tm9-801.com

Does anyone have any of the correct 1/4" x 20 hex head with phillips head or straight screwdrivn/er slot? I need some to complete my engine rebuild.

Still looking for some of these screws. Here are some pics to help identify. Prefer the phillips version. Any help would be greatly appreciated.



Does anyone have information as to what year GMC switched from the straight to phillips screws? I know GM was one of the first to use phillips screws in 1937 on the Cadillac cars. Also I know that engine serial number 270442893 used straight screws while 27072594I used phillips. TM10-1563 shows the straight screw slots while the switch to TM9-801 changes to phillips screws.

Your cover bolts are both 'late'. The 'early' type was called a 'stovebolt'. Basically a round head screw with a phillips drive.



Another shot:



These were used till approx 43 when they where changed to what you have, and more common. There were a few reasons why they changed, and I believe I read this in a copy of Army Motors.. but I can't find the issue.

Phillips drive was a torque limiting feature. You can only turn so hard until the driver slips out of the screw/nut. But mechanics were stripping them out trying to fix leaks with torque rather than with new gaskets (changing a lifter cover gasket is a chore).

It looks like the 41's and early/mid 42's had the 'stove bolts'.

TM10-1500 lists PN 147835 BOLT - cover to cylinder block (1/4"-20 x 1/2") and thats a 'round head' bolt per the TM

So they switched to the hex bolts.

TM10-1562 Parts Manual lists it as a hex head bolt, but different part number:



The 1945 SNL-G-508 page 78:



There is a 42 Parts book that could be referenced... I don't have that one.

Sheesh! I didn't realize they were so easy to find...

I'm not sure what the question is..

OIl pan bolts? 'Tappet' (aka push rod side) cover? Valve cover?

Look up your local fastner company. My local fastner shop has a $5 minimum and can special order.

Not sure where you have found these but I have not been able to locate them locally or on the web. Yes, it is easy to fine a similar fastener but not the correct one. It you have a source please list.

I may have been incorrect in stating that these were used on the tappet/lifter cover. Could have been only the straight slot (early) and phillips (late) pan head machine screw (stovebolt). The hex head, both early straight and later phillips slots, were definately used on the oil pan.

More info and more questions. After going over my manuals again and looking at several late 40's civilian GMC engines I have the following to add. All pictures in manuals prior to the April 44 edition of TM9-801 show either the phillips or straight pan head screw. I do have a copy of TM10-1268 from 2/2-1942 and it calls out that the tappet cover and oil pan use P/N 147835 which is a pan head phillips screw 1/4-20 x 1/2". The front timing gear cover also uses the same screw but in 3/8", P/N 155327, and 5/8", P/N 147837, length. They also call out a separate lock washer, P/N 103319, for each screw. The oil pan also uses a flat washer in addition to the lock washer, P/N 103339. However, on page 190 of the April 44 edition of TM9-801 manual they show the hex head screw with the phillips slot.



Notice that the screw in this picture attaching the tappet/lifter cover has the hex head with a flat face and the phillips slot. This is the same screw head as was used to attach the lower oil pan sump to the oil pan of my engines. From this picture we know this type screw was in use early 44 and maybe in late 43 which corresponds with the information you have.

For those with the two piece oil pan there are two noticeable differences in the tappet cover/upper oil pan half and the lower oil pan sump screws. The lower sump screws are 1/4-28 (fine thread) vs the 1/4-20 (coarse thread) and they are 5/8" long vs 1/2" long. See picture of lower sump screw.



Finally I mentioned referencing the post war civilian engines. They use a screw that looks like the one referenced in your TM10-1562 Parts Manual (what year is this manual from?) and the 1945 SNL-G-508. Do either of these manuals have any pics? I do not have these so can not reference. See pic of post war GMC engine screw.



Note that the civilian screw has the integral internal tooth washer as is described in TM10-1562 and SNL-G-508, while the flat faced screw from above does not. The question now is does anyone have any pictorial evidence of the recessed face hex head with phillips slot screw being used? Does anyone have any examples of the flat faced hex head phillips screws in 1/4-20 x 1/2"?

"All pictures in manuals prior to the April 44 edition of TM9-801 show either the phillips or straight pan head screw."

Yes, but the Parts books state otherwise, as I posted.

TM10-1562 (May, 1943) was the last TM10 parts book, and the tappet cover lists "Bolt and lockwasher 1/4-20x1/2 HEX HEAD int tooth" PN 191044

The last wartime SNL also lists the tapper cover bolts: "Bolt hex head, S. cd-pltd 1/4-20x1/2 with int teeth lock WASHER" PN 191826

Regardless of the TM photos, the part numbers and descriptions are for hex head bolts starting in early/mid 1943 (maybe even late 42).

The line drawings in the SNL-G-508 (45) and TM10-1562 show the stove bolts, not hex bolts.

Stove bolts for the tappet cover through AT LEAST mid to late 42. Retro-Roco has a mid 42 CCKW parts book that would tell if they still list the tappet covers as screws of bolts. It's documented that the TM-10-1562 states BOLTS, as does the later SNL.

Remember that the photo's were reused FREQUENTLY from TM to TM so showing stove bolts in a 44 TM means little.

If you are asking what is the correct drive is (straight, Phillips, recessed) for the bolts/recessed head bolts that would be a little harder. If you have a civvy book that lists the GM part number and has a drawing that would most likely be your answer. But no, the TM10-1562 does not show the PNs for the bolts, nor does the SNL, it just lists the PN.

Since the Part number for the later bolt does show a Stock Number of H101-0191826 it may be able to look it up in another 'standardized' parts reference book.

Maybe poll CCKW owners to get a consensus?