Get out the measuring stick!

OK, time to take some measurements to see what type of condition the engine is dimensionally.


Started off by measuring the pistons.  The workshop manual says to measure the pistons 1/8″ below the cross slot.  Not sure what that exactly means, so I measured them just as the picture shows in the manual.  I also measured them at the base of the skirt to see what type of taper has worn as they originally are larger at the base of the skirt.

IMG_1893  IMG_1894

Cylinder Bores

I then measured the cylinders 1 1/4″ (30mm) from the top as specified in the workshop manual.  I measured them both perpendicular and parallel to the crankshaft.

IMG_1891  IMG_1892

Piston to Bore Clearance

The piston to bore clearance specifications for a new engine are 0.0013 to 0.0017″.  The results I determined are as follows:

Piston Cylinder Piston to Bore
Cross Slot Base of Skirt Perpendicular Parallel Clearance
1 3.999 4.000 4.0025 4.0035 0.0035
2 3.9975 3.999 4.004 4.0035 0.0065
3 3.998 3.9985 4.004 4.003 0.006
4 3.999 4.0005 4.004 4.0032 0.005
5 3.9975 3.9985 4.0038 4.004 0.0063
6 3.998 4.000 4.0038 4.003 0.0058
7 3.996 3.996 4.0035 4.0035 0.0075
8 3.998 4.0005 4.004 4.004 0.006

Visually the pistons and bores are both in great condition with no significant scoring or damage.  The ridge at the top of the bore only measures 0.001″.  I have decided to seriously consider using the pistons again as they are the original high quality Cadillac forged units.


I also measured up the crankshaft.  All of the bearing surfaces are in great condition with no scoring.  According to the manual, the Main bearing journals should be 2.625″, and the big ends 2.2488″ to 2.2493″.  The measurements are almost perfect:

Front Main 1&2 Main 3&4 Main 5&6 Main 7&8 Rear Main
2.623 2.249 2.6235 2.249 2.6235 2.249 2.6235 2.249 2.624


The only thing left to measure was the ring to groove clearance in the pistons.  The oil rings and middle rings all measured 0.002″ to 0.003″ which is great.  The problem is with the top rings, which I was able to slide an 0.008″ feeler into.  The new spec is 0.0022″ to 0.0035″.  That makes them a little on the loose side, which makes me a nervous.


After thinking about it for a while, I compared the actual thickness of a 5/64 and a 2mm ring.  The 2mm ring is 0.006″ larger, which would make them just about a perfect fit!  I sent off am email to Hastings Piston Rings to see if they have a piston ring which matches the Cadillac design, but 2mm thick.  This would be a great solution if they do.

If I am able to solve this I will definitely use the old pistons again.

Front Wheel Arch Inner Rear Panels

I also took to the inner wheel arch panels to clean them up ready for a coat of paint.  I used a 3M Scotch Brite Varnish and Paint removal wheel.  It did a pretty good job, however next time I will buy the more aggressive one.


I spent about 10 minutes on each panel cleaning them up and removing a lot of the surface rust.

IMG_1898  IMG_1899

I have them now soaking in a rust remover to try and remove as much as possible before painting.


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