Oh No! 6/2/2021

I was supposed to pick up the car tomorrow, but I got a call from Butch Dennison yesterday.  They were doing the final tuning on the carbs on the rolling dyno and the engine was putting out a lot a black smoke at high RPMs.  This should have been noticed when the engine was on the engine dyno, but the exhaust goes out of the building and it may not have been noticed, or not checked at high RPMs.

So today they pulled the engine and tomorrow will take it apart to determine the problem.  It's likely to be that the piston rings not sealing properly.  If so, they may have to re-hone the cylinders and install new rings.  I'll know more tomorrow after the engine is apart.

Well, they didn't find any problems, so new rings were ordered.  They also removed the crank so they could hone the cylinders to the ring manufactures surface specification.  After that was done, they re-installed the crank and after being properly torqued, the crank would not turn.  The number 2 main cap was the issue.  This was one that was broken when I purchased the car.  My machinist said that he could have it welded and be like new.  Well, it looked like new, but that process softened the cap.  It worked when installed the first time, but this time, the mating surfaces crushed about 4½ thousands thus causing the issue with the crank.

They had repaired Jon Shirley's 250 GTO after three main caps had failed, so they planned on using the same source for a main cap.  However, it turns out that the ones available are for the number 1 cap on my engine, which is both wider and taller.

In the end, they ended up making a main cap from scratch, using 6061-T6 aluminum.

Of course, the block had to be line bored again and then was sent out for a very precise line hone to meet the 2.5062 - 2.5067 specifications.  As you can see, the tolerance is ½ of a thousandth.  That makes it obvious why the 4.5 thousands crush caused problems.  You can also see the slightly taller number 1 cap.

So now, the engine is being re-assembled.  Then they will run it on the engine dyno, carefully checking for excessive smoke.  Once it works well there, back in the car and onto the rolling dyno for final carb tuning.  Stay tuned, hopefully there won't be any other issues and I'll get the car soon.