Combination crankshaft - flywheel lignhtened or not for a 2.0 and 2.2 ?

[Flieger]

Saw this one at a local skunkworks of sorts:

[tadd]

I think that was from a Supertec event. That selection of cranks is in a pic on pelican (from another angle). IIRC, its an 2.8/3.0 RSR crank, 964 and last is a supertec crank.

Duh, its labled in the pic .

t

[BURN-BROS]

Originally Posted by tadd

I think that was from a Supertec event. That selection of cranks is in a pic on pelican (from another angle). IIRC, its an 2.8/3.0 RSR crank, 964 and last is a supertec crank.

Duh, its labled in the pic .

t

Hi Tadd,

The engineer did not state why one would do such a thing, but surmised that it must not be an issue and left it at that. If I were to guess it's due to lack of space inside the case and the boxer layout effectively limiting the imbalance to the adjacent journals.

When a crank is balanced, it is balanced at it's extreme ends and does not take individual throws into account. crankshaft flexing at high rpm a can show up due to this.

The crank in the middle is a 956/961 66mm stroke crankshaft. They refer to it as a replacement crank for the 959 which is unverified. It does have a 961 part number.

[tadd]

Aarron:
I might be getting old timers but I thought the 959 was an odd stroke... 67 mm seems to come to mind. Bruce Andersons book would be the source (and they are at home so I can't verify).

It does illustrate that with Ti rods the factory wanted to remove material....

t

[356RS]

956 has a 66 mm stroke and the 959 has a 67 mm stroke.

[BURN-BROS]

Originally Posted by tadd

Aarron:
I might be getting old timers but I thought the 959 was an odd stroke... 67 mm seems to come to mind. Bruce Andersons book would be the source (and they are at home so I can't verify).

It does illustrate that with Ti rods the factory wanted to remove material....

t

You are right in regards to odd stroke. I cannot personally verify what the application was other than possibly a late 956 crank or a 961. Engine specs on the 961 are hard to come by....at least for me. The 959 link is only a statement made by one of the big guys who supply parts to the historic cars.

The 961 crank shows the change from a production based race crank like a 906 or a 2.8 RSR crank to a full counterweighted design. Notice the counterweights present between each main bearing on the 961 and Supertec crank versus the 2.8 RSR crank.

The main weakness on the RSR crank was the 24mm width rod journals. It reduced the cross-section of the crank throws causing a harmonic response.

The 917 utilized the same 24mm rod width and experienced the same harmonic issues when the 70.4 stroke was used.

Both cranks were developed around the same time.


BTW, apparently 959 cranks are still available for a list of 13,086.27

[Flieger]

Originally Posted by tadd

I think that was from a Supertec event. That selection of cranks is in a pic on pelican (from another angle). IIRC, its an 2.8/3.0 RSR crank, 964 and last is a supertec crank.

Duh, its labled in the pic .

t

In fact I have never been to Supertec. It is from Kundensport in Camarillo- right by Aaron.

[Flieger]

[Flieger]

Another view:


More cranks:

[356RS]

Those distributors look familiar.

[Flieger]

Originally Posted by 356RS

Those distributors look familiar.

What a coincidence