Author Topic: This drives me nuts - need input (Read 5632 times)

Scott Richlen · « **on:** May 27, 2014, 07:25:32 AM »

I have a PA-61 rear exhaust that is fantastic. But every once in a while the header screws come loose by the end of the flight and the header is either loosely attached or pretty much just hanging there, free. I've checked with Randy on this and done what he says, but every once in a while it still happens. Even using locktite and locktite cleaner beforehand! I must be doing something wrong, but not sure what it is. Has this happened to anyone else and what did you do to cure it? Any suggestions?

Scott

Avaiojet · « **Reply #1 on:** May 27, 2014, 07:31:34 AM »

I would check the prop for balance.

john e. holliday · « **Reply #2 on:** May 27, 2014, 08:00:08 AM »

Have you faced off the mating surfaces to see if there are any gaps. Also if you use a gasket, pitch it.

Brett Buck · « **Reply #3 on:** May 27, 2014, 08:22:34 AM »

Quote from: Scott Richlen on May 27, 2014, 07:25:32 AM

I have a PA-61 rear exhaust that is fantastic. But every once in a while the header screws come loose by the end of the flight and the header is either loosely attached or pretty much just hanging there, free. I've checked with Randy on this and done what he says, but every once in a while it still happens. Even using locktite and locktite cleaner beforehand! I must be doing something wrong, but not sure what it is. Has this happened to anyone else and what did you do to cure it? Any suggestions?

Face off both sides of the interface with 240 w/d paper until it is dead flat. Clean it with acetone or lacquer thinner. Don't use a gasket, use high-temp silicone header sealant from the auto parts store, very thin, but cover the entire mating surface on header side including around the screw holes. Push the screws, with lockwasher, through the holes, and make sure a bit of sealant gets on the threads - just a tiny amount down in the grooves. Screw it down reasonably tight, but don't overtorque it, since you might strip the threads or break the screw off. Good to go.

Don't use the method from the silicone instructions (get it just snug, wait overnight, then tighten down hard). Just crank it to the final torque immediately. This removes almost all the sealant from the joint, just enough to fill all the sanding grooves. Do it right and you will have to put a fair bit of force on it to get it off later. If you leave any significant bond line thickness, it may blow out later. The tiny bit on the screws acts like locktite but can easily withstand the temperature and the large amounts of oil.

We have never had a header come loose using this method. Even when we flew it 15 minutes later, without bothering to let it set up.

Brett

Doug Moon · « **Reply #4 on:** May 27, 2014, 08:35:22 AM »

Quote from: Brett Buck on May 27, 2014, 08:22:34 AM

Face off both sides of the interface with 240 w/d paper until it is dead flat. Clean it with acetone or lacquer thinner. Don't use a gasket, use high-temp silicone header sealant from the auto parts store, very thin, but cover the entire mating surface on header side including around the screw holes. Push the screws, with lockwasher, through the holes, and make sure a bit of sealant gets on the threads - just a tiny amount down in the grooves. Screw it down reasonably tight, but don't overtorque it, since you might strip the threads or break the screw off. Good to go.

Don't use the method from the silicone instructions (get it just snug, wait overnight, then tighten down hard). Just crank it to the final torque immediately. This removes almost all the sealant from the joint, just enough to fill all the sanding grooves. Do it right and you will have to put a fair bit of force on it to get it off later. If you leave any significant bond line thickness, it may blow out later. The tiny bit on the screws acts like locktite but can easily withstand the temperature and the large amounts of oil.

We have never had a header come loose using this method. Even when we flew it 15 minutes later, without bothering to let it set up.

Brett

I do the EXACT same way. I think the sealer I use is permatex gold HIGH TEMP. Works like a charm.

Doug Moon · « **Reply #5 on:** May 27, 2014, 08:39:54 AM »

I was in a pinch once and needed to go fly but no permatex on hand so I used 5 minute hobby epoxy. I dont recommend this. I put just the tiniest amount on there. But it held for several years and then I needed to get bearings replaced or something that caused me to need to remove the header. I kept expecting it let go any time but it never did.... Haha...

Brett Buck · « **Reply #6 on:** May 27, 2014, 08:50:11 AM »

Quote from: Doug Moon on May 27, 2014, 08:39:54 AM

I was in a pinch once and needed to go fly but no permatex on hand so I used 5 minute hobby epoxy. I dont recommend this. I put just the tiniest amount on there. But it held for several years and then I needed to get bearings replaced or something that caused me to need to remove the header. I kept expecting it let go any time but it never did.... Haha...

Paul does it that way, and I tried it, too, and it worked fine.

Brett

Dave_Trible · « **Reply #7 on:** May 27, 2014, 09:00:10 AM »

I might have to try that. Stan Powell put me onto an aluminum duct tape gasket, non-permanent lock tight and lock washers. I retighten the screws right after the first run. Heat sets the lock tight. This has solved most my header leaks....but pipes are another matter with the .76 back pressure.

Dave

Mike Haverly · « **Reply #8 on:** May 27, 2014, 09:07:48 AM »

This is the stuff I used per instructions from the Bay area.

http://www.grainger.com/product/3DPT6?gclid=CjkKEQjw75CcBRCz2LiEs5OPsZoBEiQADgUma9SZRRlQ8CCR3K0nFYmMw6ewvq2r_9XEHBWR2tZIHprw_wcB&cm_mmc=PPC:GooglePLA-_-Adhesives,%20Sealants%20and%20Tape-_-Thread%20and%20Gasket%20Sealants-_-3DPT6&ci_src=17588969&ci_sku=3DPT6&ef_id=U4SomAAABAIPdba5:20140527150040:s

I bought it in 2006 and just now threw out what was left. It got bad from sitting around and not being used. Works well used as Brett suggested. Don't get carried away or get sloppy with it because it sticks to about anything it touches and can be difficult to remove.

Tim Wescott · « **Reply #9 on:** May 27, 2014, 09:30:56 AM »

Use good quality new lock washers of whatever style that Randy or PA recommends. I was told, years ago, by a mechanical engineer who specializes in making bolt-together assemblies stay bolted together on helicopters*, that bolts loosen under vibration because at some point in the cycle the joint gets squeezed tighter than the bolt is holding and the bolt floats. At that point, the bolt can walk, and it usually walks looser. Lock washers -- little sharp edges notwithstanding -- primarily keep bolts tight because they act as springs, which keeps the bolts from floating, which keeps them from being able to walk.

So if you put scruddy old lock washers in there that were sitting in your flying box because you found them on the pavement at the flying field -- please replace them.

* Helicopters basically fly by vibrating. Don't let all those stories of blades generating aerodynamic force fool you -- if a helicopter isn't vibrating violently, it's not flying.

Scott Richlen · « **Reply #10 on:** May 27, 2014, 01:23:38 PM »

Thanks guys! I'll be getting out the wet or dry and the RTV...

Scott

Steve Fitton · « **Reply #11 on:** May 27, 2014, 08:12:02 PM »

I use an aluminum gasket between header and engine. I am always chicken to really bear down on the bolts (and I've never used lockwashers, maybe I should). I have learned to run the whole power system on the test stand a few times, and I snug the bolts down after each of the two or three test runs. After a few heat cycles, the bolts stay tight and remain tight till I remove them.

RandySmith · « **Reply #12 on:** May 27, 2014, 08:30:28 PM »

Clean both the mating surfaces, IF and only If you see dings are abnormal dents etc, use some 400 wet sandpaper and flatten them, Use metal duct tape as a gasket . this is the tape I have used for over 25 years now,It looks like think polished aluminim tape . I never have headers come loose , use blue locktight on clean grade 8 bolts, you can use lock washers if wanted. The metal Duct tape has a sticky side with paper backing, stick it onto the header ...ONLY, then you can very quickly use a #11 Xacto and trim out the hole in the middle and the 2 bolt holes, DO NOT forget this step...some have... Bolt them together and put 15 inch pounds torque on the bolts, They will stay this way and very very rarely have I ever heard them coming loose.
DO NOT use gasket material that is thick, it will crush and the bolts will get loose, '
DO NOT get the bolt holes in the case full of silicone.
be VERY careful if you use silicone
DO NOT use cheap bolts, or worn bolts or washers.

Randy

Scott Richlen · « **Reply #13 on:** May 28, 2014, 06:11:30 AM »

Randy:

This is what I have been doing! I use the aluminized duct tape and the bolts that you include. I have tried it with and without lock washers. However, I don't know if I am torquing them to 15 pounds. What tool do you use so you can know that?

Thanks,
Scott

RC Storick · « **Reply #14 on:** May 28, 2014, 08:27:24 AM »

Maybe the holes and bolts are not clean enough. Once clean use a lock tight primer then the blue lock tight. Let sit until dry.

Allan Perret · « **Reply #15 on:** May 28, 2014, 10:50:20 AM »

Quote from: Scott Richlen on May 28, 2014, 06:11:30 AM

However, I don't know if I am torquing them to 15 pounds. What tool do you use so you can know that?

You would need a torque screwdriver in the 10-50 inch range, decent ones are going to start around 100 bucks. If Harbor Freight has cheap ones I would not trust it. Most guys just do it by feel. Good method is to use a long Tee-handle allen wrench. For 15 inch-pounds you would need to apply 5 lbs twisting force on a 3" lever arm; or 3 lbs force on a 5" lever arm. Size of the lever arm is where you place your thumb and finger on the tee handle. Remember, 15 inch-pounds is only 1.25 foot-pounds.

Scott Richlen · « **Reply #16 on:** May 28, 2014, 04:00:27 PM »

Randy:

Would this one work?

http://www.amazon.com/Neiko-Pro-Grade-4-Inch-Torque-Screwdriver/dp/B000RZ1D86/ref=sr_1_1?s=hi&ie=UTF8&qid=1401313298&sr=1-1&keywords=torque+screwdriver

Also: where do I get more screws?

Sparky: I used the cleaner/primer. Still came loose.

Thanks

Randy Cuberly · « **Reply #17 on:** May 28, 2014, 04:37:55 PM »

Quote from: Scott Richlen on May 28, 2014, 04:00:27 PM

Randy:

Would this one work?

http://www.amazon.com/Neiko-Pro-Grade-4-Inch-Torque-Screwdriver/dp/B000RZ1D86/ref=sr_1_1?s=hi&ie=UTF8&qid=1401313298&sr=1-1&keywords=torque+screwdriver

Also: where do I get more screws?

Sparky: I used the cleaner/primer. Still came loose.

Thanks

Hi Scott,
I'm Randy but not the one you were addressing, obviously. However I have had one of those very torque drivers and it is excellent. Mine was checked for calibration at the Raytheon Missile Systems tool room and passed muster for thier specifications (which are very rigid through out the full scale).

This one gets my blessing. I find I don't really use it a lot but when needed it is very handy!

That price is a good deal, I think I paid considerably more for mine a couple of years ago!

Randy Cuberly
PS: I'm a big believer in belt and suspenders in situations like this so I use both Blue loctite with the primer Sparker suggested and lock split washers. I'v never had a header come loose in use. PA65s, PA51, PA61, ROJett 65 and ROJett 67. None of these engines are vibraters and should not be such a problem unless as suggested before you have another problem like unbalanced props or wimpy engine mounts etc.

RandySmith · « **Reply #18 on:** May 28, 2014, 07:14:47 PM »

Quote from: Scott Richlen on May 28, 2014, 04:00:27 PM

Randy:

Would this one work?

http://www.amazon.com/Neiko-Pro-Grade-4-Inch-Torque-Screwdriver/dp/B000RZ1D86/ref=sr_1_1?s=hi&ie=UTF8&qid=1401313298&sr=1-1&keywords=torque+screwdriver

Also: where do I get more screws?

Sparky: I used the cleaner/primer. Still came loose.

Thanks

Hi Scott

Yes that will work, I can send you ,more screws if needed, just let me know, The details I described have worked all over the worlds for decades now, If you are still having problems I need to know more about your plane and setup, because it maybe you have something else that is very wrong. Please double check taht you have NO silicone down the threaded bolt holes, that will NOT work if you do, the holes MUST be cleaned of the debris.

Randy

Brett Buck · « **Reply #19 on:** May 28, 2014, 07:52:42 PM »

I have seen all the different types of gaskets fail repeatedly. It's not something you are doing wrong, it is endemic. Just face it off, use silicone or even 5 minute epoxy, and move on with your life.

The bolts should be a little bit tighter than you can get it with a ball driver. I use a regular allen wrench and get about 1/2" bend in the long side, which is pretty tight.

While you have the silicone out, seal the spraybar to the case on both sides using *tiny* amounts right on the flange, and right on the nut. Don't get any in the fuel path or you will be very sorry. It will run *much* steadier afterwards, particularly on the ground. That one, you do need to wait for it to set.

Brett

RandySmith · « **Reply #20 on:** May 28, 2014, 08:05:15 PM »

I have seen silicone gaskets fail, more than onced, and I have seen them cause all sorts of other problems, In 25 years I have never seen the gasket material I use fail, never. THe gasket materials that are more than a few thousands thick will as Brett says, fail repeatably, The Metal tape will not fail.
The technique I described above will not fail either. I is proven bullet proof over many decades by many many pilots that use my techniques .

Randy

Scott Richlen · « **Reply #21 on:** May 29, 2014, 06:25:14 AM »

Randy/Brett:

Thanks for all of the advice, I'll be able to use it. I have been setting the screws by hand with a ball driver with a very small handle. So, that is probably what I'm doing wrong. I'll order that torque screwdriver (thanks to both Randy's for confirmation.) I'll also check the balance on the prop and spinner.

Randy - please send me more screws.

Like I said before, this engine gives a great flight run and does every thing right. I just need to keep that header from coming lose.

Thanks again,
Scott

Steve Fitton · « **Reply #22 on:** May 29, 2014, 07:31:40 AM »

Scott, remember it is better to undertighten and then ask questions like you have done vs gorilla tighten the screws and strip out the case!

Lauri Malila · « **Reply #23 on:** May 29, 2014, 08:19:45 AM »

Hi Randy,

Can you please specify which "blue Loctite" you recommend? Like a ref. number or so. There are all kinds of Loctites in differend colours. Actually, the weakest one I use at work is blue too. It's not enough for header screws.
I use quite strong one, #603, for mounting my muffler.
About the seal, I have allways been happier with epoxy instead of silicone putty. The aluminium tape is yet to be tried.

Lauri

RandySmith · « **Reply #24 on:** May 29, 2014, 09:39:17 AM »

Quote from: Lauri Malila on May 29, 2014, 08:19:45 AM

Hi Randy,

Can you please specify which "blue Loctite" you recommend? Like a ref. number or so. There are all kinds of Loctites in differend colours. Actually, the weakest one I use at work is blue too. It's not enough for header screws.
I use quite strong one, #603, for mounting my muffler.
About the seal, I have allways been happier with epoxy instead of silicone putty. The aluminium tape is yet to be tried.

Lauri

Hi Lauri

I use the #24200 medium on the header bolts, it is made to take back apart with hand tools:

" Loctite® Threadlocker Blue 24200 ® is designed for the locking and sealing of threaded fasteners which require normal disassembly with standard hand tools. The product cures when confined in the absence of air between close fitting metal surfaces. It protects threads from rust and corrosion and prevents loosening from shock and vibration. Loctite® Threadlocker Blue 24200® is particularly suited for applications on less active substrates such as stainless steel and plated surfaces, where disassembly is required for servicing. "

Using the stronger ones such as RED 271 or Green locktight can be a problem later.. The blue has always worked well for this application.

By the way, for your aluminum mufflers and hi heat the #2620 Red Hi Temp paste is a great product, I use that for putting together my mufflers, I would use that on header bolts, if ,I never wanted to take them off :-)

Randy

Lauri Malila · « **Reply #25 on:** May 29, 2014, 01:18:02 PM »

Thanks, Randy.

Got to check the #2620, it may be usefull. I got really nice thin wall dural tubing from Antonov plant, the latest muffler's baffles stay in place only with interference fit!

Lauri

RandySmith · « **Reply #26 on:** May 29, 2014, 03:45:16 PM »

Scott I sent out Grade 8 HoloChromes bolts to you today, 5/8 x 4-40 for your use with washers, I also threw in some pressure sensitive aluminum tape
Please remember to remove the backing and cut out the holes.

Randy

Scott Richlen · « **Reply #27 on:** May 30, 2014, 08:15:42 AM »

Thanks Randy! I've ordered the torque screw-driver and it is on its way also. Hopefully I'll get a couple of flights in next weekend before going to Brodaks. This seems typical: new plane, not enough flights (10 so far), and here comes Brodaks Fly-In. Happily, the SL-3 flies very similar to the SL-2.

Scott

Phil Tolfree · « **Reply #28 on:** May 31, 2014, 08:43:45 AM »

Hi Scott and the rest of you guys. I've been nosing around for a while here and just joined. Well, I joined to add my sixpence worth (2c to most of you) to this thread. If you abrade your mating surfaces Scott, as Brett suggests, please be very careful to ensure no grit from the wet and dry goes in the cylinder. A particle of aluminium oxide or two bouncing around or caught in a port will wreak havoc.

Cheers
Phil

(Apologies for the correct spelling in this message... I'm English.)

Scott Richlen · « **Reply #29 on:** May 31, 2014, 07:06:56 PM »

Randy:

Received the bolts today, Thanks much. The torque screwdriver also came in the mail, so I'll be putting everything together and hopefully flying next weekend.

Scott

Randy Cuberly · « **Reply #30 on:** May 31, 2014, 08:08:54 PM »

Quote from: Phil Tolfree on May 31, 2014, 08:43:45 AM

Hi Scott and the rest of you guys. I've been nosing around for a while here and just joined. Well, I joined to add my sixpence worth (2c to most of you) to this thread. If you abrade your mating surfaces Scott, as Brett suggests, please be very careful to ensure no grit from the wet and dry goes in the cylinder. A particle of aluminium oxide or two bouncing around or caught in a port will wreak havoc.

Cheers
Phil

(Apologies for the correct spelling in this message... I'm English.)

Hi Phil,
Welcome to Stunt Hanger.
That's good advice to Scott, however He's a relatively experienced flier and I'm sure he knows to be careful around the exhaust port and stuff it with paper towels or something similar before using the sandpaper on it.
Do you fly stunt Phil?

I'm sure we'd like to hear more from you!

Randy Cuberly

roy cherry · « **Reply #31 on:** May 31, 2014, 11:53:55 PM »

hi guys when i used to fly i/c motors i just used a smear of 24 hour jb weld cleaned mating surfaces as described in earlier posts but if dissasembly of motor is requerd you really dont need to take of the heador not on a pa any way as mine never needed much fettling if i did need the heador off a sharp tap with a small hammer did the job mine are still good after 14 years shame i dont use them any more noise issues in the uk are proving electrick better for our flying feilds here in the uk roy cherry

Scott Richlen · « **Reply #32 on:** June 01, 2014, 04:15:25 PM »

Randy C.: thanks for standing up for me, but I seem to always find new and innovative ways to screw up! Well, actually, sometimes they aren't so new and innovative, so, thanks also to Phil for the reminder.

One thing I goofed on was to construct the cowl so that you have to take the header off to remove the cowling (see my comment, above.) I am usually careful on my ships to put the split line running through the needle valve and the muffler (at least when it is a side exhaust). Not in this case. So the cowl goes under the knife this week to fix that error. Hopefully I'll be able to do it without having to repaint anything that shows!

I got one more weekend to get some flights in before Brodaks. Interestingly, this last weekend had really choppy air so I wouldn't have flown my SL-3 even if it were repaired.

Scott

Randy Cuberly · « **Reply #33 on:** June 01, 2014, 04:31:11 PM »

Quote from: Scott Richlen on June 01, 2014, 04:15:25 PM

Randy C.: thanks for standing up for me, but I seem to always find new and innovative ways to screw up! Well, actually, sometimes they aren't so new and innovative, so, thanks also to Phil for the reminder.

One thing I goofed on was to construct the cowl so that you have to take the header off to remove the cowling (see my comment, above.) I am usually careful on my ships to put the split line running through the needle valve and the muffler (at least when it is a side exhaust). Not in this case. So the cowl goes under the knife this week to fix that error. Hopefully I'll be able to do it without having to repaint anything that shows!

I got one more weekend to get some flights in before Brodaks. Interestingly, this last weekend had really choppy air so I wouldn't have flown my SL-3 even if it were repaired.

Scott

Happens to the best sometimes Scott. I'm a little negative about being able to cut in without having to sand and paint however. I think I'd just bite the bullet and go all the way...repaint tose parts that have to be cut.
It's possible to mask all the parts that don't need paint refinish and repaint those that do and blend carefully and rub out so the repair isn't really noticeable. The masters can do it so well you can't tell there was a repair. Windy Urtnowski did several columns on repairs that covered things like this. Other guys that I've seen do miracles are Pete Peterson and Lou Wolgast. Randy Powell )On this Forum) can probably give advice on how to accomplish this also.

Randy Cuberly

Scott Richlen · « **Reply #34 on:** June 09, 2014, 05:49:24 PM »

The rest of the story...

First I modified the cowl so I could more easily get at the header bolts. Then, since I had lost one of the bolts last time the header came loose, I tried to use one of the header bolts that Randy sent me (Thanks again for the quick help Randy!!) It was too long (even with lock washer). But in the process of cutting it to the correct length, I realized that the remaining bolt was actually bottomed out in the hole (there was just a tiny bit of movement of the header with that single bolt fastened - and it was the wrong movement!! That slight amount of looseness from the bolts bottoming out was apparently allowing a fine vibration that would cause things to come undone.) So, take a look at the header picture, below. None of the countersinks are this deep on my other three headers. So, I carefully trimmed both bolts as needed, and followed Randy's directions exactly to put everything together.

When I flew on Saturday, I retorqued the bolts after each flight while the engine was hot. After the first three flights they stopped moving during retorquing.

Thanks again everyone for the great advice!
Scott