AA Pistons

[Sander/DVK]

Anybody who have experience with the AA piston/cylindersets? The reason why I like them is the shape of the pistons. Like Wiseco, so very light.
Maybe I want to use them for my 2110 project, but they are so (too??)  cheap 

[Sander/DVK]

Just saw this topic: http://cal-look.no/lounge/index.php/topic,1261.0.html

The seller Kekonaii have removed all his add's, and is banned on the samba 

[Lids]

The seller you refer to was not shipping parts.  Also avoid QSC as they are AA pistons that have failed QC.

http://aapistons.com/index.php?main_page=index

[A-C]

http://www.aircooled.fi/shop/index.php?categoryID=381
http://www.aircooled.fi/shop/index.php?productID=1319

Ask more,  info@aircooled.fi   English/Swedish

[Mike Lawless]

There's been a lot of bad publicity surrounding the AA piston, as there were some pretty catastrophic failures recorded. I don't know anything other that what has been reported by others. I can tell you I've got two seasons on a set and still running them, as does Muffler Mike Sheldon and a few others with no reliability issues. Mike Sheldon runs his in a turbo configuration, and his 2000/lb car is well into the 10s. Mine is a high compression NA deal running low 11s in a 1900 lb car and going 8500 rpm. Mine were purchased in the summer of 2006 and I think Mike bought his not too much before then.

However....
I can tell you that the piston came out of the box with just a little over .001" piston to wall clearance. Myself as well as many other experienced engine builders feel this is way too tight for a racing piston. The Wiseco, similar in construction and appearance calls for .005-.006" clearance. Based on that I had the barrels honed to 3.705" or .004" bigger for a total clearance of .005". That solved the too tight clearance issue but created another problem....ring fit. Since the standard 94mm ring is made for a 94mm (3.701") bore, installing then into a bore .004" bigger creates and end gap close to .040"...way too wide. I went through a couple different ring configurations trying to keep the leakdown figures within reason, till I finally went with a total seal gapless top ring and drilled eight .040" gas ports. The thing sealed up tight in two runs and ran it's highest MPH speed and best ET ever, and has maintained less that 1% leakage after 60 plus runs.

Now whether or not the guys who had failures honed the barrels for the extra clearance or not, I can't say. But some appeared from photos I've seen to have pulled the pins through the bottom of the piston as if the piston had seized in the bore. I just can't say for sure. But those failures created a firestorm of bad publicity for AA and Kona (Kekonalli).

Having said that, this will be the last season for me to run these. I will be changing to something else in the off-season. I hope the info is useful

[Lids]

Thomas emailed me at the time and said mine were from the first batch.  He also says that these pistons need an extra .0015” to .002” piston to cylinder clearance to use na and turbo.

[benssp]

I read the thread on the CLF, decided to stick with good ol Mahle pistons and Century cylinders

[Airspeed]

..., till I finally went with a total seal gapless top ring and drilled eight .040" gas ports.

Very usefull Mike!

Do you have a pic of how and where you drilled these 'gas ports'. Heard many times this term, but I am still clueless of what it is exactly and what it does...

Thanks in advance,
Walter

[Harry/FDK]

Thanks for sharing Mike.

[Mike Lawless]

The gas ports are drilled through the top of the piston to intersect the VERY BACK of the top ring groove, so half the diameter of the drill breaks though. The combustion gases will pass down the ports and force the ring outward against the cylinder wall, increasing ring seal. It's common practice for very narrow rings in race motors, and the total seal gapless top ring is perfect for this. Pat Downs used this same package in the HVWS pump gas motor building competition a couple years back. Not recommended for the street as the small holes will carbon up and close off. Since a race motor is taken down frequently for maintenance, the ports can be cleaned. The holes are very small and must be carefully drilled. A fixture exist for this, but I used my rotary indexing table on my mill to do it. I have no photos, but I can probably whip up a schematic later if anyone is really interested.

[jrice]

from my personal experience...

They had an original run of these piston which where a good option... Then when the second batch came over the metal used was much more Pouress and weaker metal. If you are able to get a set of the originals then you should be okay.. However, if you get a set of the second batch (as I did) you are in trouble. 1 pass and the Pin boss let go and pulled the rod out the bottom...

[Mike Lawless]

Jeff, on your pistons, were the skirts coated with graphite? Some of the guys with failures got ones without the coating and these may have been the bad batch. It seems they came out in batches that were coated, then not coated, and then they were coated again.

I guess there no clear way to tell which batch.

[jrice]

Mike,

I did not have the coated ones.

Jeff

[Lids]

The first batch had little blue dots (paint) on the inside of the piston.

[Bewitched666]

Sander for your 82 crank maybe its wise to use the b type piston.

Gr,
Stanford

[Mike Lawless]

Well, even though mine seem to be from "The Good Batch" and there have been no indications of anything going bad on inspection tear-downs, after all the negative discussion on the Cal-Look forum (US), there's enough mistrust to change them out after the season concludes. I feel they may be on borrowed time.

CPs with Dykes rings and Autocraft barrels will be in the 2009 motor.

[Ohio Tom (DdK)]

Hey all. I'm new to this form...

Anyways, I have used AA's on sevral motor builds. They all are working fine.
I have found that you need to check the piston to cyl clearance as it can vary from batch to batch.
Hone to fit and they work/last just fine.

My race motor sees 8,000rpm every time I race it. 40+ passes on it this season and she's doing fine...