I've been a first class fitter and machinist for 26 years and it has always been bolt diameter = thread depth as a minimum. Of course you can use more thread depth if you want and most tapped holes are deeper than 1 x diameter.
As for 3 times the diameter?? Buy a 1/2" bolt and nut for eg. and i guarantee the nut won't be 1 1/2" thick.

Anything will strip if it is over tightened too much. As i said, most modelers use too much force when tightening small bolts.

The high temp Permatex thread sealant is used to seal the thread in O2 sensors on the manifold &converter , hot there?

We're not talking about a steel bolt threading into a steel nut here. We're talking about a steel bolt threading into an aluminum, mystery alloy Chinese cylinder. I still maintain that I'll take advantage of all the threads I can. The engineers that insist on sticking with their text book theories can use 4 threads of engagement as they wish.

I try to use socket head bolts to fasten the muffler to the engine. I drill a small hole through the head of the bolt and wire the muffler bolts together just like on full scale aircraft. I have never lost a muffler or bolt using this method and don't need any loctite.

I guess I am the only anti-loctite flyer. I have been flying since 1958 and have never used any type of loctite. I believe that if you do a proper pre-flight and use anti-seize when you assemble your model, problems are few. A clean bolt or screw, with anti-seize, properly torqued/tightened will stay there. Do not retighten when bolts or screws are hot but wait until first flight when engine is cold. On most OS mufflers if you continually tighten the bolts while engine is in use/warm, the bolt will snap. For those applications where you cannot get to the bolt due to cowls or bulkheads just safety wire during assembly. Just my three cents

Slightly off topic, I wanted to mention I used Permatex High-Temp RTV Silicone Gasket Maker to fix a problem with a 4 stroke. It had been involved in a midair. It looked fine but ran lean. Finally, using a different color fuel, I discovered leaks in the intake manifold and the needle assembly - probably from stress caused by the crash. Used this on both and leaks stopped for years.

As the late great Harry Morgan said: " Just the facts "


1. I have always used REDloctite on my gassers, the mufflers stay put until I want to remove them unless I have an overheating issue.

2. I have never stripped the threads in the cylinder.

3. The muffler bolts DONOT get any hotter then head temps. Do I really need to point out the the entire cylinder is a heat sink that for the most part has 50+ MPH of airflow?

4. The more bolt engagement the more surface contact area for the loctite. This is a no brainer.

5. If you are cleaning you bolts and threads then using loctite, silicon, ultra copper or whatever and are still having your muffler work loose, odds are you have a vibration issue or are running too hot or both. This would apply to 95% of cases.

1. That's what i said. When screwing into softer metals you need more thread engagement. I agree, the more the better.
2. Another reason i don't buy Chinese engines. The quality isn't there.
3. Just for the record, a 5mm bolt has .8mm pitch so going by the bolt diameter, there would be 6.25 threads of engagement.

Permatex Ultra Copper for gasket and threadlock. Works well for gas or nitro.

On the carb and exaust mounting I find using studs works the best that way you can locktite the studs in and use the star washer on the nuts without over tightening everything,on all my engines I check to see if the threads go to the bottom of the hole and use a bottom tap to make sure I get all the threads I can.never have ever lost anything because of lose nuts or bolts.just some thoughts.

Good idea with the studs.

+1 on Ultra Copper for both......never had a muffler loosen up on me and never had leaking of oil residue around the mufflers/engine.

Hesitated using Loctite only because I feared not being able to get the bolt out.......no proof that it would do so but just didn't feel comfortable using it.

But as with any other subject where folks have their choice of products/procedures do what you know works for you and be happy!

To much time wasted on the trivial and not enough on flying!

I use red Lock Tight # 271 on a lot when I wont to take it apart just add a little heat

I dont under stand why it holds for people on Mufflers R/L

O K Lock Tite 272 up to 450 F

L T 2620 up to 600 F

Google Lock Tite will tell you every thing you would wont to know about L T R/L

I get a charge out of those folks that decry the data given in engineering textbooks.
Where does that data come from? Its nothing more than the results of findings of thousands of individuals, both engineers and non engineers.
So you are going to ignore all of those individuals and say you know better. Thats pretty egotistical don't you think?

The only trouble with this is some mufflers have recessed bolts and you can't get to the heads.
I have a little Chinese engine that has recessed bolts. I have tried every concoction made and the bolts wont stay in. I am going to have to buy longer bolts and spacers so that I can get the heads out where I can wire them.

Perhaps I agree with the engineering textbooks but don't always agree with how some engineers interpret them.

Likewise, over the years I have certainly witnessed plenty of engineering practice and theory applied incorrectly.

+1 Personally I'm not a guy that wants to hear what something can't do, tell me what it CAN do LOL.

Dirtybird, do you know what the operating temp of your little chinese engine is?

I have seen guys that used a plate on the outside of the muffler with long bolts.....I have never had a muffler come loose using split locks and Blue Loctite so I'll just keep with what works for me. I did check the head temp of my DLE30 this week 171F at idle 197F at full throttle this was a ground check. The outside temp was a cool 38 at the time so I'm sure the summer temp will be higher.

I agree with all, on not over heating,and keeping vibration to a minimum........helps keep them tight also.

Sorry....I was directing the plate answer to Dirtybird

No I do not know what the temperature of the engine is. I have been running it on a test bench with a smaller size prop and it seems to be breaking in nicely. Its hot. Its just that I cannot keep the muffler on. I have longer bolts and am going to wire them.
On the subject of engineering. Anytime anyone, including engineers, make an extrapolation of observed data, its questionable.
One of the worst extrapolations you constantly hear is,"I have been doing this for years and I have had no trouble". The basic problem is the environment you are in will probably not apply in all cases. It will have more credence if the statement is "the data collected by all people in this country finds this true". But then you are getting close to what is in the engineering handbook

That pretty much sums it up. The engine is not getting adequate airflow and is getting hot. What does your engeneering book say about thermal expantion of different alloys in different enviroments?


I decided my last sentence was a little over the top so I deleted it and offer appoligies to anyone it may have offended.

[/quote]
No I do not know what the temperature of the engine is. I have been running it on a test bench with a smaller size prop </span>and it seems to be breaking in nicely. Its hot. Its just that I cannot keep the muffler on. I have longer bolts and am going to wire them.
On the subject of engineering. Anytime anyone, including engineers, make an extrapolation of observed data, its questionable.
One of the worst extrapolations you constantly hear is,''I have been doing this for years and I have had no trouble''. The basic problem is the environment you are in will probably not apply in all cases. It will have more credence if the statement is ''the data collected by all people in this country finds this true''. But then you are getting close to what is in the engineering handbook
[/quote]


That pretty much sums it up. The engine is not getting adequate airflow and is getting hot. What does your engeneering book say about thermal expantion of different alloys in different enviroments?


I decided my last sentence was a little over the top so I deleted it and offer appoligies to anyone it may have offended.


[/quote]

I realize I should be doing something to reduce the temperature but the instructions say to bench run it for 1 hour. I like to follow the instructions of the people that made it. They know a bit more than anyone else. They have tested a few more than anyone. I have a smaller prop to reduce the load and it I don't run it wide open. It seems to be responding nicely. If it don't I will just send it back and say I followed instructions.
I have not checked an engineering book about thermal expansions. Thermal dynamics is a very complex subject that I did not study in college. I think if I should need expertise in that area I will seek out someone that has and get their advise.
I did talk to an ME about the depth of thread requirement of a steel bolt in aluminum block. He said the coefficient of expansion of steel is less than aluminum so the clearance would increase with heat and result in a loose bolt. He said I should use an aluminum bolt so the clearance would remain the same at all temperature. Then the bolt would stay tight. I think that is the problem with the bolts in the exhaust. They are a steel bolt in an aluminum block. At least I think they are steel.
By the way do you have a spelling checker? If you don't, maybe you should get one.

I didn't realize that an occasional mis-spelled word lessens my experience.

We could use aluminum bolts to retain our mufflers but their size would have to increase quite a bit to insure adequate strength. I think overall, aluminum bolts would introduce more problems than they could cure.

After a very bad experience with aluminum bolts that were retaining the carb on a 3W60 engine, I don't care for them anywhere on one of our engines. And yes, I know that DA uses those pretty red anodized bolts on many of their engines and even these get replaced on my engines. More free lance, back yard engineering on my part I guess.

Truckracer, I see no issue with steel bolts as long as engine temps are kept within reason. I baited Dirtybird to a certain degree when I asked him about engine temps. Most guys are not going to have a temp gun, I have been running gassers for 15 years and have not needed one often enough to justify the cost. If I'm having issues with muffler bolts coming loose I just take it as an indicator that my engine is getting too hot.