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-   -   Con Rod Position (http://forums.pelicanparts.com/911-engine-rebuilding-forum/398836-con-rod-position.html)

88911coupe 03-17-2008 03:35 PM

Con Rod Position
 
OK, did a search, read Wayne's book and maybe I missed this but here's my question. Do the con rods need to be kept in their same relative position on the crank? I have marked them but did not send them with the p/c's, heads etc. since I may just get them measured locally. My concern is if a shop removes the markings I have made I won't know which journal they came off of. I don't want to use a dremel or anything considering how stressed these pieces are. Note that I did not keep track of how they were connected to each journal on the crank since it appeared it was a mirror image. BTW, the bearings look great, very little "apparent" wear. I realize the numbers need to match up when reassembled.
TIA

ChrisBennet 03-17-2008 06:51 PM

I weigh them and pair them up with the heaviest nearest the flywheel.
-Chris

88911coupe 03-17-2008 07:01 PM

Thanks Chris...you answer would seem to indicate that I can put them back in a different order that they were removed...correct?

304065 03-18-2008 02:53 AM

Buck, they aren't married to a particular position. You can put them back in any order you please BUT observe the weight-matching principles for best results.

For example, because I am an OCD nutcase, I have weighed all my rods, pins and pistons, and have figured out the optimal combination of all 18 parts that results in the minimum weight difference between each cylinder's assembly. The heaviest, as Chris says perfectly, go near the flywheel end (has to do with flexing of the crank).

There is a drawback to my approach, however, which is that if you blow a piston, the balance will be affected, because you will be replacing that piston with one of a different weight. No big deal for most street engines, and there's nothing to say you couldnt' log that piston's weight and match the replacement.

Check the spec book for the factory max difference in weight, it's a huge number, a few grams. Here's my OCD thread where I talk about rods.

http://forums.pelicanparts.com/showthread.php?t=363493&highlight=connecting+rod+w eight+difference


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