Repair bent or twisted crankshaft. DA 150
11-24-2014, 09:16 AM
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Repair bent or twisted crankshaft. DA 150
Does anyone straighten bent or twisted crankshafts? I have 2 DA 150s with bent cranks and would like to try getting them straightened before shelling out $200.00 apiece for replacements. Thanks.
11-24-2014, 09:55 AM
#3
The best option really is to send them in. There could be more damage then just the cranks, bearings and hubs come to mind. You would also need new gaskets and the silver silicon sealant they use on the cases. IMO better to get it fixed correctly and with a warrantee.
11-25-2014, 05:33 AM
#8
I apologize if you feel that I have crossed some sort of line. Although it's not really the question you had asked, it is the best option none the less. DA is better set up to service their products then anyone else. Yes it's the most expensive route but it's also the one with least risk.
11-25-2014, 07:09 AM
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Hummmmmmmm thats interesting I have been here all of the time and have fixed so many twisted cranks I have forgotton.
FYI Speedracer the factory considers .003 total run out to be within specs. I think that is a joke I try to get mine to run with in .0001. So maybe the factory is not always the best after all.
FYI Speedracer the factory considers .003 total run out to be within specs. I think that is a joke I try to get mine to run with in .0001. So maybe the factory is not always the best after all.
11-25-2014, 07:12 AM
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I was truly thanking you for your opinion speedracer. One of the greatest enjoyments I get from this hobby is figuring out how to fix things that are deemed unfixable. I've been doing it that way for over 20 years. One of the reasons I was asking about having the crankshafts straightened was because I didn't know if anyone did it. Of course I know that DA has incredible service. It's one of the best things about the company. So thank you again for telling me again about something I already knew about. So speedracer. Do you know of anyone who straightens crankshafts?
11-25-2014, 07:20 AM
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Thanks cyberwolf. One of the things that's stumping me is that I've put digital calipers all over the cranks and can't find any more than .002 variation, but when I put them back in the crankcase I get a wobble of the output shaft. Is there anyway the case could cause the wobble?
11-25-2014, 07:29 AM
#13
Guys, it's not really about repairing a bent or twisted crank, I agree that is a fairly simple process. It's having the experience to know what else to look for. The hub could be damaged, the connecting rod bearings could be damaged. These are things that may appear to look good. If you guys have the experience to successfully repair the engines then by all means go for it.
11-25-2014, 08:16 AM
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With a .0001 dial indicator that only reads to .200 total I am very sure. Yes a G-62 crank is one that twists as well and can be twisted back to run straight.
It is not the size of the crank that makes it wobble when turned, it is the fact it is out of alignment with itself.
What happens is when a prop strike happens the front of the engine stops at once ,since the crank is not a solid piece and pressed together with pins the rear half tries to keep turning for just a fraction of a second twisting the back part of the crank and making it out of align. Some cranks are pinned and that can be fun too although there pinned they to can still twist as a rule those I won't even touch.
Sometimes a mill vice can be used, while others need to be in a lathe just depends on how severe the crank is out.
How the straighten a twisted crank well the first thing a person needs is a good dial indicator preferable a .0001 read but a .001 will work I heard of some using wooden V blocks a brass dowel and a hammer. Myself I use a little more expensive tool called a lathe or milling machine. As for how I do it .well lets just say I do it and leave it at that. I was taught by a master 40 some years ago, when we used to rebuild crankshafts for bikes and snow machines, not like today where they just toss um out and replace with new.
Want to have some real fun try doing a 6 cylinder boat engine, it will drive a person nuts.
It is not the size of the crank that makes it wobble when turned, it is the fact it is out of alignment with itself.
What happens is when a prop strike happens the front of the engine stops at once ,since the crank is not a solid piece and pressed together with pins the rear half tries to keep turning for just a fraction of a second twisting the back part of the crank and making it out of align. Some cranks are pinned and that can be fun too although there pinned they to can still twist as a rule those I won't even touch.
Sometimes a mill vice can be used, while others need to be in a lathe just depends on how severe the crank is out.
How the straighten a twisted crank well the first thing a person needs is a good dial indicator preferable a .0001 read but a .001 will work I heard of some using wooden V blocks a brass dowel and a hammer. Myself I use a little more expensive tool called a lathe or milling machine. As for how I do it .well lets just say I do it and leave it at that. I was taught by a master 40 some years ago, when we used to rebuild crankshafts for bikes and snow machines, not like today where they just toss um out and replace with new.
Want to have some real fun try doing a 6 cylinder boat engine, it will drive a person nuts.
Last edited by Cyberwolf; 11-25-2014 at 08:18 AM.
11-25-2014, 02:31 PM
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Speedracer:
At times you are right about sending in the engine to DA. However, there are those that are knowledgeable about engine repair/overhaul. The factory is not always best. I think it is funny that when people post about a "DA" engine. The majority including yourself say "send it to DA". I agree somewhat with that statement when a hobbyist purchases an engine and has no clue of the inner workings of the engine or how to tune the engine using the needles. For those guys, yep send it in. For people like the OP and myself among others. I prefer to fix em myself.
Just sayin.
Glenn
At times you are right about sending in the engine to DA. However, there are those that are knowledgeable about engine repair/overhaul. The factory is not always best. I think it is funny that when people post about a "DA" engine. The majority including yourself say "send it to DA". I agree somewhat with that statement when a hobbyist purchases an engine and has no clue of the inner workings of the engine or how to tune the engine using the needles. For those guys, yep send it in. For people like the OP and myself among others. I prefer to fix em myself.
Just sayin.
Glenn
11-25-2014, 03:23 PM
#19
Glen, I really can't argue with you there. However this being the internet just how does one determine who is qualified to do what? This morning I logged in and saw someone who I'm not familiar with, has less then 10 posts and states that he has 2 engines with bent cranks. The safe assumption was that he is relatively new to gas engines and still developing pilot skills so I sent him to the manufacturer. True, assumptions usually hold some risk however that is all I had to work with this morning. Different strokes, I have been in this hobby for 37 years now, I am completely capable of doing my own engine work as well. In fact I was once offered a position at DA by Dave Johnson. I however choose to send mine in for work other then a carb rebuild simply because with 4 teenagers at home I can't afford the time.
11-25-2014, 05:12 PM
#20
I know one guy that has a perfect flat steel plate. In that plate are holes bored for various crank sizes. I guess a lot of cranks can be checked for run-out & then placed in position in correct bore in plate. Using a brass hammer & tapped in right place will work. Keep checking as you go to get to a .001 run-out. I would say experience is best, not everyone has that skill...........
11-25-2014, 09:14 PM
#21
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I have straightened a few with vblocks and a hammer. An old machinest buddy used to heat and jack in an old lathe he had around... . I checked in my lathe them after hammering the straight, but never wanted to put the stress of pushing/ jacking on my lathe. Cyberwolf you should share some of your knowledge as there arent many around with the skills anymore
11-26-2014, 04:51 AM
#23
Back in the day I worked at a place called Morgan's Kawasaki in Lancaster California, we had a race team that included a couple of flat trackers and three road racers, I was a part of the road racers group and everything we raced back in those days were two cycles. Anyway we worked on what we raced and replacing needle bearings, or knife edging and balancing the connecting rods were part of it from time to time. This meant a complete tear down, reassembly, and alignment of the crankshaft because the rods were one piece with no removable caps. I along with one other racer ran a Kawasaki H1R 500cc triple and was taught to tear down, reassemble and align using a hydraulic press, lathe, wooden v blocks, a brass mallet, feeler gauges and dial indicators. It is actually a simple process if one is mechanically inclined, for those that are really not and I am not saying anyone is not, then I would just send them to Desert Aircraft, I say this because from my own experience of running nothing but DA engines for the last decade or so, they have always taken great care of any warranty issues and crash issues alike for me, in fact on more than one occasion all I paid for was shipping charges. Something else to consider, although I agree aligning the run out to within .00001" is the s@%t, many come back and bolt a prop or a prop and spinner combo that are not suitably balanced, let me restate that, they come back and bolt on a prop or a prop and spinner combo that are not anywhere in the vicinity of being balanced for the task at hand defeating the point altogether.
Bob
Bob
11-26-2014, 07:05 AM
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+ 1 sensei As far as me sharing my knowledge, I have tried that on here before only to have allot of flack from folks so I keep it to myself from now on.
11-26-2014, 09:23 AM
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I straightened crankshafts from smaller engines like the Zenoah 20cc, 38cc and a MVVS 26cc gas. I did not open any of them. If the crankshafts are not bent too strong, you can go the same way.
Instead of the prop, you mount an absolutely flat steel-or aluminium plate. Remove the spark and mount the engine to some kind of test stand. Then put some measuring-clock to your plate. Logically, your measuring results will be more precise, the bigger your radius from center of your engine becomes.
Start turning the plate slowly and watch the clock. Don`t damage your device, if the clock can not show more than one or two millimeters of moving !!!
The image shows the repair of one of my two Zenoah 20cc. The clock was a type, showing one millimeter in a hundred parts. As you see, the radius don`t need to be huge to receive precise results. In this example, I had about 80mm.
Well, I remember, I grabbed the plate with my two hands and put the shaft in shape again. I think, it was bent about something less than one millimeter. This should be the limit at a radius of 80mm !!!
I was able to reach about one or two hundreds of a millimeter. Keep in mind, that the crankshaft is running in ball-bearings. According to this fact, don`t try to reach the zero-point. You can only become crazy, trying the mission impossible. And the material of your crankshaft will thank you, not to be bent twenty times even to the other side. It had enough stress from our crashes or somrthing.
In my case, my machine met the model of my own club-buddy, flying in front of public, finishing a small french event in May 2009. That f....... audience gave us a big applause...... but that`s another story.......
My 20cc was sent to Toni Clark first. I bought it there in 2008. Toni`s companion Gerhard Reinsch called me back late in the evening to tell me about the damages and the repair costs. They would have been 10 euros less than the price for a new engine. The main reason for this, was the ignition box. It has kinda dome, which the cable is screwed onto. The dome was broken off completely from the box, nothing left.....
So I wanted the engine back, the way it was.
And this engine is still running. And it is the engine, that has more hours than any other of mines. Of course, I had to buy a new ignition. But this was by far cheaper, than a new engine.
In case of your DA 150, you need a bigger plate. But you will realize, you are able to bring this shaft in shape!!
If you first testrun your DA, have a close look at the running at idle speed. Can you bring it down to the rpms you had before the damage???
If not, or if the idle is not really stable, your front bearing could have suffered too much from the damage. Possibly, It can still do its work for years. But it could be a pressure-leak now, such as the first generation cylinder gaskets from DA85 or 170.......
I compared my fixed engine to an absolutely new one by mounting the same prop to them and measuring the movement of the prop-tips. To my surprise, I had less movement with my fixed engine.
Also make sure, that the crankshaft is not turned in itself, as it can occur hitting the ground with a two or more cylinder engine. Of course, I don`t talk about dead stick hittings. There you have almost no risk, turning the shaft in itself.
If you are able to change the front bearing yourself, don`t be afraid of replacing all the gaskets by a high-temperature silicone. If you don`t want to replace the cylinder gasket, fearing a too high compression or changing the timing of your DA, make an aluminium-dummy and mount it with silicone.
If you want to do the same, start with the rear half of the crankcase!!
Mount all parts such as the isolator, reed-block, carb eventually venturi to it. Be aware that the two bolts are not screwed to far inside the case, otherwise you will block the shaft with them or scratch it.
Give this unit some minutes to dry and look inside. If there was too much silicone moving inside, that could prevent the reeds from working freely. Just pull it out with ease.
Use a type of silicone, not damaged by fuels or acids. Most of them stand temperatures of 250°C currently and 300°C short times. Really enough for our purposes.
I hope, I could help you, wish you safe flights!!
Pedro
Instead of the prop, you mount an absolutely flat steel-or aluminium plate. Remove the spark and mount the engine to some kind of test stand. Then put some measuring-clock to your plate. Logically, your measuring results will be more precise, the bigger your radius from center of your engine becomes.
Start turning the plate slowly and watch the clock. Don`t damage your device, if the clock can not show more than one or two millimeters of moving !!!
The image shows the repair of one of my two Zenoah 20cc. The clock was a type, showing one millimeter in a hundred parts. As you see, the radius don`t need to be huge to receive precise results. In this example, I had about 80mm.
Well, I remember, I grabbed the plate with my two hands and put the shaft in shape again. I think, it was bent about something less than one millimeter. This should be the limit at a radius of 80mm !!!
I was able to reach about one or two hundreds of a millimeter. Keep in mind, that the crankshaft is running in ball-bearings. According to this fact, don`t try to reach the zero-point. You can only become crazy, trying the mission impossible. And the material of your crankshaft will thank you, not to be bent twenty times even to the other side. It had enough stress from our crashes or somrthing.
In my case, my machine met the model of my own club-buddy, flying in front of public, finishing a small french event in May 2009. That f....... audience gave us a big applause...... but that`s another story.......
My 20cc was sent to Toni Clark first. I bought it there in 2008. Toni`s companion Gerhard Reinsch called me back late in the evening to tell me about the damages and the repair costs. They would have been 10 euros less than the price for a new engine. The main reason for this, was the ignition box. It has kinda dome, which the cable is screwed onto. The dome was broken off completely from the box, nothing left.....
So I wanted the engine back, the way it was.
And this engine is still running. And it is the engine, that has more hours than any other of mines. Of course, I had to buy a new ignition. But this was by far cheaper, than a new engine.
In case of your DA 150, you need a bigger plate. But you will realize, you are able to bring this shaft in shape!!
If you first testrun your DA, have a close look at the running at idle speed. Can you bring it down to the rpms you had before the damage???
If not, or if the idle is not really stable, your front bearing could have suffered too much from the damage. Possibly, It can still do its work for years. But it could be a pressure-leak now, such as the first generation cylinder gaskets from DA85 or 170.......
I compared my fixed engine to an absolutely new one by mounting the same prop to them and measuring the movement of the prop-tips. To my surprise, I had less movement with my fixed engine.
Also make sure, that the crankshaft is not turned in itself, as it can occur hitting the ground with a two or more cylinder engine. Of course, I don`t talk about dead stick hittings. There you have almost no risk, turning the shaft in itself.
If you are able to change the front bearing yourself, don`t be afraid of replacing all the gaskets by a high-temperature silicone. If you don`t want to replace the cylinder gasket, fearing a too high compression or changing the timing of your DA, make an aluminium-dummy and mount it with silicone.
If you want to do the same, start with the rear half of the crankcase!!
Mount all parts such as the isolator, reed-block, carb eventually venturi to it. Be aware that the two bolts are not screwed to far inside the case, otherwise you will block the shaft with them or scratch it.
Give this unit some minutes to dry and look inside. If there was too much silicone moving inside, that could prevent the reeds from working freely. Just pull it out with ease.
Use a type of silicone, not damaged by fuels or acids. Most of them stand temperatures of 250°C currently and 300°C short times. Really enough for our purposes.
I hope, I could help you, wish you safe flights!!
Pedro