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Author Topic: ST 46 G21 Question  (Read 1292 times)

Offline Dick Pacini

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ST 46 G21 Question
« on: May 17, 2010, 07:34:19 PM »
My son recently returned my 1974 Supertigre 46.  It had never been run until 2000 and then only 6 flights.  He took it apart part way and did the anti-freeze/crockpot gig and it looks like new.

In the original box, along with a whole bunch of needle valves, spraybars and venturis was a plastic bag with a small headed screw that has the screwdriver slot wallowed out.

I observed a tapped hole on the backside of the cylinder/crankcase that is obviously the home for this screw, which probably is for wrist pin access. I tried to install it but it only went in a couple of turns. 

I called my son and asked and he said he removed it during teardown, but couldn't budge the sleeve, so it went in the pot with the sleeve still in.  When the cooking was over, he attempted to replace the screw but it wouldn't go.

Any idea what happened?
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Offline Jim Kraft

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Re: ST 46 G21 Question
« Reply #1 on: May 17, 2010, 08:12:00 PM »
I don't know why you can not get the screw back in, unless while cooking it got some crud in the threads. A little heat from the heat gun, and a glow plug gasket on top of the piston slid into the exhaust port, and turning the engine over slowly, will push the sleeve out. Then, if you are unlucky like me, you will not be able to pull the wristpin out of the hole in the case. What I did was to drill a hole in the front of the case inline with the rear hole, to have a place to push the wristpin out from the front. That dude was tight. I had crockpoted it, heated it, and just could not get it out. The engine had been setting for a number of years. I did get it out, and then tapped the front hole for a 6-32 screw. I destroyed the pin pads in the process, but made some new ones out of some stock that I got from Scott Riese for my McCoy's.

Back to your screw problem, I would look closely at the threads on both the screw and the case. You may be able to clean them up enough to get it back in. Good luck
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Jim Kraft

Offline Dick Pacini

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Re: ST 46 G21 Question
« Reply #2 on: May 17, 2010, 09:14:39 PM »
Quote from: Ty Marcucci on May 17, 2010, 07:39:44 PM
Yes, he broke it  LL~  Send it to Tom Lay.  He has done 10 for me. New bearings, hardened sleeve and rings, new venturi, much more powerful than the old ST .46 stock engines.  H^^

Well, just so you don't get the wrong idea about my son, Tony, he has been an extremely successful RC Pylon Racer for years.  His whole family flies and his teenage son set a national record a couple of years ago.  My son has done extensive construction with carbon fiber and has even had his process published on the web.  He has had engine manufacturers send him new products for testing and evaluation.  He and his wife also own a hobby shop in AZ.  He has been in and out of model airplane engines countless times.

That being said, the threads appear clean on both parts...and, if I may add, I have been involved in manufacturing and machining most of my working life, last owning a contract turning shop for 21 years.  Threads are not a mystery to me.

I am just trying to figure out if the crockpot process had any effect on these parts.
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Offline Jim Kraft

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Re: ST 46 G21 Question
« Reply #3 on: May 17, 2010, 09:27:17 PM »
Dick; I do not know of anything the crockpot and antifreez would do, but you never know I guess. I imagine you have tried a little lube on the threads, as sometimes the crockpot will leave the metal extremely dry. Other than that I do not know. I can not remember if the screw is aluminum or not. I bet you will get it figured out. I did crockpot my Tigre 46, and had no problem like that.
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Offline EddyR

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Re: ST 46 G21 Question
« Reply #4 on: May 18, 2010, 06:36:16 AM »
Dick    Changed my answer as I miss read your question. The wrist pin hole can be left open.
 Also when removing the piston and sleeve do not remove the sleeve all the way before removing the wrist pin. The sleeve will hold the piston in place till the pin is removed. One of the most common problems with the ST/40-46's is a frozen wrist pin. Common complaint I hear "is the motor just doesn't have much power"
Ed  Note I changed the first line
« Last Edit: May 18, 2010, 09:07:23 PM by Ed Ruane »
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Offline Paul Smith

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Re: ST 46 G21 Question
« Reply #5 on: May 18, 2010, 07:58:13 AM »
If you'r not entering the engine in a beautyt contest, you could jist dispense with the buggered-up wrist pin screw and plug the hole with epoxy or silicone.  I've done that on smaller G21's where the hole isn't even needed to disassemble the engine.
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Paul Smith

Offline Air Ministry .

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Re: ST 46 G21 Question
« Reply #6 on: May 22, 2010, 04:05:33 AM »
Try a drop of oil.

Inspect threads under Magnifying eye glass.

An 'ezy out' if the pins hollow  would beat a jack hammer .
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