retransit

My Feedback: (18)

Tom, what's your source for the E-clips?

Bob

Kmot

My Feedback: (24)

I dug out my factory original link pins and measured them. The diameter of the pin is 6.5mm and the diameter of the area the C-E-Circlip goes is 4.0mm.

Rev, it's all good. Like frets24, I normally refer to them as circlip's myself.

Bob, that page is from McMaster-Carr. http://www.mcmaster.com/#e-clips/=jipm50

I re-used my circlip's also, and ran the engine several times, as seen in the videos I made. I probably got lucky in that they did not fail.

I currently have my engine mounted on my test stand, ready to run with the new Olivier R.I.M. manifold. But I think it would be better to be safe than sorry. So I am going to order the new e-clip's from Mcmaster and pull down my engine and replace them.

frets24

My Feedback: (15)

The more I ponder the spiro-lox clip the more I'm liking the idea. They would be tedious to take off once installed but, they would not create the 3 point contact stresses like the e-clips. Maybe by spreading the retaing stresses equally around the entire suface of the ledge on the pin there would be less chance of having the ledge chip and fling clips and other debris through the engine. Installation and removal would be very much like installing piston rings.

Thoughts, ideas?

Or maybe this type.....just brainstorming here.

It seems the e-clips are problematic. Is it possible that in a position where the clip opening is centermost(pointed toward the crank/propshaft center) that the centrifugal force can cause them to dislocate. At 7k rpm even a small weight can create a sizable force/moment.

retransit

My Feedback: (18)

Quote:

ORIGINAL:

Tom, the Sonic/McDaniel unit I have says to use a 4.8 volt NiCd pack. They do not recommend any other chemistry. I'm using a 4500 mah D-cell @ 17.2 ounces. It lasts my usual three flights with it set at 50% of throttle. Occasionally a cylinder will drop out and I reduce throttle, when safe, to pick up the igniter.

Bob

retransit

My Feedback: (18)

Tom, so just to make sure I get the correct one, is the number I need to order 98543A114?

Bob

Kmot

My Feedback: (24)

No, get the ones that fit the 4mm locking area. These:

5-7 4 0.74 8.85 0.7 100 98543A112 3.15

That is what I just ordered, anyway.

retransit

My Feedback: (18)

OK, thanks.

Bob

Kmot

My Feedback: (24)

I spent a lot of time getting my engine and associated equipment set up on the test stand. And now I just took it all off. Argh! [:@]

But in the long run it hopefully will be worth it, installing new link pin retaining clips (a 4th description! lol...)

Now I just have to wait. Should be here Tuesday I think.

Kmot

My Feedback: (24)

Frets, I like retaining rings better than circlip's. Easier to install and remove, normally. But these would require a special plier because the holes would be so small for the plier tips.

frets24

My Feedback: (15)

A fourth! oh, no!

Maybe we should just refer to them as LPRC's from here on. Just to confuse the uninitiated as it were[8D]

Tom,
IIRC you work on full scale engines and aircraft don't you? With that type of experience what do you think about the idea that these clips might be being slung off at rpm?

frets24

My Feedback: (15)

With regard to the snap rings and small snap ring pliers; I'm thinking a $9.00 set of ring pin-point pliers is a heck of a lot less expensive than an $800 engine.

I think this is the route I'm going to pursue. Mainly because there seems to be a lot of issues with the clips(by any name) and as much as I rack my memory I can't think of a single instance where I can recall an e-clip type retainer on the inside of any automotive, motorcycle or aircraft engine or transmission and I have to believe there is a reason behind that.

Additionally, I don't think I would be able to settle into a comfortable flying session with this engine as it is due to the constant nagging at the back of my mind; "when is one of those clips going to let loose and destroy my plane?"

Of course anything can go wrong, mechanically or electrically, during a flight but don't we endeavor to minimize the risk exposure as much as we possibly and reasonably can?

I had already picked up a handfull of mil-spec "e" type clips from my machinist friend and replaced them while I had the engine open before but with Rev's recent situation and the current discussion I'm not feeling good about this type clip at all. I'm really starting to believe this is an rpm, positioning and centrifugal force issue and it can't be resoved using a clip that does not more fully encircle the pin.

I'm hoping that there won't be enough of a mass difference between the two types to be of any consequence. I'll weigh them up when i find some.

Kmot

My Feedback: (24)

I worked as an A&P many, many years ago.

As for being slung off, IMHO that would not happen on a freshly installed LPRC.

And further:

Why the link pin retaining clips are failing:

I have a theory.

When the C-E-Circlip is new, unused, it has a certain malleability about it. When it gets installed on a pin, it gets 'worked' by being expanded over the pin and then sprung back to size. I.E., it gets work hardened slightly. Now if we remove the circlip, from the pin, it gets worked again. So it has been work hardened twice so far. If we go ahead and reuse the circlip after overhauling our engine, it gets worked a third time. It has now been work hardened three times, which has reduced its malleability and made it more brittle. And to further degrade the situation, the clips have almost assuredly been scratched during this process, creating stress points that can lead to failure. As frets24 pointed out, the military maintenance reg's will not allow for a scratched circlip to be used, nor will it allow a used circlip to be reused.

I think all of us, who have been tearing down and then reassembling our engines, need to heed what Rev has pointed out to us via his unfortunate yet timely experiences. I am happy that Rev's engine did not suffer a catastrophic failure and that he will be flying it again. It is serendipity that the rest of us have learned about this as a result of his minor grief.

I know there are lots of people subscribed to this thread and lots more that read it but do not post in it. All of them are benefiting from this new insight.

Kmot

My Feedback: (24)

Fret's, got a link to those pliers online?

Kmot

My Feedback: (24)

As I suspected, looking at a photo of my engine I can see evidence of the link pins rotating during engine operation. So the idea that the placement of the circlip allowing it to be thrown off is sort of moot.

retransit

My Feedback: (18)

Tom, i placed my order with McMaster and at the bottom below the total it says "Applicable shipping charges will be added." Seems a bit odd to not reveal it before consumatiing the deal.

Bob

frets24

My Feedback: (15)

The rotation is exactly the problem I was envisioning. Even if we intentionally position the clip "properly" it will still wind up in the "danger" position at some time. Since we cant see the rate of rotation it could be slow enough to allow it to be in such a position that the opening is to the inner side. I posed the question of mass and force on one of the other forums and using the equation provided I'm getting a force of @7.25lbs pulling at that little lightwieght clip. Imagine holding the pin horizontaly in the air with the clip attached, tying a piece of string to the clip and hanging a 7lb weight from it. I'm thinking that when you rotate that clip to the position of the opening being at the top, it's going to drop that weight on my toe[X(]

It is amazing how much of a multiplier RPM can be. I figured the clip at 1.5 gram as a guesstimate since I didn't feel like tearing into my engine today.

Even if it's spinning at the full 7k that's still 7k opportunities per minute for the pull to overcome the ability to hang on.

Link to c. force discussion;

http://www.rcuniverse.com/forum/m_11...m.htm#11246324

Very insightful and well explained principles of work hardening above, Tom.
Light scratches fron being shaken around in a box of 100 clips or sliding across our benches aren't a problem. It's the light little gouge from when our tool, removing or pressing into place, slips and scores the clip.

I do have a tendency to over think stuff sometimes so I won't be offended at all if you say, "Lee, I think you've hit your head on something" (I have heard this before!)
So, not trying to be controversial or arguementative...just hoping maybe we can collectively suss out some ideas to make our engines more reliable and save our investment



Ring Tools:

I was actually just guessing at the plier prices based on what I remembered paying several years ago when I was rebuilding a couple of transmissions. I did find these though and the third set is like the one I have from NAPA


http://www.harborfreight.com/snap-ri...eads-3316.html

http://www.harborfreight.com/10-inch...set-97406.html

http://www.harborfreight.com/11-piec...set-92374.html

Kmot

My Feedback: (24)

I have a set of Blue Point snap ring pliers that I bought off the Snap-On truck decades ago and I thought it cost $300 back then. None of them have tips small enough to do the holes on a 4mm retaining ring.

http://buy1.snapon.com/catalog/item....re&dir=catalog

That said, I just was looking at the 4mm size at Mcmaster and they do not use holes, but instead use a slot. That might be doable.

I bought a small set from HF once, to keep at home so I would not have to bring my work tools home. The tips bent with hardly any pressure.

Bob, that is just how McM does it. Not to worry though, as the shipping charges I get are always very reasonable.

Kmot

My Feedback: (24)

Double post.

frets24

My Feedback: (15)

Sounds like my first set of pex ring crimpers for plumbing. 20 years ago they were $500 each and we had to 1/2'', 3/4'' and 1"...now, about $60 each.

The slotted rings are easier with just a fine piont flat blade screw driver. Engage one slot then twist the blade into the other expanding the ring in the process. usually takes some fine tuning of the screwdriver.

The ones at HF may have the copper tips for the smaller size. The first set I picked up at Autozone were trash too. The ones from NAPA I wasn't able to pull up-may be NLA from them. They weren't terribly pricey as I recall. Still have them. Another repurposed tool for snap rings is a small set of plier like thingies that are supposed to be for wrapping wire around in jewelry making. the points are small, close tightly and hard. Just takes a bit of dexterity to use them as openers since they are single hinged just like normal pliers.

Kmot

My Feedback: (24)

lol.... I have 'fine tuned' lots of screwdrivers. And chrome plated Snap-On wrenches, and chrome plated Snap-On sockets, and Snap-On needle nose pliers, and.......

When a job has got to get done you do whatever it takes.

Reverend

My Feedback: (3)

Tom and Frets,

thanks for those very conclusive theories. i would never have guessed, that there would be 7lb pulling on that little clip @ speed... In Addition, zentrifugal forces will turn the clip into the worst possible position with its lagrest weight on the outside and the opening pointing inward.

Anyway, I am getting myself a big pack of those clips from a local store and from now on everytime I will be using a new one.

Thanks again,
Rev

Reverend

My Feedback: (3)

Right, popped out of the office at lunch and went to a proper hardwarestore.

I have sucessfully proven, you can also buy 7 for EUR 5 ($6). Who needs discounts? [:'(]

But I want the engine up and running for the weekend.

My name is Philipp. I am addicted to radials. I need to fly the Stearman.

Carosel43

Imust say i dont agree with the 7lbs calculation. were it true the engine would need to be balanced with fractions of a gram and that is simply not the case. Something in the math cant be right :s

378

My Feedback: (4)

They don't weigh seven pounds. There's just that much force pulling them towards the cylinders. The pistons probably have several thousands of pounds of force tugging them towards the heads even though they weigh a fraction of one. The counterweight also pulls significantly harder than it actually weighs.

Carosel43

i am aware of that. i still dont believe they have that much load on them