I broke in a NIB Tower Hobbies .75 engine the other day. Nothing new to me. I've got 8 of these engines.

But, this one was so tight when fresh out of the box, that I was afraid to even turn it over for priming. I ended up running the throttle to full and then blowing through the muffler/pressure line to force some fuel into the engine before I fired it up.

It was so tight that it was literally squeaking at TDC. I was flipping it with my chicken stick, and it would squeak every time it went past TDC. I had to flip it about 6 or 8 times before it finally fired.

It was so stinking tight that it wouldn't even stay running--even with the glow igniter on it. I didn't even have time to get my hand on the throttle stick and run it up to full before the piston would seize at TDC and kill the engine. I was cringing. I was thinking that this couldn't be good for the rod. I wanted it to stay running just long enough for me to get it opened up to full throttle. It was squeaking while it was running at idle for the 1/2 second or so before it would die again. I was starting to get a sick feeling in my stomach. It just kept dying and sticking the piston at TDC. I had to start it 3 or 4 times before I finally got the throttle slammed open and removed the igniter.

I finally got it started and got my hand on the throttle to run it up to full speed for the break in. I removed the igniter immediately and ran it at a rich 2-stroke.

I started out with a cheap Top Flite 10-8 and Omega 5% fuel. I had it running close to 15,000RPM and still rich. I only ran it about 3 or 4 minutes before shut it down for 20 minutes and let it cool.

I kept increasing the prop size slowly and I kept the RPM up near 15,000RPM and rich 2-stroke during the break in. I went up in size to several different props.

(I've got 6 props that I use to break in these TH .75 engines. They start out small and slowly get bigger as the engine gets stronger. Some of the props are chopped down versions of larger ones, and some of them are stock. I got a little felt bag that I keep these props in--and it's specifically for breaking in the TH .75 engines.)

I went through three 12oz tanks of fuel before I called it good enough. I backed it off peak about 7 or 8 clicks and decided to go fly it.

This one is a SCREAMER!! The best one yet. It's turning a Pro Zinger 13-6 on 5% Omega fuel between 12,500--12,800RPM. Thats NOT peaked RPM. Thats my flying RPM with it 7 or 8 clicks on the rich side. I'll lean it out 1 click per flying session untill it's done.

I've just never had an ABC engine this tight when new. Maybe I should remove a couple head shims and see what it does.[>:]

GOOD GAWD!! If there was ever an engine that needed to be mounted in a speed plane--this is the one. I'll bet this engine would turn an 11-7 or an 11-8 at close to 14,000RPM--maybe more. I might take this engine out of my 3D plane and put it back in the box for now. I can take another engine out of the box and run it in my 3D plane.

I got a GP Cosmic Wind Minnow Sport racer ARF here. That might be just the right combination of airframe and rediculous power.[sm=bananahead.gif]

Do you feel better now?

I love enthusiasm such as this. Thanks for sharing your story. I'm an engine man too, so I understand your feelings.

Yeah: Don't you just feel for their shiny little insides when your turning over a brand new tight one. And then, when you think you've caused so much damage trying to start this squeaky engine that it will never run, it fires right up and goes like a good 'un.

I've had a couple of MVVSs that were really tight - turned into great engines.

Next time, use a monokote heat gun to warm the cylinder before starting it up.

I have two Tower .75's, they were the second to the tightest engines I've
seen. The tightest was a Jett 90L.

Now that I'm through cringing after reading your break-in story....I'll offer
my technique.....it's real simple. Heat the engine with a heat gun to take
away that awful pinch, and you won't hear that awful knocking. My first
Tower .75 knocked loudly on the first start-up, but it only lasted for a few
seconds. That's when I developed the heating technique. I sure works good,
and the engines will love you for it.

My Tower's turn the 11-7 1/2 MAS at 14,000 flat. That's the best prop I've
found for speed on my F-20. I tried a couple APC's at first....they were pathetic.

I do all my ABC engines now with the heat.

FBD.

My TH 75 did that same thing when I went to break it in last winter. Scared me, as I had never broke in an engine like that. I've got probably 2 gallons through mine. I've got it mounted on a Four-Star 60, and it has to be twice as fast as the one with a Saito 100 on it. The Tower 75 is a real screamer, and light as well.

FBD, that engine on the plane on the left has a gold head???????? Is that a GMS? Or is it a photo color problem?

Also, I have three Tower 75's. The two I am using have lost their purple head an they are now back to natural aluminum.

However, as you all have said they are good running engines and both of mine after many, many flights still squeak a little occasionally when they are first started. I am getting ready to put #3 in to service.

In addition to the 75's I also have two .46's and they are great also. I bought a GMS .47 and it is a screaming demon.

Yes, that is a GMS .47, another screamer.

I did my break in at the field. No A/C power available to run the heat gun. But, thats a great idea. Might have to fire my engines in the driveway from now on. Neighbors will love that.[X(]


I absolutely LOVE engines. I just love to hear an engine scream like nuts. I've turned my break in procedure into a crazy ritual. But, it works well, and I seam to get good results from it. It's overly complicated, and not for everyone, but I do it this way because I think I get the most out of the engine by doing the break in at maximum RPM.

I just can't tell you guys how worried I was getting when I was listening to that engine squeak and knock at idle. I was just praying for it to stay running long enough so that I could get my hand on the TX and slam it to full throttle.

I was thinking, "Gotta get that cylinder hot and get it to expand or I'm gonna ruin this sucker."

I took the head off it last night, and it has 3 shims under the head. I am going to un-bolt it and stick it back in the box for now. I've got another one in a box that I can put on this airplane. I want to keep this engine for a speed plane. I guess, if the other one thats still in the box is just as tight--then I'm wasting my time, but I won't know untill I fire it up and see how it does. Shoot, it might run just as good as this engine does.

This will be the 7th TH .75 that I've fired up. The 8th one is still in the box. But, out of the 7 that I have run, this one is by far the most powerfull and the tightest.

I just couldn't believe how tight it was, and wanted to share with the rest of you gear heads. I was giggleing while I was doing the break in.[sm=lol.gif] I have a pretty good feel for where they will be at during different times of the break in, and I could tell that this one was going to be a lot stronger after the second time I fired it up. Wish I had a video camera.

FBD:
I've seen a couple pics of your F-20. Which one is that? I mean, who makes it?

Does it have retracts? Factory retracts? Or your own installation?

Thanks

That is the 60 size cermark F-20. They are no longer in production. []

They came with retracts, but they were the cheap Hobbico ones, replaced
with Robart by me.

Dave.

Now, if someone would reintroduce the F-20 without the fake air intakes, or, if the fuselage space is needed, fair in the intakes. That would eliminate a lot of drag.

I would rather they provide the retract pockets and let me install the landing gear of my choice - such as Robart's.

Shortening the nose a good bit would be a great idea. Less tailweight would be needed. Lower the canopy a good deal - still less drag.

The K&B 3.5 in my shrike has been run about 25 times so far and is still so tight that it regularly stalls the starter. It's the only engine I've got that I can't rely on hand starts, it's still too tight.

I looked at the Pheonix F-20, but I'm unsure about the quality. I'd also like a plane with retracts.

I have a NIB Patriot XL kit here, but the cost of the pneumatic retracts is keeping me from building it. The TH .75 isn't enough engine for it anyway. Not for REAL speed.

A 40-50 size ARF with mechanical retracts would be just right for my first go-fast plane. I could slap this TH .75 in it and have some fun.

Well, that TH .75 is actually a Super Tigre and they bought the rights to have them built in China.
It sure is one helluva engine. Been running one for about a year and it still is a powerhouse.
It even has more HP than a Fox which is darn hard to beat.

By all means, get it up to full power when you start them because you want the heat to expand the cylinder ahead of the piston. Don't run them very rich either. They must heat up or the piston/cylinder fit will be too tight and wear will take place.

3dbob

This isn't good for an engine. Do like someone earlier suggested and use a heat gun to warm up the engine before turning it over. This will expand the cylinder and give the piston a little extra room to break in and size itself to the cylinder as you run it in. It can cause piston & rod damage so don't take a chance and use this simple device to give the engine a chance.

Mine was the same way. Really tight! Runs like a batouttahell though!

Another tip for pre warming the engine. Park your car/truck facing the sun with the windows rolled up. Place the engine on the dash for a short while. It will warm up nicely in a reasonable climate. If you have everything ready on the stand, you should have time to bolt the engine on and get it running before it cools down much. Worked great on my Jett 50.

Irvine ABC 53 and 46 that I have been running in where very tight when new, and got very powerfull later[sm=thumbup.gif]

Pre heat it by holding the engine in the exhaust stream of your running warmed up car, real close right in the exhaust pipe. That is what we used to do in the winter time to make easier starting for our engines.

I saw a Guy heat one up on his exhaust pipe for the first start-up....

....worked like a charm.

FBD.

Got to love them tight engines.

But Iam confused, my TH 61 is a sreemer too but is it a copy of GMS or a Super Tiger ??
Rich

Some opinions:
The reason for heating up the piston/cylinder ASAP is to lessen the wear on the bushings (conrod) during the first couple of minutes of running.
Picture the lower end of the conrod riding on a film of oil that keeps it centered. The faster it spins, the more force to keep it centered on the crank pin.
Now add side forces imposed by the piston going up and down. This will cause the rod to not be centered on the crank pin but to rub against it causing a bit of polishing for a final fit.
Now picture extreme loads because the piston/cylinder are extremely tight. This can cause excessive wear on the conrod so that the bushing is enlarged excessively.
This also applies to the piston/cylinder. Heated up properly, it wears more slowly to polish the piston/cylinder fit and allows particles to be carried away. Run slowly, the fit is very tight and more grinding than polishing occurrs.
The best way to break-in an ABC(ABN, etc.) is to quickly get it up to operating temp (rich side of peak) using a smaller than normal prop. After about five minutes, the parts are polished and the engine is initially broken-in. You will probably see an increase in performance for about an hour, then it should be fully broken in.
Is this the only way of breaking in an engine? Of course not. As people state above, they have gotten good results with various methods. This method should, however, make your engine be all that it can be.

George

I have a mag 52 in my F20. How do you think this compares to the Tower 75? Likewise, how does the TH engine compare to a Jett 50? Specifically, which would be the "ideal" engine for speed, taking into account weight of each engine?