Hey everyone, I just recently got hold of a 42 GMC truck. The engine was rusted stuck and after sitting for a while, soaking in diesel has broken free and now runs. Number 4 cylinder misses on an idle, it has 50 psi compression and cylinders 5 and 3 fire so I know the head gasket is good. The valves work and theres lots of spark so I was wondering is there a plug recommended for a tired engine with low compression? Any ideas welcome: Thanks
By the way, over the years Ive seen lots of factory rebuilt six-bangers painted this green (about the color of a bar of Irish Spring soap), any ideas who the rebuilder was?
50psi is bad.Did you check the compression wet?First check dry compression write down.Then squrt a few shots of oil in the cyc and recheck compression again.If the compression increases,your rings are bad.If they stay the same it's your valves.compression at least 100psi.If two cyc side by side the same low comp it's usually the head gasket.Hope this helps out.The plugs NAPA should help ya out
The only specialty plug I've used that actually seemed to help a tired engine was a "booster gap" plug with a break in the conductor back inside of the porcelain insulator. It's supposed to allow voltage to build up and fire an oil-fouled plug instead of bleeding off through the fouling. It doesn't sound like you've got that kind of problem.
Try doing a cylinder leakdown test by putting compressed air into the cylinder through the spark plug hole with the piston at the top of the compression stroke. The crankshaft is locked by putting the truck into high gear and setting the parking brake or using wheel chocks. Listen for piston ring leakage at the oil fill cap, or valve problems at the carburetor or tailpipe. Bubbles in the radiator would indicate a cracked head or a head gasket leak into the cooling system. All the cylinders should be within 10% or less of the same compression pressure, and 100 PSI or slightly less should be considered the minimum acceptable pressure. Be aware that different compression gauges can give widely differing pressure readings on the same cylinder, so be more concerned with uniformity between cylinders, not an arbitrary PSI reading. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
ya I know a few rednecks.Thay all drive chevys to, Proud member of the Old Dominion Stovebolt Society AND A MARINE trucks range from 1942 1/2 ton to 1965 fire engine
