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:D. 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

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.

RE: TH 75 vibration problems ?
 

There are no vibration problems with the Tower .75. It is just the RPM that they turn.:D 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.:D

RE: TH 75 vibration problems ?
 

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

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.

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

RE: TH 75 vibration problems ?
 

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

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.

RE: TH 75 vibration problems ?
 

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

RE: TH 75 vibration problems ?
 

Interesting thread about TH 75 break in...

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

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.;)

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.

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.

RE: TH 75 vibration problems ?
 

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

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.:D 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.:D

RE: TH 75 vibration problems ?
 

Charley,
How many TH .75's have you run?:eek: I am speaking from experience with these engines.:D 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.:D

RE: TH 75 vibration problems ?
 

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

RE: TH 75 vibration problems ?
 

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

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.

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?

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.;)

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

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.

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.

RE: TH 75 vibration problems ?
 

Hay Micro,

Maybe you need to work out more. :D 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

RE: TH 75 vibration problems ?
 

Hey, better check your theory with a wattmeter, the 7AH 12 gel cells like the one i have in my flight box won't hold the voltage when placed under the heavy load of a starter, this is why your lawn tractor battery will spin it and it will probably stay at 12V, and your hint is not a hint becuase when you put more volts to a DC electric motor it will also increase the amperage which means more power.

RE: TH 75 vibration problems ?
 

And back to the original question, i used regular silicone when reassembling the muffler after i read advise on here about doing so and it has worked fine since, now on my Magnum .52XLS it is spitting black goo all over my F-22 and it is because the center part of the muffler is loose and the nut it tightened all the way to the end of the threads, i will have to remove that one to silicone and add some washers to the bolt so i can get it tight.
On a side note i also have two of the .46 tower mufflers on my TT PRO.46's and i haven't touched them and they haven't came loose or spewed out the black goo.
As for the carb on my TH.75, on the test stand the carb barrel locking screw fell out during the second run, put back in and tightened it really good, has been fine since. The set screw on the throttle arm fell out on my second flight on a new plane, 10min WOT was not fun but the plane survived and the set screw was replaced with a machine screw with locktite, has been fine since. The LSN will slowly turn itself out when the engine runs, i tried a new o-ring but it still does it, i've heard that there might be a problem on the LSN that the groove might have been machined too deep, i've read a tip on using some dental floss to wrap around the groove before puttin the o-ring on, i will try this as this plane/engine has been out of commision for awile.

All in all this engine needed the most work out of my 12 2 stroke glow engines, but it does run quite well when you work out all the bugs.

RE: TH 75 vibration problems ?
 

That's what I was telling you, in a nutshell. You can have all the starter in the world AND you can toss in another 6 volt battery -your reference to 18 volts - but if the combination of batteries can't supply the necessary current (power) you won't spin the engine. Get it now? :D

CR

RE: TH 75 vibration problems ?
 

Hi!
OK! Here we go!
No modern ABC, ABN or AAC engine needs preheating with a heatgun to start. This could perhaps be used with old K&B ABC pylonracing engines in the distant past ;) but not today with our modern ABN set-ups!
Most modern glow engines (two stroke)are ABN and are set up so loose that they are easily flip started with a finger! And more easily soo with an electric starter!
Use either a 12V 10A Motorcycle battery or a 14,4V , 2000mAh LiPo cell to power your electric starter.
7A Motorcycle battery works too, but it cannot deliver enough amps when it comes to starting big 20cc -25cc four strokes in the long run.

When it comes to all the Chinese two stroke engines, like the ASP, Magnum, SK, Kyosho GX and SC with a two part silencers, they are notoriously bad! As the silencer screw will always loosen when the engine gets hot.
The only solution to this problem is screwing the the two silencer parts together with small metal screws and using silicon as gasket.

RE: TH 75 vibration problems ?
 

So your new TH.75 from the last batch of new in stock TH.75's was loose enough to turn it over with a starter? mine sure wasn't.

RE: TH 75 vibration problems ?
 

[/quote]

That's what I was telling you, in a nutshell. You can have all the starter in the world AND you can toss in another 6 volt battery -your reference to 18 volts - but if the combination of batteries can't supply the necessary current (power) you won't spin the engine. Get it now? :D

CR
[/quote]

No, i stil don't get it, the 18V battery i was using is capable of over 40amp draw while holding it's voltage and it would still not turn over this engine and that was the reason for preheating the engine with a heat gun, after the second tank the engine was loose enough to use my regular starter setup with no problems, remember this is a made in china engine and tolerances are not always spot on, so a tower engine from 2 years ago might have been loose enough to break in normally but from what i've been hearing the new batch has been extremly tight.

RE: TH 75 vibration problems ?
 

I've been doing this for a long time and I've found 3 engines that I couldn't hand start and wouldn't turn over with starter. Two were Tower .75s. They were so darn tight, I thought I would harm the engine by turning it over by hand. The third was an Evolution .36. It was so tight that I took it off the plane, a Plug-N-Play profile from Hangar 9, was it a Patriot?? I'm not sure. I thought I was going to tear the nose off. It would not flip it was so tight. Of course I put oil in them and also fuel, but the cold fit was so tight that it was wiping or squeezing the oil out.

In all 3 cases, mounting on a test bench and heating with a heat gun opened up the sleeve and allowed them to be started. After a couple of runs, I could hand flip and start them easily.

As for heating with a heat gun, I don't see the down side. As soon as the engine starts, assuming it isn't totally rich, the sleeve heats opens up to running clearance. This is the design of ABC type engines with brass sleeves and tapered bores. It would appear to me that cranking them over with a high torque started where you go past the "crunch" many times would do more damage than heating the cylinder to cause it to open slightly. I can't see how heating causes any damage.

RE: TH 75 vibration problems ?
 

I've got a couple of Chinese made engines and never had the problems you mention.

RE: TH 75 vibration problems ?
 

Profile planes will show vibration to a much greater extent than full bodied planes

RE: TH 75 vibration problems ?
 

My TH 75 engine was very tight and I preheated it before starting it on the bench. I also relieved the cylinder to piston clearance before running the engine. Will do it again if an engine will not turn over to my satisfaction when cold.

Long time mechanic and Mechanical Engineer.

Bill

RE: TH 75 vibration problems ?
 

Hi Guys,
Well My fix for the two peice muffler is to install
a Nylock nut instead of the supplied one.
Go buy a 6-32 or 8-32 Nylock nut , after installing
on the muffler, run the engine thru one or two tanks
Than retighten the screw and nut.
No more lost back half of muffler.

By the way Charlie try to get Your hands on a new TH 75
Than You too will see how tight they are.
Just My .02!!!
Hoss Allen

RE: TH 75 vibration problems ?
 

I understand the preheating you did, but why would you mess with the fit?:eek: I am also a mechanical Engineer.:D The fit will loosen up a little after the first run, and reward you with High Performance.:D
My Tower .75 with the highest time (13 + gallons) still has enough compression, that you can grab a blade and pick the plane up on one side and hold the tire off the ground untill you get sick of holding it, and it will not bleed down.:D

RE: TH 75 vibration problems ?
 

I've been breaking in a new Aviastar 46. It was so tight when I took it out of the box Ithought it was siezed. A couple drops of castor in the plug hole fixed it right up. There was no way my starter could have turned it without it. It does vibrate a lot though. Another tank or two will fix it, I hope.

RE: TH 75 vibration problems ?
 

Frankly it appeared that the final tumbling process created some slight burs on the top inside of the cylinder, probably a result of the tumbler being loaded with too many parts. In any event the fit was not to my liking, I had already paid for the engine, and the maximum exposure was only $110.

Bill

RE: TH 75 vibration problems ?
 

You can hone and burnish chrome