kenh3497

Does the circlip have a single tang and how was that tang oriented? The tang should be virtigal in relation to the cylinder bore. If horizontal, the tendency is to vibrate and weaken with the piston motion being the cause.

Ken

MTK

The engine is being returned from Hobby Services. No other response from them. I doubt that diagnostic work was done to figure out why it's eating retaining clips.

I still have two engines nib that I will sell to a sport flier somewhere.

drac1

My Feedback: (4)

Giving up on the 33 Matt?

MTK

It's got all the power, top end and mid range we want. But it looks like the wrist pin retention is its Achiles heel. RM had his issues and had to move on. i just might have to move on too. One more failure and I just might sell all my GTs.

The DLE just doesn't have the same guts to turn 21" props. The DA is still unknown. YS, I just don't want to run nitro methanol and all the rusting that goes with that. I don't know, maybe it's time for electric

drac1

My Feedback: (4)

Oh no..

I think everything has it's problems, just need to work out what will accomplish what you want to do I suppose. Even electric have their short comings.

I will run my 33 eventually, but I will stick with YS for comps. Love 'em.

MTK

Well, not ready to throw in the towel yet. The first engine gave me such good service for so long with zero maintenance, I'm finding it hard to accept. I've just got my second engine into service and it has about 2 gallons through it. That's not a lot of flights to make any judgements yet.

If I was to get into the electric deal, I would get a crs to go with it. I only flew one notable flight on a well set up model and I had better speed control than anything I've ever flown. Twin props push back much more air and do so at a slower speed, which means thrust is significantly greater. Ideally, we should develop a crs for IC. It's really the better propulsion system for what we do.

drac1

My Feedback: (4)

Contra also has it's problems to overcome. But just like everything else, a good set up works well.

MTK

Ken,
The clips have twin tangs. They are the type where you squeeze the tangs to insert into the slots, just like many engines use.

Another way to retain the wrist pin is using a circular retainer made from spring wire. If I recall, Webra used that style and it worked great. The natural springiness of the wire really pushed hard into the groove with little chance of vibrating loose. This isn't fool proof either but might be better than circlips.

drac1

My Feedback: (4)

These are standard heat treated spring steel internal circlips. If you have tried to destroy one, (I have), you would know they are virtually indestructible. These circlips are not designed to have force exerted on them and in this situation there would be very little. I am also extremely doubtful that they would fail due to vibration. It would be more plausible to think that the groove in the piston would be the problem, but even then it doesn't make sense to me as there would be minimal pressure applied to the circlip.

Obviously there is a problem somewhere and it would be very interesting to know exactly what it is. It's more than likely we'll never know the real issue.

MTK

The shipment I got from Hobby Services was a new engine, not my old, rebuilt one. That's ok but we lost the opportunity to learn why it ate the retainers in the first place.

They found debris in the bearing and that's new. I inspected the main bearing in the case, not out of the engine, after removing the crankshaft, and didn't see anything. It doesn't mean it wasn't damaged, just that I didn't see the damage.

I did not change the bearing when the engine ate the retainer the first time. If the bearing had metal bits in it, I would have felt some grinding and didn't. So I didn't think there was anything wrong with the bearing and kept it in service. Maybe there was damage and metal shrapnel in it, and it found its way into the piston skirt. Somehow it might have dislodged the retainer clip. It's far fetched but can't be eliminated as a possibility.

The lesson here could be that in such a failure, at least the main bearing should be replaced also. A big thank you to HS for giving me this bit of info at least. That and a replacement.

The engine had been incredibly reliable for nearly five years. It ran smooth, clean with minimal carbon build up, with power to burn and with outstanding field manners. I got spoiled with the ' Fuel, 2 Flips, Fly, Repeat'. The main concern, I have a pair of them in service now. Is failure of this type just waiting in the wings?

drac1

My Feedback: (4)

Good news on the replacement.

Maybe that is indicative of a design flaw? Or quite possibly just good customer service from a good company.

speedracerntrixie

My Feedback: (29)

Perhaps the wrist pin is getting hot enough to remove the temper from the clip? My experience with those clips is once snapped into the groove they are there for good unless one has the correct removal tool. Maybe someone on the assembly line got lazy and found a shortcut to install the clips that is damaging the groove?

drac1

My Feedback: (4)

If it was getting that hot, the engine would seize anyway.
Circlip pliers are the only way to remove and install small circlips without damaging something. I doubt they would be taking short cuts.

speedracerntrixie

My Feedback: (29)

You would be surprised, for the past decade I have been involved in manufacturing aerospace components that end up selling for several million dollars and guys end up taking shortcuts that cost thousands to correct. If someone feels he or she can install clips faster with a wood dowel then the appropriate pliers I can see it happening.

drac1

My Feedback: (4)

Yeah, short cuts are taken. But in this case I reckon it would take longer than using the correct pliers.

MTK

Shawn, I don't think so. Hauling the loads I install, my verticals are unlimited, never sagging, ever. I duct ram air and treat exits properly to draw hot air out. My engines are cool enough to touch at landing.

Well, I suppose it's possible, shortcuts..... RM and I, at least, have had the same problem twice each. RM got aggravated enough to switch to other engines. I don't know how many others are seeing the same failure mode. I'd guess one assembler can assemble dozens in a day so shortcuts are plausible.

kenh3497

I was given a Stihl chainsaw that had compression but the cylinder was cored. Cause.... The wrist pin circlip broke. It was a single tang clip. The other good side broke as i was removing it. I've also seen this happen in some of the .15 racing engines we used in Quarter Midget of years past. Many possibilities... Wrong temper of the material, bending past the yield point of the material or any combination of factors.

My guess is a bad batch of clips snuck through QC and they will run their course and all will be happy again.

Ken

drac1

My Feedback: (4)

That is a common fault with that type of circlip.

I'm pretty sure this is the circlip in the GT33's and it would be extremely unusual for this type of circlip to fail unless a side force has been exerted to the circlip. Even then, it would take a lot of force and I can't see how that would happen. There is nothing that can brake off due to vibration.
But Matt has had two failures now and RM has had one, so something is not right. I would suspect a groove problem more than the circlip failing.

MTK

Scott, that is the clip in question. In operation there is no side force that I can think of. By side force I believe we are talking along the diameter.

That does not mean a greater side force than necessary was exerted during installation both by the original assembler and by me. I don't have the proper pliers to install it. I used a pick, placing the first tang in the groove by hand and then picking the second tang into the groove. It seemed to seat well. I could be wrong.

Come to think of it, it wasn't hard to do at all using a pick. Maybe too easy. Wonder if the clip is smaller than necessary. Hmmmm!

drac1

My Feedback: (4)

1. Correct.

2. I wouldn't think so.

3. Well worth the investment.

4. You may be onto something there. Even the small ones are quite springy and are not very easy to install without the correct pliers. It's also easy to twist them by installing them that way Matt. That's getting back to my piston groove theory.
( I have installed/removed large circlips with screw drivers, punches and hammers when I didn't have the correct pliers available, but 5 or 6" diameter circlips around 3/16" thick are very tough indeed).

The measurement between the two points I have marked, should equal the diameter of the groove.

kenh3497

Seeing the type of clip... Now I can see that it is very unlikely for it to fail. As mentioned, the issue, IMO, lies in the groove diameter, width or possibly the cross section of the groove. With that said if the wrong clip is used that could also be the problem. My vote would be for the groove to be incorrect. I've always felt the clip should be a tight fit in the diameter. if you can easily move the clip with a pick, it is to loose. The clip should have some drag in the groove.

Here is a link to a chart showing correct ring and groove dimensions. English- http://www.arconring.com/stamped-ret...ings/internal/ Metric- https://www.rotorclip.com/cat_pdfs/dho.pdf

There is also a correct and incorrect way to instal the snap ring. The "square" side of the ring should be placed away from the force pushing against it. In a wrist pin application the square side should face out.

Ken

big_G

Matt....any updates on the 33?...I'm probably gonna build a gas 2 meter this off season, and value your opinion.

Gary

MTK

Gary, nothing new to report. I commissioned another 33 in my Delta and it's working the same outstanding way my first one did. Same carb and pipe settings as the first. It has about 6-7 gallons through it or about 100 runs. I used the 20.5x10 PN on this one.

Delta has been in the shop lately for a face lift so no recent flying.

Ron had a lot of issues with his 33's, enough so to move to the much less expensive EME line. The DA 35 also had some issues according to Ron.

if you don't have a plane for your engine yet, consider buying my nib Shinden.

drac1

My Feedback: (4)

Hi Matt,

I wonder if the 21" prop was maybe a bit too much load, somehow exerting pressure on the circlip?

it will be interesting to see how it lasts with the 20.5.

MTK

Scott, I can't see how. The engine easily hauled the 21"x10 woodie hybrid turning just about 7k on avgas. It sounded happy. But I only ran it briefly then switched to the lower load.

A couple years ago i had also tried a 19x13 woodie hybrid with wider blades and the engine met its match there, bogging down to around 6500 and running hotter than normal. Too much load and definitely more than my 21x10 hybrid. Wasn't happy and you can tell. My 21x10 is a true narrow blade design.

I think Ken is right. When I installed the new set of clips I probably didn't seat them properly. I don't buy what Hobby Services said about the bearings being bad with shrapnel in them.