help needed with flathead block.

flathead4rd

flathead4rd

Well-known member
I need to have my Mercury block tested for a crack. I can't see any with just a visual inspection. Anyone have a source in the Detroit area? Pistons, crank and valves are still in. #3 had water in it as well as #7. Oil pan had a lot of water in it. I think Magnaflux is my next option. Thanks to all who reply or have additional questions.
 
Thanks Tim & Tubman. That looks like a good way to test what I'm looking for. Didn't know there was such a kit available. Appreciate your replies. Is there any specific torque you use on the head bolts?
 
Can't answer about torque, but glad to see this is back in stock. Speedway has not had any in stock for at least two years. Please report back after you receive it and try it out.
 
It’s not real hard to make one but, I was happy I bought mine from Speedway when I had the chance a few years ago. I put a shut off (ball valve) between my air hose and the regulator. Set the pressure I wanted, shut the valve and removed the line. The only issue I had was the rubber sealing washers for the bolts. You want to grab some of these washers. I hope I’m posting the right picture……I’m sure somebody will comment if these aren’t the right ones………you didn’t mention the head gaskets but I would look those over real close also…….Mark
 

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Hey Flatford 8:

I just looked those up. I think they are the same as Toyota drain plug washers. Dorman makes them. I just got a bunch from Rockauto and paid around $0.49 vs. the $2.49 Napa is charging.

I'll report back. If they are the same, I'll list the Dorman part #.
 
Ok……as I think about it,……the pic I saved might be the ones for the top of the filter canister …… anyway, get some washers with rubber coating to fit the bolts that hold the plate to the block…….Mark
 
Slightly different but on the same lines of the rubber washers, IF you have a pipe gasket supply house OR any gasket material supply house near by, you can get a couple of scraps of 1/16th or 1/8 neoprene sheet like I did and make a full gasket.....Fortunately for me when my customer water jet cut my plates he also water jet cut some gaskets for the plates out of the above materials. The neoprene is good to at least 150psi
 

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You'll need to remove the valves and anything else so it's a bare block. Don't mix up the valves, make something to keep them in order. Most good machine shops can magnaflux it, but you'll need to explain to them where all these flatheads crack, which is potentially everywhere. Make sure they check the entire block even down below the valves and down inside the cylinders especially if it's been bored out a lot. Look at the sides of the block to make sure it hasn't cracked there from freezing. Cracks from the head studs to the valves, cylinders and water jackets.

I bought one of those pressure testing kits years ago from Speedway. You really need to do both the magnafluxing and pressure testing the coolant passages on a flathead.
 
Flathead Fever said:
You'll need to remove the valves and anything else so it's a bare block. Don't mix up the valves, make something to keep them in order. Most good machine shops can magnaflux it, but you'll need to explain to them where all these flatheads crack, which is potentially everywhere. Make sure they check the entire block even down below the valves and down inside the cylinders especially if it's been bored out a lot. Look at the sides of the block to make sure it hasn't cracked there from freezing. Cracks from the head studs to the valves, cylinders and water jackets.

I bought one of those pressure testing kits years ago from Speedway. You really need to do both the magnafluxing and pressure testing the coolant passages on a flathead.
Click to expand...

Agreed on the need to do both. Pressure testing should be first. No sense going further if it doesn't pass a pressure test.
 
Flathead Fever said:
You'll need to remove the valves and anything else so it's a bare block. Don't mix up the valves, make something to keep them in order. Most good machine shops can magnaflux it, but you'll need to explain to them where all these flatheads crack, which is potentially everywhere. Make sure they check the entire block even down below the valves and down inside the cylinders especially if it's been bored out a lot. Look at the sides of the block to make sure it hasn't cracked there from freezing. Cracks from the head studs to the valves, cylinders and water jackets.

I bought one of those pressure testing kits years ago from Speedway. You really need to do both the magnafluxing and pressure testing the coolant passages on a flathead.
Click to expand...

Actually, I've used a set of stock heads to leak-test an 8BA. Just make sure the heads aren't crackled, you need good gaskets, and make a block-off plate where the thermostat housing goes. Then you don't even need to remove the valves. I even made a kit to test the block while still in the car. (Leaking water pumps make it kind of difficult, though).Out of the car I use a plate to block off the water pump.
 

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The other area that flatheads crack is the oil pan rail. The water passages extend down and freezing will crack the oil pan rails. These cracks are usually visible, but mag testing and/or pressure testing will confirm.
 
rockfla said:
Slightly different but on the same lines of the rubber washers, IF you have a pipe gasket supply house OR any gasket material supply house near by, you can get a couple of scraps of 1/16th or 1/8 neoprene sheet like I did and make a full gasket.....Fortunately for me when my customer water jet cut my plates he also water jet cut some gaskets for the plates out of the above materials. The neoprene is good to at least 150psi
Click to expand...


Very nice!
 
38 coupe said:
The other area that flatheads crack is the oil pan rail. The water passages extend down and freezing will crack the oil pan rails. These cracks are usually visible, but mag testing and/or pressure testing will confirm.
Click to expand...

Also, always check the valve valley. The casting is quite thin there. I was out $800 AFTER getting a block fully cleaned, machined, etc. and only to find a 12" crack in the valve valley while pressure testing upon return from the machine shop. Shop claimed they did it, but obviously they didn't.

Lesson learned.
 
I also tested some blocks using the stock heads and some scrap steel plate. And some sort of neoprene sheet ordered online. The "neoprene" I bought wasn't much good and was fussy and real limp. Ended up using thin sheet metal also cut to head gasket shape for reinforcement. Of course you can't look down in there for bubbles, but you can sure see if it holds pressure.
 
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