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

RE: TH 75 vibration problems ?
 

Well Guys,

I'd looove to get my hands on a new TH .75 to turn over; er, if it was free. :D Anybody want to send me one? I promise I'll return it. I won't even start it up. I'll just put a 14" prop on it and see if I can turn it through compression.

I have a real hard time believing they came out of the factory so tight they couldn't be turned through compression. Someone said they were afraid they'd break something if they forced it through compression. OK, but that's an opinion, not a fact. But what the hey, if it breaks, back it goes as defective.

As far as 40 Amps battery capability goes, that's not a lot of current. A couple of hundred is more like it in order to run a heavy-duty starter on a stubborn engine. My heavy-duty starter, on a lawn tractor battery will spin a G38; it ought to spin a TH .75.

One can relieve the piston to cylinder clearance without disassembling the engine. Fox used to sell Lustrox for quick break in of some of his high performance engines, including the ABCs. Lustrox was jeweler's rouge AFAIK. I'll bet Duke laughed his arse off at the markup in that deal. :D

Taking all of the replies into consideration, I can see when one would preheat the head/cylinder, on an individual-engine basis. I'll never argue with a method that several people say worked for them.

Peace,

CR

RE: TH 75 vibration problems ?
 

I never said you could not trun it over.;) I said it would sqeak to a stop and then go past TDC with quite a bit of force.;) It only takes about 10-15 seconds with a Monokote Gun to loosen it up nice.
My highest time engine will still stick on TDC if it stopped there, and cooled off.;)
I would never think of loosening the machined fit, that is why they are as powerfull as they are. The cylinder is in perfect harmony when at operating temps.:D
There is no measureable amount of leak down with these engines.:D:D

Fox probaly used it because his maching was so lack luster and crude.;)

RE: TH 75 vibration problems ?
 

I suppose you meant "probably" and "machining," SP? Now you've ticked me off! [:@] Duke forgot more than you've ever learned about building engines. Into the bit bucket with your posts!:D


CR

RE: TH 75 vibration problems ?
 

I made a starter (for my shop) by taking apart an old broken starter and used the shaft and cone in my 18v cordless drill. I have several TH engines (3- .46's; 3- .61's; 2- .75's) and all were hard to turn over by hand. So- I took out the plug, put them in a test stand, poured some high quality oil down the carb and into the top of the cylinder head and gave them a healthy spin with my drill/starter for about 20-30 seconds with the plug out (cover the plug hole and don't run it dry). Then- I immediately put the plug in, hook up the fuel line, started the engine and begin my traditional bench break-in.

All my TH engines run strong. I have a .61 that at last count had over 400 flights. I haven't worn one out yet- but my oldest .61 is certainly getting very easy to turn over nowadays. I love my TH engines. And my OS engines. And my ST and Magnum engines. All are unique and have their quirks.

With that said- the TH mufflers do tend to leak, rotate, and fall off. The RTV method in Post #29 works great. I also add a dab of RTV to the threads of the screw that runs through the body of the muffler, and to the screws that hold the muffler to the engine.

I have also had the rotating throttle piece come out (new screw) and had the throttle stick full open which resulted in a full-throttle 12 minute flight on my Delta Vortex followed by an very nice dead-stick. That was my fault for not paying attention to the throttle end point and jamming full throttle all the time. Smoothed out the divot in the little channel, set the end point properly and no more problems.

Now- when I get a new TH engine, I take off the muffler, RTV it as described, break it in on the bench until it stops moaning at me when I hand crank it cold, and go fly. True- it can be a bit of a headache- but I like playing in my shop and building as much as I like flying so it's good for me. I can see where the folks who love to fly but hate to build or otherwise piddle in the shop could get frustrated. That's my definition of diversity! RC-er's come in all shapes and sizes.

Have fun- Jim

RE: TH 75 vibration problems ?
 

Here is my new home for 3rd .75. It is almost done.;) I made a starter about 10 years ago that will start everything up to a 43 CC gas engine. I used an old Sulivan "SUPER TORQUE" boat starter along with a 9AH Gell Cell battery. I can easily start Saito 1.50-1.80's along with my friends MT 42.;)