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Bored? You'll think about stroking when you see these rods.

Ahh, a salacious thread title worthy of the digital mosh-pit that is the OT forum!

But Gentle Engine Rebuilder, I do not disappoint! Check out these connecting rods, fresh from the workshop of Dr. Ing. Steve Weiner, who is the Proprietor of Rennsport Systems, which is located at 6416 S.W. 33rd Pl., Portland, Oregon 97201, where the phone number is (503) 244-0990.

First, the group. Nice, no? I furnished Steve with the old rods, a set of ARP 6003 rod bolts and nuts and the bushings, and he did the rest. Steve went to the trouble to preload the ARP bolts before any machining operations, because the big end takes a different shape depending on the preload applied to the bolts. So the bolts were set using a stretch gage, and he was kind enough to note the torque at which that stretch was reached, as a guide for my reassembly. (I'm going to use a stretch gage myself but it's good to know the ballpark figure so you don't accidentally exceed the stretch value or spend all day creeping up on it.



Next, a few details: the small end, showing the bushing which was honed exactly to 130mm center-to-center distance. No "stretching."

Look how Porsche used to cast in the part number!

Next, look how differing amounts of material were removed both for weight-matching and end-to-end balancing.

And now, the mass. Here's my setup for measuring, a little crude because the electronic balance only goes to a tenth of a gram (That was an inside joke for those of you who have been following this build. )



Finally, the statistics on the mass. The whole group was weight-matched with the ARP bolts which are heavier than the factory bolts. I know this because the individual rod weights are about the same and yet material was removed, so the bolts and nuts must weigh slightly more. This came out extremely well, and it will be a simple matter to orient the heavier rods at the flywheel end. Speaking of overkill, this is WAY less than the factory ever specified for the max weight difference between the rods. Once I weight-match the rods with the pistons and pins, I'm hoping for close to zero differences. This engine is going to run like a sewing machine!



A HUGE thanks to Steve Weiner for his guidance, attention to detail, free advice and for being a generally righteous human being. Beautiful work! And the pricing of this service was appropriate for the amount of work that went into this job. Steve's given tons of free advice over the years and I am pleased to be able to reciprocate when the opportunity presents itself!
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Old 08-23-2007, 05:02 PM
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Nice John! I note that the weight was taken off the small end. Any ideas why this was done as opposed to the big end. I am under the impression that taking it out of the big end was the standard methodolgy to get even weights... Though, theoretically, to make truely equal rods one may have to balance both small and large ends... doing this is probably way over the hedge...

Best regards,

Michael
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Old 08-24-2007, 12:39 PM
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Love it - just when I think I'm a sick bastarage - I see this and start feeling normal
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Old 08-24-2007, 02:59 PM
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Quote:
Originally Posted by euro911sc View Post
Nice John! I note that the weight was taken off the small end. Any ideas why this was done as opposed to the big end. I am under the impression that taking it out of the big end was the standard methodolgy to get even weights... Though, theoretically, to make truely equal rods one may have to balance both small and large ends... doing this is probably way over the hedge...

Best regards,

Michael
My guess would be that the higher the weight is in the recriprocating mass, the worse it is. So, any weight savings up high would be a good thing. Also, relating to this, less mass slinging laterally on the pistons and pins.
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Old 08-24-2007, 03:15 PM
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Ed and Michael

A proper rod balance job results in rods whose big ends all weigh the same, and whose small ends also all weigh the same (plus or minus whatever tolerance you are shooting for), resulting in rods themselves which all weigh the same. Which is one reason why rod balancing is a bit of a stretch for the shade tree mechanic, as you need to make a jig to ensure that you are always weighing things in exactly the same way.

Making pistons weigh the same is about as far as I have gone. Rods get sent out, though I think I saw someone's home setup in a post once.

Another issue with removing rod weight is where and how you do it. Notice how smooth the surfaces are where weight was removed from the small ends. And how you can't really see where it came off the big ends. One thing is for certain - the nice rib on the big end cap is not to be seriously messed with - it is there to strengthen the cap, not to serve as sacrificial metal for balancing. A local machine shop once ruined a set of 911 rods for me by grinding on this rib.

Walt Fricke
Old 08-25-2007, 11:52 PM
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Note the pic of the big end......weight off the side via a chamfer.
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Old 08-26-2007, 07:19 AM
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Thumbs up

Quote:
Originally Posted by J P Stein View Post
Note the pic of the big end......weight off the side via a chamfer.
Nice catch JP! Its so subtle I totally missed it the first time I looked. It is really apparent when looking at the 1st pic of all the rods. Looking at the joint below the nut you can really see it. That is the same place mine were balanced. I did not see anything taken from the tops of mine. Next time I'm in the garage I'll look.

Best regards,

Michael
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Old 08-26-2007, 04:55 PM
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What did they charge?
Old 08-27-2007, 06:29 PM
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I guess we're looking at two different things.
This picture shows a certain lack of quality in bushing prep. Note to gash in the bushing, little or no cross hatching and bushing edge is poorly finished.


Note the inconsistent edge on the thrust surface on the big end.



Will any of this matter? maybe not but why not shoot for a slightly higher standard.
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Old 08-27-2007, 07:43 PM
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Hi John.
One more quick question:
You went through all the trouble to rebuild and seem to be taking great pride in it so why not rebuild the big end of the rods?
Or am I just seeing things?
It doesn't look like the big end was resized.
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Old 08-29-2007, 12:42 PM
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Jim,

You are just seeing things-I am still trying to figure out Macro photography. In response to your posts I actually went back and looked at the rods last night-- the big ends have been resized, you can see a cross-hatch from the tooling, and I checked them for roundness with my bore gage, and the edges of the bushings are smooth, no gashes. Again, not that it would make a giant difference because it's a street engine, but these were done to a very high standard-- even if my photos don't do it justice.
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Old 08-30-2007, 04:11 AM
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I agree that photos can be deceptive but I was also wondering what was up with this rod?
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Old 08-30-2007, 02:53 PM
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Henry,

You are correct, there is a slight low spot there adjacent to where the sides of the big end were refinished. I measured how low.

First I set up a height gage on my surface plate with a test indicator. The test indicator was zeroed out on a gage block (I chose 10mm because it was handy).



I then deducted 10mm from the 21.8-0.1mm spec for big end width on page 35 of the little white book.



Then the rod was introduced without moving the height gage, and the difference measured.



The result: the difference in height is about 0.08mm (0.00314 inches). (Photo shows a different spot than you pointed out but I measured everywhere.



In terms of absolute measurements the "surfaced" portion is about 21.78mm, deducting 0.08mm gives you 21.70mm which is right on the factory's low limit for the low area, which doesn't go all the way around the circle.



Now, what should the rod to sidewall clearance be? According to Wayne's book p.205, sidewall clearance should be between +0.200 to +0.0400mm (0.00787" to 0.01575").

How do you measure side clearance at Supertec? Do you use a feeler gauge on one side of the crank, one on each side? What spec do you like to see?
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Last edited by 304065; 08-31-2007 at 06:00 AM..
Old 08-31-2007, 05:57 AM
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We use a general rule of .007"- .012.
The truth is after 30 years of building these engine you can actually tell pretty close what the clearance is by feel or more accurately, sound. Rattle the rod back and forth and you can hear the clearance. It is very difficult to measure to rod journal on the crank so this method proves more than adequate.
The key is to start with a rod in which you have complete confidence.
That means rebuild it (all of it) and then measure it.
If a rod feels/ sounds too loose we use a feeler guage in multiple places around the rod to verify thrust.
If the engine is intended for racing then we lean towards the looser end of the spec and run higher oil pressure.
We also prep the big end thrust surface with dry film lubricant.
We are experimenting with DLC (Casidium) in place of dry moly but at this time a lack of competent coating suppliers has left this process very expensive.

John
I noticed that Jim questioned if the big end of your rods were rebuilt and you said they were.
The picture you posted would lead me to believe that they were not resized but just scuffed.
This is just an observation, not a criticism.


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Last edited by Henry Schmidt; 08-31-2007 at 07:43 AM..
Old 08-31-2007, 07:40 AM
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more research... Thanks John.
Old 12-29-2010, 10:31 AM
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You know, you can just go up to the "thread tools" button and click on "subcribe to this thread". You do not need to post.
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Old 12-29-2010, 10:58 AM
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^^^ I did not know that... Thanks.
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