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G606818C

For a 22nd series motor, the suffix "C" was an indicator for a running change in piston and piston rings.

G606xxx appears to be a fairly early engine in 48 production so there is a chance it could have cut threads in the block. I am sure the rolled thread studs will not thread into the cut thread blocks easily because of the larger diameter and different shape and believe that is what Packard is saying in the article. I do not know how the cut thread studs go into rolled thread blocks but with the cut thread studs having smaller diameter threads as mentioned in the article that could be why there is an issue. Here is the bulletin explaining the studs.

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Here's a much larger file of the stud we removed. You can zoom in and see the threads are rolled and they stick out from the shank. This is the style of stud I'm buying. Bruce Blevins does not offer a #403255, but the studs he does offer (#341119) meet the description of the newer studs.

Here's what Bruce wrote: "THE STUD HAS ROLLED THREADS WHICH ARE CORRECT FOR A PROPER STUD. AS TO WHEN THE STUD WAS MADE I CANNOT TELL. IT APPEARS TO HAVE A ROUNDED TOP, WHICH PACKARD DID TO IDENTIFY WHICH END OF THE STUD TO PUT INTO THE BLOCK. THE ROUNDED END STICKS OUT. ON A CORRECT STUD THE PITCH DIAMETER OF THE THREAD GOING INTO THE BLOCK IS OVERSIZE BY ABOUT .005 INCHES. PITCH DIAMETER IS THE THEORETICAL DIAMETER HALFWAY BETWEEN THE TOP AND BOTTOM OF THE THREAD. THIS IS TO MAKE THE STUD GO IN TIGHT AND NOT LEAK. HEAD STUDS SHOULD GO IN TIGHT. IF YOURS DO NOT, THEN EITHER THE STUD IS WRONG OR THE THREADS IN YOUR BLOCK ARE WORN OUT AND MAY HAVE TO HAVE INSERTS INSTALLED. I DO NOT BELIEVE PACKARD EVER USED SEALANT ON THEIR STUDS.

AGAIN IT IS BEST IF YOU GIVE ME THE PART NUMBER FOR YOUR STUDS. I USE THE ORIGINAL PACKARD PART NUMBERS IN MY CATALOG, WHICH I ATTACHED. MY STUDS ARE HARDENED AND DOUBLE BLACK OXOIDED. I ALSO ROLL MY THREADS LIKE PACKARD DID AND THE BLOCK THREAD IS OVERSIZE PER THE PACKARD BLUEPRINT. MY WASHERS AND NUTS ARE STAINLESS STEEL. IF HAVE ACORN NUTS AND REGULAR HEX NUTS.

I am posting this while I check a later year, 1949-50, which might list the 403255 part.

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You're absolutely correct, Howard. The custom eight engines used 38 #403255 studs. 7/16-20 3-3/32"

I'll email Bruce to see what he advises. Thanks.

This would be trivia, unless after rebuilding an engine, it didn't leak.

So int he 20s and 30s, according to the blueprints, head stud threads were rolled, with the flat end of the stud going in first with slightly over-sized threads and the rounded end up. This made the studs fit tight in the block to prevent leaking. The shank on these studs is smaller in diameter than the threads. How do you make that without shaving the unthreaded center section of the shank?

But in 1939, the first 1940-model 356 Super 8 engines were apparently built using cut threads whose shank diameter is equal or greater than the thread diameter. There were leaks.

Then 8 years later (after a few years hiatus due to war), Packard realized that the cut threads leaked, so they return to making studs with rolled threads.

Were the cut threads to save steel because of the oncoming war? Would metal conservation have begun in 1939?

Inquiring minds want to know.

I would be curious if the threads were all formed the same way thru those versions. Threads were originally cut on a lathe or with a die which actually cuts metal away from a round rod or blank. At some point pressure forming was invented and almost all mass production bolts are made that way today..

In the pressure rolling process a blank of material is rolled thru a grooved set of plates moving in opposite directions. Because of a slight taper, as the material rolls thru extreme pressure is generated to squeeze the rolling metal blank. The threads are fully formed by the time the blank exits the plates and machine. No material from the blank is lost in that operation but is rather compressed and displaced. Controlling the size, shape of the grooves and pressure of the plates determines the shape of the threads and whether they are slightly smaller or larger than the blank. After threads are formed then the hardening and plating is done.

It could have been a matter of cost or obtaining new machines was the reason for the changes.

my daughter Molly prepped some video on our experience starting the rebuilt engine last Saturday. Because of the water leaking around the studs, John has pulled the head. We're now waiting for new studs etc.

mktx.com/packard/enginestart.mp4

mktx.com/packard/tailpipe.mp4

mktx.com/packard/settiming.mp4

mktx.com/packard/driveaway.mp4

The new rolled-thread studs #403255 7/16"-20 3-3/32 for this '48 356 engine have been ordered from Bruce Blevins. Because he focuses on pre-war Packards, he lists them in his catalog as #341119 because Packard made #341119 with rolled thread before 1940, but as Howard pointed out, they made #341119 with cut-thread after 1940 to early-'47 (and so #403255 may not work in '40 to early-'47 356 engines because Packard returned to rolled thread for 356 head studs giving them the #403255 number to distinguish them from those 1940 #341119 cut thread). Whew.

I also ordered stainless acorn nuts #141987 same as #228531 from Bruce.

The cylinder head washers for the '48 356 are G103342: ID 15/32 (.46875), OD 59/64 (.921875), 5/64 (.078125) thick.

Bruce was out, so I found #91950A048 316-stainless at McMaster-Carr. I ordered 3 packs to get 75 washers total because, even though we only need 38, they have a range of thickness .051"-.080", so we can cull out the thinner ones. Onward and upward.

The grill housing is back on. The studs arrived, but some look like the oxide on the block threads have been cleaned, so we're waiting to find out why. In the meantime, I would like to know which studs do not go into water.

I know I've seen a cylinder head torque sequence illustration, but can't find it now. We may be able to use the silver threads in the block positions that aren't exposed to water. But which ones are they?

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Can't help on which studs go into the water but if they are out you could try a wire or rod in the holes to see which are deeper than others.

Here is the sequence and the torque specs.

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