I am just repeating this question from the beginners section, probably not getting an answer there.

I have a 55ax on the GP Reactor 46 but the engine does not seem to have compression randomly, mostly when it gets hot (at running temperature, set half a turn back from peak rpm with now cowl) and cuts at some point in flying. Now, why the engine doesnt have compression is another issue and I will fix it later by replacing the piston-liner set (engine hasnt been opened, most likely it wasnt run-in properly). For the time being I want to continue running the airplane with a 75ax. That specific engine is an older engine which did give me problems on another airplane but those could be tank height issues. I plan to achieve 2 targets b y using the 75ax- find out whether the 75 is reliable and continue flyng this airplane with a bit more power and throttle management in 3D

My question is - is the engine too big for the Reactor or should I go ahead and make the swap? or should I order and install a 65ax on it? I couldnt find reviews of the 65ax anywhere

Ameyam

I have a reactor with a 46ax and it is a good flying plane. As for a 75 being to much I can't anwser. I thought I would tell ya my expereance with the 55 in a sundowner. Mine was always dead sticking on me because it was running hot. I am now almost at 3 and a half turns out from closed on the high end. Mine is very reliable now. Not saying that is your problem but these engines don't do well in closed cowls.

And I am running a OS F plug! An idea that I read on here from someone!

skillet92,

I am running the 55ax without cowl- wide open. I tuned it with the thing vertical and it a bit back from absolute peak rpm. Then while flying it, I started to hear it struggle misfiring when in the air after 4-5 mins with half tank still left, so I promptly lined up for landing and it cut even before I could finish the turn to go to my lineup point.

Next time we started her and tuned her, it cut just as we placed it on the ground. Then, when we tried to start her we noticed that it was simply turning over by hand- no compression. After a couple of seconds it cooled sufficiently to regain compression. This has happened several times over the last few weeks- both the compression thing and the deadstick part. So I have given up on it. Think we had not run-in the engine properly before flying was closed down in Jan last year due to some unrelated issues.

I am thinking that with the 65ax, 75ax and 95ax using the same mounting dimensions and the 65ax being considerable lighter, I will go for the 65ax instead. However, I cant find any opinions regarding this engine on the internet of forums.

Cant use the F Plug- tried it but it keeps pre-firing at full throttle

Ameyam

The .55-AX is one of the best running, most reliable engines on the market. I have ran them in cowled applications with zero issues. The key is airflow. air has to be directed over the cylinder and the air exit should be at least 3x the size as the inlet. A lot of people make the mistake of an exit that is too small, myself included.

It definitely sounds like there is something wrong with yours though. Hopefully you'll be able to figure it out, they are great engines.

As for the .75-AX I imagine you can make it work. People overpower airplanes all the time. I personally wouldn't do it but that doesn't mean it won't work. Just be prepared for CG issues and heavier wing loading.<br type="_moz" />

My .55AX kicks axx in my Venus .40, and it's mostly under a cowl. It sounds to me like you have engine tuning/breaking-in issues; the AX line of engines is incredible - right from the box. I have had several, ranging from .46 to 1.20, and all ended up in cowled airplanes.

If you like to hang your plane from the prop all day, then no real reason not to mount the .75. The plane won't 'fly' very well, but most 3D people aren't flying the wing for sustained periods of time. Biggest issue will be fitting the engine, and more importantly balancing the plane. And then longevity issues due to extra stress (from weight and power) on the airframe, which you may or may not notice.

The plane was designed to have a certain range of wing loading, which you will be overloading based on spec. It won't 'fly' the way it was designed, but that doesn't mean in won't leave the ground and do exciting things in the air.

The 55ax weighs 18.52oz o 525g with muffler. As against that, the 75ax weighs 26.46oz or 750g w muffler. For the 65ax data isint available with muffler but without that its 17.5oz (497g as compared to 405g or 14.29 oz for 55ax) and assuming muffler to be same as 55as, it would be about 650gms or 22oz. That is the reason for shift for preference from 75 to 65- its much lighter. With respect to the stresses, I have already had a hard langing due to deadstick and reinforced everything a couple of weeks back. I will fit a lower pitch prop (14x4) anyway of the 65.

With regards to my problems with the 55ax, thats another story. When I got it last year, my instructor decided to fly it without break-in inspite of me telling him to do the break-in first. Though we ran her rich, I think that is where the problem lies with both this 55 and the 75 earlier, so when I get the 65 I wont take off without running in with atleast 4-5 tanks as per manual, no matter how much time it takes.

I did manage some hovering today with the 55 and given more persistance it will do ok I am sure. I dont hang by the prop all day. The first flight is always pattern with low throws to calm my nerves and thereafter I will hover in the second flight after I get ove my thumb-shaking. Beyond that I am still getting a hang of the other 3D moves, insufficient air time has prevented me fro trying them much though I do them on the sim.

What I really need is some data on how the 65ax is

Ameyam

Your original post said you were having issues with the .55, but were considering making repairs. You said you'd consider using a .75 you had laying around, but were concerned about weight, and problems you may have with that engine.

Now you're talking about buying a .65AX?

The AX line of engines gets great reviews. There are always haters, but basically these are engines that provide adequate power (not the most, not the least) and offer a ease of use and little-to-no break in time. I would be confident that I was getting a good engine if I were to go with the .65AX. If something were significantly wrong with the motor, you'd be backed by great support.

That being said, it seems like you are having unfortunate issues with two of those engines. To me, it sounds like there is something wrong other than the engines. I'm not sure why you'd want to get a third before you have the first two figured out.

I think the best advice is to repair the .55 and figure out what's going on with your engines. It is less expensive than buying a new engine (and with only marginally more power) and will hopefully teach you something along the way. That engine will be enough for aerobatics and some 3D, depending on how you prop it.

If you're concerned about performance, a good 4-stroke is always an option as it gives better throttle response and generally allows for a larger diameter prop. However these can be more complicated than the AX engines, so maybe not a good idea yet.

http://www3.towerhobbies.com/cgi-bin...?&I=LXWFK1&P=0

I've received a brand new .55-AX on a Friday after leaving work, bolted it on that evening, started it quickly to make sure it works then shut it off immediately so I didn't bother my neighbors. The next day I went to the field, set the needle slightly rich and flew 4-5 times that day without any problems at all. I'm not saying that it doesn't need to be broken in but it isn't as critical as it might be with other engines. I think yours just has a problem or defect. Either the cylinder head is coming loose, there is a problem with the piston or cylinder or something like that causing compression loss. They are good engines but even the best stuff can have problems from time to time. Nothing is perfect unfortunately.

You might be able to stick your battery way back in the tail to make the .75 balance. If you do get it to work, the plane will be ballistic. That's not necessarily a bad thing.
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I think that inadequate break-in is the issue. Even last year, when I started flying it I was having dead sticks with the engine. I had two airplanes ready (the other had the 75 with similar issues but could be more attributed to the tank being 1-1.5" above the carb) and subsequent to the break in flying, I put in a FS 91sII in that airplane (and lowered the tank). After a break-in I never had problems with that engine. It was damn relaible and ran till it finished the fuel. I am using the same fuel in all engines- klotz with 10% nitro.

My 55 is already mounted at the 45 deg angle, so mounting the 75 that way is no prob. The airplane can take a larger prop- 14x4 in its stock config. I was running a 13x4 on the 55 but had tested the 14x4. If a larger prop is required I will put in a set of larger wheels than the 2" Dubro rubber I am currently using.

I have the following engines lying around

1) 55ax- if I rebuild with a new piston and liner- 18.52oz (525g)
2) 72a- it was meant for another airplane and was bought box damaged. It could be a little under powered as it would be equivalent to a 48 size engine- 18.7oz (530g)
3) 75ax 26.46 ounces- (750g)
4) FS91sII which is a very reliable engine and currently in another ageing airplane. Its lighter than the 75ax (by 2.26oz or 64g) and has a little less power. It will require a rebuild of the Reactor because the throttle servo will not be in the correct place- 24.2oz (686g)

The reason to consider a 65 (about 650gms or 22oz) is simply the weight saving. So if the 65 is required, I will need to order it. Else I will need to take a call and put the Reactor into storage and take out the Phoenix Extra 60" with the 120ax which I am preparing for quite some time


Ameyam

Reoeatubg myself:

I think you are just not used to ABC type glow engines.

When the cylinder gets hot, the engine may indeed feel like there is little to no compression as the piston will slide far more easily in the cylinder.

You should feel some pushback because of the trapped air in the cylinder head, but this is still considerably less than when the engine is cold.

FYI: I have one well worn .75 Tower engine that feels like it has absolutely NO compression even when cold, but that engine remains a STUMP PULLER.... a very powerful engine.


The 55AX is perfect for that plane, you should NOT be trying to fix one problem by introducing another.

Fix the fact that the engine cuts out.

You likely have plumbing or pressurization issues, or you are still running the engine too lean in spite of what you may think is the proper setting.
You'll need to find what is to blame and deal with that.

Opjose, we can discuss on the thread in the beginners forum if thats ok with you. No point in duplicating threads

Ameyam

I had a similar problem with my 55AX. It ended up being a head bolt had vibrated loose. I tightened that up and she ran like a dream again. This happened a few times so I ended putting thread locker on the head bolts which solved the problem.

Cheers

At Opjose's suggestion last night, I heated the head by means of a hair drier till it was so hot I couldnt touch it (loss of compression only happens when its hot) and then tried to tighten. The allen key slipped on the heads but they wouldnt tighten further. I had already tightened them when it was cold

Ameyam

I always use the 18% oil by <font size="3">volume</font> fuel that is a blend of castor and Klotz that is recommended in the OS instructions. Only after it says this does it allow that good quality all synthetic can be used. It also doesn't say 18% by <font size="3">weight</font>, which is said to be done by some fuel manufacturers. I use Sig (actually 20% oil) and Omega (only after break-in, works fine in high temps).
That being said, I have a 46AX (11x6 APC) and a 55AX (12x5 APC) in my two Kaos's that run like tops. 4 Gallons through the 46 and 2 through the 55 and they're great, one flip starters.
I did read a thread about the pressure taps being plugged in some AX mufflers, that would make them go lean and quit.

A buddy has a Reactor with an OS 46 AX and an APC 12 1/4x3 3/4 prop that seems like magic in it's ability to 3D. Might be him, though. He chose the engine because of it's power to weight. That prop on a 55AX would seem killer.

Hope you get your's figured out.

Chris...