Binding Piston Solution. Re Enya

Hi

In some previous posts, there was some discussion about enya sleaves distorting and binding on the piston when the head was tightened down.
I should add, this has been experience by several on new or vertually new engines that have NOT been flown, crashed or abused in any way.

The discussion seemed to point to a very slight machining error in the sleaves. As these enyas have a one piece cylinder/crankcase, the sleave can not tilt (due to it's close fit in the cylinder) to accomodate any error in the seat or sleave face. Any error results in the sleave face contacting the seat on one side only. The pressure of tightening the head even moderatly, distorts the sleave out of round to bind on the piston.

A solution one person found, wast to true up the sleave on a lathe.
This is not an option for most of us however so the following is what I did.

I lapped the sleave into it's seat with a very small amount of fine valve grinding paste. If I hade to do this again, I would try a finner abraisive like pumice pre polish powder from a lapidary store.
I applied a very small amount of paste to the sleave seat, wiped most of it off to avoid (as much as possable) getting the grit between the sleave and cylinder. Then pressed the sleave down onto the seat in its correct port orientation. I took a vernier caliper measurement of the hieght of the sleave above the cylinder top.
Then gently rotated the the sleave back and forwards by small incriments either side of it's correct port orientation.
Constantly checked the port orientation and remeasured the sleave protrusion above the cylinder. Continued to lap in until the sleave had settled into the seat by 0.1mm (.004 inches).
Dismantled and cleaned up , flushed, cleaned, flushed. Did I say cleaned and flushed all of the paste out of the motor. Oiled and reasembled the conrod, piston sleave cylinder and head.

Nipped the head down nice and tight and tested the piston movement with plug removed. piston sliding nicely with no tight spots or resistance.

SO SUCCESS!!!!

Reassembled my son's motor and have run it a few times without problems. So happier now and running in continues.....

This is a big relief to me as I thought I had ruined his motor by taking it apart. So many many thanks to those who contributed in previous discussions that led to correctly identifying the problem.

Ps. The reason I took it appart was to investigate bubbles forming in the slot between head and cylinder. Turnes out that fuel was leaking from the crankcase, between sleave and seat, migrating up between the sleave and cylinder to boil out under the head.

Thanks for sharing this solution. I hope non of my Enya 15s has that problem.

LAST EDITED ON May-17-04 AT 12:39 PM (CDT)
 
Ken,

Good going! You may also find that truing the cylinder flange and main casting fit cures that 'bubbling up.'

Another tip: pay attention to headbolt torquing sequence. I use a triangular pattern on six-bolt heads, sort of a star of David pattern.

Looking at the head with prop at "12 o'clock" -- some engines have bolts at 12, 2, 4, 6, 8, and 10 o'clock, others at about 11, 1, etc.

Pick a "12 o'clock" bolt to start from. Turn it in until it just starts to tilt the head, then back out a bit. Skip to the "4 o'clock" bolt and do the same. Then to the "8 o'clock" bolt.

Then go across the head to the "2 o'clock" bolt, then the "6 o'clock" and the "10 o'clock." Each time you've turned all six in some, check that the shaft and piston still move as freely as before.

Continue the sequence (e.g., from the "10 o'clock" to the "4 o'clock" and so on) with small, equal turns of (the driverpreferably an Allen key in socket head bolts -- easier to see your progress).

If uneven torquing shows as slight binding, back out each bolt a quarter turn or so and try again.

The head bolts don't need enormous torque. For example, a strong, but comfortable effort on the short side of an Allen key should be enough. If they're loose, you'll see some blowby when you run it next. Run the engine just enough to get it thoroughly warmed up. Let it cool COMPLETELY, and check whether headbolts have loosened at all. If so, use the above sequence to snug them in.

>Ken,
>
>Good going! You may also find that truing the cylinder
>flange and main casting fit cures that 'bubbling up.'
>
>Another tip: pay attention to headbolt torquing sequence. I
>use a triangular pattern on six-bolt heads, sort of a star
>of David pattern.
>
>Looking at the head with prop at "12 o'clock" -- some
>engines have bolts at 12, 2, 4, 6, 8, and 10 o'clock, others
>at about 11, 1, etc.
>
>Pick a "12 o'clock" bolt to start from. Turn it in until it
>just starts to tilt the head, then back out a bit. Skip to
>the "4 o'clock" bolt and do the same. Then to the "8
>o'clock" bolt.
>
>Then go across the head to the "2 o'clock" bolt, then the "6
>o'clock" and the "10 o'clock." Each time you've turned all
>six in some, check that the shaft and piston still move as
>freely as before.
>
>Continue the sequence (e.g., from the "10 o'clock" to the "4
>o'clock" and so on) with small, equal turns of (the
>driverpreferably an Allen key in socket head bolts -- easier
>to see your progress).
>
>If uneven torquing shows as slight binding, back out each
>bolt a quarter turn or so and try again.
>
>The head bolts don't need enormous torque. For example, a
>strong, but comfortable effort on the short side of an Allen
>key should be enough. If they're loose, you'll see some
>blowby when you run it next. Run the engine just enough to
>get it thoroughly warmed up. Let it cool COMPLETELY, and
>check whether headbolts have loosened at all. If so, use the
>above sequence to snug them in.
>
>

Ron B.
F4Fguy

Lou:

Go to the head of the class!

Got there before me.

>
>I lapped the sleave into it's seat with a very small amount
>of fine valve grinding paste. If I hade to do this again, I
>would try a finner abraisive like pumice pre polish powder
>from a lapidary store.

Ken;

You can also use Crest or Colgate toothpaste (not the gel, but the chalky texture variety) It will cut the aluminum as well.

Well done Ken, we all knew you could do it!. Many years from now when your son's son is trying out his first U\C model using that very same Enya 15-5 you can say with much pride "yea I hand lapped that engine".

"Good on yer Mate"

Just looked at the instructions for the current production SS25 CL Enya, there were just 2 items regarding maintainence: "do not disassemble for the pure hell of it", and : "do not over torque headscrews". Ok, I paraphrased the first item. Don