The Stovebolt Site Forums The Shop Area General Truck Talk 2nd ride in the '51 GMC and Larry Isgro

Hi All,

I'm the guy who went down the driveway backwards in a '51 GMC with no brakes and survived - check the link below my signature if you've not read the story. I took the second trip in the truck Tuesday and had to report. It was a nice day here in Atlanta – temp got up to about 57 in the afternoon – bright blue sky. Second time she’s been on the road in quite a while (bad luck if a cop sees this).

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First off, I’ve got to complement Larry Isgro on some beautiful work rebuilding my carb. It’s so pretty I kind of hate to put it on the old truck. It looks a little bit of out of place.

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Anyway, the first time I drove the truck was December 15. Since then the gas tank’s been pulled and boiled out and the carb’s been rebuilt. I also replaced the old fuel filter.

I pushed her out of the garage into the driveway and pulled the block drain and the radiator drain – I’d left it in the garage full of water after flushing it out the first time. Thanks for Ashton51’s suggestion to pull that block drain and snake it out with a wire. I did it on Dec 15 and it really cleaned the crud out. Just like happened to you Ashton51, I again got crud out of the block this time – not stopped up, but lots of suspended stuff. I flushed with clean water and worked it with a stiff wire again until I had clear streams from block and radiator. Then I put in two more jugs of Prestone Fast Flush and filled it up.

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Interesting thing here. I loosened the sender on the head for the temp gauge to vent the system while I filled it up. I ran the hose a bit then stopped. I could hear air whistling up past that loose fitting. I kept adding water until I got a bit seeping out there, then tightened it back up. That’s a good tip for venting your head when refilling the cooling system on a GMC engine. Wish I could remember who talked about it on oldgmctrucks.com – sorry – but it probably saved me from engine overheating and possible damage. That and the info about the 1/8” hole drilled in the flange of the thermostat are the bits of info you just don’t get out of a shop manual.

It was time to go. I put a small splash of gas down the carb throat and stuck the air cleaner on. Full choke, step on the starter. She spun over 3 or 4 times and sputtered – I patted the gas pedal and she caught. Still no exhaust system, so pretty loud out of the shorty stack off the exhaust manifold (exhaust is soon on the list). Larry’s carb was just as advertised, put it on and fire it up. Nice work, Larry.

Notwithstanding the freshly rebuilt carb, I’ve still got some missing at idle. The truck seems to be getting good spark but runs unevenly. The next two things for me to get to are checking the timing and adjusting the valves. I also still wonder if the short exhaust stack may cause a problem by having no back pressure. I let her warm up until my cheapo replacement temp gauge showed 120 or so, and down the driveway of danger we went. Brakes are working great (fortunately) – really solid.

Again, the truck ran solidly when I put it under a load. Pulling hills in 2nd gear it didn’t miss a beat – no skipping or missing. Loud, but running good. If I got up to 25 or 30 and “floated,” neither accerating nor decelerating, but maintaining speed, the engine sputtered and stumbled. It’s not nearly bad enough to make you think it’s going to die, but it’s not right. Still, it was a beautiful day and I was out driving that puppy.

I was making a hell of a racket and having a fine time. The tires are so flat-spotted it feels like riding in a buckboard (that’s what happens after about 30 years of sitting). I got 2 miles up the road to the stop sign to go home and decided to go to the gas station instead. I’d got my brake light working while the gas tank was out, so I was feeling all legal (yeah, right).

Made it to the station with no problems other than a lot of bemused looks.

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I put 5 gallons of gas in the fresh tank and checked everything. Nothing was leaking, oil looked clear and clean. Turn the key, step on the starter, fired up and off we go. I didn’t have any problems going home and managed to back up the driveway this time, although I still spun tires a bit – good news is that the clutch is strong.

I let it cool completely, then drained the cooling system again. This time I didn’t get any more rusty crap out, so I put in some rust preventative and 2 gallons of antifreeze/coolant.

Next up I could do timing & valve adjustment, but I think I’m going to get her up to temp and dump the oil hot, then drop the pan. I want to get a look at the oil pump pickup screen and at the bottom of the oil pan. Since I’ve never done that before, you can be sure I’ll be looking for pointers from all of you.

More as it develops,

David Bush

Most of your running issues are caused directly by your open pipe: no back pressure. Leave the timing and valves alone until you fix what you know is wrong, is my suggestion.

Do you think running the engine without an exhaust system could damage it in any way? I'll need to drive it a few miles to the muffler shop that's going to fab the exhaust for me. I don't think it's a problem, but then again I've never run an engine with nothing but an 8" stack below the manifold before. Opinions?

David Bush

If it has to be open, the longer the pipe, the better. If you have only a few miles to go and they're on flat country, I'd say do it, but with a light throttle. The biggest risk is to hot exhaust valves and seats which might burn if cold air travels back up the pipe to the valves - which it could, if the pipe was short enough. I might clamp a 24" extension on to what you have, to be safe.

Run with the choke partway closed to keep everything cooler. Don't run it that way any longer than you absolutely have to.

No offense, hotshoe36, but I'd love to get some more opinions on this. Frankly, I hate to spend the money to get a pipe extension so that I can drive it to the muffler shop after which I won't need the pipe extension anymore. That said, I don't want to screw up my engine either. The budget's running kind of low at this point, though.

Thanks,

David Bush

I've always heard if your exhausts are too short cold air can suck back in and damage (warp) the valves.

We run short through the hood headers on our mud bogger and our demolition derby cars and we have warped valves in the past.What we had to do is carry caps to cover the exhaust when we shut them off.So id say no to driving it just to be safe.

I put a temporary system on mine with a junkyard muffler, some flex pipe and a couple of hangers. It sounded just like a factory exhaust and allowed me to listen carefully to the engine.
I would think that the open exhaust would be hard on the ears.

I kind of like it, actually (but then again, I was one of those kids with the playing cards in the spokes). It's good to hear it run after all those years of sitting. Today I went to the auto parts store and bought some exhaust pipe. This will still result in a straight pipe with no muffler, but the pipe length is now about 4 feet. Got everything hooked up, but can't check it out until tomorrow if it's not raining. I'm kind of curious as to what she'll sound like.

David B