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Something strange happened at the field today - 9/23/2012 1:49 AM   
karolh


 

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Status: offline 		My friend was maidening his 50cc Goldwing Extra 330/ DA50 model today when shortly after takeoff on it's first flight the engine stopped. Luckily he was able to land the model safely enough, though breaking one leg of the CF l/ gear at the axle connection.

An inspection of the engine revealed that the 4 aluminium cylinder mounting bolts had all shared and only the spark plug being attached to the HT lead had kept the cylinder from coming completely loose. The cylinder and the rest of the engine is servicable but it will require a new piston and ring.

This makes me wonder what is the purpose of using aluminium bolts instead of steel bolts as most other engine manufacturers do, as if weight saving is the reason then the advantage of doing so at best must be miniscule.

Karol

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RE: Something strange happened at the field today - 9/23/2012 2:46 AM   
captinjohn


 

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Status: offline 		I have a Desert Aircraft 50cc engine....but the cyl base bolts do not seem like aluminum????

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RE: Something strange happened at the field today - 9/23/2012 8:06 AM   
TimBle


 

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Status: offline 		Aluminium ? No Way, Can't be!
The torque required to hold the bolt in reduces the tensile load the blt can carry. They WILL snap. 
Must be a mistake. Engine should be sent back to the manufacturer unless the bolts were the idea of and fitted by the owner.



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RE: Something strange happened at the field today - 9/23/2012 8:09 AM   
Ernie Misner



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Status: offline 		Let us know if they were indeed aluminum!

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RE: Something strange happened at the field today - 9/23/2012 9:10 AM   
Mr67Stang



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Status: offline 		I for one would like to see this. Pictures?

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RE: Something strange happened at the field today - 9/23/2012 10:12 AM   
MetallicaJunkie



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Status: offline 		theres no way they DA would use aluminm bolts.... they may have been "silver" in color, but wdre actually stainless....not quite as soft as aluminum and not quite as hard as black carbon steel

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RE: Something strange happened at the field today - 9/23/2012 10:33 AM  1 votes
Cyberwolf



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Status: offline 		Karolh you are indeed correct in thinking the bolts are made from Alum. and anodized red. The back case bolts are made from Alum also. Only the prop hub bolts are steel in any DA 50-100 engine I have ever seen or worked on. Why there sheared off i'm sure was the fact they worked loose over time and the pressure from the piston and ring going up and down popped the heads off. Many don't know that pound for pound Alum is stronger than steel. The cylinder bolts doesn't require a great deal of torque on the bolts ,but they do need to be kept tight. Anyone that has the stock bolts (RED) in there DA engine, use a magnet on them and see for yourself.


http://www.desertaircraft.com/images/engines/50-small.jpg

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RE: Something strange happened at the field today - 9/23/2012 1:21 PM   
Rocketman_



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Status: offline 		It is not all that strange to hear of the highly touted DA engine popping those pretty red aluminum bolts. I am acquainted with an expert flier who will use nothing other than DA engines and sends his engines to DA for annual check ups but, in spite of that, he had a cylinder pop off. He told me about his experience after I told him that I had read about DA's blowing their heads off.

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RE: Something strange happened at the field today - 9/23/2012 3:07 PM   
karolh


 

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quote:

ORIGINAL: Cyberwolf

Karolh you are indeed correct in thinking the bolts are made from Alum. and anodized red. The back case bolts are made from Alum also. Only the prop hub bolts are steel in any DA 50-100 engine I have ever seen or worked on. Why there sheared off i'm sure was the fact they worked loose over time and the pressure from the piston and ring going up and down popped the heads off. Many don't know that pound for pound Alum is stronger than steel. The cylinder bolts doesn't require a great deal of torque on the bolts ,but they do need to be kept tight. Anyone that has the stock bolts (RED) in there DA engine, use a magnet on them and see for yourself.


http://www.desertaircraft.com/images/engines/50-small.jpg



Phew, I was beginning to think that I had forgotten what a red anodized aluminium bolt looks like.

Karol

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RE: Something strange happened at the field today - 9/23/2012 4:00 PM   
K-Bob


 

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quote:

ORIGINAL: Rocketman_

It is not all that strange to hear of the highly touted DA engine popping those pretty red aluminum bolts. I am acquainted with an expert flier who will use nothing other than DA engines and sends his engines to DA for annual check ups but, in spite of that, he had a cylinder pop off. He told me about his experience after I told him that I had read about DA's blowing their heads off.


In fact, that is very strange to hear. More than likely some one had the head off and overtorqued the bolts when re-installing. DA suggests replacing them if you ever remove them.



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RE: Something strange happened at the field today - 9/23/2012 4:37 PM   
TimBle


 

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Status: offline 		Indeed.
Overtorqueinng an aluminium bolt is murder. The twist in the material increases the static tension in the bolt. When the engine fires the pressure rises and the tensile stress in those bolts can easily be exceeded. Correct torque is an absolute necessity. 
Replacment of those bolts if they are ever removed, is an absolute necessity - aluminium work hardens and thus will get brittle with repeated engine cycles. 
If this is true for DA engine then it's very wise to adhere to the recommended service interval for those bolts.


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RE: Something strange happened at the field today - 9/23/2012 4:41 PM   
flycatch


 

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Status: offline 		I find it refreshing that there are those in this hobby who know what they are talking about.

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RE: Something strange happened at the field today - 9/23/2012 4:58 PM   
lopflyers


 

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quote:

ORIGINAL: flycatch

I find it refreshing that there are those in this hobby who know what they are talking about.




Me too, unfortunately most dont, and is difficult to tell the difference

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RE: Something strange happened at the field today - 9/23/2012 5:30 PM   
Rocketman_



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quote:

ORIGINAL: K-Bob


quote:

ORIGINAL: Rocketman_

It is not all that strange to hear of the highly touted DA engine popping those pretty red aluminum bolts. I am acquainted with an expert flier who will use nothing other than DA engines and sends his engines to DA for annual check ups but, in spite of that, he had a cylinder pop off. He told me about his experience after I told him that I had read about DA's blowing their heads off.


In fact, that is very strange to hear. More than likely some one had the head off and overtorqued the bolts when re-installing. DA suggests replacing them if you ever remove them.



It is more likely that DA didn't replace the bolts because as I said in my previous post, the owner sends his engines back to DA for annual checkups and service because he does not work on his own engines. Perhaps it is difficult for some to believe that a product from a well known manufacturer can fail without the user causing the failure.

< Message edited by Rocketman_ -- 9/23/2012 11:32 PM >

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RE: Something strange happened at the field today - 9/23/2012 5:37 PM   
tony0707


 

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Status: offline 		Da engines have been around a long time
Surprised this has not been posted here before
Cylinder heads coming off and damaging an expensive piston and liner is never acceptable in my opinion for any reason
This truly is ODD


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RE: Something strange happened at the field today - 9/23/2012 6:01 PM   
Truckracer


 

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Status: offline 		Strange this thread should appear just on the same day I'm replacing those pretty red bolts with steel ones on my older DA100. For those who have never examined a DA jug closely, the top surface of the cylinder retaining flange is angled quite a bit from what would be parallel to the mating surface. Those aluminum bolts have to conform quite a bit (that means bend) as the head contacts the surface and is further torqued to specs. If you ever remove one of these bolts the bend in the bolt just below the head is quite easy to see and is present on every cylinder retaining bolt. This is not uncommon for many of our cylinders regardless of brand but the steel bolts seem to conform to the task better than aluminum.

By the way, my guess is that the aluminum bolts are a carry over from the early 3W days when they used quite a few aluminum fasteners. 15 or so years ago, the aluminum bolts retaining my 3W 60 carb broke in flight with less than pleasant results so I have never cared for aluminum bolts ever since.

Do a few searches and you'll find the DA aluminum bolt failing problem is not uncommon.

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RE: Something strange happened at the field today - 9/23/2012 6:25 PM   
TimBle


 

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Status: offline 		I'm just surprised that DA would still be using aluminium retaining bolts on the cylinder head. Sure it saves weight but it invites more problems than necessary.
Although aluminium may be stronger than steel per lb we still need UTS and toughness and unfortunately aluminium simply fails to deliver in these areas.


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RE: Something strange happened at the field today - 9/23/2012 8:29 PM   
koastrc


 

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Status: offline 		This one of those things I enjoy about the business of model aircraft. Why use aluminium? Only thing that comes to mind is galvanic corrosion. Perhaps as the thread goes on we shall find out. Thanks for the comments about a very good and interesting subject. Even us know it alls may learn something.

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RE: Something strange happened at the field today - 9/23/2012 11:02 PM   
TimBle


 

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Status: offline 		Aluminium to aluminium won't really create galvanic corrosion concerns. More concerning is galling between the two parts as they vibrate at slightly different frequencies.
What can create galvanic corrosion is the steel spring washer usually used underneath the hex / socket head of the bolt. But I can't see DA making an amateurish mistake in this area.


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RE: Something strange happened at the field today - 9/24/2012 12:45 AM   
captinjohn


 

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Status: offline 		I will replace my DA 50 cyl bolts with steel ones...coated with a touch of anti-seeze.  I do not like any bolt made out of aluminum.   Capt.n.

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RE: Something strange happened at the field today - 9/24/2012 1:09 AM   
karolh


 

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Status: offline 		Good idea Capt,n if only for the peace of mind it will give.

Karol

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RE: Something strange happened at the field today - 9/24/2012 2:02 AM   
dirtyoldman00


 

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Status: offline 		Ive got five DA engines 50's and they all have aluminum bolts and when I orderd spares they sent new aluminum bolts You mess with the bolts youll blow your warranty

< Message edited by dirtyoldman00 -- 9/24/2012 2:38 AM >

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RE: Something strange happened at the field today - 9/24/2012 2:17 AM   
captinjohn


 

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quote:

ORIGINAL: dirtyoldman00

Ive got five DA engines 50's and 85's they all have aluminum bolts and when I orderd spares they sent new aluminum bolts You mess with the bolts youll blow your warranty


How much do they charge for the spares?   Also it sounds like if you mess with anything....you blow the warranty.   Their easy out of it all.

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RE: Something strange happened at the field today - 9/24/2012 2:37 AM   
dirtyoldman00


 

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Status: offline 		spare bolts were cheap like a 50 cents apiece but they were a bear to torque you need a long 5mm allen wrench Ive read in many old threads this happens alot I would say probally from fuel or mixture or ignition timing off it would have to back fire to blow the head off you definatally cant re use them

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RE: Something strange happened at the field today - 9/24/2012 3:01 AM   
Truckracer


 

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quote:

ORIGINAL: dirtyoldman00

Ive got five DA engines 50's and they all have aluminum bolts and when I orderd spares they sent new aluminum bolts You mess with the bolts youll blow your warranty

My DA engines are so far out of warranty that it doesn't matter any more what kind of bolts I use!

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