BillS

Inspect and clean.

Received a Tower .75 engine last week. The engine had a bind and didn’t turn through top dead center. Disassembled the engine and it appeared to have lapping compound on the piston. Burs were also found the on the sleeve at the top.

Although not a lot of trouble to fix the engine should not be run without inspection and cleaning and in this case fitting the piston.

One might guess that lapping compound was to assist in quicker break in.

Bill

Charley

My Feedback: (2)

This reminds me of when Duke Fox used to sell jeweler's rouge, under some name he dreamed up, for quick break-in of his lapped piston engines. What the heck did he call the stuff?

CR

scott17

Lustrox was the fine, Garnet the rough.

pe reivers

A glow engine is supposed to be tight in top dead center. The difference between a loose engine may be as much as 10% top hp and low end torque.
The running in sequence will take care of that tight fit, but after running in, it still should be tight and stuck if left in top dead center for an hour or so.

ace4-40

Only an ABC engine should be tight at TDC. Ringed and lapped engines should NOT be Tight at TDC. An ABC does not need any kind of lapping compound. That would defeat the whole purpose of making an ABC engine and hinder its performance.

w8ye

My Feedback: (16)

The Tower 75 is a ABC engine

Ram Jet

Lapping compund? Slow down and break it in sweetly. You don't need lapping compound if you are patient use say 25% lube initially and run rich.

Bill

Ram Jet

You are a more tolerant man than I. I would have it back on Tower's doorstep.

Bill

w8ye

My Feedback: (16)

Towers seem to vary a little as to how tight at TDC they are when new. I had one that I put 100 flights on before I sold it and it still had the tight place at the top.

Charley

My Feedback: (2)

Right! I remember Lustrox, now that you twigged my memory. Thanks! Don't remember Garnet though. []

CR

rcdude7

My Feedback: (264)

One who does not know any better might guess that, the truth is that it will only ruin the fit of the piston and sleeve. A tight fit when cold is what you want with a ABC cylinder/piston.

I would send that engine back to where it came. Even if you manage to clean the compound out before you run it, there will still be some embeded in the piston and it will only shorten its life.

Maybe the engine you recieved was a return, sold to you as new.


Mike

Ram Jet

100% RC dude.

Bill

Motorboy

The piston/ sleeve was lapped due tooling marks must be removed and fit togheter and the sleeve must be tapered to make the engine easy starting without loss of compression.

In case the piston was embeded with lapping paste, the piston was not cleaned free for lapping paste before use.
Take contact with dealer about this problem. But in case you dismantled the engine, the warranty can be void.

ace4-40

ABC engines are not lapped with anything. If there was lapping compound in it, someone put it in or someone a the factory screwed up.

Even back in the day of lapped engines using lustrox was a bad Idea. It was poured into the intake while the engine was running. This not only lapped the piston/cylinder, it lapped the crankpin/conrod fit and crankshaft/crankcase fit and that was the front end seal. Bad idea making it bigger/looser rod big end a sloppy fit.

Lapped engines needed a slow long break in. Trying to speed up the process usually ruined them.

w8ye

My Feedback: (16)

I used to fly control line and back in the late 60's I bought a new MCoy 40 Stunt that had been customized by George Aldrich. After he sat on my money for several months the engine finally came and I tore the engine apart to see what George did to the engine to make it so great. The engine had Clover valve grinding compound all in it! After cleaning the engine out, I flew it once and sold the engine at the flying field.

Motorboy

ace4-40, i am model engine builder and know what i am talking about this lapping procces both in older "iron" engines and ABC engines.....

See the pic of the piston and sleeve are lapped in post #25 and #16: http://www.rcuniverse.com/forum/fb.asp?m=6286262 , http://www.rcuniverse.com/forum/fb.asp?m=6267829 .

Read in post #22 how the piston and sleeve are worked, lapped to fit togheter, translated from russian: http://www.rcuniverse.com/forum/fb.asp?m=6281801

All parts who are lapped must be cleaned with ultrasonic bath to remove all lapping pasta out of all pores in the material. In case homemachinist: all parts are washed in gasoline/kerosene to remove all lapping pasta before use.

Bax

My Feedback: (11)

A Tower Hobbies engine should not have any abrasive compound in the engine when it's new. If it did, then it should be returned for exchange. Likely, the factory messed-up, or the returns department messed-up and sent you a previously-sold engine. We get people all of the time who think a tight, ABC-type of engine is defective because it's tight at the top. Some people actually try to "rectify" this by trying to lap the engine or otherwise re-work it. Some will then return the engine as "defective", even after they've tried such rework. Occasionally, the returns department might miss such an engine...it depends upon what is written in the return letter. .....Yes, some people will "bend" the story a bit in hopes of getting the engine returned.

w8ye

My Feedback: (16)

One of the guys I fly with has only a Tower 75. He's been flying it for 3 years now. Never a moments trouble. Alway perfect, needle valve rarely needs adjusting. Tolerant to many different fuel changes. The head is still purple after all this use.

BillS

On a side note the engine was assembled with two head gaskets, one .004 thick and one .0085 thick. One might guess that the compression can to be adjusted but no mention was found in the instructions.

Bill

DarZeelon

I think I might be using words previously written by someone else...


Oh, dear!


No ABC, AAC, ABN, or ABL engine should be honed with any abrasive, prior to, or during the break-in.

Such an engine must be tight around TDC.

Those that are loose are worn out from new; and those that are just a little tight, just don't last as long as the really tight ones.

BillS

Most of the tightness was a result of burs at the top inside of the sleeve. The engine would not have turned through top dead center without excessive force.

It has been fixed by a little time with fine emery and steel wool. I elected to fix the engine simply because I know how and it was easier than returning it. Inspect and clean was important. The engine looked good in all other respects.

The engine had not seen fuel and showed no signs of disassembly. It had a small squirt of lapping compound after final assembly. One might guess the burs were created when the cylinder was tumbled for cleaning.

Bax, thanks for the concern.

Tower was business like and prompt with the order and did all the correct things.


Bill

DarZeelon

Quote:

ORIGINAL: BillS

Most of the tightness was a result of burrs at the top inside of the sleeve...

Say, what??

Burrs? Or do you mean loose metal shavings?

The piston does not rise as far as the top of the cylinder sleeve. And if there happen to be any burrs in the sleeve, they would be around the circumference at its very top (or bottom).

The sleeve is honed after the chromium plating is electro-deposited.


How can there be any burrs?

ace4-40

Dar is 100% correct. ABC engines are HONED and not lapped with any kind of lapping compound. If you find it in an engine, the manufacturer didn't do it. Lapping, running, disassembling, ultrasonically cleaning and reassembling the number of engines made by a company like OS would add a huge price increase and take forever to make the numbers they make.

I watched a guy ruin a squeaky tight K&B boat engine years ago by putting lapping compound in it. Never turned up after that. He took most of the taper out of the liner. Wouldn't listen to anyone when they told him it was SUPPOSED to be tight at the top.

microsprint9

I just got my tower .75 a few weeks ago, mine was stuck at TDC or close to it, heated it up with a heat gun to get it back down and removed the head and back plate, found one tiny pc of aluminum shaving inside, now just waiting for a nice day to get'r fired up, i will definatly preheat with the heat gun before attempting to start it. And based on my other engines, the tighter the better.

BillS

Dar

There were no shavings in the top end. The sleeve was rough at the very top. There were no burrs on the bottom of the sleeve, which I found strange.

The piston in the Tower .75 goes to within .023 +/-.001 to the top of the sleeve.

In my opinion the burrs were introduced after plating.

Bill