Jump to content
HybridZ

Piston Guided Connecting Rods


MAG58

Recommended Posts

Well I was tearing down my JY motor to build so it can go in the Z car when I found an interesting bit of technology that this engine uses: Piston Guided connecting rods, meaning that the piston is what dictates fore-aft movement of the rod, and not the crankshaft. I personally have never seen it before, and have really only read of it recently in NASCAR and on other MBZ engines.

 

Anyone care to weigh in on this?

 

I've took a few crappy pics, I apologize before hand for the useless Macro feature on my camera.

 

DSCN4133.jpg

DSCN4134.jpg

Link to comment
Share on other sites

Looks like a simple full floating piston pin setup to me...

 

Engineering-wise it would make far more sense to have the rod located fore/aft by the crank - cast/forged steel on the crank throws and a larger diameter to minimize twist/flex... as opposed to lightweight piston pins and aluminum pistons that are not only much lighter weight but moving up/down - sure disaster.

 

Now I could see a combination of both to minimize any loss of straight up/down motion as a way of maximizing efficiency of the rotating process and possibly pick up a fraction or so of horsepower...but then one would have a horror story in blueprinting/shimming between piston pin bosses and the connecting rod...

Link to comment
Share on other sites

It's full floating. But here's the interesting point. The small end of the rod is what is milled for clearance. There's no more than .002 slop in the top. At the big end, there is probably a quarter inch rock back and forth.

 

I was wondering if there were any other engines that got this little bit of technology. A quick trip to google showed that apparently Joe Gibbs and Hendrix have been using them very recently in Nascar.

 

Edit: I pose this question since this has been used in Mercedes since the inception of the M103 in 1984ish. The reasoning behind it is that if I go to MBZ and ask for a set of stock replacement pistons they want 374 bucks a piece and the only company I've talked to (Ross, CP, Wiseco, JE, etc.) personally that said they could do it with standard forgings was JE, in fact, they're really the only people that have any knowledge of them. Ironically Wiseco just got a set of pistons in their tech dept that have piston guided rods and they're just as new to it as I am.

Link to comment
Share on other sites

Mag, how consistent in width are the journals on the crank? Does it seem like it could be turned into an "either/or" deal, where you can index location from either big or small end, or are we forced to use the small end?

 

It obviously works given the mileage that these engines see, but I have to wonder why they did it that way...

Link to comment
Share on other sites

Yes they're all the same width and as far as I can tell could be crank guided, though the end of the journal is substantially more radiused than what I'm used to seeing on other cranks.

 

And the reasoning behind this is, as far as I can tell (if anyone truly knows why, please inform me, it's the point of this thread), is that it allows a narrower rod at the crank side (with the caveat of increased pressure due to less contact patch) to reduce friction and intimately increase efficiency of the motor. Since the pin is designed to rotate inside the conrod bush, they extend the wrist pin towers in to contact the rod thus making that the load bearing surface, not the crankshaft.

 

 

But, until someone can confirm or deny this, it's purely conjecture.

 

 

And I have yet to find any part of this motor that was designed for no other reason than to make the engine expensive.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...