DLE 35RA Muffler bolts

[wfahey415]

Had my muffler come loose today and both bolts managed to find their way out of the cowl. I went to the DLE website and checked the exploded view for my motor, it lists a part number for a host of bolts but does not specify the actual dimensions of the bolt. Does anyone on here know what the size/length of the bolt is and a good place to source them? I am guessing 5mm but do not have the foggiest for thread count and length.

Thanks in advance
Bill

 

[wfahey415]

Found them. 5 x 24 mm. I thought I would go ahead and post it here in the event anyone does a search in the future.

Bill

 

[Bipenut53]

I believe the thread pitch is .8 so it would be a 5mm x .8 x 24mm bolt.... Real question is why did it come out? I have found most of the time the engine is getting too hot.....

 

[AKNick]

I had mine come loose during my 5th gallon. It actually ended up in the cowling after I did a pop-top. You could audibly hear the exhaust note change and feel the loss of power. I had to grab some bolts like you did. One thing I noticed was that the stock threads did not protrude out the cylinder casting, so I got the next size longer bolts. I have seen from other forums that people will throw away the gasket it comes with and use a light film of red RTV instead, no-body trusts the gasket I guess. One more thing to consider is Nordlock washers. They are designed for high vibration applications and people seem to really like them for exhaust bolts. I bought some off ebay "clips and Fasteners" or just go to their website. They come in pairs (25 pairs in a package). Two gallons later no problems.

http://www.clipsandfasteners.com/Vibration_Proof_Lock_Washer_3_16_5mm_p/a19282.htm

I have heard of heat being a contributing factor, but most of the consensus is that these little engines have such high vibration to begin with and that the holes aren't a perfect fit with the stock muffler... which to me just means a poor design.

Hope that helps.

 

[Bipenut53]

Well.... I hate to contradict but, I have found that if the mixture is correct (key part here) and if engine cooling through the cowl is sufficient, then you won't loose bolts. You have two dissimilar metals, aluminum cylinder head and steel bolts, the aluminum heats faster loosening the grip on the bolts coupled with engine vibration will cause the bolts to come out. Yes nordlock washers will hold them in but that is just masking the problem. Just my opinion and my experience from the past...

 

[AKNick]

Can't say that I disagree. My DLE35RA Muffler is a sloppy fit. You can lightly snug up the bolts and you can still move it around pretty good. With that said, the muffler is going to eventually try and wander with all the vibration going on, even under torque. I figure that any way you can prevent those bolts from coming back out is a good improvement.

Nordlock Demonstration Video
https://www.youtube.com/watch?v=mgwmuZuJ02I

 

[Bipenut53]

Can't say that I disagree. My DLE35RA Muffler is a sloppy fit. You can lightly snug up the bolts and you can still move it around pretty good. With that said, the muffler is going to eventually try and wander with all the vibration going on, even under torque. I figure that any way you can prevent those bolts from coming back out is a good improvement.

Nordlock Demonstration Video
https://www.youtube.com/watch?v=mgwmuZuJ02I

Ok [MENTION=3929]AKNick[/MENTION], I understand what you are saying here but, at the risk of being seen as a PITA :veryshocked: a couple things stick out here to me, first you said you got longer bolts to protrude through the casting of the exhaust flange, that you threw away the gasket and that the muffler is a sloppy fit. Yes in that condition, the bolts will come loose and the Nordlock washers will hold fine. I am one to try to resolve the original cause. It seems to me that the manufacturer and designer (DLE) designed and tested this engine and all its parts (yes they test at ideal conditions). But they released this engine with the bolts, muffler and gasket as being sufficient for the job at hand. If properly installed, and with proper fuel mixture (the manual calls for 30:1) and proper engine cooling, minimum airflow ratio being 3:1, exhaust airflow being 3 times greater than air intake, I tend to go with more airflow exit, you can use the gasket and original length bolts and I also use red lock-tight you will not have this problem. It just depends on how you choose to remedy the problem. I try to keep my engines running as cool as possible for extended engine life.

I need to qualify my statement, I am a GM trained auto technician of over 30 years, I have dealt with perceived design flaws many times, mainly when customers put "cool looking" wheels and tires on their vehicles, customers come back to the dealership complaining of tire wear and wanting an alignment under warranty just to find out that the cool wheels and tires they bought have the wrong offset throwing the scrub radius, camber and toe way off from the original design points causing the tire wear.

Just my 2 cents

 

[AKNick]

Ok @AKNick, I understand what you are saying here but, at the risk of being seen as a PITA :veryshocked: a couple things stick out here to me, first you said you got longer bolts to protrude through the casting of the exhaust flange, that you threw away the gasket and that the muffler is a sloppy fit. Yes in that condition, the bolts will come loose and the Nordlock washers will hold fine. I am one to try to resolve the original cause. It seems to me that the manufacturer and designer (DLE) designed and tested this engine and all its parts (yes they test at ideal conditions). But they released this engine with the bolts, muffler and gasket as being sufficient for the job at hand. If properly installed, and with proper fuel mixture (the manual calls for 30:1) and proper engine cooling, minimum airflow ratio being 3:1, exhaust airflow being 3 times greater than air intake, I tend to go with more airflow exit, you can use the gasket and original length bolts and I also use red lock-tight you will not have this problem. It just depends on how you choose to remedy the problem. I try to keep my engines running as cool as possible for extended engine life.

I need to qualify my statement, I am a GM trained auto technician of over 30 years, I have dealt with perceived design flaws many times, mainly when customers put "cool looking" wheels and tires on their vehicles, customers come back to the dealership complaining of tire wear and wanting an alignment under warranty just to find out that the cool wheels and tires they bought have the wrong offset throwing the scrub radius, camber and toe way off from the original design points causing the tire wear.

Just my 2 cents

This is what's great about forums... people who share their experience with each other without pointing fingers. I said "some throw away the gasket", I also said "the original bolts did not protrude out the casting" meaning that the bolts were not grabbing all of the threads. That's what I meant at least. Oh and it's 2.8:1 for an aircooled gas engine to be super oober technical.

Also...here we go...heh... I'm a certified Airframe & Powerplant mechanic, with an Inspection Authorization, and in Avionics, who owned his own business for 2 years maintaining planes... not sayn' anything... just sayin I don't want to sound like a know it all who proves his background. I just wanted to share what I came up with to help others. So I am done here comparing experience knowing that we both have plenty of it to bring into this hobby. Thanks for sharing your insight and maybe we can learn from each other.

 

[Bipenut53]

That's great Nick!! so then you also know that on aircraft engines, they NEVER have a steel bolt threaded directly into aluminum, they use thread inserts into the aluminum and that is where I feel the design flaw is if there is any. My respect sir!! That is the direction I should have gone after the Air Force lol I too like forums for discussions like this and others can make up their own minds and I also learn lots from others as well!! Thank you Nick!!

 

[wfahey415]

Guys, I really appreciate the feedback! On my setup, I DID NOT use the gasket but went with the high temp silicone method that I have read elsewhere on forums. I used Blue Loctite on the threads but do not recall if I used a lock washers or not. If the motor came with lock washers for the muffler bolts then I used them, if it did not, then I did not add any. As for cooling, I may not have enough. The front of the cowl I think has plenty of intake openings but I may not have enough exit space to let the hot air out. Maybe I am borderline on the exit space. I have had several flights on this plane with no issues. However, yesterday was very hot and humid with little to no wind so maybe that coupled with a marginal opening caused the failure yesterday. It happened immediately following a tumble, coming out of it I noticed the change in sound and the engine didn't respond like it normally does.