Valve TrainDear Ole Mechanic;

I have a problem with my Antique? Classic? 1969 Chevy pickup.  While the engine was out being overhauled, I slicked up the body and had it painted.  The problem is with the overhauled 250-cubic-inch inline six-cylinder engine.  I got it back in the truck and it seemed to run just fine.  I took it out for several ‘break in’ runs.  After I had put about 800 miles on it, the problems started.  It seemed to be missing when it got warmed up and it wouldn’t pull near as strong as it did just after I installed the engine.  At about 900 miles. I could hear a tapping in the engine that sounded like a loose rocker arm or a collapsed lifter.  I pulled the rocker cover and two of the rockers had about a quarter of an inch excessive play and a third one had between three-eights and one-half of an inch play.  The rocker adjusting nuts were all still tight and the other rockers seemed to have the correct adjustment.  I removed the three loose rockers and pushrods.  The rockers were OK, but the pushrods were severely worn on the rocker arm end and there were fine metal shavings everywhere.  Now what do I do?  What caused the wear?  What else do I need to check?  How can I keep this from happening again?  Help!

Wondering about Driving an Antique


Dear Wondering Antique;

Ouch!  The first thing to do is to take the worn pushrods and rockers and have a talk with the person that overhauled the engine.  See if he can spot any problem with the pushrods or rockers.  I suspect that the ends of the pushrods were not properly hardened.  They should have been hard enough to withstand being either too loose or too tight.  Even if the rockers had rough machining where the pushrods contact them, the pushrods should have been hard enough to keep from wearing the way that they did.  Don’t expect too much from the guy that overhauled the engine unless he offered a warranty when you took the engine to him for the overhaul.  Probably most mechanics today don’t remember or were never taught about inline six-cylinder engines or flat-tappet camshafts.  Be prepared to discuss the type of oil and any additives that you used in the engine as well as your engine break-in driving.  He may even want to look at the engine while it is still in the truck.  At this time a calm discussion will get you a lot further than shouting and finger pointing.

After talking with the engine rebuilder, the next thing that you would want to do is check the camshaft for wear.  This can be done with the engine still in the truck and the camshaft still in the engine by using a long travel-dial indicator.  With the engine crankshaft turned until the cam lobe is at its lowest point, position the dial indicator on the lifter or pushrod.  Then turn the crankshaft by hand till the cam lobe is at its highest point.  Write down the measurement and then repeat the measurement on all of the other cam lobes.  There may be a difference between the intake cam-lobe measurements and the exhaust cam-lobe measurements, but all the intake lobe measurements should be the same and all the exhaust lobe measurements should be the same.  If there is a difference of ten-thousandths of an inch or more, then the cam is worn and it and the lifters will need to be replaced.  Another way to check for cam lobe wear would be to remove the camshaft from the engine and measure the lobes with a micrometer.

The next thing you should do is check for wear from all of those fine metal shavings you mentioned.  You should check the main bearings, rod bearings and oil-pump wear.  Yes, checking the bearings can be done without removing the engine from the truck, but it would be a lot easier if the engine were out of the truck.  It would also make the next step a lot easier too.  That step is to flush the block and oil passageways to remove all of those fine metal shavings.  For flushing I would recommend a solvent flush followed by a flushing with a light weight, high detergent oil like Automatic Transmission Fluid.  A bunch of rags will be needed to wipe things out after all of the flushing.

If all of this sounds like it is beyond your capabilities, then you may want to discuss having the overhaul person do the work.  While defective pushrods are not the fault of the person that did the work, he might give you a discount.  While you are discussing the additional work, you may want to ask about parts and workmanship warrantees.

OK, your questions were:  Q: “Now what do I do?”  A: Discuss the problem with the overhauler and check for other wear.  Q: “What caused the wear?”  A: Improperly hardened pushrod ends.  Q: “What else do I need to check?”  A: For other wear caused by the pushrod metal shavings.  Q: “How can I keep this from happening again?”  A:. Use quality parts and bribe Murphy --the one that says “If anything can go wrong, it will.”  As for your “Help!” plea all I can say is, Ain’t it fun working on old stuff.  I remember pulling the engine out of my race car twice in one weekend and then three more times during the following week--all for the same clutch/flywheel problem.  Once I got it fixed, it ran the rest of the season.  Remember, it should all be about having fun.  If is isn’,t then I suggest you find a different hobby.

Herr Professor Nuzanbolts