I think the engine in my truck is an 81A...

[Capt Kirk]

Nice truck!

[third_edition]

I think I am running into a "damned if you do and expensive if you don't" scenario here in that the truck needs some work to get it running and I was told by the seller that several valves were stuck (no compression on these cylinders).
I originally was going to do a full rebuild with new rotating assembly, valve train, aluminum heads, intakes and dual carbs - now... maybe not.
This block apparently won't take much of an overbore and the original crank journals won't support much of a grind (for more stroke).
Pistons are available, but they end up being fairly expensive and won't give me the cubic inch increase I need for a decent compression ratio.
That really reduces the benefit of the cam, heads and induction.
I think that my new plan will be just to check the engine out and freshen it up if it the block is not cracked and then wait until I can afford to put in a little more powerful power plant.

[JSeery]

Ok, guess I messed the part about won't take much of an overbore. What is the current bore? And what overbore is it currently at? What is the undersize on the crank? If you want a 4 inch crank, you would need to acquire a mercury or aftermarket crank. I'm just not following the concerns yet. The compression can be increased by the type of head selected or milling a head to get what you want.

I might suggest you read some books on what these engines are capable of, a good start would be JWLs and Ol Rons books. Threw in a couple of others I like.

[third_edition]

Well... as an 81A block, most of the advice I have been getting is that the cylinder walls are not as thick as the 239 motors and any re-bore should be limited to .060".
I could put a 4" crank in, but I would have trouble finding .060" over 221 pistons with the correct pin location. The existing crank could be reground, but as it already uses small journal rods, there doesn't seem to be much room for improvement there and finding floating oversize rod bearings could be difficult. Honestly, I'm coming to the conclusion that this is not the right block to invest in if my goal is to build a "midrange" performance motor. The right block would seem to be a 59 series block. In the short term, I could throw some rings and bearings in, do a valve job and spend $2000 for a motor that will probably be pretty reliable for the next few years. this truck still needs: paint, brakes (complete), transmission (clutch probably as well), electrical and all the rest of the unknowns to get it on the road.

[third_edition]

Oh and by the way, I will take JSeerys advice and buy some books

[JSeery]

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If you can find a block cheap enough that might be the least expensive route.

[Bruce Lancaster]

It is pretty common practice to bore 24 stud 221's out to 239, actually.
There were 2 81A engines, 1938 and '39 up. Yours, if further examination shows it to be an 81A, is the '39 up, shown by the picture of the crank pulley...it has the long crank. The short pulley extension behind the nut shows this.
In the parts book, the differing blocks are shown by the suffixes, 81A-####- A and 81A -####-B...the early was replaced at the very end of '38 production, the late one was necessary for '39 deluxes to take the crank pulley fan...
The 1938 24 used the short 68 crank used in '36-7-8 21 stud engines, and the '38 was the only 24 stud using that.

[third_edition]

Ok, being able to bore out to 3 3/16" opens up a lot of possibilities - plenty of piston options.

I think my next step will have to wait until it thaws out and I can pull it apart and check the condition of the block.

[Bruce Lancaster]

First, unless there were other warnings, unstick the valves and see if that's all it needs! Common storage problem due to oil running downhilll...
See if they will push down, if so just keep oiling down the guide, turning, and pushing. If they can be pushed, they will likely free up in a few cycles and all you'll need is a pair of head gaskets. If not...you've gotten your rebuild underway, or, if cylinders look pretty good, maybe just a new set of valves and guides will get you rolling. Engine has hard seats, things will oft clean up fairly easily.

[Tinker]

i concur. What do you want out of this truck?

Ive been driving a motor that just needed a burnt valve replaced ($7), now been 5 yrs. great compression. Plan at least another 5 or more.

Also have another one with a full blown rebuild.






.

[Tinker]

Originally Posted by JSeery

Ok, guess I messed the part about won't take much of an overbore. What is the current bore? And what overbore is it currently at? What is the undersize on the crank? If you want a 4 inch crank, you would need to acquire a mercury or aftermarket crank. I'm just not following the concerns yet. The compression can be increased by the type of head selected or milling a head to get what you want.

I might suggest you read some books on what these engines are capable of, a good start would be JWLs and Ol Rons books. Threw in a couple of others I like.

Only read/have 3 out of 4. Thing i like about JWLs and Ol Rons are they are objective, based on tests. The other is more a how too only, still good, great for specs.

[third_edition]

Originally Posted by Tinker

i concur. What do you want out of this truck?

Ive been driving a motor that just needed a burnt valve replaced ($7), now been 5 yrs. great compression. Plan at least another 5 or more.

Also have another one with a full blown rebuild.






.

I want to drive it (a lot) but I also want to show it off - compression, cam and loud duals for the sound factor - dual carb flathead for the show factor. I live in "rusty land" - most people have never seen the type of vehicles which were being driven more than 40 years ago.