Merc crank in a 24 stud pencil test block

[GB SISSON]

I did some searching on this, but my question is fairly specific. I bought 8 'good' blocks last year in one lot. They came from the seller's father in law who left the flathead world. They were stored in a dry shed 2 miles from my home. Story was he junked 14 blocks and these 8 were the keepers, one of which had been tanked, magged and machined. I later bought a std size merc crank on one of the other islands. I dropped it off at the machine shop two weeks ago and I will have it in my hands later today. Looks like the prepared block is a pencil test block bored to 3 3/16 +.040 over. I have a set of merc pistons at .040 so this looks like the block that makes the most sense. It's even drilled for adj lifters. So the question of the day is... Is this bored too far to make sense for this build? The rest of the engine will be stock. I just like the 4" cranks for pulling our island's many hills. The engine in my current project '47 tonner PU is quite tired so it may go in there OR I may put the woodie's 3 1/16" engine in that truck and use the stroker in the woodie. Either way, no hot rod. Once again I have managed to sandwich my simple question into a giant paragraph. I do have nice 59ab and 8ba blocks to choose from, and no I am not interested in selling any of them as I am 65, just starting to look towards some kind of semi-retirement and I love these flathead projects. Thanks in advance. GB

[cas3]

the one i did last i had to go to 80 to get cleaned up, so 40 sounds good to me. sure i would rather have used a better block, but this one was good enough for me, and i hate to tear down another motor hoping to find better, and just end up with more scrap iron. we most likely will never wear one out with better oils today and our limited use. you got the 8ba rods too?

[rotorwrench]

I would get the cylinder walls ultrasonically tested for thickness if it was mine but I know that might be difficult for you. The 221 engines that started life at 3 1/16" on the cylinder bores have relatively thin walls. If it hasn't gone through them yet then it's a good sign. If they are paper thin then that would not be good. You never know on some engines though. It may have enough to get by.

[flatheadmurre]

If it was a 3 1/16 from start and now is 3 3/16 +040 your in the zone where ultrasonic testing is going to tell you what can or can´t b done...

[GB SISSON]

I will call the machine shop that did my crank and see if they can test it. It's quite a large and well equipped shop. What's the limit? Is there a good number for a flathead block? I kind of suspected you guys would say to ultra sonic test it. Once I haul it to the mainland and another trip to pick it up, I might as well just take them a 59ab or an 8ba with a lot of wall and have it bored .040+, but then there is the other testing etc. Maybe I should drop off a couple for tanking and testing while I'm making the trip.

[TomT/Williamsburg]

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My mother always said, " never waste a trip" so yeah, bring some other stuff to have done as well. If your block is no good, having one already there to bore to +.40 will save a trip ....

[leon bee]

What does "pencil test" mean?

[flatheadmurre]

Originally Posted by leon bee

What does "pencil test" mean?

The "lip" above the front cover is wide or narrow depending on how the block was cast so if you are able to put a pencil there and it won´t fall off it passed the pencil test...

[GB SISSON]

And if it passes the pencil test, then that means it started out as a 3 1/16" bore block. Both are 24 stud. If the cleaned and machined block had been an 8ba or 59ab style block bored to .040, there would not be any issues with wall thickness, so I'd just start the build with my new crank and not think about the walls.

[corvette8n]

Cool picture, one can never have too many blocks.

[flatford8]

We have similar plans for retirement Gary....Mark

[GB SISSON]

Here's a picture of the pencil test for those of you that want to know. I called Valley Machine and they don't do ultrasonic testing so I had to build my own apparatus after work to check wall thickness. Expect a very scientific approach from the guy that tests adjustable lifters with a 5lb flour sack, makes teflon buttons with a router jig instead of piston circlips, and hones kingpins with his wife's wooden spoon. All 3 are building up the miles with no hint of failure and I'm having a great time in the process. Would you buy a used car from this man? I would, but that's just me.

[flatheadmurre]

If you´re going to build s few you might want to find yourself a ultrasonic tester.
They are around used and i see some real cheap ones made in waitan...not sure how good though...
It´s not the tool that makes the mechanic...it´s the knowhow...

[marko39]

looks like the parts were well taken care of. i like the cradles for the cranks.

[GB SISSON]

Just like my steering box inquiry last week, I am already gaining new and valuable information on this subject. I made up this caliper just for reference. It showed walls of around 1/8" on all parts I could test on the over-bored 3 1/16 pencil test engine. The pointed end goes down the nearest coolant hole, and the bent side goes into the bore. At zero thickness the two outside points are flush. I later tested an array of 8ba/rt and 59ab type blocks bored .030-.040 and found wall thickness about 3/16". All my measurements I could get were very consistent, showing minimum core shift. There's a part of me that would like to bore some more holes in the deck surface for checking the high side and then tapping and a cast iron plug, but seems too reckless, even for me. I will look into ultrasonic tester. And Cas3 I have a couple boxes of rods, like maybe 75 to pick from. I'd like to make a jig to test for straightness. Is 1/8" ok wall thickness?

[Mart]

I like the improvised caliper gauge. Very interesting.

[rotorwrench]

1/8" should be OK if it is consistent throughout. It's pretty close to where you could bore it for 1/8" thick sleeves as well. Near to an additional +.015 would allow for a 1/8" sleeve to go back to 3.0625" if my math is correct.

[Barn Junk]

Another method to get some idea of the cyl wall core thickness if you have a selection of 24 stud blocks available for comparison, heads off and a variety of longer drill bits of varying diameters.

At the bottom of the cyl head block surface, there is a fairly large hole between each of the two outside cylinders. Drill bits of various sizes can be inserted, in the water jacket at an angle, between the two cyl cores to get some relative measurement of their thickness. 81A blocks should take a larger drill bit than say a 59A block.

[42merc]

'41 '42 Mercury blocks had a 'raised deck' and 3 3/16" bore.
Also would pass 'the pencil test'.

[Step-down]

I'm sorry I,m slow, so if the pencil stays on the lip show on the photo above it 's 3-1/16 "
I have a 40' and haven't take the head off yet but the pencil stays on lip without falling .

[rotorwrench]

I check the deck ports on those prewar engines. That is the best way to tell if they are a 221 or a 239. The 239 always has the round center ports. 221 engines are always keystone shaped.The 99A family of prewar engines is not as common in this day and age so most are likely 221. The pencil test just tells you whether it is prewar or not.

[GB SISSON]

Well according to 42 merc, there were some exceptions.... I picked up my beautiful merc crank today at the quarry. Their diesel mechanic was on the mainland and had a pick up at Valley Machine so he brought it back to the island for me. .010 on the mains and .020 on the rods. I plan to use the insert type 8ba style rods. Today I looked up 'ultrasonic thickness tester' on ebay and amazon. Industry standard rig is about 1100.00, but a lot of testers out there from 65.00- 250.00 That claim to do what's needed. Anybody have experience with these?

[deuce_roadster]

The person who does all my flathead machining sonic tests the blocks and the minimum wall thickness he will build on is .100. The sonic testers need nothing on the inside as it is calibrated to a known thickness so you can test many places you couldn't get at with your calipers. I would think any shop that bores engines would be able to sonic test for you.
I have a NOS 41 Merc block which is 3 3/16" that passes the "pencil test" 99% of blocks that do pass this test started life as 221 3 1/16" bore blocks but exceptions do exist.
Good luck

[GB SISSON]

I ordered an ultrasonic tester on amazon. Has 5 stars, if that means anything. I also read that you can test for accuracy by using it on something of known thickness or something you can easily mic. We'll see. I also re-inspected my stash of other blocks and find them to be in very good condition (visually), so we'll get that crank into something good. https://www.amazon.com/gp/product/B0...4JPBPJA54647YZ

[GB SISSON]

My tester arrived, but the instruction booklet says that it's not recommended for cast iron due to its granular nature. I did however grind a flat area on both legs of my caliper. When its pointed tips are closed together, I set my digital slide caliper to zero and read the thickness of the bores in the negative scale. I get very consistent results and for the most part the thickness is right around .125 with small variations. Always thicker at the top.There is a place at the bottom of #1 cylinder at the front where the thickness is .075, but it gets thicker as it goes up. The rear side of that cylinder is thicker than the rest, suggesting the dreaded core shift. I suppose I will take it somewhere for a sonic test, but if my results are accurate, what to do? Meanwhile I have been thinking of using one of the other blocks. The blocks are stored on a concrete floor under a deep lumber rack and hard to see where they are. Yesterday I received two Jegs engine stands. 4 wheel type for 39.95. I was quite shocked at the good quality. At 1000 lb capacity, I plan to weld a 1/4" plate to the base to hold a 59 ab type block upside down and hang an 8ba endwise from the stand. 4 of these units will hold the 8 blocks up off the floor and easy rolling across the slab to my engine area. Question of the day, Is it ok to suspend an 8ba endwise for extended storage periods?

[JSeery]

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Originally Posted by GB SISSON

Question of the day, Is it ok to suspend an 8ba endwise for extended storage periods?

I wouldn't see a problem. The issue with the earlier blocks is the thin casting in the 1/2 bellhousing area and the bellhousing depth moving the majority of the weight of the block further away from the mounting points. With the later blocks the mounting points are right at the back surface of the block similar to most modern blocks.

[rotorwrench]

When the thickness is reduced too much there can be hot spots but they would tend to be closer to the top of the bores where the combustion takes place. If most of the measurements are over .100" then it may work OK. Corrosion can be the cause of thin spots as well as core shift.

[GB SISSON]

I had also thought that most of the problems associated with a thin wall would be more of a problem higher up. I have been thinking of using something called 'Evans Coolant', which is some kind of oil with a very high boiling point. No cavitation or corrosion but $$. At least the wall wouldn't get thinner. Hmmm, I'm encouraged about that block.

[tubman]

Before you get enamored with Evans coolant, do a few searches on the various "old car" boards.

[Bored&Stroked]

Given the testing you've been doing, I don't see a problem with the block - as long as you pressure test it before sinking a bunch of time and $$$ into it. Speedway has a pressure test "kit" that works well - given the number of blocks you have, it would be worth having. Here is my basic block selection/validation process:

1) Initially wire brush all the transfer areas between the valves and bores - then wipe everything off with a good solvent (like lacquer thinner). Do the same on the pan rails. Take a good magnifying glass and inspect these areas for cracks.


2) Have the "good blocks" hot-tanked (or baked/tumbled) and then magnafluxed - to validate that they are good blocks. If you can, it is always good to get as much casting flash and sand out of the block water jackets - can make a big difference in cooling. Consider using a de-rusting solution in the water jackets.


3) Then do a sonic test to validate cylinder wall thickness - I don't like to go below .100 on anything . . . and preferably .125 or thicker. I take the probe and measure 12 points on every cylinder - three locations up/down the bore and all four sides. Write everything down to document the results - may come in handy during the boring process (to "shift" a bore around a bit to account for core-shift).


4) Then pressure test the block to 40 - 50 PSI . . . to ensure you don't have any casting pin-holes or cracks up inside the exhaust ports.


Now - I'm ready to go to work and do the necessary machine/rebuilding work . . .

[GB SISSON]

Lots of great advice here, and pressure testing seems highly worthwhile. Thanks! I found the speedway kit and it looks fine, but over the last year I have been thinking about building one and now that I see how simple their's is, this is what I may do. Call me a cheapskate, but I'm trying to get something put away for retirement.... Ok, I have a lot of 60 mil epdm rubber roofing left over from my woodie project. So I make a 'head gasket'. just the 24 holes on a rectangular piece. Then I use a head for the block off plate. This epdm is like a truck inner tube but flat. Next a couple of gutted water pumps (I have a crate of them). Somewhere I introduce a schrader valve. Pump it up, check with a good tire gauge. How about a section of old bicycle tube with it's valve intact, hose clamped to the water pump's neck ?..... BTW, I already assembled one engine stand this morning and welded a 20" piece of angle to the stock plate. The legs of the angle welded to the plate. 45 degrees with little effort and no math. My wife's at work and I told her I'd be painting the bathroom today. I better get going.

[leon bee]

After I made the rubber "head gasket" piece and put the head on, I aired it up and after a while the rubber blew out at one of the water passages. I had some thin galvanized flashing, cut and drilled a piece just like the rubber. So new rubber, sheet metal, then the head. Holds pressure good.

[JSeery]

Originally Posted by GB SISSON

..... BTW, I already assembled one engine stand this morning and welded a 20" piece of angle to the stock plate. The legs of the angle welded to the plate. 45 degrees with little effort and no math.

That's how I built the one I am currently using.

[rotorwrench]

Using a cylinder head to provide closure on the deck will allow a leak test but it hampers finding where a leak might be coming from. Fabricating a plate takes time & material. The cost of those kits isn't all that bad when you consider what your time is worth. A single plate should fit both sides.

[Bored&Stroked]

Another option is to take an old cylinder head and "hog out" the areas around the bores and valves - can be done, but is a lot of work. You definitely want to be able to see into the valve pockets/ports, the transfer areas, etc.. I put some soap in with the water, makes it easy to see "bubbles" in bad places! (Well - hopefully not!). Good luck

[GB SISSON]

OK... Best of both worlds! A fellow barner has sent me a pm offering his speedway tester to use on my blocks. He only needed it once. I just pay the shipping. I like how it is open at the cylinders for visual inspection. And B&S, added soap is an excellent idea. We've all seen the tiny bubbles on that evasive inner tube leak.