Packard Forum Index » Post-War (1946-54)

Yeah, me too, Thanks Ross. I suppose I'll start looking for a good 356 head.

Warren

OK, now back to your sticking valve. When you have the head off check the guides, valve stems, and valve springs carefully, and do measure the valve stem to guide clearance, remembering that the exhaust clearance is larger than the intake clearance to compensate for the greater thermal expansion of the stem.

To check the guides for wear and eliminate stem wear from the equation, I often purchase one new valve and use it to check the clearance. Obviously if it's excessive with a new valve, the guide needs replacement and the exhaust guides will wear the most. But I doubt your problem is with excessive guide-to-stem clearance; if it's an intake that's sticking, I suspect the clearance is either too little, or the valve stem and guide has accumulated excessive carbon and gum which a good cleaning should resolve. Though there are special tools for cleaning guides, I often use a brass rifle barrel cleaning brush of about 38 caliber, with plenty of lacquer thinner. Of course a properly sized ream will also clean the guide and resize if that is needed.

If the valves are sticking after being serviced the inside of the guides are corroded and varnish collects within pits which then creates little wedges that close off clearances once the motor cools.

On the subject of the cylinder head I think that is an interesting issue given that engineers were fully aware that the L-head motor is subject to pre-ignition. I assume because the compression stroke creates a front that is not evenly distributed and causes diesel type combustion. The L-head motor is much more suseptible to piston noise than OHV motors.

That these rebuilt motors do it more as they age points to hot spots in the aluminum cylinder head probably from corrosion. Or perhaps the carburetors are worn and the Economizers are closing off too much under moderate throttle. I drove a 359 once that had an NOS carburetor and it did not ping.

The 356 head swap is academic, but a better solution would be to use lower compression pistons. A good machinist can turn .060 off the top in a mill. All that is required is the right specification. .060 is about one compression unit for a cylinder head. Of course for a motor rebuild the piston specification could be had from the manufacturer.

I was dealing with one of these pinging things and heard all about distributor curves and what not from now deceased experts, but I never bought it. Fortunately for the case I was handling the detonation was from over heating. The owner agrued with me that if the gauge is no solidly on Hot the motor is not overheating, even though it was spewing coolant out the over flow in the shop.

So I just fitted a 160 thermostat with out telling him what I was doing. He came in and started yelling at me that I wasn't installing the thing the right way. The car didn't have seat belts and I told him to drive it a fast as he wanted.