Fox .15x Problem Child

NEW222 Tue Feb 12, 2019 5:51 pm

Yesterday evening I had received teh Fox .15x engine from crankbndr. First initial thoughts were that it is a thing of beauty. With that said, I had one little project on the go to finish up before looking at it. So, I put my rear end in high gear and finished project number one so I could tackle the Fox. First, I disassembled it, or should I say removed the head and backplate carefully. I also put on a propeller. I then tried carefully to see if there was any movement in the piston. There was none. I then thought what the heck. I went and borrowed a pair of my dads long reach needle nose pliers. I put a piece of tape on each jaw then put them into the exhaust port to see if I could get the pin to move. To my amazement, it just slid right back into place with a very gentle squeeze! I put in a couple drops of oil on top of the piston, one on the bushed connecting rod/crank pin connection, and a couple on the crankshaft. It spun over a bit stiff at first, then freed up a lot. I then assembled the engine and it had good compression. I was happy and thought I was done. That is when I realized that the cylinder liner was out of place. I was going to leave it for the evening, but a few minutes later, I found myself back at it. Using a heat gun and a pair of pliers, I got the liner out. I was honestly shocked as I would have thought that the liner would be completely solid where the pin would be riding as I thought that is what caused the problem. However, there are cutouts in the liner on both sides of the pin. Regardless, I re-assembled the engine again with the liner correctly oriented and it is as good as new. With that said, I also posted on another site about it. Also, I read that the pin should be a tight press fit. I did not completely remove it so I do not know if it is inserted properly. So, in just a minute, I will be back in the lab disassembling it yet again to see if there is possibly something amiss. Update to follow this evening!

crankbndr Tue Feb 12, 2019 5:59 pm

That engine looked like it had never been dissembled, all the screws looked factory with no tool marks.
Good job, I didn't think of needle nose.

**Cribbs74** Tue Feb 12, 2019 6:34 pm

When you get it fully dissassembled could you take a picture of the liner removed from. the case?

I am not understanding what you are saying about the cutouts for the piston pin. If that pin is loose in the piston then it will gouge the cylinder over time.

Ron

Ken Cook Tue Feb 12, 2019 8:18 pm

Run it. These engines are very common and generally are very inexpensive. They multiply like Babe Bees. Like most Fox's, you get 10 of them and find that 1-2 stand out from the others.

NEW222 Tue Feb 12, 2019 9:34 pm

Well. Just a little update. I took it apart to try and get a picture and now there is definately something wrong. It no longer spins like it used to and the piston gets hung up above the ports. It used to freely spin, but now does not. It gets hung up on every revolution. So it now looks like somehow I pooched something with the piston and cylinder assy. Off to keep playing with it as I do not know what happened.

NEW222 Tue Feb 12, 2019 9:36 pm

Hopefully I can come back with a better update, but am not feeling optomistic at this point.

Just an update. Took it back apart again to see if I could find the problem with no luck. Before, it would pop when flipped over by hand. Now, it appears to hang up near top dead center. As well, as mentioned, there is resistance throughout the whole stroke, and in turn, when the head is off, it pushes the liner up as it gets to top dead center, and it never did that before. It is not the wristpin, as it goes in and slides well below the ports. If anyone may know what may have caused this, I am open to any suggestions. Also to note, since using the heat gun yesterday, I had not needed any tools to remove the cylinder liner, and it was able to come out with just my fingers, so I have almost ruled out damaged liner. Thanks for reading my newfound frustration, but I do like a challenge, and this is exactly one of them. Huh...

NEW222 Tue Feb 12, 2019 10:44 pm

Cribbs74 wrote:When you get it fully dissassembled could you take a picture of the liner removed from. the case?

I am not understanding what you are saying about the cutouts for the piston pin. If that pin is loose in the piston then it will gouge the cylinder over time.

Ron

Sorry Ron, I have a picture on my phone that I can now upload. But I think I might now better to answer your question without it. What I was reffering to by cutout, I think I can now say I believe I meant ports in the cylinder liner. There are three ports in the liner and what I meant is that the pin on the rear of the piston rides along the piece of steel between two of the ports. But the pin in the front of the piston is visable through the port, meaning that it is possible for the pin to slide forward out of the piston some. Also to be clear, the pin in front is only visable through the liner when it is out of the engine. When installed, I cannot see it. Sorry for being unclear as anything bigger than an .049 is still relatively new to me.

**Cribbs74** Tue Feb 12, 2019 10:48 pm

Remove the piston/rod and liner. Try pushing the piston through the liner to TDC and see if it goes smoothly. If it does then it’s not the piston or cylinder. If it doesn’t then check for burrs. Did you use tools to remove the liner?

Usually you jam wood in the exhaust port and use the piston to force the liner out.

If all that checks good, reassemble and try and rotate it through with the head off. If that goes ok re-install the head and torque the head in a cross bolt pattern. Don’t crank down on the head screws just good and snug.

Let us know how it goes.

Ron

NEW222 Tue Feb 12, 2019 10:56 pm

Thanks for the tips Ron. I will try those tips tomorrow as it is late now and am typing from bed..... However I can tell you this. The piston assy goes smoothly up until it gets just past the ports in the liner. That is then when it starts hanging up. Originally I used a pair of pliers to lift it out the first time when using lots of heat to remove it. I was very careful when doing so. Since then, I had not needed to use anything other than my fingers.

I will definately keep you posted tomorrow evening.

**Cribbs74** Tue Feb 12, 2019 11:24 pm

If you used pliers in the exhaust port to pry then there is a good chance you have a burr in the liner. Clean it thoroughly and look at the ports through a magnifying glass. It should be visible and can be carefully scraped away with a sharp blade.

Looking at those pictures the piston pin should be riding within the cylinder walls never to an open port. It may just be the piston is rotated in the liner.

When you reassemble make sure you align the exhaust port perfecty even in the case by eyeing the liner through the exhaust stack opening.

NEW222 Wed Feb 13, 2019 6:55 am

Yes I did use needlenose pliers to set the pin, but they were padded and did not actually touch the liner. After that was done, I did have the engine turning over as it should. Something went amiss during the last disassembly for the pictures. However, moving on. I could not sleep knowing something was wrong, so I got up last night to work on it. Together and apart a few times with no luck. Rolled piston around with calipers and all appeared good. Reassembled again and chucked it up with my drill and using oil, let it spin for a while. Apparently something happened as it is almost back to where it was. So as of now I will leave it assembled and run it. Fingers crossed and hope it gets nice out sooner than later so I can do it! I just want to hear it run.

crankbndr Wed Feb 13, 2019 7:14 am

Just curious does it look like its been run much?

NEW222 Wed Feb 13, 2019 8:43 am

Honestly I would not think so. There was a bit of castor varnish but not very much. I did look at the piston and cylinder upon first disassembly and it looked very nice. I did not look at it again after last night's episode, and quite honestly, I don't want to take it apart again to look. Very Happy

on another note, would anyone here happen to know the thread pitch of the head screws on this engine. I would like to but cap head screws for it. Thanks.

GallopingGhostler Wed Feb 13, 2019 9:23 am

NEW222 wrote:on another note, would anyone here happen to know the thread pitch of the head screws on this engine. I would like to buy cap head screws for it. Thanks.

3-48.

GWILLIEFOX Wed Feb 13, 2019 10:21 am

The exhaust port is slightly wider than 180 degrees. It is split by a bridge. When properly assembled, the cylinder bridge is behind the bridge in the exhaust stack. In this position EACH end of the wrist pin will be slightly covered by the liner and the pin can't move either direction.

I think you rod is twisted. Put the engine back together without the head. Look down at the piston baffle. It should be parallel to the crankshaft axis, not turned at all.

NEW222 Wed Feb 13, 2019 11:21 am

Thanks ghost for the info on the screw size. That is definately a big help.

GWILLOEFOX. Thank you for that excellent picture. I did not want to disassemble the engine again, but with your picture I really want to see. When I looked before, it looked like the rear end was completely behind the bridge as you call it, and the front totally exposed. However I do not feel I have this problem but will indeed check. If I also may ask, or tell. When i reinstalled the liner, i made sure to have the 'bridge' of the liner equally spaced between the 'bridge' in the exhaust port.

Thank you all for the comments and help. It is greatly appreciated.

GWILLIEFOX Wed Feb 13, 2019 12:26 pm

All good, but is the baffle parallel to the cranks axis?

NEW222 Wed Feb 13, 2019 1:35 pm

Without getting close and personal with a caliper, yes it is.

YakNine Wed Feb 13, 2019 2:04 pm

Are there any scratches in the piston? You also might have temporarily softened up some castor goo with your heat gun in the top of the bore and had it set back up get some penetrating oil in the cylinder to soften up the goo if you are sure there are no burrs and see if the piston moves more freely. if its a low time or un-run engine a thin bit of castor can easily cause the bind yet be hard to see, TJ

NEW222 Wed Feb 13, 2019 7:34 pm

Ok. Well another update! So, it does now spin free as it did before, however, with one little caveat. It did somehow lose a little bit of compression. This loss in compression is not scientific, but the 'pop' when turning over the propeller by hand appears to be a bit less than before. However, there still is a 'pop'. Thanks to the pictures by GWILLIEFOX, I now had something solid to go on. So, reluctantly, I did disassemble the engine for a LAST time... This was just to compare things from his pictures to the engine I have here. Here are 3 pictures of my piston/cylinder liner assemblies from the top, front, and rear. The top view, is marked with Sharpie marker inline with the baffle on the piston, and it was marked before disassembly so I could compare photos. I do now know and understand that the whole pin is not covered, but rather a small part of the edge to keep it in place. When re-assembling the engine, I did so by eye and lined up the exhaust side liner 'bridge' equally in the center of the bridge of the exhaust. I then compared such to my 'witness marks' that I made with the marker. Everything lined up perfectly. With that said, I would like to thank you all for your time, and help in this matter. I would also at this time like to apologize if I came across yesterday as being a bit harsh, as it was not done intentionally and I was just beating myself up over the engine not going together nicely. With that said, below are the pictures.

This is from the rear facing forward

This is from the front facing rearward

This is from the top, showing baffle and witness marks

Last thing to note. After comparing my parts to the pictures by GWILLIEFOX, I also turned my connecting rod around to match his as in his pictures.

Ken Cook Wed Feb 13, 2019 8:45 pm

When I take a Fox apart, I lay a piece of 400 on a piece of glass and flatten the back of the case. If the backplate is leaking due to a poorly mating gasket surface or loose screws it can play havoc. It can result in not running or shutting off not too mention the loss of compression your suggesting due to disassembly. Fox is notorious for poor castings and this not only trues it up but it can smooth out porosity flaws, scratches in the backplate from the rod rubbing can also be cleaned up. I also do the same with the liner by spending a little time sanding the surface where you placed your Sharpie marks. This can increase the compression a tad by assisting the seal from the head gasket. Put a prop on the engine and submerse the engine upside down in water and you can see if it's leaking. You can also check the backplate the same way. This is the reason I use Permatex anaerobic on backplates because many times Fox engines aside from the 4 bolt back plates and coffin back cases have little surface area to support the gasket which can squish it out when tightened.The .15X uses a very thin paper gasket which works ok but repeated removing can deform it.

If there's a Fox plug in that engine, it could also be a source of compression leak. Fox plugs can leak badly around the post where the insulator is. It may work and run and afterwards, the engine can feel as though there's no compression due to this leak.

NEW222 Fri Apr 26, 2019 3:15 pm

Well, it is officially time for an update. Today I finally caught up with stuff and it allowed me soem free time to run the Fox .15x I was gifted earlier this year. So I bolted up the engine on a plate and mounted it to my bench. I ran a standard 2-line tank from my air car to it using only one line, and the overflow open. I grabbed a piece of fuel tubing to the needle and adjusted it to what I thought was good. Filled the 4 oz tank with about 3 ounces. Primed the engine and 4 or 5 flips later, still nothing. Disappointed, yes. Then I grabbed my electric finger and field tote. Never charged the battery yet this year either so I tested it. Weak, but usable. I literally just touched the spinner, and off it went! Ran decent so tried playing with the needle. Thought it was rich, so I leaned it out. Engine died. Started again and richened it. Got ut gurgling, so turned teh needle back in a couple clicks. Let it run out the 3 or so ounces. First thing I realized is that this thing really sips the fuel. Forgot to time it, but was all of 10 minutes! I was using my standard 5% Omega fuel with a little added castor to bring the oil content up. I could run it with more nitro, but I am happy with it as it is for the flying I will be doing. I took it off the bench and cleaned it up so I can mount it on the Ringmaster Jr, which I will be doing shortly. The only other thing to note is teh temperature of the engine. Only a couple of minutes after running, the engine was cool to the touch. I could not really feel any heat anywhere. What that means, I do not know, but I have not had an engine cool like that after running before. Good, bad?

getback Sat Apr 27, 2019 8:53 am

The world of Fox engines , man i am happy it ran for you after all that !! Hopefully it will pay off when time comes to fly that bird ! Good job on the clean up ( pat on the back for U) Thumbs Up

GWILLIEFOX Sat Apr 27, 2019 9:13 am

Good job! The first time you ressurect a cast off is a milestone you'll long remember. Also, an 8 x 3 1/2 prop is the preferred size.

NEW222 Sat Apr 27, 2019 2:53 pm

Thank you for teh compliments. Also, thanks for the propeller recommendations. I read online 8 x 4, 8 x 6, while I could not remember which when I went to teh LHS, I settled on 8 x 5. Seems to have some good power with that propeller. However, next time at the LHS, I will look to see if they have 8 x 3.5.

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