DLE 55 Crank Broke in Flight
No way in Heck can you apply enough pressure to the spinner bolt to ever to break the crank , now over tightening the hub bolt may have a bearing on things but I really don't think that was what the issue was. I agree with what w8ye said about the metalurgy being wrong, DLE dosen't make there cranks, there farmed in just like alot of the other parts of the engine are. I can see where they could get a batch of bad cranks or anything else for that matter. it's just that heat treatment is a little harder to spot than other items. I really doubt that DLE is going to do a hardness check on each crankshaft before assembly.
And that brings up a second problem and that is improper fillets cause stress concentrations and resulting fractures. Look at the crank at the point of fracture and observe that it broke where there was a sharp corner?
david
This is twice now that I have lucked out and been able to safely land my plane. I do not want to try my luck a third time. What could be causing this. Should I press Hobby Services for a new engine? Could there be anything in mysetup that could cause this or is it likely to be in the motor.
I bought the engine from him spinner and all.
The spinner was not relieved to fit the prop and was distorted and undoubtably wobbled.
I put the engine on a plane immediately and have run it for four years with the same exhaust pipe he sent with the engine and a different spinner.
It is no different from any other Saito 62 Golden Knight and does not vibrate.
After hardening the part must be drawn back in a oven at 550 F for one hour. If this is not done you get stress cracks in fillets.
And that brings up a second problem and that is improper fillets cause stress concentrations and resulting fractures. Look at the crank at the point of fracture and observe that it broke where there was a sharp corner?
We also checked the shaft hardeness and found it to be fully case hardened.
I find it hard to believe that my 55 is alone in its material quality.....Nevertheless, this is the second shaft I've heard of that has broken right at the threads of the prop stud. It's got to be vibration induced. All of the things the WYE8 and others are saying about balance, etc , should be done to make certain balance is right.
If excess vibration continues, one should check the timing. I suspect retarded timing may be a hidden cause of excess vibes, and it's a cause that's easily overlooked.
Wealso changed the position of the Hall sensor to vertically down in my modified engine. This required cutting a new keyway on the prop drive hub, so making certain ofwhen the engine is fired is an important piece to this puzzle. One shouldn't have to cut a new keyway in his engine of course, but checking the spark pick up and moving the pick up a few degreesare straight forward if notsimple to actually do
To respond to the questions above. I checked the balance on the spinner, and it was fine. I do not know the make of it, but the spinner and prop were running true without any obvious vibrations. As I stated above the prop that was used during the ifrst failure was balanced, and even though it appeared fine I replaced it with a new balanced prop. I am by no means a small engine expert and messing with the timing on these motors is not something I have any experience with. I have wondered if there could be an issue with the tuning, but the engine runs smoothly and does not hiccup or backfire. I am at a loss.
Sorry to not reply back to this any sooner. My life has been crazy to say the least the past several weeks with the birth of my first three children.
I have a DLE 55 that broke a crankshaft at exactly the same place. It had very little radius in the shoulder. It was not under warranty.
Back to the engine. I shipped it back to hobby services last week so we will see what they find. I checked the spinner and it is a true turn and it is balanced.
I dont know what is worng. Maybe I am just unlucky.
I would call them and press them hard for a new engine.
Hobby Services are pretty good to their customers. Tell them after two identical failures, you have lost confidence in the engine and are afraid to put it back in and it is obvious that they can't find the problem. What is going to take, a crash, etc. Also, you have lost a good portion of the warranty period and flying season in downtime. Time to start with a fresh one.
Also, I would get a backup. Flying season is too short up here to be messing around with their delays.
I would call them and press them hard for a new engine.
Hobby Services are pretty good to their customers. Tell them after two identical failures, you have lost confidence in the engine and are afraid to put it back in and it is obvious that they can't find the problem. What is going to take, a crash, etc. Also, you have lost a good portion of the warranty period and flying season in downtime. Time to start with a fresh one.
I received a brand spanking new engine from Hobby Services last week. I included a letter with the broken engine when I returned it to them explaining the problems and giving a timeline of the events. I asked them to please provide a new engine or extended warranty on the repaired motor as my warranty was expiring on 12-30-12 and I knew I would not get the opportunity to test the repair prior to the warranty period ending.
Hobby Services, Thank You for making this right. I appreciate the good customer support.
Now I just need to find a little time to mount and use the new engine.
Thanks