm a little leery. I'd rather have fresh lubricant flushing through it than the same grease taking a beating every flight. Maybe I should give it a try sometime though, I might learn something new.

It sounds like your replacement engine is running good. Did you leave the stock bearings in place? That thing should really be screaming now with the cool fall air.

Yes, stock bearings in the new engine, and yes, it is screaming! It actually ACCELERATES in vertical uplines, even after a vertical snap it will accelerate up out of site in less than 5 seconds - I love it!

So the replacement bearing is not in the plane, but is sealed, not shielded. This means there is grease packed in the bearing. If I open the seals, I imagine I will have to remove and clean out the grease(?). Will a previously sealed bearing, with no grease, have enough lube from the fuel? I have no intention of replacing the bearing until something goes wrong, but the way I've been treated from OS/Hobby Services I'd call them and see if they'd replace it should it go bad within the 2 year warranty.

Chuck, I haven't rebuilt or pulled apart an AX engine yet, I just started fooling with them this year. {really like them} My last rebuild using Boca was one of my OS 1.20 FS pumpers. The stock rear bearing was sealed both sides {sealed = rubber} The one Boca sent was opened. The stock front bearing was shielded front only {shieled=inclosed metal} The one from Boca was shieleded front and rear. Boca was very firm about using there bearings as they sent them to me. This was A voice on the phone, not there web site. OS said to use there bearings. I had the Bocas in hand. Opened or sealed rear?? I didn't think it made a lot of difference unless the bearing let go and the seales would help keep the bearings from bouncing around inside the case. I was sure the front shieleded bearing was going to over heat, it did!!! Fired up the engine and it was cooking in A hart beat. I pulled the bearings out again and removed the rear shield and that cured the over heating problem right away. This was just A case of who to listen to and I made the wrong choice. Common sense would have been better.
Joe, I thought you replaced the bearings in the 120 you sent in and got A replacement engine for??? I'm so confused!!! Don't want to read this thread again to figure it all out. So, what did you do?? Replace the bearings in your new 120??? All this thinking hurts my head!!!

Sorry for the confusion. I replaced the bearing in the first (bad) engine, and found the issue with the engine when I was putting it back together, so I took out the new bearing, put the old one back in, and sent it in for service/replacement. Now the Boca bearing is in a bag on a shelf, and stock bearing in the new OS.

Boca on the phone was pretty adamant about me using an open bearing in the rear, so fuel could lube the bearing. I went against his advice and with the advice of a few other pilots. OS and Boca say to use a bearing that is at least open on one side for the rear bearing. The front is shielded (rubber).

Anyway, new engine is a freakin' animal, and yes, it starts on the first flip just about every time. A 1.20 two stroke starts THAT easily with a little chicken stick, you just can't beat that!

Thank you Joe, I got it all straight now. I think, I'm sure, kinda sorta!! At least my head doesn't hurt now!! I don't use the chicken stick, I was taught the back snap years ago and all my engines except one will start that way AFTER they have been started once with A starter. Most the time during the summer they will back snap on the first start of the day. No reason for you to start back snapping them though, just thought I would bring it up. I'm the only one I see doing it but it looks cool and dazzles people. I do have spinners on all my engines too so no real danger but it sometimes freaks people out. Just something I do, my advanced instructor was an old pattern pilot and A YS man so it's how he did things and A lot of the time I do too. [8D]

I started using a chicken stick because it was the cheapest way to get started. I actually got an electric starter, but with the stick I can hear and feel what's going on, and know right away when something isn't right. Plus I don't mess up my spinners with the rubber and heat from the starter. I like keeping my hands away from the prop, so no temptation to back snap, well, not too much temptation - I'm sure it does look neat

I fired up my plane today

The engine currently in my Venus II (120AX) had been replaced by Hobby Services. It has a handful of tanks through it from the end of last summer. I ran it with the tank mounted at the firewall for initial break-in with the intent of moving the tank back to the CG and reinstalling the pump.

A couple of weeks ago I performed the surgery on the plane. Tank's mounted at CG, lines are all run, etc. I decided to double check the settings so I ran a supplementary tank on the outside of the plane and restored the needles to factory settings. In one small tank of fuel I had the settings dialed in, nice transition, 2300rpm idle and 9000rpm with 10% fuel and a 15x8 APC prop. I ran another small tank of fuel, playing with all ranges of rpm, transition, etc, and boy am I happy with this thing! People say OS engines are broken in after a few tanks. From experience I found that after a few gallons, the transition smooths out, the high end power increases, and the idle rpm drops to sub-2000rpm. It's getting there. One more full gallon of fuel and I'll have better performance with a bigger prop. Oh and my engineering neighbors were around and asked about how to start it. They were like "do you have a starter, or do you 'old skool flip it?'" And I was like "well, it's an OS. I have a starter, but I never really need to use it". With that I turned around, attached the glow ignitor, and she started up on one flip, as usual

These engines are SO EASY! Easy, reliable, durable, and backed by some top notch service.

This feeling I have from OS engines makes the price tag totally worth it!

Joe, the old way to break in the OS two strokes was to just fire them up, set the high end, set the low end then fly the plane. We would do a gang of BIG loops and stall turns. Going vertical would heat the engine up and going down would cool it off. Very easy and worked very well, the engines were broken in after a couple of tanks. I have been told the new OS engines are made with a lot of different metals and require more break in time and the old way of doing it in the air isn't the best way to do it anymore. I'm sure Bill Baxter has writen something about it in the engine forum. I no longer do a lot of work or use a lot of the two strokes so it would be nice to see what Bill has to say about this. I do know that I too really like the AX line and find them very user friendly but I could say that about all the OS engines I have used over the years.