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Author Topic: Sick Tower 40 -- bent rod?  (Read 3160 times)

Offline Tim Wescott

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Sick Tower 40 -- bent rod?
« on: April 03, 2016, 01:24:11 PM »
So, my wife and I are now crashing and learning together, her because she's a beginner and me because I find myself suddenly left handed.

She put a Tower 40 nose-first into the ground last week.  It's got a peculiar problem.  In the shop, when there's just oil in it, it flips over nicely and feels just fine.  In the field, when I put a prime in it, it binds at the top of the stroke.

I just took it to the field for the second time, thanks to the "feels fine if it's just full of oil" bit.  The first time my flying buddy diagnosed a bent rod -- now I'm wondering if that's it, or if it's something else.

I'm going to be taking the engine apart soon -- what should I be looking for?  Does anyone have any suggestion (other than a liberal application of fuel to things I'm checking) to bring the problem to light in the shop?

Thanks in advance.
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #1 on: April 03, 2016, 06:10:19 PM »
New information:

I disassembled the engine (it's in the crock pot now), and saw nothing wrong with anything -- no unusual scuff marks or bits of dead animals in the bearings, etc.

What I did notice was that the piston seems to have an excessively tight fit in the upper liner -- if I got a brand-spanking new ABC engine I'd think it was somewhere between normal to a bit excessive.

This is an engine that's run just fine for me for years.  There's no scuff marks on piston or sleeve, there's no sign that the plating is peeling off, etc.  All I can think of is that the sudden cool-down from the crash affected it somehow -- she did bury the nose in nice soft damp dirt when it was last flown.  But it doesn't seem like that would be enough to mess things up.

So -- advise?  I think in the absence of any suggestions I'll probably see if I can "break it in" and end up with an engine that's usable (on the theory that the only thing I can break is the P&L), at the same time that I go looking for a new piston & liner on eBay.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline RandySmith

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Re: Sick Tower 40 -- bent rod?
« Reply #2 on: April 03, 2016, 08:47:59 PM »
Quote from: Tim Wescott on April 03, 2016, 06:10:19 PM
New information:

I disassembled the engine (it's in the crock pot now), and saw nothing wrong with anything -- no unusual scuff marks or bits of dead animals in the bearings, etc.

What I did notice was that the piston seems to have an excessively tight fit in the upper liner -- if I got a brand-spanking new ABC engine I'd think it was somewhere between normal to a bit excessive.

This is an engine that's run just fine for me for years.  There's no scuff marks on piston or sleeve, there's no sign that the plating is peeling off, etc.  All I can think of is that the sudden cool-down from the crash affected it somehow -- she did bury the nose in nice soft damp dirt when it was last flown.  But it doesn't seem like that would be enough to mess things up.

So -- advise?  I think in the absence of any suggestions I'll probably see if I can "break it in" and end up with an engine that's usable (on the theory that the only thing I can break is the P&L), at the same time that I go looking for a new piston & liner on eBay.

You can clean it all up, use a brake cylinder hone to put a scuff on the cylinder sleeve, try to spin iy one direction while moving for and aft, then put it in the other end and spin doing the same thing, you should ends up with a cross hatch...spin marks that spiral in both directions up and down, and cross each other, this should just be a light scuffing, and should break the very shiney surface up.
Then run it in

Randy
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #3 on: April 03, 2016, 09:03:39 PM »
Quote from: RandySmith on April 03, 2016, 08:47:59 PM
... use a brake cylinder hone to put a scuff on the cylinder sleeve ...

I don't know why I'm sitting here trying to scare myself out of doing that when the engine isn't usable as-is.  Particularly because it sounds sensible.

Do you know any reason why this would happen?  I'd hate to trash the engine fixing the wrong problem.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Fitton

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Re: Sick Tower 40 -- bent rod?
« Reply #4 on: April 04, 2016, 02:55:46 AM »
Hopefully the crock pot cleaning fixed it.  It sounds exactly like what my FPs and Fox 35s would do when they had a bunch of castor varnish:  flip over fine until they were primed, then suddenly bind up and not be startable.  Crockpotting fixed it and switching to powermaster kept it from coming back.
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #5 on: April 04, 2016, 10:19:53 AM »
Quote from: Steve Fitton on April 04, 2016, 02:55:46 AM
Hopefully the crock pot cleaning fixed it.  It sounds exactly like what my FPs and Fox 35s would do when they had a bunch of castor varnish:  flip over fine until they were primed, then suddenly bind up and not be startable.  Crockpotting fixed it and switching to powermaster kept it from coming back.

You give me hope.  I'm still a bit worried because it started up quite suddenly -- there was no hint of it pre-crash, and then post-crash it's a Big Problem.  We'll see what it's like when it comes out of the crock pot.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Phil Krankowski

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Re: Sick Tower 40 -- bent rod?
« Reply #6 on: April 04, 2016, 10:28:39 AM »
Before you hone it, remember that the plating is very thin.

I would bench it at home, heating the head and top of the cylinder with a heat gun for a few minutes and get it to run like an excessively tight break in.  If it did "shrink" with a sudden chill the it probably will loosen up with a couple good hot runs on the bench.

Hope it is just varnish and the cleaning sets it straight.

Phil
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Offline RandySmith

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Re: Sick Tower 40 -- bent rod?
« Reply #7 on: April 04, 2016, 11:59:48 AM »
The plating is very very thin on the OS FP AND LAs,
  The plating on the Tower 40 is  NOT thin, and is real hard chrome,
 but your not going to be honing it for so long that you grind thru the chrome, don't worry, just do it long enough to scuff the sleeve in a spiraling manner in both directions. should take no longer than about 20 to 30 seconds , each directions, make sure to check the fit, after cleaning, and before honing
Randy
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #8 on: April 04, 2016, 12:16:44 PM »
Quote from: RandySmith on April 04, 2016, 11:59:48 AM
The plating is very very thin on the OS FP AND LAs,
  The plating on the Tower 40 is  NOT thin, and is real hard chrome,
 but your not going to be honing it for so long that you grind thru the chrome, don't worry, just do it long enough to scuff the sleeve in a spiraling manner in both directions. should take no longer than about 20 to 30 seconds , each directions, make sure to check the fit, after cleaning, and before honing
Randy

Just out of curiosity -- does the honing make it so that the sleeve will take wear from the piston, so that the piston will be worn by the sleeve, or a bit of both?

I'm hoping that crock-potting it will make it magically better.  I'm not making any bets, mind you, but I'm hoping.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline RandySmith

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Re: Sick Tower 40 -- bent rod?
« Reply #9 on: April 04, 2016, 03:15:58 PM »
Quote from: Tim Wescott on April 04, 2016, 12:16:44 PM
Just out of curiosity -- does the honing make it so that the sleeve will take wear from the piston, so that the piston will be worn by the sleeve, or a bit of both?

I'm hoping that crock-potting it will make it magically better.  I'm not making any bets, mind you, but I'm hoping.

Hi Tim

the crosshatch cut into the sleeve facilitates the break in process, where the piston beds into the sleeve making for a good fit, without it, trying to wear into a slick shiney sleeve is hit or miss, and would take way longer.
By the way, the process is the same for a ring engine, the ring needs that surface to wear properly into the sleeve

And  remember, you want some interference fit at the top of the stroke between the piston and sleeve

All I have told you   ONLY applies  to a  round un-damaged part, if you have dented sleeve  or piston  case   none of this will wwork

Randy
« Last Edit: April 04, 2016, 05:31:30 PM by RandySmith »
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Offline bob whitney

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Re: Sick Tower 40 -- bent rod?
« Reply #10 on: April 04, 2016, 04:14:00 PM »


  sounds like u could have hit hard enough to slightly bend the case and sleeve. is the shinny spot on the front of the sleeve??
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #11 on: April 04, 2016, 04:33:04 PM »
Quote from: bob whitney on April 04, 2016, 04:14:00 PM

  sounds like u could have hit hard enough to slightly bend the case and sleeve. is the shinny spot on the front of the sleeve??

No scuff marks.  The sleeve is bright and shiny up to the top of the piston stroke, & then it's dull.  There's all sorts of marks on the outside of the sleeve, but that's from sitting inside a well-used engine.

When I said "damp dirt" I mean dirt that's just this side of mud.  Our field is very forgiving to accidents this time of year.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline RandySmith

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Re: Sick Tower 40 -- bent rod?
« Reply #12 on: April 04, 2016, 05:32:39 PM »
Quote from: Tim Wescott on April 04, 2016, 04:33:04 PM
No scuff marks.  The sleeve is bright and shiny up to the top of the piston stroke, & then it's dull.  There's all sorts of marks on the outside of the sleeve, but that's from sitting inside a well-used engine.

When I said "damp dirt" I mean dirt that's just this side of mud.  Our field is very forgiving to accidents this time of year.

Are there  any plier  marks  on the top of the sleeve?

Randy
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Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #13 on: April 04, 2016, 06:15:35 PM »
Quote from: RandySmith on April 04, 2016, 05:32:39 PM
Are there  any plier  marks  on the top of the sleeve?

Randy

No.  I know better, and to the best of my knowledge the only other person who's had it apart is Mike Haverly: I would trust him more than I trust me.
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Sick Tower 40 -- bent rod?
« Reply #14 on: April 04, 2016, 09:00:07 PM »
Works.  Thank you all.  I just dragged it out of the crock-pot, cleaned it, and reassembled.  It all fit right, the piston fit now feels exactly right, and I've run a couple of ounces of fuel through it with no incident.

Steve, you seem to have nailed it.  The piston had considerable varnish on it, which scrubbed off after crock-potting.  I'm still mystified at why it showed up so quickly, but the problem seems to be fixed.

Randy, thank you for your help.  I didn't need it this time, but I'll keep in mind that you do the same thing for ABC engines as regular old car engines when you want to mess with the fit.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

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