1941 truck block A99

[3W Hank]

I’ll just bought at LARS a big bore D block as it fit perfect for my ideas.
Guy had it for 40 years and it came out from a outsell in LA.
Story goes not go back who useded it, but its a very nice porting/relive work.
I was at my 3 block ( all cracked in some way ) and has new ROSS 1/8” bore over std 1947 59A so bore is 3 5/16”.
This block now has the same bore but it do need a hone plus one sleeve, so I need a custom set of piston and both Roos and CP can do that.
It was sonic checked ( document was included ) and pressuare tested and wall is average 1/4”.
Its cool as it is a 1941 block, and it can be both Merc or truck but number is grinded off at rear (?)
Intake is rised ( they was cast that way only 1941 )
If it's thicker than others, well I don't know - but storys say that.
It was a hot rodders choice I guess in that era as it was bigger bore from factory than the Ford std blocks.
So block itself and the work got my attention ( even if it means freight to Sweden and machine works and a set of custom pistons )
But with this old blocks one never know…
Look at portings. I love it.

 

[Kurt in NJ]

From what can be read of the story #3 has pinhole leaks, either a casting flaw or deep rust pitting. You mentioned a average wall thickness of 1.4 inches, something is wrong with that figure. Having a pinhole means that at least in one area the wall thickness is 0, it not the average thickness it’s the thinnest area that you have to worry about.
In the picture it looks like a ridge is visible and looks like the bore below it was rusty, probably needs more than just honed.
Look at the rust conditions of the water jacket— deep pitting could mean more pinholes are exposed when the bores are enlarged even slightly, a sonic check won’t show the localized small pits.
In my pictures is a comparison of 2 blocks I have the one has some deep rust pitting in the water jacket, I would worry about finding a pinhole, it also already has a sleeve , the other block is already at 3-3/8 with one of the cleanest water jackets I have seen, no cracks, not even the ones considered factory.
Don’t be blinded by the “pretty” porting, look closer before spending the money on shipping.

 

[petehoovie]

I’ll just bought at LARS a big bore D block as it fit perfect for my ideas.
Guy had it for 40 years and it came out from a outsell in LA.
Story goes not go back who useded it, but its a very nice porting/relive work.
I was at my 3 block ( all cracked in some way ) and has new ROSS 1/8” bore over std 1947 59A so bore is 3 5/16”.
This block now has the same bore but it do need a hone plus one sleeve, so I need a custom set of piston and both Roos and CP can do that.
It was sonic checked ( document was included ) and pressuare tested and wall is average 1.4”.
Its cool as it is a 1941 block, and it can be both Merc or truck but number is grinded off at rear (?)
Intake is rised ( they was cast that way only 1941 )
If it's thicker than others, well I don't know - but storys say that.
It was a hot rodders choice I guess in that era as it was bigger bore from factory than the Ford std blocks.
So block itself and the work got my attention ( even if it means freight to Sweden and machine works and a set of custom pistons )
But with this old blocks one never know…
Look at portings. I love it.

 

[petehoovie]

From what can be read of the story #3 has pinhole leaks, either a casting flaw or deep rust pitting. You mentioned a average wall thickness of 1.4 inches, something is wrong with that figure. Having a pinhole means that at least in one area the wall thickness is 0, it not the average thickness it’s the thinnest area that you have to worry about.
In the picture it looks like a ridge is visible and looks like the bore below it was rusty, probably needs more than just honed.
Look at the rust conditions of the water jacket— deep pitting could mean more pinholes are exposed when the bores are enlarged even slightly, a sonic check won’t show the localized small pits.
In my pictures is a comparison of 2 blocks I have the one has some deep rust pitting in the water jacket, I would worry about finding a pinhole, it also already has a sleeve , the other block is already at 3-3/8 with one of the cleanest water jackets I have seen, no cracks, not even the ones considered factory.
Don’t be blinded by the “pretty” porting, look closer before spending the money on shipping.

 

[3W Hank]

Yes after 3 blocks cracked I'm warned that this old block's on a pallet means issues and red light.
I know this might be a issue but I take the chance since its allready payed and are at a shipper in LA and freight is payed.
So even a sonic test will not show the issue, the document is what it is so say thickness is 1/4" thick.
Pressuare check say 1 pinnhole ( guess rust so there was a leak )
I bought a sleeve, or maybe I should sleeve all cylinders, then I can use my Ross pistons. Yes allot of work but material is 250 USD. Pistons will be way more.

 

[petehoovie]

Yes after 3 blocks cracked I'm warned that this old block's on a pallet means issues and red light.
I know this might be a issue but I take the chance since its allready payed and are at a shipper in LA and freight is payed.
So even a sonic test will not show the issue, the document is what it is so say thickness is 1/4" thick.
Pressuare check say 1 pinnhole ( guess rust so there was a leak )
I bought a sleeve, or maybe I should sleeve all cylinders, then I can use my Ross pistons. Yes allot of work but material is 250 USD. Pistons will be way more.

 

[KiWinUS]

Mate I have sonic checked a bunch of flathead blocks to include a 99a of my own. If your block is already 3.312 and the sonic sheet is correct that is the thickest walls I have ever seen by a long shot. You may want to sonic check again to be sure the sheet you have belongs to that block.

 

[Bored&Stroked]

I would think the cylinder walls would be closer to .150 from all the ones I've tested. If this thing is really that thick with a 3.3125 bore, I would be surprised. This is especially true in that they said there was a pinhole in a cylinder wall. I've never seen a pinhole in a .250 thick cylinder wall. Have it sonic tested and pressure tested again - and have them test each bore in 12 places - 90 degrees apart and every 1" down the bore.

It the cylinder walls are good and there is only a leak in one cylinder, then only sleeve one bore. The more sleeves you install, the more you weaken the deck and the more it wants to do the "hula dance". All of a sudden you might find issues with water leaks around cylinder sleeves . . . that is a bad situation.

It appears to need a bore job - just go to the next available size for metric rings. I always determine my ring package BEFORE I order pistons and bore the block. Modern metric/mm rings make a heck of a difference in overall parasitic HP loss - I run them on every flathead I can. Talk to Ed at Ross . . . he will work with you on ring availability and a custom piston order.

Also, put the crank you're going to run in the block - with the rods you're going to use and determine the exact compression height you need. Have the decks checked out first - in case they need to be square decked and trued (side to side for the same compression height). If you do all of this accurately, then you can tell Ross exactly where the pin needs to be and the pistons will have the correct squish for whatever heads you're running. Obviously, the heads and chamber heights need to go into the equation.

I like to setup my pistons for a .040 squish (up to .045). This almost always takes some work to determine how I want to achieve this (given heads and piston selection). I determine the head gaskets I'm running and where the piston needs to be - then order the pistons to exactly match the compression height I determined.

Best of luck!
B&S

 

[Flathead Fever]

I was at the LARS. I saw your nice clean block there and the others the guy had for sale. I have about 20 of them out in the garage so I figured I didn't need anymore, plus it looked heavy. It's time to stop buying stuff and actually build one of my unfinished projects.

 

[KiWinUS]

I would think the cylinder walls would be closer to .150 from all the ones I've tested. If this thing is really that thick with a 3.3125 bore, I would be surprised. This is especially true in that they said there was a pinhole in a cylinder wall. I've never seen a pinhole in a .250 thick cylinder wall. Have it sonic tested and pressure tested again - and have them test each bore in 12 places - 90 degrees apart and every 1" down the bore.

It the cylinder walls are good and there is only a leak in one cylinder, then only sleeve one bore. The more sleeves you install, the more you weaken the deck and the more it wants to do the "hula dance". All of a sudden you might find issues with water leaks around cylinder sleeves . . . that is a bad situation.

It appears to need a bore job - just go to the next available size for metric rings. I always determine my ring package BEFORE I order pistons and bore the block. Modern metric/mm rings make a heck of a difference in overall parasitic HP loss - I run them on every flathead I can. Talk to Ed at Ross . . . he will work with you on ring availability and a custom piston order.

Also, put the crank you're going to run in the block - with the rods you're going to use and determine the exact compression height you need. Have the decks checked out first - in case they need to be square decked and trued (side to side for the same compression height). If you do all of this accurately, then you can tell Ross exactly where the pin needs to be and the pistons will have the correct squish for whatever heads you're running. Obviously, the heads and chamber heights need to go into the equation.

I like to setup my pistons for a .040 squish (up to .045). This almost always takes some work to determine how I want to achieve this (given heads and piston selection). I determine the head gaskets I'm running and where the piston needs to be - then order the pistons to exactly match the compression height I determined.

Best of luck!
B&S

Exactly my thoughts as stated above. Thanks Dale. I thought maybe it was just my observation on the wall thickness. I would be very surprised to see any flathead with that bore size and that thickness cylinder walls. Cheers mate.

 

[3W Hank]

Good info, thats why I put this out.
I guess seller had this to his local machine shop and documents are to this block, so he don't know more than the story how he got the block.
It might be totally wrong data he got back, but I will check this again.
Me, I has no experiance of wall thickness on the 41 truck blocks or any other FH.
As I stated, I took a chance.
I got a sleeve included and freight will not be expensive but if block is vasted its not fun of course. More sad on the block itself than my money.
One thing I feel odd this was done way back as he had it for 40 years and it came from a outsell of a race shop in San Fernado vally, so my guess its before the CSB era.
It shore is a pro port work.
But why do all this work to a block rusted inside, it make no sence so I guess its a casting issue pinn hole. I seen good block had this before, not new to me.
So I will install sleeve and ruff hone ( Rottler diamond ) see what it goes then T/S sell mm rings so the rings set the final diameter.
Well its a long step from my new Jason Line Hemi block that has 5/8" cylinder walls and 1" thick deck..
But I like the block, hope for the best.

 

[bcatcmc]

These comments might not help 3W Hank but are subject related.

After I bored out my `40 truck block .060 “ over I had to wait 2-3 weeks for the correct hone stones to turn up, fortunately in that time a very small rust bleed half way down number 8 bore appeared. I pushed and prodded with a scriber but nothing conclusive so I decided to sleeve it. As the photo shows it looks a bit ugly at 3.440 “ bore diameter ( the sleeve OD ) . ( please disregard my sarcastic cohorts artwork )

More than probable a pinhole than general corrosion , all the tests would certainly of helped but in the end there has to be a bit of luck involved.

I never did find any cracks in the block , although my test gear was low tech a strong light and a jewellers eyepiece.

 

[3W Hank]

I guess the truck 1940 also had a std bore at 3.1875" as the 1941.
So .060" over is 3.2475".
This block I has is 1/8" ( .120" ) over or 3.3125".
3.440 minus 3.3125 = 0.1275" / 2 = 0.063" wall.
So you hit into a zero wall thickness at ca 0.063" more in diameter ( 3.440" ) from my cyl diameter, but my block was sonic tested to has 0.25" at a cylinder diameter at 3.3125".
All block is inviduals and core shift or rust from enviroment etc but its a big step from ca 0.25" to 0.06" !

 

[Kurt in NJ]

If the block is that thick at the pinhole it could be filled with a crack repair pin and finished flush with the bore —- then pressure tested again.

 

[petehoovie]

These comments might not help 3W Hank but are subject related.

After I bored out my `40 truck block .060 “ over I had to wait 2-3 weeks for the correct hone stones to turn up, fortunately in that time a very small rust bleed half way down number 8 bore appeared. I pushed and prodded with a scriber but nothing conclusive so I decided to sleeve it. As the photo shows it looks a bit ugly at 3.440 “ bore diameter ( the sleeve OD ) . ( please disregard my sarcastic cohorts artwork )

More than probable a pinhole than general corrosion , all the tests would certainly of helped but in the end there has to be a bit of luck involved.

I never did find any cracks in the block , although my test gear was low tech a strong light and a jewellers eyepiece.

 

[3W Hank]

Kurt,
I'm not used to work with those old parts, but I has ofcourse install a sleeve ex a rod issue or a pinnhole ( this can be in the good muscle 60's block )
As I has not fully inpected this block ( will be on boat to Sweden ) I can't say either if sonic is correct tested or how and where or how big this hole is.
If it can be pinned, I can't say but it feels like a hard issue so I think a sleeve is a must, but maybe people here has experiance with this old time block can say.
Ideas is never wrong.

 

[Bored&Stroked]

The way I look at it . . . is since this engine has been ran a bunch and it has some sort of pinhole, it is most likely NOT a casting flaw - it is most likely due to rust and thin cylinder walls. The only procedure I would consider is a sleeve and then only if the sonic test shows that I have enough material to work with and if it passes a mag test. Then I'd sleeve the one cylinder and then pressure test it - before any additional work or money is put into it. I surely wouldn't order pistons or other parts until I was dang sure it was worth taking a chance on.

If the cylinder walls are under about .125", then I'd be concerned about putting a lot of $$$ into it. If I could get away with a sleeve, very slight bore/hone and it passes a pressure test, then I might put it together and see how things go.

If the cylinders are under .125 - it is one big gamble and usually these sorts of gambles don't produce many winners . . . at least not for long!

I noticed they denote .006 taper - so it will need to be bored. If everything is a go, then consider 84.5 mm rings --> 3.327 bore. Then run 1.5, 1.5, 3.0 mm modern rings (or another appropriate metric ring set). Then, once you know your exact compression height, work with Ross to make pistons for this bore and ring package. Modern rings are a whole lot better than the ancient Grant/Hastings stuff we all tended to run.

Things to Ponder: One has to step back and think --> "if this pinhole is a result of rust . . . how many OTHER pinholes are just waiting to rear their ugly heads?"

 

[3W Hank]

Yes it shore is a case, and I dont think seller had any intetion to fool me, and one can only speculate if block has .125 or .275 wall.
If I knew a old racer in Ca etc that has parts try to help and sell me a good block but how to get hold if those guys ?
-I has zero connection and I was on my third block here.
One here in Sweden has allot of old cool/good speedparts he bought in USA ( as I get it one need to be the chosen one and told me this guys not ooen any doors. I beleive him. I did try to get a cool block from him and a super nice light crank ( he has several ) but nothing for sale, so that is how the song goes.
I has no hard feelings as own stuff as its a drug itself and the meaning in Sweden to had several grille and V8 32 radiator is : one can get need for them and they dont sell new so better keep them.
Connection or parts is not for all. I accept it. And all worked to get the stuff.

So this guy had this block at LARS.
His buddy was Dough Clem and he knows many Sweden hot rodders and a good friend to me, that tell me guy was honest. I has nothing to think he changed history or documents.
I did like the work and I new it was ( thin wall at ca .30”…
Now I learned thick is .25” !
So why the sonic was off ex 50% or more I cant say, never used one ( no need )
But what concerns me, why did someone put all that work in a beat up rusted block, well I cant get that, plus the work started way over 40 years ago, at that era it must been allot of better blocks to get/use.
I like to stay positive, but I know it is a vaste.
Hope for the best.
I spend 70K in this car get parts by parts and most is just junk or need huge work.
One told me in USA vs 32 and old speed parts, you to late for the party.

 

[Bored&Stroked]

Naw, you're not late to the party by any means . . . there are actually more speed parts available now days then when I first got into these engines in 1974 or so. It is no different with modern high-performance parts. There are many that are plain beat to death and lots of guys selling beat-up junk as a "great deal" - the game is always the same no matter what engine or what era.

You'll now soon enough when you get the block and have it sonic tested. As long as they have a good sonic tester and know how to calibrate it, you'll get a pretty good idea as to what general cylinder wall thickness you have to work with.

Side Note: I had a big-bore race block that I acquired - was at 3 3/8 bore. I bought it for about $300 a few years ago. I knew it was a gamble as my sonic tester told me the bores were about .110 or so. It had one bad cylinder. When we went to bore it out for a sleeve, we hit swiss cheese at less than .080 depth. Rust had taken its pounds of iron out of the block . . .

I scrapped the block - but could not risk the amount of money and time I would have had to put into it . . . only to blow out a cylinder or have ring seating problems due to too much cylinder wall movement.