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Redline Racer
 
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Question Need crank drilling advice

I'm soon going to have a short block to finally get to work on and I was planning on having the crank cross drilled. Of course, it is deceptively simple sounding...

Exactly how should a 944 crank be cross drilled, or perp drilled as I have seen mentioned as another option? Let me see if I can organize my thoughts well enough to follow.

1. I read in an engine blueprinting book (focuses on GM V8 builds) that they oftern cross drill the main bearings so that the oil supply to the rod journals is constant regardless of crank angle. Most main bearings have oil feed groves on only the top half of the bearing shell. The 944 had grooved mains on both halves until early 84 and then went to a standard solid lower main half. The grooved bearings cannot hold as much load, so the lowers were upgraded. The book specifies that drilling two intersecting holes at right angles will greatly help oil flow to the rod journals, since at least two oil feed holes will always be exposed to the oiling groove in the main. I assume that the V8 cranks they are dealing with have a straight through oil hole in the mains like the 944 does, but maybe they run a single hole halfway through the journal like the rod bearing holes...I don't know!

So is drilling an extra hole perpendicular to the original oil passageway through the mains on a 944 crank effective or advised? I have seen no mention of this particular cross drilling in any of the threads on the subject.

2. What I have seen in the threads (but not in the blueprinting book) is cross drilling, or perp drilling the rod journals themselves. First, what's the difference between the two techniques? The rod journals do only have one feed hole drilled to the center of the journal pin, rather than straight through like the mains. Also, it seems that the consensus is to drill only the #2 and #3 journals. Someone did a flow test on a 944 bottom end and found out that the #1 flows more than any of the others, and the #2 and 3 flow hardly any in comparison to the rest, especially in a low pressure condition. He found drilling just the 2 and 3 journals increased flow, or rather equalized the flow, but drilling all 4 did not change the original flow characteristics. Seems like 3/16" was the determined optimum drilling size.
http://forums.rennlist.com/rennforums/924-931-944-951-968-forum/343714-crank-modifications-cross-drill-vs-perp-drill-vs-enlargment.html
http://www.nasaforums.com/viewtopic.php?f=40&t=4398&st=0&sk=t&sd=a

So what's the difference between cross and perp drilling, and which way is best?

Finally, should I do the mains, the rod journals, or both? Should the mains be drilled as well as the #2 and 3 rod journals, or should just the 2,3 rod journals be drilled, and how should they be drilled?

Thanks in advance!
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Last edited by HondaDustR; 08-31-2009 at 06:26 PM..
Old 08-31-2009, 06:23 PM
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HondaDustR,
I have no experience on the topic. I did find a couple of pictures showing cross drilling techniques at the 928 forum to help me understand somewhat.
http://forums.rennlist.com/rennforums/3855652-post10.html

Gl on the project
John_AZ
Old 08-31-2009, 09:55 PM
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Crossdrill is making another oiling port 180 degrees from the original, so basically drilling straigt through. Perp or perpendicular drilling is going 90 degrees instead. Perp drilling is said to be more effective because it is adding oiling to the section of the bearing under load as the crank rotates along the inside of the rod. Whichever you go with is up to you really.

No need to do the mains, they are already crossdrilled. Don't think I've ever heard of a spun main on one of these blocks either. Always the #2 followed by #3.

I think either will do you fine, I would ask whomever is doing your machine work what they are most comfortable doing. If it was me I would perp drill #2 and #3 only. Coupled with a pan baffle, good oil, good oil cooling and a windage tray i don't think much else can be done to increase bearing life short of going dry sump (which is what i plan on).

Last edited by Techno Duck; 09-01-2009 at 12:00 AM..
Old 08-31-2009, 11:55 PM
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Quote:
Originally Posted by Techno Duck View Post
Crossdrill is making another oiling port 180 degrees from the original, so basically drilling straigt through. Perp or perpendicular drilling is going 90 degrees instead. Perp drilling is said to be more effective because it is adding oiling to the section of the bearing under load as the crank rotates along the inside of the rod. Whichever you go with is up to you really.

No need to do the mains, they are already crossdrilled. Don't think I've ever heard of a spun main on one of these blocks either. Always the #2 followed by #3.

I think either will do you fine, I would ask whomever is doing your machine work what they are most comfortable doing. If it was me I would perp drill #2 and #3 only. Coupled with a pan baffle, good oil, good oil cooling and a windage tray i don't think much else can be done to increase bearing life short of going dry sump (which is what i plan on).
Yeah, I figured the mains were already crossdrilled from the factory, was just confused on the exact details of the terminology and process.
I don't think you could spin a main bearing if you tried! The rods definitely seize/fail first. All 5 mains on my old crank are pristine in stark contrast to the #2 and #3 rod journals which are totally caked with melted torn up copper bearing material. Interestingly, #4 looked nearly untouched, just 1 or 2 bad scratches, and #1 had patches of burning/scouring and a little bit of silver bearing material stuck to it. #2 and #3 are destroyed, so there's a definite unbalance of oil delivery.

Now for perp drilling, which 90 degrees from the existing oil hole should it be drilled, since obviously, there are two possibilities?
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Old 09-01-2009, 03:58 PM
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Lindsey Racing does this and could probably describe it (and the rationale) pretty well.
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Old 09-02-2009, 07:39 AM
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Quote:
Originally Posted by Porsche-O-Phile View Post
Lindsey Racing does this and could probably describe it (and the rationale) pretty well.
I would send it to Lindsey and not your local machine shop. There are a few things in there that might screw up the average hot-rod dudes.
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Old 09-04-2009, 03:05 PM
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Quote:
Originally Posted by mistertate View Post
I would send it to Lindsey and not your local machine shop. There are a few things in there that might screw up the average hot-rod dudes.
I may just end up doing that. What kind of things are you talking about?
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Old 09-05-2009, 08:46 AM
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I know many of the above members follow Rennlist. I thought I'd post a current link on the crank drilling topic for others who search. I was interested in the suggestion of "flow restriction" in the oil galley.
After searching, the only conclusion is many opinions on both. What Techno Duck suggests is most often mentioned.
http://forums.rennlist.com/rennforums/924-931-944-951-968-forum/521773-flow-restrictors-in-the-1-and-4-oil-galleys.html

GL on the build
John_AZ
Old 09-08-2009, 07:52 AM
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That's pretty interesting.

Quote:
According to their research, the #2 bearing gets almost no flow ad idle which is the cause of the premature wear.
Well then, there actually is a good reason to high idle my car at stoplights besides it just being one of those weird things I do out of habit...and impatience.

With the issues with the internal screens to catch machining shavings that will trip up shops that don't know about them, I wouldn't have anyone other than Lindsey Racing work on it. I emailed them and found out that they drill out the factory plugs and install threaded plugs as part of their cross drilling service to allow the oil galleys to be easily cleaned after machining.

I was considering going for the whole package of magnafluxing, drilling, balancing, and medium lightenning from LR, But as a tragic end to a good thread, I've been talked into forgoing the crank work this time around, since "it's only a daily driver and probably won't make a noticable difference" even though I drive the snot out of it any chance I get. I can't help it...that's just the way I do it. I can't stand taking forever to get up to speed, and just poking along like there's all the time in the world and somehow I'm making my car last forever and getting 3 extra mpg just doesn't make any sense. It might when I'm 60, but until then... I guess there's a point. It lasted 160K before I screwed it up, even with lots of high revving. I would like to do a day at summit point or do some auto-X one of these days without worrying about killing it.

I'll be back to build a REAL motor. Once I get enough of life taken care of I'll hunt down a 16v to build.
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Old 09-08-2009, 05:19 PM
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