After discovering one broken head stud about a month ago, I began the teardown for a rebuild on my 78SC track car (95k miles). Late last night I finally had a chance to pull the heads and Ps&Cs. Turns out there was only one broken head stud - #1 cylinder, intake stud. From what I have read this is pretty rare, but the good news in the mystery of a broken intake side stud was solved. This engine was rebuilt around '84 (more on that later) and when it was rebuilt the mechanics replaced one of the exhaust (dilivar) studs with a steel stud - yes, just 1 on the whole engine. So, cylinder #1 had 3 steel, 1 dilivar stud.
I knew from the PO that this engine had been short-stroked around '84 when it was imported from Europe. PO believed it was a short stroke 3.2 - the car pulled very well, was dyno'd 3 years ago with 192hp at the wheels and last year (when I bought) had leakdown of 4-5% each cylinder.
After getting the heads off I finally had a chance to get a good look at the Ps&Cs. They measured at 97mm, yup, from a 3.3L 930 engine. I haven't mic'd the rods yet, but according to Henry Schmidt on this thread (
http://forums.pelicanparts.com/showthread.php?t=319262&highlight=930+cylinders), different pins and an offset bushing result in a 3.12L short stroke.
So, now to the fun part - the good news I thought at the time is that these cylinders are Nikasil, meaning they can be reworked. The 930 cylinders are odd though, having cooling fins on only one side! Once we got the whole thing apart though, we found significant pitting/corrosion on cylinders 4 and 6 at the head/cylinder mating surface and on the pistons - oh, and all the top rings were broken on all pistons.
Here are some pictures:
Cylinder mating surface pitting:
Head Pitting:
Piston Pitting:
Anyone seen anything like this before? Anyone have any theories on what caused this?
My theory is this: you'll note the pitting is along the exhaust side, as it is for all damaged cylinders. The exhaust side is also the side that lacks cooling fins. I'll bet the additional heat on that side over the years has continued to eat the material.
I'm also assuming at this point that the Ps&Cs and the affected heads (just 4&6 really) are toast - I realize it is tough to get an accurate feel from the pictures, but if anyone thinks differently, I would be interested to hear their thoughts.