blw
Posts: 4321
Joined: 3/15/2004
From: Auburn,
AL, USA
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AAC life
Is there a longevity issue with the aluminum bores?
In a word, no.
There are many ways to make an engine cylinder, the old classic is an iron block with a ringed piston. Works great, has a long life, but it's heavy. Many of the older engines actually had iron pistons, the "Stovebolt" Chevys for example. They were tin plated to prevent problems with similar metals rubbing. Some diesels still use iron crowns and aluminum skirts on two piece pistons. Strong, but still heavy.
Air cooled aviation engines often are built with the cylinder fins turned as part of the steel cylinder, using ringed aluminum pistons. The aluminum cylinder head sometimes has an iron "Skull" cast into it, usually it's plain aluminum, and usually has internal threads to allow it to be screwed onto the top of the cylinder if it is a radial engine. Some, like the old Kinner radials, had a flange at the top of the cylinder and the head was fastened with short screws.
In an attempt to lower the weight further, some makers used a finned aluminum "Muff" pressed on the steel cylinders. This worked, but the cooling was not as good because of the joint between the steel and the aluminum - it tended to open as the aluminum expanded more than the steel. With sufficient air flow there was no problem, but they did tend to overheat if idled too long. As an example, this was a problem with the early Technopower radials.
Almost universal in our early model engines was a steel sleeve with either a ringed aluminum piston, or a piston made of "Meehanite" iron alloy with a lapped fit in the bore.
The first real change in construction was the ABC engine, using a brass sleeve in the aluminum muff, chrome plated tapered bore, with an aluminum piston. The brass expands more than the steel sleeves did heat transfer isn't a problem. And by taking advantage of the expansion, the piston fit could be controlled very nicely. But the brass was still heavier than the aluminum.
Two makers took a side track from the ABC; Thunder Tiger and OS engines started using nickel plating instead of chrome. TT has never had a problem with the ABN engines, I've only heard of one failure, caused by a bearing coming apart. Bits of bearing removed the plating. OS, on the other hand, has a lurid history of liners peeling. They seem to have it right now, shelling looks to be a thing of the past with OS. Their reputation was so badly damaged by the peeling that with the AX engines they started calling it "ABL" instead of ABN. It's still ABN even with their new name.
There were some experiments in here for running a ringed piston directly against an aluminum cylinder bore, probably the first one most of you heard of was the Chevrolet Vega engine. This engine had problems, but they were not caused by the piston/cylinder fit. The way this was made to work was a high silicon content in the aluminum. I have a Mercedes 500 AMG, 26 years old, with the same type block. At its last overhaul standard size pistons and rings went back in, wear is not a problem. There is a variation on this called "Nikasil," this is a process applied after the block is machined, it allows a less expensive alloy to be used for the block.
Chrome plated aluminum? Way back in the late 40s and early 50s, McCullough (yes, chain saw McCullough) started chrome plating directly on the aluminum cylinder bores, not just the chain saws but also the engines they built for target drones. Porsche (cars) was also working on the same thing. They both got it to work fine after some teething difficulties,
So now, using 50 year old technology, we can eliminate the steel liners that didn't cool well, and the brass liners that are heavy. What we can't do, is run a lapped piston. It has to be a ringed engine. I'm sure some have tried, but I know of none that have been successful without a ringed piston. For obvious reasons, this construction method is called AAC for Aluminum piston, Aluminum bore, Chrome plated.
This AAC is the best yet for our engines. Good heat transfer, light weight, and a bulletproof cylinder bore.
In the Saito AAC engines I have never seen a cylinder replaced due to failure of the plating. I have replaced them due to scoring from a disintegrated bearing, others due to crash damage, even one where the owner tried to lap the valves and ruined the valve seats. Plating failure? Never.
There are still other methods I've not discussed, for example Norvel has what they call "Revlite" which I think is a variation of anodizing, but I'm not sure.
And you can tell your buddy that YS uses something similar to Nikasil, but I'm not sure of their process. And OS four strokes are all ringed pistons in the easily worn steel cylinders, except the FL-70 which uses ABN in a tapered bore and no ring on the piston.
If you make it through this, congratulations. I did run on here.
After run oil – how the #% do I get it in the crankcase?
Some few twins have two crankcase ports, but none of the singles do. As a result when you try to force the ARO in it tends to blow back out. No problem.
Got a plastic squeeze bottle with a tapered spout, the sort that you put your tomato catsup or mustard in. Best if you can see the level of the contents. If the tip is small enough to go into the vent hose you’re done. If not a short length of brass tubing can be forced in the tip, or you can cut the tip back to get a larger diameter that will let you push the vent hose inside.
Fill it about ½ way with your favorite AR oil, and you are ready.
Pull the vent hose out the top of the plane, or if not convenient turn the plane over, just be sure the hose is pointing up. Attach your new oil bottle to the hose. Then holding the bottle with the tip down turn the engine slowly.
While the piston is going down in the bore you’ll see bubbles in the oil bottle, then when the piston is going up it will draw oil back into the engine. Keep turning until you have drawn an ounce or so of oil in. Unhook the bottle, turn the plane back upright (Or the hose back out the bottom) and spin the engine for a few seconds with your starter. This last will make sure the oil is run everywhere inside the engine, and blow any excess out.
Simple, isn’t it?
< Message edited by w8ye -- 5/20/2007 4:34:13 PM >
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The Complete Saito Notes by Bill Robison - 
