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Old Jun 16, 2008, 06:19 PM
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ABC or AAC?

If you were to rebuild an engine and had the choice what woudl you take and why?

Steven

(25$ more for the aac)
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Old Jun 16, 2008, 06:35 PM
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Tokoroa
Joined Mar 2004
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It depends on what I was going to use that motor for.

AAC is lighter, which can be a bonus if you need the ultimate power to weight ratio (most Saitos are AAC) but ABC provides a greater measure of protection against lean runs or poor cowling.

Tell us what the engine is and what you're planning on using it for.
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Old Jun 16, 2008, 06:38 PM
And You're Not
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Jett claims that the AAC sleeve is less prone to deforming at the top of the sleeve. From the Jett FAQ

Quote:
Question:
Is an AAC engine more likely to wear than an ABC engine?
Answer:
Eight years ago I would have probably said yes. That is the conventional wisdom. In fact, I read not long ago in a racing forum a comment by a prominent racer stating just that. The opposite is true. That is why I make my premium engines with AAC liners. Do you remember how nice it was to just change out a piston ring every so often? Well, using an AAC engines is very much the same. We get engines that look like they have been through the Great War, and when torn down and measured, we find the AAC liner is like new. In most cases, all we have to do is fit you a new piston and you are right back to "good as new". It saves you about 1/2 the cost of rebuilding.

The secret of AAC lies in the increased heat stability of the aluminum vs. the brass. With chrome on the liner you do not get wear in either case. What you get is warping of the top part of the brass liner due to heat and stress. The brass, when overheated, tends to "bell mouth" and loose its taper. The aluminum does not do that. About the only thing that will hurt the AAC liners is FOD (foreign object damage). Keep your engine and runway clean!
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Old Jun 16, 2008, 07:56 PM
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Well its a jett 50 fire going on a small q500 type plane would like to get 130-140mph out of it

Steven
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Old Jun 16, 2008, 11:52 PM
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Ummmm...same answer as I just gave on RCU .

AAC all the way. I have the Enya 60X which is AAC and they just never seem to wear out. The reasons given by Jett were found by George Aldrich (from memory). Whatever...go for the AAC.
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Old Jun 17, 2008, 10:50 AM
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Everett Wa.
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Quote:
Originally Posted by XJet
It depends on what I was going to use that motor for.

AAC is lighter, which can be a bonus if you need the ultimate power to weight ratio (most Saitos are AAC) but ABC provides a greater measure of protection against lean runs or poor cowling.

Tell us what the engine is and what you're planning on using it for.
How does ABC give better protection? It has a greater thermal mass?
Other than costs I think that AAC is the way to go. There is a higher possibility of plating failures as there is the zinc strike.

Konrad
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Old Jun 18, 2008, 12:13 AM
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One apparent difference with AAC (judging by the Enya 60X) is that they don't have any pinch when new. There's certainly never been any reports of peeling with them and everyone says they last forever. I know mine has had a lot of use and it's still as good as new. Strangely, even though I use 20% all castor there's never been even a hint of carbon on the piston crown or in the exhaust.
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Old Jun 18, 2008, 12:31 AM
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Tokoroa
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Quote:
Originally Posted by downunder
One apparent difference with AAC (judging by the Enya 60X) is that they don't have any pinch when new. There's certainly never been any reports of peeling with them and everyone says they last forever. I know mine has had a lot of use and it's still as good as new. Strangely, even though I use 20% all castor there's never been even a hint of carbon on the piston crown or in the exhaust.
You are correct.. an AAC won't have a (very) tapered bore because the expansion coefficients of the piston and the bore will be pretty much the same -- whereas in an ABC the bore will expand faster than the piston.

That means the cold clearances are not much different to the hot clearances.

A *good* AAC job will last forever (excluding the effects of foreign object damage) and Saitos are a good example of this.

Also, by chroming straight onto the bore, the heat of combustion can be conducted more effectively to the outside of the cylinder and therefore the engine will run cooler.

AAC engines are often quite a bit lighter than ABC -- one only has to compare the weight of the now discontinued Saito 80 (ABC) with the newer Saito 82 (AAC) to see that.

It's interesting to note that most of the cheap Chinese gas engines on the market today are AAC.
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Old Jun 18, 2008, 05:46 AM
NM2K
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Quote:
Originally Posted by downunder
Ummmm...same answer as I just gave on RCU .

AAC all the way. I have the Enya 60X which is AAC and they just never seem to wear out. The reasons given by Jett were found by George Aldrich (from memory). Whatever...go for the AAC.
-----------

I'm with Downunder on this point. AAC is superior for those wanting the best in high performance. I'm talking about unringed two-stroke engines, not anything else.

Ed Cregger
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Old Jun 18, 2008, 04:11 PM
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so aac it is ,

Thanx for the help!

Steven
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