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Old 09-11-2019, 08:59 PM
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55 gmc

Having Grandad's early '55 GMC 100 painted, and need to repair long crack in outside of engine block at bottom, a few inches above the base of the block. Anyone have any success with block sealers? We'd like to use the original 248 six,mated to a four speed factory GM Hydromatic, if possible. This seeps fast enough that it cannot be driven any distance. Our son advises, yank the six, and see if it can be welded, if not, drop in a small block??

Any help appreciated.

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Old 09-11-2019, 10:31 PM
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Welding cast iron is not very successful. The engine would need to be removed, disassembled, and cleaned. The process of welding complex iron castings is to grind out the crack, bake the block in an oven to about 300 to 500 degrees remove to weld. peen the solid weld and return to the oven. allow temp to drop about a hundred degrees remove and hammer peen again.drop another hundred degrees, hammer peen again. either return to cooling oven or cover with a heavy insulating blanket to allow slow cooling. Next day inspect for a solid block with no new cracking adjacent the weld. If non you've got a good repair, if there's new cracks it's junk. Another crack fig process is to drill an tap a hole then insert a plug, then drill and tap an overlapping hole and insert another plug repeating this process to the end of the crack. It's a slow and tedious process that is surface feature and thickness dependant.

In the end it depends on what you want a restoration, mild modification like installing a 292 in line 6, or converting to a V8. Any not original engine will get you into mount fabrication as engines since roughly 1959 are mounted quite differently.

A mild mod with a more modern inline 6 like the 250 or 292 are so similar looking to the original that only a trained eye would spot the difference. The ancient 4 speed Hydromatic uses the Buick,Cadillac, Oldsmobile, Pontiac bellhousing bolt pattern any modernish Chevrolet or GMC engine uses the Chevrolet pattern, so keeping the old hydromatic would require an adapter, and again you're into mount issues as these are different for the bellhousing and trans as well these days. The old 4 speed Hydro is not anywhere related to modern 4 speed automatics. The mount differences also apply to V8's.

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Old 09-11-2019, 11:29 PM
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Why not use a 305 v6?

"Should" fit, close to the correct era, "should" bolt up to the hydromatic, it is a really overbuilt engine with some unique features make it the last engine you will need to get that truck down the road for the next 500k.
That being said the thing is an odd ball, parts are hard to find which makes rebuilding them expensive, they are heavy, I would say around 850lbs. This is due to heavy castings like the water pump/timing cover that is I want to say 80ish lbs.
The thing is a low reving torque beast that when you lift the hood will get respect from those that know and lots of questions from those that dont.

I could not think of a better engine to run in a 55 restro mod that I wanted to run for years without issue.

Do some homework on it and ask around. You will see why I am recommending it over other engines.
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Old 09-12-2019, 09:47 AM
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Thanks for the replies. As I thought, it's unlikely that any of the "stop leak" miracle products would work. Glad to see the detail of welding cast. A local shop used to do such welding, including heating in a forge, etc. I believe that this is the last of the older, narrower frame designs, as the late 55's are the more modern look. We did find a block, online, but it's "local pickup" in Oregan,and we're in Indiana....a bit too much risk for that ride.

Yes, mounts are interesting, I believe a single mount at the front, under the radiator , and side mounts at the rear, at or near the engine-transmission joint.

Like the idea of the inline six, and will investigate the 305 (a friend had one, many years ago, and liked it).

Again, thanks for the replies.
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Old 09-19-2019, 04:46 PM
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Locate a diesel engine "servicing" facility; diesel engines don't come cheap, and block repairs for cracks and such are common place. At least they will be able to tell you if it's possible to repair your block. Otherwise, step up to a 302 GMC six cylinder.
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Old 09-19-2019, 11:01 PM
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.......hadn't thought of that. That's a great idea. We'll look into it when we pull the motor.

Thanks for the advice!
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Old 09-20-2019, 03:40 PM
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Check into "Lock-n-Stitch" pinning for crack repair. works very well for what you describe. I've seen a lot of old tractor blocks repaired this way.

Check for a local machine shop or diesel shop if you don't want to try it yourself.

Metal Stitching & Thread Repair Inserts. - Turlock , CA - LOCK-N-STITCH, Inc
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Old 09-21-2019, 12:23 AM
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This is the first I've heard of this, and it looks like the solution to my problem. I'll look into this, as it appears that the repair can be made with the engine in the truck, as the entire crack is accessible. Apparently, this has been around for quite a while; thanks for the advice.
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