jbloom

I've always used a 6" wrench to tighten the prop nut. Lastnight, while tightening the prop on my Super Tigre .90 I hear a loud pop. I investigate. I find that the drive washer has split. So what's your opinion? Was this a defective drive washer, or did I apply just too much elbow? I find it hard to believe that it broke without me getting a sense of over torquing. hehe.. I'm not a mighty dude!.. :-)

Flyboy Dave

My Feedback: (21)

My guess is that it was a rare instance where the cast piece just plain broke
from having torque applied to it. Add to that, just because of the washers size
it could be argued that the design could lend itself to the type of failure.

Who knows....you might just be having a bad day.

FBD.

aussiesteve

I had an identical failure on the drive washer of my ST51 last year. - also Tightening the washer with very little leverage (I use the correct sized spanner which is about the same length as a 6" adjustable). As a Professional Engineer who started his working life as a mechanic - I am certain that I had not over torqued the nnut.

I had a lot of trouble getting the part from the ST agents in Australia so I eventually contacted ST via their website - they were excellent and provided me with a new washer very quickly (In my case the engine had only run for a couple of tanks of fuel and I was changing the prop to a better one for the model).

I suspect that there may be either a design QA/QC issue with these items as mine also cracked through the web instead of between the webs where you would expect the failure to occur. Maybe thay need a normalising process in the production of the part.

Kostas1

[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFZ47&P=7]Take a new one from Tower![/link]

MMM,just buy a new one from Tower and don't make "big" thoughts for what resulted in this failure!

Dr1Driver

Let's see...tapered brass collet on a hardened steel shaft with a cast AL piece being tightened down over it. Something's gotta give if it's too tight, and it did. Given the number of times it happens (almost never?), I'd say mark it down to stuff happens.

Dr.1

William Robison

My Feedback: (3)

Cast washer with a centering cone? What is surprising is that there are not more failures. Most manufacturers using a centering cone have fully machined drive washers, much stronger.

Bill.

Dr1Driver

Good point. Webra has used machined drive washers for years.

Dr.1

William Robison

My Feedback: (3)

Saito and K&B are two others using machined drive washers on a centering cone.

Bill.

w8ye

My Feedback: (16)

I had a Saito 91 drive washer do the same thing. It split right where the seam in the collet was.

Enjoy,

Jim

William Robison

My Feedback: (3)

Jim:

That's a new one to me. I've never seen a Saito washer fail, except in a crash.

Bill.

William Robison

My Feedback: (3)

Addendum to my last - The washer failure was distortion, not a crack.

So I've still not seen one split.

Bill.

w8ye

My Feedback: (16)

I got the Saito 91 used and the washer was cracked upon inspection. I had figured that it actually happened in a crash.

Enjoy,

Jim

jbloom

The new one is on order from Tower.. Cost was $5.49 and $15.99 to make sure I have it by the weekend.. :-) I checked the LHS's in the area, and none of them had it in stock.. soooooo

At least I'll get to fly!

Kimhoff

My Feedback: (22)

Since I am not an ST fan, for that kind of money I think I would have tossed it in the trash and bought another brand. Tower hobby engines are much superior to the ST line!

bigchap

i had a super tigre one break on me but didn't realise,my engine kept spitting props and it took ages to figure it out,the crack was barely visible.

jbloom

I've heard both sides of the fence. It seems folks either really like the ST, or they hate it. I'm a big fan of Super Tigres. Though I'll admit I've had to tinker with this a bit more than usual. I got it used, so I don't know what it's history has been. I got rid of the ST carb and put an OS 7D on it. That seems to have cleaned up a lot of the midrange issues it was giving me. I have a G51 that I bought new and broke in using the steps in the manual. It fires up with the first pop of the starter, and isn't shy about jerking my Thrush around the skies. So spending the extra money on shipping wasn't such a big deal for me. I can't think of a better engine $21.00

w8ye

My Feedback: (16)

Back before the Italian Super Tiger factory shut down, my area was Super Tiger country. Everyone had them.

I think the Super Tiger carb is one of the better ones made.

Enjoy,

Jim

Flyboy Dave

My Feedback: (21)

My S.T. carbs have been great....set and forget. All but the one on the 3000.
It was a tiny little thing, it looked like it came off an old .35 []. I never even
tried it, I put a Magnum 1.08 carb on it straight away.

FBD.

cessna098

Attached is a picture of the broken drive washer on a ST .51. The engine is new. Put a prop on it for the first time using just a 4-way prop wrench and the drive washer split. This is a Chinese made engine and the drive washer is cast aluminum. A fellow club member has an older Italian made ST .51 and it's drive washer is machined. I called TOWER and they directed me to their warranty people. I received a free replacement drive washer 2 days later.
Dennis

DarZeelon

JBloom,


Since you still have the packaging, I would guess this engine is quite new; well within the ST warranty period.

So I would guess you just threw away $21.48, for something that was supposed to cost you nothing flat...


MVVS uses machined drivers that resist ham-fisted modelers.

In previous engine versions that had a 6 mm crankshaft thread; it was the shaft that broke from such 'treatment' (and replaced outright under warranty) and never the prop-driver.

jbloom

Actually, the drive washer came from the .90. It wasn't new, it was used. I've had that engine for about a year now. It had been sitting in the garage of a club member who'd pass away for three years before I got it. When I got it, it was siezed. I cleaned it, lubed it, replaced bearings and started flying it. So there isn't any warranty to speak of on that engine. So no, I didn't throw away $21.48.

The new engine I spoke of is my ST .51.

Sorry for the confusion.

DarZeelon

I got it, JBloom.

I confused the box in Cessna's post (.51) with your .90. I was wondering why the .51 box is in the photo...

Actually this type of breakage is not from torque, but from tension.
Applying torque to the prop-nut 'stretches' the prop driver on the 'growing' diameter of the lock-collet, as the prop driver goes further up on its taper.

When the collet is a non-locking type, with a less shallow angle, the forces are less likely to stretch it enough to cause it to split.

downunder

Ahhh....I see you have the CL version

I bought mine (also CL) back in May '95 and it's got the cast drive washer. My even older S45 also has a cast driver...at least as far as I can tell, I can't get the driver loose but it's got the same drive ribs which are definitely cast and not machined.

If you're going to use yours for CL stunt then rest assured, you've got one of the very best stunt engines available unless you go exotic with Jett or Nelson

DarZeelon

Brian,


Have you, by any chance, tried the MVVS #3077A Akrobat C/L Stunt engine lately?

cessna098

Yep. I'm using my ST .51 for control line. It's in a Pathfinder and hauls it effortlessly in a steady 4 stroke through the entire pattern. Even in a slow, steady 4 stroke it pulls hard and maintains good line tension even in the wind.

Unlike my other ST engines (older ST .60 RC blue heads), this engine does not have killer compression. Without a prop mounted I could not turn the older ST engines over by hand. But I can turn this .51 over by hand easily. Because of similar weak compression, a fellow club member sent his Chinese ST .51 CL engine to Frank Bowman. When he got it back (with a new ring and the cylinder mated to the case) it had GREAT compression. I'm jealous.

Dennis