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TH 75 vibration problems ?

Old 08-18-2009, 08:48 AM
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prgonzalez
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Default TH 75 vibration problems ?

In about two weeks I will start breaking in my first TH 75 engine that I am installing in my US60. I will follow the advice of heating the head with a heat gun prior the first start.

Now to the question is: Are you having problems with the silencer being loose, vibrating too much, spitting black stuff due to vibration, or even loosing the silencer during flight?

I met this pilot at our field and he is having all of the problems above. He even lost the carb barrel locking screw and the barrel came out of the carb during flight right after seeing something coming off of the plane (silencer).[X(]

Please advise and comment your break in experiences and recommendations.

Thanks
Pedro
Old 08-18-2009, 08:59 AM
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ArcticCatRider
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Default RE: TH 75 vibration problems ?

Make sure the prop is balanced. On occasion...the spinners are out of balance, too.

2 piece mufflers have always come apart in midflight..."spitting black stuff"....probably shouldn't be happening.

Also, if you need to ream the bore in the prop hub, make sure you don't over do it. I've seen guys drill a 5/16th hole in a prop that goes on a 1/4 inch shaft..don't do that! Same goes for spinners. Make sure you use the correct bushing.

At lower speed...you can expect it. Larger single cylinders will vibrate....no way around it.
Old 08-18-2009, 09:02 AM
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Default RE: TH 75 vibration problems ?

There are no vibration problems with the Tower .75. It is just the RPM that they turn. I put blue (Low strength) loctite on the carb barrel screw, and allways take the muffler apart, and assemble with RTV. It not only keeps it together, but it makes it spotless clean while running.
Old 08-18-2009, 10:15 AM
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Charley
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Default RE: TH 75 vibration problems ?


ORIGINAL: prgonzalez


Now to the question is: ........, spitting black stuff due to vibration, or even loosing the silencer during flight?

Thanks
Pedro
Spitting black stuff is a symptom of an ABC engine that's not quite broken in. Vibration in a single-cylinder engine is to be expected but vibrating hard enough to shake things loose sounds like prop/spinner out of balance.

Where did you hear that business about preheating the head?

CR
Old 08-18-2009, 10:27 AM
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ArcticCatRider
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Default RE: TH 75 vibration problems ?

It's also not a bad idea to get some Christmas ornament wire, or some other really thin, light flexible wire to hold the two halves of the muffler together...that way if they come apart, at least you don't lose the back half.

I've JBwelded a lot of them together, too. My favorite option, however is to ditch the stock muffler and get a Macs pipe.
Old 08-18-2009, 11:58 AM
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Default RE: TH 75 vibration problems ?

All,

I agree with all of you. I too believe the issue is more an out of balance prop/spinner than a problem with this engine. I have never read anything like that about this engine in this forum and I was quite surprised when I saw this airplane coming down this weekend after loosing the silincer and carb barrel screw. However, I am here with my first TH 75. So, I decided to cover the bases before firing it up the first time.

I will try the RTV in the silencer and will go with JB weld in the extreme case.

CR,

I have read it in other threads here in RCU. It is about expanding the sleve piston a bit by heating the cylinder before the first ignition.

Pedro
Old 08-18-2009, 01:44 PM
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Charley
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Default RE: TH 75 vibration problems ?

ORIGINAL: prgonzalez


CR,

I have read it in other threads here in RCU. It is about expanding the sleve piston a bit by heating the cylinder before the first ignition.

Pedro
Don't think I'd do that. While some may think it will make it easier to turn the engine through the "pinch" I believe that generating expansion from the internal heat of combustion is a better way to go. The internal parts need to heat together in the normal manner, IMHO.

What does your user's manual say about break in procedures?

CR

CR
Old 08-18-2009, 01:56 PM
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ArcticCatRider
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Default RE: TH 75 vibration problems ?

I agree with Charley. I've never heard of "preheating" a motor before break-in. I've broken in a lot of motors....

I wouldn't waste the time if I were you...follow the manual...run the thing a few clicks rich..and it will last you a long, long time.
Old 08-18-2009, 02:57 PM
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Default RE: TH 75 vibration problems ?


ORIGINAL: ArcticCatRider

I agree with Charley. I've never heard of ''preheating'' a motor before break-in. I've broken in a lot of motors....

I wouldn't waste the time if I were you...follow the manual...run the thing a few clicks rich..and it will last you a long, long time.
Okay, after thinking about it, you guys are right again. No pre-heating and will follow break-in instructions per manufacturer.

Thanks for your advice.

Pedro
Old 08-18-2009, 03:42 PM
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Default RE: TH 75 vibration problems ?

Interesting thread about TH 75 break in...

http://www.rcuniverse.com/forum/m_55...tm.htm#5904725

Old 08-18-2009, 05:30 PM
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Default RE: TH 75 vibration problems ?

I guess if you have never heard about heating the cylinder head, you have never been around a Tight True ABC engine. A little heat with a heat gun on the Head is done all the time with tight Car, Boat, and Airplane engines for the first start up. OS's if these are the engines you are used to are not ABC engines and do not have there cylinder to piston fits any where near as tight. All the pre heating does is loosen the fit slightly so you can start it with out it sticking at top dead center, and dramaticaly reduces the stress on the crankshaft and connecting rod on the first start up.
Old 08-19-2009, 09:06 AM
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Default RE: TH 75 vibration problems ?

It is interesting reading and knowing about different experiences by contributors here on RCU. What is even more interesting is the passion everyone defend their own knowledge based on their experiences.
Old 08-19-2009, 11:00 AM
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Default RE: TH 75 vibration problems ?

It's okay to have not heard 'everything' yet. The day you stop hearing something new is the day you stop learning. Even the newest rookie at the field can teach you something if you are listening.
Old 08-19-2009, 04:39 PM
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Charley
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Default RE: TH 75 vibration problems ?


ORIGINAL: MOTORMAN37
I guess if you have never heard about heating the cylinder head, you have never been around a Tight True ABC engine. A little heat with a heat gun on the Head is done all the time ........
I have and have had many "Tight True ABC" engines. I remember a ST.61 ABC that really squeaked. Also a Rossi. I've heard of the preheating gig before, just have never found it necessary. Just broke in a friend's OS .46 AX. We did it by the manual (his choice) and didn't need to preheat it. It started easily and ran well.

The TH .75 owner's manual has very detailed instructions, including break in procedures. It doesn't recommend preheating.

One thing universally true in this hobby; there are as many opinions as there are, er, people. Doesn't mean any of them are right...or wrong.... just lots of them...............

CR
Old 08-19-2009, 06:01 PM
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Default RE: TH 75 vibration problems ?

The AX you were talking about is not a ABC engine, and is no wears near as tight to begin with. I know what works, since I have broke in a half dozen TH .75's, and they all are returning stunning performance after many gallons of fuel.
Old 08-19-2009, 06:26 PM
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Default RE: TH 75 vibration problems ?

Charley,
How many TH .75's have you run? I am speaking from experience with these engines. I simple heating of the head and cylinder with a Monokote heat gun is all that is required to enable an easy start the first time. I have TH .75's with over 12 gallons thru them that are tighter than a brand new OS AX.
Old 08-19-2009, 07:03 PM
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Default RE: TH 75 vibration problems ?


ORIGINAL: MOTORMAN37

The AX you were talking about is not a ABC engine, and is no wears near as tight to begin with.
OK it's an ABN; so what? Same thing applies. The instructions don't tell you to preheat it. We didn't and it's humming.

CR
Old 08-19-2009, 07:06 PM
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Charley
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Default RE: TH 75 vibration problems ?


ORIGINAL: MOTORMAN37

Charley,
How many TH .75's have you run? I am speaking from experience with these engines. I simple heating of the head and cylinder with a Monokote heat gun is all that is required to enable an easy start the first time. I have TH .75's with over 12 gallons thru them that are tighter than a brand new OS AX.
Only one; belonged to a guy I taught to fly. We broke it in by the book without a heat gun. Quit trying to be right and accept the fact that there are many ways to success. One of these is the manual that came with the engine.

CR
Old 08-19-2009, 09:18 PM
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Default RE: TH 75 vibration problems ?

Okay, okay......

I have an Evo .46NT that was almost as tight as what you guys are saying. It let out a big squeal when turned over by hand before ever being cranked up.
Old 08-19-2009, 10:00 PM
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Default RE: TH 75 vibration problems ?

One of the original questions was about the silencer producing black stuff due to parts vibrating/rubbing against each other.

For those that have run one or have several TH 75's, what's your experience about that?

Did RTV work in all cases? or Was JB weld the ultimate solution?
Old 08-20-2009, 12:54 AM
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Default RE: TH 75 vibration problems ?

RTV has fixed it for me, but I do that before I ever run them. I never have black gook (aluminum and oil) come out of my exhaust.
Old 08-20-2009, 09:03 AM
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Default RE: TH 75 vibration problems ?

My ABC Super Tigres, My Rossi's, Picco boat motors...all are plenty tight near the top...and I haven't used the heat gun on the intitial run..just my .02
Old 08-20-2009, 09:46 AM
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Default RE: TH 75 vibration problems ?

Heating the engine came from F1 race engines that were so tight that they would not turn over. If you did not do it, it would scuff the piston and ruin the motor. Maybe not nessasary today but does not hurt either.
Old 08-20-2009, 05:02 PM
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Default RE: TH 75 vibration problems ?

My new TH .75 would not turn over at all unless i preheated the head, i also mentioned this in a previous post about the TH.75 so maybe thats where he got it from, i'm telling you i couldn't turn it over putting pretty good pressure on a 12" prop, even with 18V on my starter it still would not make a revolution, i preheated the cylinder a bit with a heat gun and it started right up, 2 tanks later the preheating wasn't necessary and it has run like a dream since, it is only 1 of my two engines that always start easily with a chicken stick ( the rest prefer a starter ) and is still really tight at TDC after a few gallons.
Old 08-20-2009, 07:08 PM
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Charley
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Default RE: TH 75 vibration problems ?

Hay Micro,

Maybe you need to work out more. I have a heavy duty starter that won't turn my HC Saito .80 when powered by a 7 AH 12V battery. Spins it fine when it's run by a 12V lawn tractor battery. Hint: it ain't the volts, it's the amps.

CR

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