Welding behind number 3?

tree hugger · Samba Member Joined: April 28, 2006 Posts: 195

Hi All
At what point is it necessary to weld behind number three on the case or is it just a standard must have conversion? I've got an AS41 case I was planning on building up out of parts I have already which may mean using a 76mm crank but 85.5 pistons. It will be essentially otherwise stock, I quess I might as well have the case welded but it has had a line bore, will it need another after welding?

Glenn · Posted: Fri Aug 10, 2007 1:20 pm Post subject:

It's never been proven that it's a "must have". If the person welding it overheats the case they can cause more damage than it prevents.

My 2180 is not welded by #3.

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LittleThunder · Samba Member Joined: May 21, 2006 Posts: 1015

Okay, I give up. Weld what and why?

57 Rag · Posted: Fri Aug 10, 2007 1:27 pm Post subject:

Glenn · Posted: Fri Aug 10, 2007 1:27 pm Post subject:

tree hugger · Samba Member Joined: April 28, 2006 Posts: 195

Sweet, thanks for the quick replies, I figured it was more for the big bore and stroke engines. The other case I have cut for 94's is welded. I'll use that for my "big"motor. Cheers Very Happy

Glenn · Posted: Fri Aug 10, 2007 1:34 pm Post subject:

Mine is 92x82.
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"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

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tree hugger · Samba Member Joined: April 28, 2006 Posts: 195

Exactly and you've obviously had no problems so thats reassuring. I wonder if some of the problem has been alleviated with newer lighter engine components and more attention to balancing or was it only ever a heat issue?

Bugzlife · Samba Member Joined: January 27, 2004 Posts: 268

Yea, no need if crank and rods pistons etc are strong, and balanced,
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sszuch · Posted: Fri Aug 10, 2007 3:53 pm Post subject:

It is a heat and fatigue issue. The constant heating and cooling of the case will eventually change the microstructure of the material, causing it to become brittle. The area behind #3 is the thinner than the other side of case and which increases the stress. Balancing is always a benefit becasue it reduces vibration and bending of the crank, but rod and piston strength is not a factor when looking at case longevity.

RonR · Posted: Fri Aug 10, 2007 8:40 pm Post subject: Third degree on # 3

We put a 1/8" radius at the base of our large bore motors. I have seen cracks, but only with sharp corner bores.

1432 · Posted: Fri Aug 10, 2007 9:36 pm Post subject:

Cracks in this area are a result of extreme loads in the combustion process. Virtually all will propagate from nearest the end of the head studs. To correct this the factory introduced the "#3 deep stud" back in the 70's to alter the studs' load path from square across the base of the bore to diagonal thru a larger area of mass, they also switched to the 8mm head studs for added protection from cracking, in most cases this is enough to prevent failure at this point, however if your engine is set up for serious abuse like drag racing, sand buggin, turbos or spl fuels welding it can be of substantial value when done correctly which means the welding of rolled mag plate material, stress relieving and line boring. Before the days of the aluminum cases it was quite common to see mag cases welded at the #1 & 4 cyls as well.

CJG · Posted: Sat Aug 11, 2007 1:17 am Post subject:

The cast is better now a days. A good engine builder will make sure of the tolerance's. Shocked

fitnessforyoutoo · Samba Member Joined: December 22, 2005 Posts: 46

57 Rag · Posted: Sat Aug 18, 2007 1:12 am Post subject:

I knew JB weld was great but dang. My motor is sitting ready to go in. Maybe I'll do it just for the hell of it. Do you do it by layers like coats or one big one? How long does it take to cure?

thanks
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CJG · Posted: Sat Aug 18, 2007 1:38 am Post subject:

no need to weld, unless you are in the 250 hp range Very Happy

lostinbaja · Posted: Sat Aug 18, 2007 3:33 am Post subject:

miniman82 · Posted: Sat Aug 18, 2007 5:05 am Post subject:

Doesn't Glenn's engine use thick 92's? Same size hole in the case as 94's...
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lostinbaja · Posted: Sat Aug 18, 2007 5:11 am Post subject:

1432 · Posted: Sat Aug 18, 2007 7:20 am Post subject:

Again the major cause of cracking in this area is excessive cylinder pressures and in street engines the major cause of this excess pressure is detonation, usually thru overheating caused by high compression, poor tuning , overloaded use/driving or a combination of. while extreme detonation kills parts quickly, lower levels of detonation have more of a cumulative damaging effect that can manifest itself in this manor (cracks). Given the fact that the use of higher compression ACVWs appears to be the trend nowadays I predict more ACVW owners will experience cracked cases not only behind #3 but also #1 cyl as well.


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