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Join Date: Dec 2005
Location: Mount Airy, MD
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Cranks with big holes
I was looking at a few pics on posts about 906 and RSR cranks. They have holes in the rod journals. Scat does the same thing on there perf 616 cranks (912).
I am cleaning up a non-counterweighted T crank for my project and this to me seems like a truly good thing to do. Since the T crank has no counter weights anything that could be done to remove weight from the non-axial rotating mass should be a good thing, right? So for a given acceptable level of force, it would now occur at a higher RPM. Assuming I did my maths correctly, and most ferrious materials are around 8g/cc a 3/4" plug removed from the rod throw (19x37 mm) would be about 80-90 grams. That is about half the total mass difference between a 2.0 rod and a Ti rod. For a counterweighted crank, one could then reduce the diameter of the counter weights for an improvement in rev up speed. Two questions then: 1. Why doesn't anyone (other than the factory) do this? Drilling holes isn't that hard. Although I think I would have to hang it off the side of the bridgeport to get it to fit... 2. How big are the holes in an RSR or 906 crank? I would guess that is as big as you can get before hitting a oil journal. Thanks in advance, tadd
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1967 912 with centerlocks… 10 years and still in pieces! |
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05-07-2006, 05:47 PM
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3 restos WIP = psycho
Join Date: Feb 2005
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Cricket...Cricket...
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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05-08-2006, 02:27 PM
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No 906 cranks out there?
Does anyone have an RSR or 906 crank on a benchtop somewhere? It would be nice to know where and how big the 'lightening hole' is. I trying to guess from some pictures, so real measurments would be sweet.
tadd
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1967 912 with centerlocks… 10 years and still in pieces! |
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05-09-2006, 12:20 PM
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Hey!!! somebody help Tadd out already!!! I wanna know his answers!!
Nabil
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'71 S track car, 2.7L & Webers forever! |
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05-09-2006, 05:56 PM
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Story so far today...
The lightening holes seem to be 16mm by pixel count, that is assuming the crank holes are M12. The pilot bearing hole is 15.5mm on my T crank and looks pretty close.
Ollies Engineering does the 'conversion' from what I gather. I will be calling tomorrow. There is no web page... tadd
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1967 912 with centerlocks… 10 years and still in pieces! |
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05-09-2006, 06:15 PM
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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I want to be cited for my hard work in Adobe Illustrator!
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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05-09-2006, 06:37 PM
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Aaron.  F.S. 1965 Solex engine w carbs/cleanerBurnham Performance https://www.instagram.com/burnhamperformance/ |
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05-09-2006, 09:18 PM
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No go
Just talked to Ollies. They don't do the holes.
 The search contiunes.... tadd
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1967 912 with centerlocks… 10 years and still in pieces! |
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05-10-2006, 09:28 AM
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