21 stud Flathead pistons

[CA Victoria]

I’ve seen some pretty odd things inside of a Model A engine but I haven’t been inside of very many Flathead V8s. ....I pulled the heads and a visual inspection of my Flathead shows 3 different pistons. 4 with no marking, 3 with directional arrows, one with std marking.
The purpose of placing a piston correctly is due to the thrust forces, I get that. So, with some pistons not marked did it matter which way they were installed?
So why do you suppose some are marked and some not?

[deuce_roadster]

Were not all from the same set. Probably "rebuilt" during the war when new parts were not available or in short supply.

[CA Victoria]

I don’t know anything about the motor except it is a std bore.
Probably not that old of a rebuild. May have used “shelf stock”
If the engine were a factory replacement short block would it have the L-B stamped on the top rail or was this only done during original production?

[rotorwrench]

Some of the early V8s had steel pistons. Ford used them for a while.

[VeryTangled]

I believe you, Tim, but a standard bore with mismatched pistons sounds to me like there's more to the story to be discovered.

Please keep us updated on this thread?

[deuce_roadster]

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Tim, the LB engines were made in the later part of 36 only, as the LB was an early style block but it had insert bearings on the mains instead of poured babbit like the 32-36 blocks with the water pumps in the heads. The LB stood for "large bearing" as the crank main journals had increased.
If your 21 stud engine has the water pumps in the block it would be a 37 or early to mid 38 block as the later 38s went to 24 studs.
Pictures of the front of the block would be good.
Not all the insert bearing 36 blocks actually got stamped LB. The main studs are 3 1/4" apart on the LBs , the babbit engines are 3"

[CA Victoria]

Sorry,
I may have let y’all astray. this is a 35/6 221 cu in engine w/pumps in the head.
Don’t know if Babbitt or insert bearings.....
My main concern is with piston placement.
I cleaned the piston tops to find all were stamped with the same “FRONT” and arrow as typically found.
But....left bank arrows points to front and right bank toward the back.
So the pistons have run for some time up side down.
If I run it and a piston fails I could ruin a good block. Rotating the pistons to their correct position doesn’t make sense either due to wear.
Initial measurements are 3.067

[flatheadmurre]

The early engines didn´t have the pistonpin offset so no marking for direction on the pistons.
If they are aftermarket pistons who knows if they are offset...some only had a cut expansion slot and that should be facing away from the thrust side of cylinder from description by manufacturer.
Some aftermarket manufacturers used the same mold with direction arrow then just machined the piston as needed sending a note about installation with the set.
So may just be correct as is...we can only guess or you have to get a piston out and measure.
It will not fail in a catastrophic way due to a piston turned around...it will wear faster and maybe make more noise as skirt get worn...but not go through a cylinder wall suddenly.

[Mart]

If the engine is coming apart I'd turn them round. I had two that were like that on my 21 stud motor. I had it apart for another reason and just turned them around. It sounds daft but I'd try and keep the rings the same as they were.

The rods also should be replaced in the same orientation as before.

Mart.

[JM 35 Sedan]

Some questions I have for you Tim, after reading all the previous posts here:

1.) After cleaning all the piston tops, you say they all have the arrows, but are they also all marked "STD" or just some as you had originally mentioned, prior to cleaning.

2.) How and where did you take the cylinder inner diameter measurement of 3.067", and was this just a measurement from one of the 8 cylinders? Standard bore would have been 3-1/16" or 3.062".

3.) Consider carefully cleaning & checking deck at the top of each cylinders bore to determine if this block has possibly been sleeved to return it to a standard bore, maybe during a past rebuild.

4.) Does the front of the block have block off plates mounted on each side of block with two bolts? As you mentioned earlier...you have a 35-36 block with water pumps mounted in heads, BUT '37/early '38 blocks will also accept the early 21 stud heads with water pumps, and then block off plates mounted in front of block would be required to cover the holes for the '37-'48 block mounting type water pumps. As someone else had mentioned, a picture of front of block would have revealed this early on in your post.

[CA Victoria]

John,
I tried pictures, no bueno......
Cleaning revealed 8x pistons the same
Measured 4 cylinders in 2x locations and at 90 degrees with a starrett inside mic. Within .0005 & round.
Nope, not sleeved, cleaned and used a magnifying glass cuz I’m old!
No block off plates.
Cylinders are glazed with some light vert. scratches.
It looks like Ford supplied in between over size pistons in .005 increments. If all cylinders are true, and these do exist, Maybe i can hone to spec and be back home again....

Great input, thanks. I am learning a lot here.

[JSeery]

If your having photo posting issues most likely the files are too large. I can post them for you if you email them to me. [email protected]

[CA Victoria]

Thank you for the offer, it was more lighting quality to be able to see the details