Compression/Deck Height

Since the new engine was installed in December, it has been running really well.  The weather has been cold and rainy.  I noticed that once it was warmed up the starter had a hard time cranking it over.  I made a mental note to pay more attention and initially thought about compression.  Then the weather warmed up in January.  We had temperatures in the mid to upper 70's, and even close to 80.  Gotta love Southern California, except for the Santa Ana winds.  Along with the increase in ambient temperature came some knocking noises in the engine once it was warmed up.  It even had increased head temperatures, and the oil light flickered at idle after a freeway run.  Argh!

When I built the engine, a machine shop owner told me not to worry about the piston to cylinder deck height since the new AMC heads had a built in raised gasket area.  I measured the gasket area in relation to the thickness of the cylinder wall and decided to take his advice.  The added compression gave the bus a bit more power to get up the hill. 

Unfortunately, once the engine warmed up on warmer days, it appeared I had a clearance problem between the piston and cylinder head.  The metal parts, especially the aluminum piston, expanded and then there was contact between the piston and cylinder head.  Not enough to stop everything, but enough to cause some noise and concern.  With this problem, there is no way I am going to be able to take the bus to the beach for a fishing outing.

Today after the yard work was completed, I removed the engine and tore it down to the short block.  I replaced the rod bearings while the case was still together, just in case there was wear from things banging around.  They looked ok, but not perfect.  I had never replaced rod bearings in this manner before, so I was a little nervous, but everything worked out okay without any parts falling inside the case.

I then shimmed the cylinders and managed to get .055 inch in deck height.  I reassembled everything and installed the engine just in time for Diana to get home from running her errands.  I had to use a work light since the sun had set partway during the install.  The engine started right up, without any hesitation by the starter motor.  I sounds smooth so far, but tomorrow should tell how it runs on a warm day.  The weather is expected to be sunny and 72 degrees.

Next time a machine shop owner says, "Don't worry about deck height," I think I will follow the book.

Happy Bus Motoring!

( o v o )

Ron