TheSamba.com :: View topic - Help me AS21 or AS41 engine case or aftermarket

Wed Oct 05, 2016 1:53 pm

Hello, I have pulled my motor out of my 71 and it has an AS21 case. I plan on rebuilding the motor and was asking if the AS41 is better or is there an aftermarket one that is even better? I see that the AS21 does not have the bus mounting points but the AS41 does. Any input would be most helpful!!!
Thanks in advance!!

Wed Oct 05, 2016 2:08 pm

AS41a is the better alloy. It might hold an align bore for a while. AS21 has memory and is pointless to align bore - you won't get any mileage out of it. At least, I didn't.

Personally, I wouldn't use a non-bus case in a bus. The mustache bar takes all of the engine torque. The cobby oil pump conversion plate mount routes all of the engine torque through the oil pump mounting studs and the lower case through-bolt. That's asking a lot of those bolts...

Wed Oct 05, 2016 2:27 pm

Yes I saw that was leaking at the oil pump. the is one reason I was wanting to change. I plan on traveling often and don't want to cut any corners on the rebuild.

Wed Oct 05, 2016 2:41 pm

the info below is probably from a bug forum but the point is the same.

The 1971 bus took an AE case, and was a 1600. My 1971 AE was good for 40,000 miles without issues when hot-rodded in my bus, and 75,000 when stock intake and exhausts were used. The original case lived through 4 align bores and about 250,000 - 300,000 miles. It eventually cracked from fatigue behind #3. I replaced it with a beefed up AE case. Occasionally AE cases come up for sale here.

Jimmy111 wrote: The AS-41 alloy was the original Elektron alloy made for the German war effort.

All cases up to the AS-21 cases used this alloy. The difference between the early and later AS-21 cases is the purity of the metals. The refining processes got much better and the quality of the castings improved.

AS-21 has a much better creep resistance than the AS-41. It was introduced as emission controls were required by the EPA. The AS-41 would creep and deform under the higher temperatures. Anyone who owned a 74 California bug would know exactly what I mean....

But AS-21 is not stronger than AS-41. They are about the same.

Some AS-21 cases are single relief so be careful when you go looking for them.

The aluminum cases are much stronger than either of the Magnesium alloy cases. But they weigh almost twice as much. But like anything aftermarket and unseasoned, they sometimes require exttra machining to get them within tollerence.

Wed Oct 05, 2016 3:08 pm

Interesting...

My info was from the (late) Bob Hoover writeup on using VW engines in aircraft (where, if something goes wrong, you can't pull over to the side of the sky and check it out):

"Early Type I VW engines are cast of AS21 magnesium-aluminum alloy. Due to the magnesium extraction process used by Dowmetal, the alloy contains trace amounts of niobium and tin. If the alloy is raised above a certain critical temperature, the metal will display 'memory' qualities. Unfortunately, the 'read' temperature is much lower than the 'write' temperature. What all that means is that an early VW engine subjected to catastrophic failure (typically required to raise the temperture above the 'memory-write' threshold), will tend to return to its heat-stressed dimensions when raised to the 'memory-read' threshold. Unfortunately, the memory-read threshold is within the NORMAL range of operating temperatures. This odd metallurgical quirk means that you can remachine a used crankcase and return it to spec with regard to alignment & bore only to see those specs CHANGE when you run the engine. And those changing specs typically result in a catastrophic loss of oil pressure which usually trashes the engine in short order. Having only three main bearings (#4 is actually a pulley bearing) and being of the 'boxer' type, catastrophic failure tends to overheat (and over stress) the center main-bearing web. This is expecially critical in the VW engine because the center main bearing web provides the only passageway for oil to reach the right side of the engine. Once that web has been heat-stressed, normal operating temperatures is enough to cause sufficient distortion to open up that critical oil passage and prevent sufficient lubricant from reaching the right-hand side of the engine. Once the memory property was recognized, the alloy used in the crankcase was changed. Crankcases cast of AS41 do not display the memory property. If you do not know the provenance of an older, used VW engine (ie, of AS21 alloy) it would be extremely unwise to consider it as a candidate for use in an airplane. Even if align-bored and decked so as to return the crankcase to spec, if you don't know the engine's history you can't tell if it has been heat-stressed. Since the only reliable test for the memory property is to do all of the required machining and then blueprint the engine after being heat-soaked for 1 hour @ 250 degrees Fahrenheit, it is usually less expensive to build your flying VW engine on a later model AS41 crankcase."

Other info (link) shows the alloys used (sequentially) as AS41, then AS21, then AS41a. Maybe Bob is referring to AS41a?

Thoughts?

Wed Oct 05, 2016 3:50 pm

Quote: Thoughts?

none what so ever.

Since I haven't built a T1 since about 2000 I don't know what is out there today. 16 years is a long time on parts availability for a T1 bus.

Wed Oct 05, 2016 4:11 pm

Thanks folks. So would it be better to go with an aftermarket aluminum block or the 41. I also had a 68 bus that the case I pulled out has the bus mounts but the only numbers on it have the VW symbol and then U0298549. There are no numbers under the generator stand. I am trying to upload a pict now.

Wed Oct 05, 2016 4:27 pm

The case with the # that starts with U is a type 3 Case.

Wed Oct 05, 2016 4:29 pm

1979vwcamper wrote: Thanks folks. So would it be better to go with an aftermarket aluminum block or the 41. I also had a 68 bus that the case I pulled out has the bus mounts but the only numbers on it have the VW symbol and then U0298549. There are no numbers under the generator stand. I am trying to upload a pict now.

I can't give you a recommendation, but UOxxxxxx stamped on top of the case means Type 3, around 1970 dual relief, if memory serves me. I ran one for a few years, and after more than 40,000 miles the local machine shop said it looked great and wouldn't have bored it if I didn't cue them in to the miles on it. So they CAN be run a long time if cared for and kept cool and lubricated. But it only takes one overheat event to warp metal, so no matter what you go with, have a VW machine shop give it a professional once-over.

Good luck!

Wed Oct 05, 2016 4:55 pm

Thank ya'll so much!!! it at least gives me an idea!!!

Wed Oct 05, 2016 6:33 pm

I am very happy with my aluminum bubble top AutoLina case. I bought it new and it sure is pretty and does the job well. No worrying if it needs to be aline bored and you can order it with the correct piston size you are going to use so there is no machining.