I'm back! My dad just bought a 1955 GMC 100, so I have another iron in the fire right now. It's closer to drivability that anything else we've ever bought, so the wrenching-to-satisfaction ratio should be pretty good! When I first got my hands on it, the first thing I did was turn the engine over (it's a 248 Jimmie six). The starter still worked great, so we tried a compression test. To my dismay, it tested 0 psi on every cylinder I checked. I started wiggling the rocker arms and pulled out several bent pushrods. I tapped the valves with a soft mallet and discovered that two of them were stuck. The valve train was a total train wreck! I immediately wrote off the compression problem as being valve related. The next thing I did was start tearing the engine down so I could inspect the bumpstick and send off the head for a much needed valve job. The timing gears looked like new...so that wasn't the problem. The cam also looked great! All of the lifters were more worn than I'm comfortable with, so we'll be getting a new set of those. When I pulled the head, I got a pleasant surprise. The cylinders were mint! There was no pitting, scratching, chipping, and almost no ring ridge! We were really excited, because this meant that the 40,000 miles on the odometer were probably legit! This brings me to my question.....should I be worried about stuck rings? I've never seen any real evidence of ring problems, but I've been worrying about them lately. I am very confident that the engine has never been stuck. It turned over like butter when we got it, and the bores show no sing of any such problem. Is it possible for all of the rings to be stuck when the engine itself never has? I'll probably soak everything in Marvel as a precaution. Is there anything else I should do? Once again, I really don't have a real reason to suspect rings. All signs point to a valve train problem. I'm just paranoid . Thanks! -Falcon_H
I would pull at least one piston, and see if the rings are stuck. If they are, and you don't do anything about it now, then you'll have to buy another head gasket to fix it again. Or just plan on buying rings anyways. If you shop around, you might find a bargain...last two sets I bought were for other similar age engines, I got them for $20 each instead of the $50-100 list price, by knowing the numbers, and shopping on ebay I have a 58 270 that didn't have much compression, I pulled the head off and didn't really see anything wrong with the valve train, so I'm guessing the rings are not doing their job. Although mine looks quite wore out, in general.
The bottom end is too valuable to risk not inspecting while the head is off. If the bore is that nice, most likely it's been freshened at least once. You'll want to check the bearings for acid etch, pull the relief valve from the oil pump to make sure the spring hasn't broken, & clean the screen. I'd ring it, period, since the head will be fresh. Is the truck 6 volt ? I'm still searching for anyone who has a 6 cylinder '55 GMC 12 volt truck that came new that way.
A few weeks ago I decided to try pouring oil in the cylinders as a leak down test. The oil took a looooong time to seep through, so I'm guessing the rings are fine. The head came back form the machine shop with new guides and valve seats just in time for winter break, so I was able to get a good amount of the engine back together yesterday. Hopefully we'll be driving down farm roads in a few days!
Do not attempt to start that engine until you pull the oil pan and make certain that its not full of sludge. and don't start it with the dirty gas tank. suspend a small tank and gravety feed the carb. When I first start one that been setting I use gas that has 1/2 pint outboard engine oil added to each gallon. Picture of sludge in a tractor oil pan. Yours could easily be in similar condition.
My 55 GMC has not been started in a couple of years. Today My 4 year old grandson Chris and I went and changed all the flat tires. We had to file the points on the 287 V8. But it cranked right up after we got it making spark. I drove it around to the shop a distance of 300 feet. The floors and step wells are gone. Ive got a real solid 59 chevy cab on a dump truck. Easiest would be a complete cab swap. But I like the GMC dash. I might just group it all together and put a add on craigslist and facebook.
Ditto on pulling the pan and servicing the oil pump. And, it's been part of my learning curve in the 50+ years of dealing with this stuff, that if you have the valves/head serviced so that, that portion of the equation is spot on, the "new" level of compression is gonna leak past the rings/cylinder wall, and you are now going to be chasing your tail again......low power, blue smoke, fouled plugs, oil consumption. Great project....learned to drive (10 years old) in a hayfield with blocks taped to the pedals, and I couldn't hurt anything......in a '52 GMC. Your '55 is a GEM....wanna sell it?
Yes im going to sell it. ive got way too many projects. And I fully realize that im in the winter of my life. If I can send this one down the road I can use the money on something else. There is supposed to be a guy coning to look at it this week. That's why I went and got it running. The engine is really good. I retro fitted a PCV on it years ago when I first got it running. Its very rusty in the cab bottom. needs brakes interior wiring ect. I want $1500 for it and the solid 59 cab. If the potential buyer don't happen. I will post some pictures.
Here is todays picture. I don't know the reason why the bumper and one dagmar is chrome and the rest not?
The Jalopy Journal
