Aluminum in oil in TCS

[4129R]

Apparently, the Twin Cam rods have rolled J threads 

Could someone please explain what "rolled J threads" are?

I understand that threads are applied to bolts by rolling, (in this case the con rod bolts which are torqued up without any spring washers), but what is special about J threads?

Does this mean the con rod thread is cut with a different type of thread tap?

[jbcollier]

Google is your friend:

https://www.threadcheck.com/whats-the-j-in-unj-screw-threads/technicalinfo/#gref

[jbcollier]

Also the internal threads are formed using a mandrel rather than a cutter:

https://www.emuge.com/videos/emuge-roll-form-tap

[BDA]

I guess the first lesson here is not to “clean out threads” automatically with a tap or die when less aggressive methods are available, especially since the kind of dirty a connecting rod would have would be very unlikely to require aggressive methods.

I have to say I was initially surprised that those threads were rolled figuring (incorrectly after remembering seeing bent connecting rods) that the rod material would not be ductile enough for them since they are formed by moving metal rather than cutting it. Cast iron is probably too hard for rolled threads and if so, threads for main caps or head studs would be cut. Still, I wouldn’t chase them with a tap unless there was no alternative. I would be even more careful with internal threads in aluminum.

Looking back, I can’t remember if I’ve always followed my advice here but I’ll make sure I do in the future!

[Pfreen]

Were the rod bolts loose?

[jbcollier]

I can’t imagine any situation where you would chase main or rod threads.  Clean them with a volatile agent and blast them with air?  Sure.

[cazman]

I'm not the expert. I had to go to Ken at Dave Bean then to Sandy at Quicksilver to get the answer. But, that is the spec on the rods apparently. I think you can get a special tap.

Yes,#2 rod was loose and it just seemed like a typical bearing problem or bad bolt/torque problem. I think the problem was a hidden, because there was no rod-knock with normal driving. I believe that the bolts loosened in the thread at high RPM and I didn't notice the sound as it was high frequency mixed in with other mechanical and exhaust sounds (as you know I did see the shavings however). It was only apparent after seeing the bad #2 bolt could basically pull out at this point. What's up with that? Well, now a look at the other rods showed that all the bolts go in way too easy and loose.

[dakazman]

the motor apart we figured out that the last person that rebuilt the motor chased the connecting rod-end threads with a standard machine tap. Apparently, the Twin Cam rods have rolled J threads and should not be chased with a standard tap. So, at high RPM the threads were giving away allowing the rod to knock and beat the bearing.

So, its new rods. The crank is good though.

 

 
   Cazman, Most rods have studs , bolts that go thru the rod and have a nut. Where did the PO run a tap? Our did you mean a Die?
You can replace just the bolts on the rods. If available.
  Where did you get the info about J-Threads? I just want to where this paper trail on TC motors comes from because i may be buying a TC.
 Dakazman
 

[Pfreen]

Here is a photo of the rod.  ARP bolts are usually used.

[dakazman]

  Aughh, now it’s coming into focus .
Thanks Pfreen
Dakazman

[TurboFource]

Cap screw rods are stronger because the rod does not have to be machined for bolt head clearance.