I'm in the process of assembling my engine, after I've got some new parts. Now when my bottom end is complete and I only have my head off, I notice that #4 piston is about 0.4mm lower down than the three other pistons both at TDC and 180deg from it.

I have a resurfaced block, new 100.5mm Wössners and the rods were checked at the machine shop to be straight. Checked the block with a steel ruler and it seems to be flat. How can this be possible, and what should I do? ...and I who thought I could drive the car this weekend after a year long break...

 

How are you measuring it?

 

With a feeler gauge and steel ruler. It's however very obvious, as the 1,2 and 3 are 0.25mm over the block, and 4 is about the same below. Block was shaved 0.09mm.

 

wouldnt this only be possible if the deck wasnt flat, or a rod was bent?

 

Did you build it? If everything was fine during assy, I would say the wrist pin hole may have been machined off by .4mm.

 

I am building it myself, yes. I would imagine that this 0.4mm difference in length should have easily been noticed, if it was due to a bent rod. I guess I don't have a choice but to open it up and measure.

 

I wish I knew what the guy who measured the rods for me had been smoking. He said they were quite good, but because they were for a Porsche he will make them perfectly straight. Now it's really difficult to trust that the other rods are good.

 

I would get a new set of rods

 

Time for a set of Wossner rods

 

Not to derail this thread, but OEM forged rods are pretty stout. How common is it, do ya'll reckon, for 951 guys do be running around with one or more bent rods in their stock longblock and not even know it? I imagine a 951 could run for some time with a rod bent to the tune of .3-.4mm.. that's only ~.0015".

 

Doug, the rod isn't bent .2mm... From the photo it looks like one of those rods is leaning by at least 3mm. You have to consider how far the rod has to lean over to the side to make the piston drop .2mm. The connecting rod becomes the hypotenuse of the triangle. I would think that any engines that have been checked by someone who isn't on crack wouldn't be slipping through the rebuild process with that much bend.

 

Wow, fire that guy