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.;)