Cobra OE rods & pistons pix & what happens when you run too lean.

[Warpath]

Here are some pictures of the stock pistons and rods from a 99 Cobra. I mentioned a long time ago that I would post them. They should be the same as MM parts. For those who don't know, the pistons are cast aluminum and the rods are powdered metal. The rods are made, machined, and then the rod caps are snapped off. The pictures of the rod ends are supposed to look like that (uneven). It saves time to make them this way and is, therefore, considerably cheaper. They are also considerably weaker compared to forged rods.

When an engine is run too lean on these engines, the ring lands will crack like mine. I took out the pieces on one piston and left them in on the second. Yes, I have two bad pistons. I had my stock engine tuned at Livernois Motorsports (don't go there!) and ended up this way. I learned better and am having a new engine built and installed at Alternative by Lidio & Co. They took apart the engine. So, I can't answer any questions regarding disassembly.

These pics are just to show you what you have and educate you about when things go bad. Enjoy!

[Warpath]

piston tops - there is a slight dish to them

[Warpath]

piston missing ring land pieces

[Warpath]

The missing pieces.

[Warpath]

The other cracked piston with the pieces still there. The ring looks chipped too.

[Warpath]

The crankshaft end of the rod showing the "crack" separating the cap from the rod. Again, its supposed to be this way. There's no damage.

[Warpath]

another view showing them separated

[Warpath]

rod cap showing surface of crack

[Warpath]

rod end showing the cracked face. The bearing is removed.

[TripleTransAm]

I read a couple of times that the whole 'casting and cracking' technique allows for better tolerance control. In the older methods, rods and caps were cast separately, then torqued and machine. This way supposedly allows for a better mating surface (since they were originally all one part, so the crack lines match up).

[sailsmen]

"Tuning" is still more Art than Science.

I had a heavily modded 914 Volkswagen-Porshe and there were several excellent mechanics that could tune to run well.

But there was one guy who had the ear for it and I got signifcantly more performance when ever he tuned it.

Funny but the car never missed or bogged with the other mechanics, he just had the right touch.

[studio460]

Great thread, Warpath! Excellent photos! Thanks!

[Warpath]

Originally posted by TripleTransAm
I read a couple of times that the whole 'casting and cracking' technique allows for better tolerance control. In the older methods, rods and caps were cast separately, then torqued and machine. This way supposedly allows for a better mating surface (since they were originally all one part, so the crack lines match up).

I've also seen the rods cast as one piece with the crankshaft hole (whatever its called) cast as an oval. The rod is cut through the oval. Then it is reassembled and finished machined. I'm not sure what advantages that has other than having very similar material properties (cast at the same time, same material batch, same everything). Anyway, tolerances can be held pretty much with any method of casting/forming the rods - separate pieces vs. one piece. Some methods take more effort to hold the tolerances than other methods. More effort means more cost. I'm not disagreeing with you - just looking at it from another angle.