VaSteve

I have been looking at 944s to use as a DD/DE car. I drove one tonight (an 83 with 50K miles) and it had the most hellaceous vibration somewhere in the middle of the tach. I did some reading here and PPBS and found that it's pretty typical of a balance shaft slipping a tooth.

What's a balance shaft? I understand that it has something to do with the fact that the 944 has such a large displacement for a 4 cylender, but I don't exactly know what it is or what it does. Certainly, I don't have one in my 911, so I'm lost.

A search here revealed only, say a million threads on how to fix it. I need more basic than that! Thanks

83na944

It smooths out the vibration inherent in the large 4 cylinder with a counter-rotating mass. It is a Mitsubishi design. Try a google search.

Mongo

944 owners are cursed with it, and 911 owners laugh at us for having it

83na944

BTW, when the balance shafts are out of time a tooth, the result is more of a buzz. The engine doesn't want to rev, either.

nine-44

What they do, each creates a vibration timed opposite of the other. They cancel each others vibration out doing so through the engine and absorbing secondary vibration inherent in inline 4 cyl motors. Hope that helps.

Dilberto

But then add another cylinder and the engine no longer vibrates. In fact, the Audi inline-5 is incredibly smooth...especially at higher RPMs. The "inherent" trade-off is the extra weight an extra cylinder provides, as opposed to the total weight gain the leaky balance shafts offer. Porsche could have easily went with the I-5 and still kept displacement at around 2.5L, without much power dilution.

Zach

Porsche-O-Phile

Haven't seen many cars with leaky balance shafts - usually it's the crank seal or oil pan gasket.

Peckster

Try narrowing your search terms, the info you need is here.

Vibrations at 3k are often balance shafts, the belt could be broken or set out of synch,it's quite common.

Get a pre-purchase inspection by someone who really knows these cars.

lucifer_sam

rubber donuts can also cause vibrations at a specific rpm, if they start to break down and get imbalanced.

here's a good example:
https://rennlist.com/forums/924-931-944-951-968-forum/208867-new-vibration.html


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