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Author Topic: ST G21 .35 crankshaft removal  (Read 2327 times)

Offline Ron Cribbs

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ST G21 .35 crankshaft removal
« on: January 22, 2019, 09:14:42 PM »
Installing a Brian Gardner ABC piston cylinder set. Need to ream the connecting rod bushing to fit the crankpin.

It would be much easier to check the fit with the crank removed from the case. Having never removed an ST crank before it appears to have a tapered fit into the drive plate/dust cover. Do I press it off or tap it out with a hammer?

Thanks for any help.

Ron
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Online Brett Buck

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Re: ST G21 .35 crankshaft removal
« Reply #1 on: January 22, 2019, 10:17:11 PM »
Quote from: Ron Cribbs on January 22, 2019, 09:14:42 PM
Installing a Brian Gardner ABC piston cylinder set. Need to ream the connecting rod bushing to fit the crankpin.

It would be much easier to check the fit with the crank removed from the case. Having never removed an ST crank before it appears to have a tapered fit into the drive plate/dust cover. Do I press it off or tap it out with a hammer?


  Neither! It does have a standard tapered split ring connection to the shaft.

    Go down the auto parts store, and get a battery terminal puller. Grind the ends sharp and with a radius to reach around and grab the back edge of the washer, and tighten it down on the crankshaft to put tension on it. Tap the screw on the puller and it will pop right off.

     Brett


viz.:

« Last Edit: January 22, 2019, 10:44:38 PM by Brett Buck »
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Offline Ron Cribbs

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Re: ST G21 .35 crankshaft removal
« Reply #2 on: January 22, 2019, 10:17:42 PM »
Quote from: Motorman on January 22, 2019, 09:46:55 PM
If you have the drive washer that is a dust cover and has no gap then you can set the back of the case on a flat metal surface, put the prop nut flush with the end of the shaft then give it a light tap with a soft metal hammer. Sometimes they pop right off. If not you can quickly heat it for 5 sec with a torch and give it a tap. Beyond that you need special tools that grip the drive washer to press it off which is the preferred method because hammering on it will hurt the ball bearings. If you want to send it to me I can put it together for you. I also have the metric reamers and hones for SuperTiger because I use to race them. just pay shipping.

Motorman 8)   

Thanks Motorman, I appreciate it. I got impatient waiting for a reply and went out and put it on the bench press and it popped right off. No damage whatsoever. Bushing is now reamed and engine reassembled. I just wasn’t sure if the crank was pressed into the bearings or just the prop driver. I certainly appreciate your offer though.

Ron
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Offline Ron Cribbs

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Re: ST G21 .35 crankshaft removal
« Reply #3 on: January 22, 2019, 10:20:57 PM »
Quote from: Brett Buck on January 22, 2019, 10:17:11 PM
  Neither! It does have a standard tapered split ring connection to the shaft.

    Go down the auto parts store, and get a battery terminal puller. Grind the ends sharp and with a radius to reach around and grab the back edge of the washer, and tighten it down on the crankshaft to put tension on it. Tap the screw on the puller and it will pop right off.

     Brett

Good idea, I’ll know that for next time. I appreciate it.
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Offline Steve Helmick

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Re: ST G21 .35 crankshaft removal
« Reply #4 on: January 23, 2019, 11:32:30 AM »
Having been inside a bunch of various Super Tigres (G.15, G.21 .29rv, G.21 .29FI, G.21 .35 & G.65rv), I've never had a problem doing it exactly per Motorman's first method. Nut flush on the threads, backplate gasket surface on a scrap of wood, and a sharp tap on the end of the crank with a soft mallet. Done deal. When re-installing the crank, make certain that it's fully seated against the rear bearing. It's so easy a caveman can do it!  y1  Steve
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Online Brett Buck

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Re: ST G21 .35 crankshaft removal
« Reply #5 on: January 23, 2019, 11:43:59 AM »
Quote from: Steve Helmick on January 23, 2019, 11:32:30 AM
Having been inside a bunch of various Super Tigres (G.15, G.21 .29rv, G.21 .29FI, G.21 .35 & G.65rv), I've never had a problem doing it exactly per Motorman's first method. Nut flush on the threads, backplate gasket surface on a scrap of wood, and a sharp tap on the end of the crank with a soft mallet. Done deal. When re-installing the crank, make certain that it's fully seated against the rear bearing. It's so easy a caveman can do it!  y1  Steve

  But you are pounding on the bearings! The pressure you are using to push off the cone/washer comes from the inner race pushing on the cone, and if it is at all tight, that load is a shock load across the bearing interface. Even worse, since you are pushing it along a cylindrical surface - your are not necessarily removing the force holding it on.

    In those conditions it should be discarded from presumed damage. It would be the same as using a press on the inner race to press-fit it on the outer race, that is just never done, or if you do, you toss all the bearings and get new ones.

     Brett
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Offline Ron Cribbs

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Re: ST G21 .35 crankshaft removal
« Reply #6 on: January 23, 2019, 02:14:12 PM »
So, seeing how it is assembled now I understand what Brett is saying. Even Motorman said the proper way is to use a puller.

That said, I was lucky in that this was a NIB never taken apart so it took very minimal pressure to slide the cone off the nose of the crank. Had it been a used, heat cycled and castor locked engine it would have taken a lot more pressure or hammering to separate the taper lock collar from the driveplate. The safe bet is to use a puller.

I also think that experience is key in not destroying things so I am willing to bet since Steve has done it many times he probably knows how much force he can get away with.

I really appreciate all the advice guys. Just need to break this thing in now!

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Offline Jim Kraft

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Re: ST G21 .35 crankshaft removal
« Reply #7 on: January 23, 2019, 06:16:03 PM »
I have put them in a vice with a block of wood on the back of the case and a block on the crank, and push them off. There again, it does put pressure on the bearings, but I have yet to have them give trouble doing it that way. The pullers are the best way to go though. I have several different sizes, and the battery terminal type work well.
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Offline Steve Helmick

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Re: ST G21 .35 crankshaft removal
« Reply #8 on: January 23, 2019, 08:07:47 PM »
Better to smack it into the ground than to give it a tap with a soft mallet or a 12" long piece of 2x4?  LL~ Steve
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Online Brett Buck

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Re: ST G21 .35 crankshaft removal
« Reply #9 on: January 24, 2019, 01:08:04 AM »
Quote from: Steve Helmick on January 23, 2019, 08:07:47 PM
Better to smack it into the ground than to give it a tap with a soft mallet or a 12" long piece of 2x4?  LL~ Steve

   You replace the bearings after you crash it, usually, too.

     Brett
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Offline Peter in Fairfax, VA

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Re: ST G21 .35 crankshaft removal
« Reply #10 on: February 08, 2019, 08:56:25 AM »
Having stuffed G21/.35s many times in combat competition, disassembly of this engine is something I've encountered.

The battery terminal puller works well for the drive washer, as others point out.

The stock rear crank bearing is weak. A replacement 3L01 bearing, or a 773L01, such as a "New Departure," is better.

To remove the rear bearing, first remove the crank.  Then heat the case in an oven to 225 and tap the rear of the case onto a block of wood.  The bearing then falls out.

Though it is true you can use a torch for a variety of purposes, the even heat of an oven is less likely to damage the engine.

Good luck with your classic engine,

Peter
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Offline Paul Smith

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Re: ST G21 .35 crankshaft removal
« Reply #11 on: February 08, 2019, 09:28:57 AM »
In the past I used a Benz-O-Matic torch. 
But now I just use an electric heat gun.  It heats up engines all you need to drop out the bearings, with a lot less risk.

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Paul Smith

Online Howard Rush

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Re: ST G21 .35 crankshaft removal
« Reply #12 on: February 09, 2019, 01:23:07 AM »
I've done this a lot. I recommend Brett's and Peter's advice. 

I now suspect that what was breaking the tabs off the brass bearing retainers was nitro weakening the brass.  The threshold was somewhere between 30% and 40% nitro.  Engines that ran happily on 30% would fail with one run of 40%. 
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Offline Paul Smith

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Re: ST G21 .35 crankshaft removal
« Reply #13 on: February 09, 2019, 06:50:57 AM »
The nitro acidity is an interesting theory.

I assumed the engine failure was related to simply getting more power out of the engine.

When running the Cox Conquest my theory proved out.  Based on tachometer and stopwatch readings, successful power enhancements reduced the lifespan from 100 runs to single digits.
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Paul Smith

Online Brett Buck

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Re: ST G21 .35 crankshaft removal
« Reply #14 on: February 09, 2019, 10:31:38 AM »
Quote from: Paul Smith on February 09, 2019, 06:50:57 AM
The nitro acidity is an interesting theory.

   I am not entirely sure it is acid (probably, but...), but brass reacts *very poorly* to glow fuel, it just falls apart after a while. Steel is no great shakes, either, old tin-plated steel tanks corrode from the inside. I saw about a 30-year-old tank recently, used normally, that developed a bunch of pinholes, dozens of them. We would fix one with an external patch, and two more would form.

     Brett
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