New Tower .61 VERY tight at top of stroke (Full Version)

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Zzyzxx -> New Tower .61 VERY tight at top of stroke (11/24/2003 3:16:59 PM)

I forget what my royal .46 and OS .46 SF were like because I broke those in like 10 years ago - but with the glow plug out I can't even turn this thing over the top by hand?

Is this normal?



michpittsman -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 3:28:51 PM)

Not unusual for ABC engines; I have seen some that actually squeeked at the top, but as soon as they fire up, the heat causes the running tolerances to loosen up.



Steve Collins -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 3:30:00 PM)

If this is an ABC engine, you should feel lucky. ABC engines have a tapered bore and rely on a nice tight piston/sleeve fit for good performance. The piston in an ABC engine does not have a ring. The tightest fit I have seen is on the Jett engines I own. Extremely tight fits, to the point of making a screeching noise if you turn it over by hand. The tight fit will loosen up some with normal wear and tear.



Homebrewer -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 5:21:36 PM)

Consider yourself lucky. The tighter the pinch the more power and longer it should last!

If you have trouble turning the engine over to start it, use a heat gun or a small torch carfully to warn the engine cylinder. This will loosen up the engine's internals enough to start it. Once you got your engine running take it immediately to full throttle and run the engine in a rich 2 stroke mode to keep the engine in its optimum temperature range.



DarZeelon -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 5:41:31 PM)

Zzyzxx,

I don't want to repeat what you read from Homebrewer and the others.

I must add: Don't you even think about running it at a four-cycle rich setting, for any length of time, during the break-in.
If you do, your piston will wear and the engine will never produce its intended power.

The engine must retain a slight pinch at TDC, when cold, to be considered in good shape.
When and if this pinch is gone, get ready for an overhaul.

This goes, BTW, for all ABC/ABN/AAC/Plasma ceramic engines, that have a tapered sleeve bore.

You may have a slight difficulty starting it from cold, especially during the break-in, but it will pay off in performance, in the long run.



Flyboy Dave -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 5:45:28 PM)

Don't be tempted to keep flipping the motor
through compression.....you can scuff the piston and the bore,
and prolong the break-in. Squirt a little oil into the top of the bore
on your final assy, before you put the muffler on. When you first start
the motor, it might "knock" for a few seconds....they are extremely tight.
...you can avoid this knocking, and the strain it puts on the rod....by
preheating the head with a heat gun, before the first start-up



Zzyzxx -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 7:12:27 PM)

Good info guys. Sounds like I got a good powerplant. This is my first kit, I'm putting it together on a 3x8 table in an apartment, things are going slow but good - probably should be finishing up all the minor details by time for spring flights.



twostroker -> RE: New Tower .61 VERY tight at top of stroke (11/24/2003 8:26:13 PM)

Finally, It sound like everybody is on the same page and giving good advice. Way to go guys!
Tim



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