Drilled Crank Thoughts...
01-02-2006, 06:38 PM
#16
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Jeff,
The drilling "like a chevy" is not cross drilling, but is instead drilling to provide oil to a rod bearing that otherwise wouldn't receive sufficient oiling under high rev conditions. You seem to make many assumptions, some of which are incorrect. For example neither Chevy rods nor bearings were used. This motor was built just like other similarly used motors, as I confered with those builders frequently (and probably tried their patiences).
Adam,
I didn't have the crank checked when I received it, as the vendor I bought it from knew the purpose of the crank. I also didn't question the way it was drilled, until I showed it to someone I trust after the failure, and he questioned why the drilling was different from his own crank. Interesting comment on having the Scat crank checked. I will have mine checked before using, as the assembly has to be balanced anyways, although finding it was bad would be traumatic....
Suffice it to say I had much longer life with stock Porsche crankshafts.
The drilling "like a chevy" is not cross drilling, but is instead drilling to provide oil to a rod bearing that otherwise wouldn't receive sufficient oiling under high rev conditions. You seem to make many assumptions, some of which are incorrect. For example neither Chevy rods nor bearings were used. This motor was built just like other similarly used motors, as I confered with those builders frequently (and probably tried their patiences).
Adam,
I didn't have the crank checked when I received it, as the vendor I bought it from knew the purpose of the crank. I also didn't question the way it was drilled, until I showed it to someone I trust after the failure, and he questioned why the drilling was different from his own crank. Interesting comment on having the Scat crank checked. I will have mine checked before using, as the assembly has to be balanced anyways, although finding it was bad would be traumatic....
Suffice it to say I had much longer life with stock Porsche crankshafts.
01-02-2006, 07:17 PM
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Stan,
The attached picture shows the short path to the main bearing that feeds the 2/6 rod bearings.(highlighted by the red cord)
As we can see the first gulp of air/oil-foam arrives here first.
The attached picture shows the short path to the main bearing that feeds the 2/6 rod bearings.(highlighted by the red cord)
As we can see the first gulp of air/oil-foam arrives here first.
01-02-2006, 08:14 PM
#19
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Stan wrote:
Hi Stan, , my initial inquiry didn't quite read the way I intended. I was just trying to narrow down if the bend in the crank could be determined to be a cause or an effect. I don't think it would be typical to check a crank for straightness if bought from a reputable source. Since your crank had machine work done to it, it would make a person even less inclined to double check it. Jeff kind of makes the point in that because a machine shop did the drilling you would think they would check for straightness afterward. I don't think its a situation that most have done differently. I for one would have probably done the same given the same circumstances. 
I'm still curious as to the actual machinework that was done. It looks like an additional oil port was drilled in rod 5 and rod 6, was that it? I haven't seen a redrilled 928 crank before, but it seems odd to drill into rod 5 as that isn't a typical trouble spot. I would expect to see 2 and 6 drilled to cope better with the oil timing, and ideally it would seem that an additional feed from the center main would be drilled to feed the 2/6. (similar to the stroker cranks)
Ed, I'm not quite following the diagrams you posted (Sorry Stan, not my crank). Basically, it looks like Taylor cross drilled the #2 main, and then drilled oil ports on both 2 and 6 rod at the off angle? Were the original main and rod journal oiling ports left alone, or were they welded closed and remachined?
I didn't have the crank checked when I received it, as the vendor I bought it from knew the purpose of the crank.
I'm still curious as to the actual machinework that was done. It looks like an additional oil port was drilled in rod 5 and rod 6, was that it? I haven't seen a redrilled 928 crank before, but it seems odd to drill into rod 5 as that isn't a typical trouble spot. I would expect to see 2 and 6 drilled to cope better with the oil timing, and ideally it would seem that an additional feed from the center main would be drilled to feed the 2/6. (similar to the stroker cranks)
Ed, I'm not quite following the diagrams you posted (Sorry Stan, not my crank). Basically, it looks like Taylor cross drilled the #2 main, and then drilled oil ports on both 2 and 6 rod at the off angle? Were the original main and rod journal oiling ports left alone, or were they welded closed and remachined?
01-02-2006, 08:24 PM
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Adam, those were the pics I was looking for but couldn't find. I think there is more information about the drilling and why in that thread.
Found it! Pics start on page 4.
https://rennlist.com/forums/showthre...=chevy+oilways
I didn't look through enough pages of the thread the first time I searched.
Found it! Pics start on page 4.
https://rennlist.com/forums/showthre...=chevy+oilways
I didn't look through enough pages of the thread the first time I searched.
01-02-2006, 09:32 PM
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What you can't see from Stan's picture is that the #3 main is not even drilled!!
His crank is NOT drilled like a chevy. This "vendor" never had the oil paths redrilled so they would be feed by the adjacent main bearing,"like a Chevy".
His crank is NOT drilled like a chevy. This "vendor" never had the oil paths redrilled so they would be feed by the adjacent main bearing,"like a Chevy".
01-02-2006, 09:52 PM
#22
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I've been wondering about this...
Looking at the second "drill bit" picture above, what about drilling the "X" tubes at a steeper angle? I'm picturing a passage that runs from the "1" bearing to the 2nd crank journal crossing with another passage from the "5" bearing to the 1st journal. Repeat for the four other rod journals.
Maybe the passages inside the crank journals would need to be different but with the "X" inside the rod journal both rods are fed from both crank journals. Is that the essence of the fabled "drilling like a Chevy?"
Add in an Accusump or dry sump and it's near bullet proof.
Looking at the second "drill bit" picture above, what about drilling the "X" tubes at a steeper angle? I'm picturing a passage that runs from the "1" bearing to the 2nd crank journal crossing with another passage from the "5" bearing to the 1st journal. Repeat for the four other rod journals.
Maybe the passages inside the crank journals would need to be different but with the "X" inside the rod journal both rods are fed from both crank journals. Is that the essence of the fabled "drilling like a Chevy?"
Add in an Accusump or dry sump and it's near bullet proof.
01-03-2006, 03:56 AM
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Originally Posted by GlenL
Maybe the passages inside the crank journals would need to be different but with the "X" inside the rod journal both rods are fed from both crank journals. Is that the essence of the fabled "drilling like a Chevy?"
01-03-2006, 07:06 PM
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Hi Stan,
The drilling that is shown on your crank doesn't make sense to me. It would be interesting to have the engineering explained as to the work done. The pics show that an extra oil port was added to just one of the rods per journal. I don't get how affecting oil delivery to one rod is supposed to help the other rod sharing the same journal?
Can anyone explain what we're seeing here?
The drilling that is shown on your crank doesn't make sense to me. It would be interesting to have the engineering explained as to the work done. The pics show that an extra oil port was added to just one of the rods per journal. I don't get how affecting oil delivery to one rod is supposed to help the other rod sharing the same journal?
Can anyone explain what we're seeing here?