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1.20 AX

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Old 06-07-2012, 06:58 PM
  #1
dbacque
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Default 1.20 AX

The OS web site states that the 1.20 AX "fits in the same space as a .91" and that it "will bolt right where the .91 used to be." Exciting claims!

So I purchase a 1.20 AX to replace the .91 FX in a plane I've been flying for several years. I expected modifications to the cowl and the muffler tunnel but was I in for a surprise. The crankcase for the .91 measures 1.7" wide while the 1.20 measures 1.86". How the heck does that "bolt right in where the .91 used to be"?

Bolt holes to prop washer distance is also different. Bummer on the fact that you want a good spinner fit. But don't worry, it will bolt right in. Yeah, after you buy a new motor mount, redrill your firewall for the new mount and then drill and tap the new mount.

In the last 35 years I've only purchased OS engines and have been incredibly pleased with their products, services and published information. I still would have purchased this engine if I had known that there was a mount difference. But based on the advertising I was completely unprepared for the install. Now I have to revert back to the previous engine while I wait for more parts to arrive.

Sounds like misleading advertising to me.

Dave
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Old 06-12-2012, 06:04 AM
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Default RE: 1.20 AX

The advertising says the engine fits in the same space, but doesn't say the mounting pattern is the same. There are differences, but the overall size allows the 1.20 to go where a .91 went.
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Old 06-12-2012, 03:19 PM
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dbacque
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Default RE: 1.20 AX

The advertising also says that it "will bolt right where the .91 used to be" and in the picture right next to this quote the engine is compared to the .91 FX. Sure does sound like you're saying it will "bolt right where where the .91 used to be". Doesn't sound like you're saying "it won't fit in the same mount".

I don't have a problem with it not being the same bolt pattern. I do have a problem with advertising being misleading.

I'm sure this airplane is going to be a monster with the increased power. I won't have any problem with the extra work. I just wish I hadn't been misled into thinking that I didn't need more parts before I tore into things and missing a weekend of flying due to advertising hype.

After flying with this engine I will post about how much I like the difference. I will be a poster boy for 1.20 vs. .91. But I still say you could have been clearer that the bolt pattern was different.

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Old 06-23-2012, 02:00 PM
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Default RE: 1.20 AX

So here's the report.

I did order a new engine mount and get it drilled to fit the 1.20 AX and the cowl. Changing the cowl engine cutout from the .91 FX to the 1.20 AX was not difficult and I still have a nice fit. The carb fits perfectly in the old carb openings and hole in the cowl to reach the .91 low speed needle was nicely lined up on the AX. Of course I did need a new needle valve hole but no problem. Personally I don't care much for the angled needle but I know others that do.

As for the muffler, I don't much care for the "Power Box" design. The biggest part of the change over was ripping out the chin of the plane to fit the large width of the muffler. It also is heavy. The weight comparisions available online don't include the muffler weight difference, this would have been good information to have ahead of time as I could have planned for the required battery move.

The engine was installed in a .90 size pattern plane that I've flown almost every weekend for the last 4 years. The 1.20 AX has given it a new life! I tried about 6 or 7 different props and and the APC 15x8 seems just about right for my application. I was always happy with this plane but the new combination is incredible. Slightly faster in level flight and tons of grunt in the verticals. My maneuvers are just massive now.

I knew I'd like the extra power and I was right. I still think that the phrase "bolt right where where the .91 used to be" is a might of an overstatement but the results are great. As I said before, I still would have bought the engine and done the work but had I known that the engine required a different mount I could have ordered the mount ahead of time and had everything on hand when I started the job. Instead I tore the entire plane down and found that it wouldn't fit. I had to reassemble to fly that weekend, order and wait for parts, then repeat the job with they arrived.

OS, A+ on the engine but C- on the advertising. We really have come to expect better from you.

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