1FastRedSC

My dad is a 44 guru, and i love porsche in general. We got into an argument the other day over balance shafts. He read somewhere on the internet that mitsubishi patented the design for balance shafts and porsche bought the patent because they couldn't get a usuable design for the 928 engine. Then later, obviously, it was implemented on the half 28 engine, or 44 engine. Is this true, because i was under the impression that they designed it themselves.

turbo944

It is true from what I've seen as well. Basically it fell to this. Mitsubishi had developed a good system and rather than reinvent the wheel (didn't Porsche invent that? ;-) ), they just bought the rights to use the system from Mitsubishi and used it because it was a well designed system. Don't think they ever needed or used it on the 928 though, that V8 is pretty well balanced without them. The reason it's there on the 944 is that an inline-4 cylinder of that size is very prone to vibration and those helps to smooth it out.

Cheers!

Peter K.

There is also some part that mitsubishi borrowed from Porsche as well. I cannot rem what it is but I am sure I have heard this somewhere.

Luis de Prat

Actually, it appears that the balance shaft concept was invented by an Englishman named Frederick Lancaster in 1911. Mitsubishi simply refined the concept and patented its own version, which Porsche found more suitable for the 944 engine.

Read more here under "Vibration Control":

<a href="http://www.geocities.com/MotorCity/3322/eng25.htm" target="_blank">http://www.geocities.com/MotorCity/3322/eng25.htm</a>

jim968

I've seen the balance shaft story elsewhere, and I think it's true. Mitsubishi apparently bought the patent from whoever originated the idea. They called it the "Silent Shaft" system on some of their engines. Porsche bought a license to use it (don't recall if it was a lump-sum buy, or a per-car payment). It's needed on our cars because the pistons are so large on a 2.5 or bigger four, and create vibration on an inline engine (my Subie is a 2.5 four, but it's a boxer engine, which tends to cancel the vibration internally).

So, yep, Porsche paid Mitsuibishi... but I don't think Mitsu originated the idea.

Jim, try tracing the history of the rotary if you want to see a twisted trail... 8)

Tom R.

they didnt buy it, they licensed the use of it, and pay mitsubishi a certain amount for each one produced. i dont think it was used in the 928 though.

check the magazine articles form the early 80s for full details.

Crackhead944S

In the "Illustrated Porsche Buyers Guide", it states that Porsche licensed the technology from Mitsubishi for the 944. If I remember correctly, it cost Porsche about $4 per car.

John Welch

The balance shafts are only need on a 4 cylinder due to the inherent imbalance with the large displacement (2.5L). A V8 doesn't have that problem.

OC Porsche

Dr. Porsche being such a practical thinker thought that reinventing this component was a waste of time, maybe it was that Mitsubishi just did it that well. I read the exact quote before but can't find it anymore.

Raceit

Just to add another point...

Mitsubishi is the one that perfected the two balance shaft method. Porsche tried it with just one, but it was never able to keep the vibration down. And the rest is history as they say. ...who ever "they" are.

xcessiv

What I recall is the Mitsu design was from 1948 for an aircraft engine, and that Porsche tried to improve it but couldn't, and decided to license it for $8 a motor. I think it was a bargain, or at least I am glad they did.

F18Rep

Interesting that Honda, and I suppose others, have variants of this idea also. 93 Accord has a single balance shaft and is quite a bit smoother running than the otherwise similar 97 Civic (no balance shaft). Also interesting that the Accord is an "interference" engine and with the additional balance shaft belt is in a way similar to our 944 engine - why do the Hondas not share the concerns for slipping a timing tooth. Belt length? Valve spring tension? Seems like I read somewhere that Honda has recently up'ed thier belt replacement interval to 90 k miles. But most PO's wouldn't dare go that far without a change. The only way I can explain more Porche belt slips is possibly how they are pushed harder by the driver. Anyone got a better theory?... This whole belt thing seem overblown to me...Bruce

944Play

You can read about it in the sidebar ("The 944 four: the heart's the best part") of this scanned article from the time of the 944's US introduction.

<a href="http://sonic.net/~johnboy/944_mt1.html" target="_blank">http://sonic.net/~johnboy/944_mt1.html</a>
<a href="http://sonic.net/~johnboy/944_mt2.html" target="_blank">http://sonic.net/~johnboy/944_mt2.html</a>
<a href="http://sonic.net/~johnboy/944_mt3.html" target="_blank">http://sonic.net/~johnboy/944_mt3.html</a>

Mitsubishi's patent is for shafts with two bearings. Porsche tried using three.

superjet.1

Interesting article. Just a correction on that the Lanchester balance shafts canceled secondary harmonic imbalances, NOT primary as stated in that articler. Primary balance is achieved through counter-weights on the crank to match the weights of pistons+rods on a per-journal basis.

Also the Lanchestor balance shafts placed the two shafts in a mirror image configuration at the same height on the block. This cancels secondary shake, but you still have a wobble due to the direction of rotation of the cranksharf. The Mitsubishi design improved on this by placing the balance-shafts one each on high and low position on opposite sides of the block. This distance is a critical 0.70 stroke-length away from the centerline of the crank.

For more info on how the balance shafts work, see this thread: <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=11;t=000339;p=1" target="_blank">Balance Shafts</a>

I'm not sure if Lanchester had a patent on his design, since the head of the U.S. Patent Office had wanted to close it down around that time because he felt that all worthwhile inventions had already been invented. Little did he know...

blackdogbd

I had a 1976 Dodge Colt, 4 door, with the "Silent Shaft", 2.5 liter 4 in 1982. The motor came as part of the highway package. It was a super smooth motor. I had the car in college and it was as close as I got to Porsche for three long years.