Boring a 59L Flathead with 3-1/16" Bore: Data and Pictures

Flathead owners,

I am looking for personal accounts of anyone who has successfully or unsuccessfully bored a 59L series block with a 3-1/16" (3.0625") bore. I have a 221 cubic inch post-War replacement block designed for pre-War cars. I want to bore it to 3-5/16" (3.3125")!

I have thoroughly searched and read Google, Ford Barn and Jalopy Journal for three days and have found two instances of "Yes, I have personally bored a 3-1/16" 59L to 3-5/16" without a problem" and two instances of "I have one of these and you can't do it." [but no account of whether it was even attempted].

Background: My engine came from a generator. It has a "59" cast in the bell with an "L" directly below it (see picture). It has a 3-1/16" bore, no sleeves, 59A-B heads, 24 studs, water jackets are triangle/round/round. It has a flat intake deck and fails the pencil test on the front. I knew this was an odd engine because right away I saw it was equipped with a 37-41 distributor, fan on the generator, and a single belt crank pulley. During the sale, I pulled the heads for inspection, I was suprised to measure a 3-1/16" bore but I figured "Great! Even more room to bore!" I did not see the "L" when I bought it because it was under grease and grime. It has compression and runs and cost me $350 (came with a super heavy radiator I could s****).

The Facts: I have included data compiled from 48 measurements taken from this block with an Oditest dial pinch guage (see pictures). There are 12 water jackets per side where I was able to reach into and pinch the cylinder wall. I noticed there was a slightly thicker band of material ~1" wide where each cylinder meets the head mounting surface.

-24 measurements were taken at 0.5" down from the water jacket opening (on the thicker band mentioned above)
-8 measurements were taken at 1.0" down from the water jacket opening (exhaust p***ages were in the way).
-16 measurements were taken at 2.5" down from the water jacket opening (as far as the caliper would reach).

The Results: I plugged the raw data into Excel.
Driver side average wall @ 0.5"= 0.339"
Driver side min wall @ 0.5"= 0.323"
Driver side max wall @ 0.5"= 0.365"

P***enger side average wall @ 0.5"= 0.338"
P***enger side min wall @ 0.5"= 0.312"
P***enger side max wall @ 0.5"= 0.360"

Driver side average wall @ 2.5"= 0.287"
Driver side min wall @ 2.5"= 0.260"
Driver side max wall @ 2.5"= 0.300"

P***enger side average wall @ 2.5"= 0.280"
P***enger side min wall @ 2.5"= .265"
P***enger side max wall @ 2.5"= .310"

The Unknown: It seems to me by going to to 3-5/16" and taking 0.125" off a wall would give me an average wall thickness of ~0.214" at 0.5" down and an average of ~0.162" at 2.5" down. The casting draft seems negligible when I pinch up and down within an inch in length.

Am I missing something/not seeing a part of this?

I can't imagine Ford having two patterns (thick wall or thin wall bore) with the same 59L designation. It seems like it would cause confusion and mixups in inventory.


I hope this will be good data for others one day. Lets hear the facts!Thanks, Joey Hoffert

 

I can't say I've bored a "letter" flathead to the max. I can say I've heard it said a million times: get it sonic tested if you're going to the extreme. Your manual method gives you a lot of good info, but I'd think the sonic testing should find those small thin spots you couldn't reach.

I don't agree that all L blocks would have the same inner cores. There seems to be dozens of core combinations out there, so don't ***ume any "letter" block is the same as the next.

 

I agree it will need to be sonic tested since there are so many spots I can't see or reach. I put the wall thickness numbers out there so others might comment whether their block is alot thinner or thicker. Thanks.

 

I have no actual do***entation or experience with those critters, but I believe that the 59 3 1/16 blocks must surely be the blocks listed under 41A part numbers in the postwar catalogs. These were late valve angle blocks manufactured specifically as replacement blocks for the huge pastwar parts market, designed to rplace all the worn-out '39-42's out there. The 59 (9 there actually designates 3 3/16 engines) came along for the ride when they used the postwar casting stuff, indicated by the valve separation angle.
I know that the cylinders are very thick up high, and I've been told that thinnest area is down at the water jacket floor. Since the sonic test is very localized obviously you need a
bunch of samples!
I don't think the letter designation is directly connected with bore at all, and I've never seen any do***ented or even believable explanations of X-Y-L 59's...

 

Don't bore it any bigger than you have to. The walls get thinner, the heat factor increases.

 

For what it's worth, I had an "L" block sonic tested and then bored it to 3 7/16.
No over heating in a circle track car.

 

Does it need a bore job? Why bore it more than it needs? Gaining a couple h.p. at the expense of longevity is a bad idea.

 

My Pops has an NOS block with a 59 on the back, and a 3-1/16" bore. Go figure.

I have a 59 Z block that's bored to 3-3/8" right now, and it needs another bore. I've got a 59 X that is at least 3-3/16. Probably came that way.

 

I think the thinner the wall the faster the heat gets to the water. I have bored many engine .155 over size. Never had one run hot. I think it is a old wives tale, that came from plugged radiators and worn out engines. Once they were bored out they ran hot because they made more heat than the plugged radiator could handle.

 

You might check with Walt Dupont..Me. over on the Barn.....he's done a lot of engines.

 

Yes,
i agree.

 

If do***entation ever surfaces it will be a treasure and finally lay to rest the tons of posts about letter blocks!

 

Yes! Yours was one of the two 1st hand accounts I found. You responded that not being able to big bore a 3-1/16 59 block was a crock and that you did indeed do it.

 

I have thought about this over and over. It takes so long (in the rustbelt) to find a good flathead...Do I really want to limit myself to only being able to get one boring job out of it?
On the other hand, I really want to experience what the Lakes racers experienced in the late 40's with a bored out and hopped up flatty!

 

I'll probably post there too in order to open up the sampling size. Thanks guys, any other experiences out there?

 

Go for it!
While you build the engine, look for a "spare" good block.....

But have sonic testing done by the machine shop.

 

I can't imagine, given all the other variables, that using an extreme bore is going to make any appreciable performance difference over the use of a 'safe' bore. Unless, that is, you are intending to actually enter compe***ion events and need the most it has to give.......but I didn't get that from your earlier comments.

On the other hand, going to the max dimension risks ruining the block or promoting an early failure.

I am very impressed with your thorough research in an attempt to avoid the potential unpleasant outcome and wish you the very best with this, no matter your final decision.

Ray

 

Thanks guys, I would like to go to a big bore because that's what I read about in The Rodders Journal and from builders like GoCat Speedshop. I also want to go all out on my AV8 build because I don't know if I have the patience to build another period correct hop up!....as I have been holding out and getting only the best non-pitted parts for many years.
I am trying to see if I need to continue looking for a "thicker" block since this is the last piece I need for my build. So far the comments are good.-Joey

 

The supposed thickest is the '39-40 99 block, but as with everything else we read that is folklore. I do know that those were used in lots of dragsters and bonneville cars, so the ancients believed...
JWL posted that all the 3 3/16 blocks were about the same thickness a couple of years ago...that was from sampling via bandsaw.
I once made some VERY crude measurements on one spot of one cylinder on a tin-can type 99. At that single place, which was accessible to my primitive caliper because of the big t****zoidal water hole, the damn thing was thick enough to have stout walls at 3 1/2! I SERIOUSLY doubt that all the rest of the turf was that thick, but I was genuinely shocked by the thickness right there.
Think of the envy from the 302 and 427 types whose blocks are often s**** after one overhaul...

 

On a flathead you have very often "coreshift(if that is the correct word)"
means the wall thicknes is not even all the way around the hole.

I run a 3 3/8 bore and it runs cool .
Had the block sonic tested.
And moved the holes a little to have eeven measurements all the way around.

****, we build Hot Rods and don`t ****ing restore cars !

So go for it with a good machine shop

 

"****, we build Hot Rods and don`t ****ing restore cars !"

Hee hee, I love it!

 

Yes, I noticed my block has slight core shift in a few places. The cool thing about it was that it almost seemed predictable. I started seeing nearly the same readings over and over (+/- .005-.010"). Then I would get another reading somewhere and it would jump to appx. minus .020" off the average. When I measured directly across the cylinder from that low reading, the other side of that cylinder would be appx. plus .020". Therefore, it would be ~.020" core shift.....not much. Pretty awesome for green sand.

FYI: This block will get an original Thickstun PM-7 high rise fully polished, Evans heads highlight polished, Mercury crank ( a gem that right now is standard/standard), cloth wiring, and a Potvin 3/8. in front of a 39' 3spd with swan neck shifter....but that's for another post. Thanks, Joey

 

After all these old blocks are worn out, they will all have sleeves anyway. It's your motor and your plan. This is a free country.

Someone will eventually either start casting new blocks of find a way to machine out the old ones and install a whole new top deck & cylinder ***embly. Whichever is cheeper to do will win in the end. So far it's still cheeper to build an OEM block as long as they and the French Simca blocks last anyway.

 

HotRodMicky, When you " moved the holes a little to have even measurements all the way around" does that effect the alignment of the piston and connecting rod to the crankshaft?

 

If you look on the pistion in the block . i mean up or down movement , not left or right.
on the core shift i always found the inner wall towards the cam gets thiner
i never found shift from left to right.

And we are talking not much there , maybe around 1/64
And yes your pistion is not centered in the head anymore, but that is not much , by claying
it.

Since Arias is making now an 0.06 oversize pistion for any stroke
i think its a good choice for blocks with a lot of coreshift.

Think 4 1/4 stroke with stock rods and 0.06 forged pistion....
Throw a 1007B or a 3/8 in there and have fun !!!

 

From my experience the differnece from 255ci to 276 ci huge, by the way the engine
feels and make power...

I think a 276 is the best engine (with a 3/8 cam and 2x97) for a (28-32) light roadster.

Well 304ci i way too much unless you upgrade your suspension and transmission..

Ask me how i know that....

 

Without sonic testing the whole thing is a guessing game. Coreshift is not your main problem, pitting on the outside of the cylinder walls (the coolant side) is the worry. Most all flatheads spent most of their life with straight water as the coolant, quietly rusting away the cylinder walls.

 

I think that is a myth....
ALL the blocks we sonic tested are thicker (if there where not even)on the outside
and that only happens from coreshift/casting

I have seen one block that has been rusted through the side of the block.....
But that was burried halfway in the mud for at least 40 years....

And with a sonic tester you can`t measure the pitting.....

 

Folks back in the day were well aware that a flathead with no anti-freeze was asking for trouble. With any freezing temps at all the block would be cracked and the vehicle went to the salvage yard. Most of the rusting happened after the car or truck ended up in the back 40 with the radiator yanked and some old dirty rags stuffed into the carb. A lot of them were junked after the valves were stuck from inactivity.

In the cold climate area that I'm originally from, if you found a flathead out of a vehicle in a salvage yard, it was always cracked or you'd find a hole in the pan for exiting con rod. If it was still in a vehicle with the radiator intact, it usually still had anti freeze in it but would have stuck valves. If the heads were off of it, it was not only rusty but was generally pulled appart because the rings were shot, it was overheated with cracked valve pockets, had a bad bottom end, or some combination of the three. The good motors are out there but they wont be around forever.

 

Interesting. If that's the case, I guess my ~.020 thickness shift is a result of the machining.