21 stud deck height, gasket thickness, etc. questions.

[Yoyodyne]

I'm building a 21 stud, the block is ready for finish machining. Stock stroke, flat top pistons and heads. I'm trying to optimize the head to piston clearance at .040".


The block deck is 10.442. The piston compression height is 1.534". With the 3.75 stroke and 7' rod that gives me a calculated deck height of .033". The block isn't bored yet so I can't yet preassemble it to measure directly.

Reading here on the 'Barn tells me the Best Graphtite gaskets are a good choice for aluminum heads, and I think that's my preferred choice. Best tells me the compressed thickness on them (PN 507G) is .053 ±.003. .033 + .053 will give me a piston to head clearance of .086. This requires cutting the deck .046 to get the .040 piston to head clearance, and the pistons will protrude above the deck surface .013.


Engine guys - Is this a reasonable thing to do? Is a .045" cut on the deck safe? The deck seems thin even before it is surfaced at all. It's a 36LB block and I only have one shot at this.
Is there a thinner gasket to use? Cometic doesn't seem to make 21 stud gaskets, but I could modify their 24 stud gaskets if necessary.
A custom set of pistons isn't going to happen at this point for this motor.

[Phil Gillespie]

Deck should be left alone!! Just a light clean up if really required.
The heads are where the machining takes place to get that 0.040 to 0.050 piston to head clearance. Best to actually measure with pistons fitted and check using head without gasket and allow given compressed thickness of gasket or use gasket. This way you should be good. standard valve train?
Phil NZ

[Yoyodyne]

Phil, the head and pistons are flat top, not domed, I can't get the head any closer to the piston by machining the head.

[Bored&Stroked]

I only machine the decks to true/square them up side to side - to get equal compression heights. I never machine the decks to tune the squish.

You really need to determine what your actual compression height is - given your crank, rods and block. You don't need a piston to do this - you do it with the crank in the block, a rod on each bank, with piston pins in (no piston) - and then mic the highest point of the pin travel - then subtract 1/2 the pin diameter. Now you know your compression heights side-to-side. You'll probably find they are not the same.

On some of my recent builds, I've ordered my pistons from Ross - and gave them the exact compression height I needed . . . to get the squish I wanted.

Question: Are your pistons actually below the deck surface??? If so, then I'd be looking for new/different pistons - should be no reason for that with a stock stroke crank and stock deck heights.

In a prefect world (using the gaskets you mentioned), you'd need to "pop-up" the piston a bit - OR, maybe use a different head gasket. You might look into the MLS ones from Cometic. They are not cheap, but you can get them in various thicknesses. What I don't know is if they make them for 21 stud engines?

[Phil Gillespie]

Originally Posted by Yoyodyne

Phil, the head and pistons are flat top, not domed, I can't get the head any closer to the piston by machining the head.

Should have paid more attention to your post.
Phil NZ

[38 coupe]

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If the crankshaft isn't ground yet get you could investigate getting the rod throws offset ground equal to the compression height the distance you need.

[Bored&Stroked]

Originally Posted by 38 coupe

If the crankshaft isn't ground yet get you could investigate getting the rod throws offset ground equal to the compression height the distance you need.

That would only work if you had really thick rod bearings - something that is probably not really available. Now, you could shoe-horn in a later crankshaft and offset grind the throws to exactly what you need . . . that could work, but there is a lot of work that goes into that whole deal.

I'll bet that once he does an exact compression height measurement, he may find his pistons are just fine (flush with the deck).

[Bored&Stroked]

Info: Cometic does make 21-Stud gaskets . . . is varying thicknesses. Here is a link to Jegs for a .040 gasket. One thing to note, MLS gaskets usually require a very fine RA surface finish - or they might leak. Check with the manufacturer before you have your decks trued up and decked.

https://www.jegs.com/i/Cometic-Gaske...0-040/10002/-1

[KiWinUS]

Are you using 35 or earlier heads.

[frnkeore]

This is what I'm going to do with my late 21 stud engine, if I ever get going on it.

I'll use a .060 Victor gasket, with my flat 40-A1 aluminum heads.

If you surface your block to Ford's production spec of 10.437 and I would recommend that, you can get this.

With your CH of 1.534 + 7.0 + 1.875 (1/2 stroke) = 10.409. 10.437 - 10.409 = .028 deck clearance. Add in your head gasket (in my case .060), that's .088. Minus .040 = .048 x 2 and that's how much I would need to add to my stroke or, a stroke of 3.846 and the piston will be out .020, with .040 squish.

From there you just get a '48 or earlier crank, with 2.139 journals (can even be ground .030), have it offset ground and the mains ground to 2.399. You of course have to mess with the rear seal, too.

Send that '<48 crank to:

Mario, at L&M Grinding, in Redding CA (530 221 7652) and for about $250, or so, he'll grind it to those specs.

The extra cubes, will also help with compression.

[Yoyodyne]

Originally Posted by KiWinUS

Are you using 35 or earlier heads.

Yes

[Yoyodyne]

Originally Posted by Bored&Stroked

Info: Cometic does make 21-Stud gaskets . . . is varying thicknesses. Here is a link to Jegs for a .040 gasket. One thing to note, MLS gaskets usually require a very fine RA surface finish - or they might leak. Check with the manufacturer before you have your decks trued up and decked.

https://www.jegs.com/i/Cometic-Gaske...0-040/10002/-1

Thanks for that. I'll call Cometic. The only gasket I can find on their site for a 221 is a drain plug gasket.
I'm looking through my junk for a used std bore piston, I'll assemble a used rod and piston into the block and see what that shows me for deck height. Like you say, it could well be different than theoretical.

[Bored&Stroked]

Originally Posted by Yoyodyne

Thanks for that. I'll call Cometic. The only gasket I can find on their site for a 221 is a drain plug gasket.
I'm looking through my junk for a used std bore piston, I'll assemble a used rod and piston into the block and see what that shows me for deck height. Like you say, it could well be different than theoretical.

If you find gaskets from Cometic, make sure you follow their advice on surface finish and have the block lightly decked to match their recommendations. Also, "square deck" it and ensure the compression height is the same on both side.

I give the exact amount I want taken off to the machine shop - so there is no guessing.

Hopefully your machine shop can mount the mains in a "saddle" such that they can truly square deck it. You should check with them and see if they have a mounting system that uses the main bearing bores.

[Yoyodyne]

Originally Posted by Bored&Stroked

Hopefully your machine shop can mount the mains in a "saddle" such that they can truly square deck it. You should check with them and see if they have a mounting system that uses the main bearing bores.

He does, it's a Storm Vulcan Blockmaster in good condition and it will be. He's been doing my race stuff for 30+ years, he's fussier than I am. Takes f-ing forever though...

[Yoyodyne]

I spent some quality time yesterday carefully measuring my parts. The same piston and rod in each corner bore gave me deck heights of .045" to .048" to the gasket surface of the block. This combined with a .053 gasket would give me a piston to head clearance of about .100". I have 3 sets of pistons, used Std, new.030 and new .100. All three have compression heights within a range of .005" total. The one I used was the tallest of the three at 1.534". The crank is fresh ground at.020, I used a .020 rod bearing shell. I checked the rod on a CMM afterward, the length is 7.0010" and both ends are round within .0002 and on size - 2.250 and .752. The block measures within Ford's nominal height. I believe the crank stroke to be correct. At .020 under it can't be more than .010 radius from the OEM stroke.



So - Has anyone here checked this and found similar results, or different heights? If all early motors go together this way with .100 deck, they would all be lazier than they could be, right? I can see that it leaves a lot of room for carbon buildup, I guess that's good for long life without service.


Cometic has a .040 gasket, that would give me .085.
To Get .040 piston to head with these parts I need to remove another .045. Am I correct in thinking that's too much to take off the deck of the block?


This motor is already Plan B after a half dozen false starts with junk blocks. To get this together in this lifetime I need to use available parts, custom pistons are not going to happen this time. Before I do that I'll start again with a 37 block, Merc crank, etc. and I need this one to go together this winter.


So I can cut the deck .045, I can just put it together as is with .100" deck, or I can profile mill the heads around the gasket opening and leave .060 of material extend down into the cylinder to close up the chamber to piston clearance. That's doable, but would be a PITA, and would require even more clearancing for valve to head clearance.


Thoughts anyone? Who else has measured this on a stock flat top 21 stud motor? And/or done anything about it?

Is it worth this effort to get .040 piston to head clearance on a 221 with a cam and 2 carbs?

[cadillac512]

Concerning decking the block...even if you do consider a fairly severe decking (may be ill-advised due to strength lost) check closely at the effect this may have on valve seat areas. I decked an 8BA block and at .020" stock removal it was nearly at the actual seating area on one side. Not sure the 21 stud is the same but worth a look.



Terry

[frnkeore]

I'm a retired aerospace, machine shop owner and still have my machine shop so, I know dimensioning.

I have Ford's drawing for the 21 stud block and the deck height of the block, is given at 10.437.

Your rod, piston (I'm going to use 1.53, estimating one of your new pistons) and stroke combo equals 10.406, that will equal a deck clearance of .031, if your block is the nominal height. With your 1.534 piston the deck clearance, should be .027. That means that your block is .018 - .021, over 10.437.

In that case, I would see no problem in cutting it down to the Ford spec of 10.437, maybe even .010 more.

If you could find another std rod crank, you could have it offset ground, to .030 under with a stroke increase to 3.78, gaining another .015, bring your deck clearance to .016 but, that's still .056 squish, with your .040 gasket.

[Bored&Stroked]

If it was me, the next thing I'd check is the actual stroke of the crank - not hard to do if you have the right depth mic. I've not built early 21 stud engines, so I have no experience on what is "typical" in the regards to true deck height, compression height, etc.. I do know that I'd surely not want my pistons "down in the hole" - having a .040 squish is key to these things really running.

I would not be decking it to achieve the clearance - unless all other possibilities have been ruled out. The decks are thin on these engines, I don't like to weaken them. But - it all depends on the intended usage. What I would NOT want to do is deck the block if the issue is potentially the crank.

Lastly, is it possible the mains/babbitt were not done incorrectly? I'm not a babbitt guy, so I have no experience to fall back on - but just a thought.

You might PM 'Brian' from over in NZ - he seems to have built a lot of 21 stud stuff (performance oriented) - would be nice to see what he knows.

[Yoyodyne]

Measuring the stroke is one thing I knew was missing, I just ran out of time. Will do that next.

This is a 36LB, insert bearings. The main saddles appear untouched.


Good 36-37 cranks that will clean up at stock stroke are hard enough to find, finding one to offset grind isn't likely.

[frnkeore]

I have a early double slinger crank with 2.5 mains, that has std rods but with surface rust.

If you like, you could have it for $25 (cost of crating) plus shipping. I could even send it down to my crank guy first, for main and offset grinding. He gets good shipping rates.

[Yoyodyne]

What's a double slinger crank? Does that fit a 36LB?

[Yoyodyne]

The stroke on #1 throw is 3.743. That's measured with 2 different starrett depth mics and checked with a B&S dial caliper. I could drag out other measuring methods but I'm confident in these tools, they get calibrated and get used daily. I have a 6" travel Starrett dial indicator but I don't think that's as accurate as depth mics and it would take a while to set up.



So the stroke is .007 short. That accounts for only .0035 of deck height.

[Yoyodyne]

Originally Posted by frnkeore

I have Ford's drawing for the 21 stud block and the deck height of the block, is given at 10.437.

Can you post that, or email it? In this thread Dale says it's 10.440-10.445 on the 59A and 8BA prints.
https://www.fordbarn.com/forum/showt...ht=deck+height

[frnkeore]

The double slinger rear main, would be a '38 crank, I believe. It should be the same as the '37 but, with 2.499 mains, instead of 2.399. Maybe someone could verify that?

Edit:
The second slinger is what the rope seal replaced, as I remember.

[Bored&Stroked]

I went back an reviewed both the 59AB and 8BA prints - they both show 10.445 - 10.450. So maybe it is different (not by much), though that earlier print doesn't show a manufacturing tolerance . . . so we don't know the low and high end of the range. It would not surprise me if all blocks were supposed to be the same . . . within a range of tolerances.

On the crank, as Frank mentioned the first slinger is the rear thrust surface and I guess also a slinger and the second one is the actual oil slinger that rides inside the pot-metal rear main seal-plate pieces. Some folks will remove the second slinger (on the crank grinder) and put in a later type rope seal. (And use the later pot-metal seal plate - or whatever you call it).

Also on the later crank, obviously the mains are different sizes from your 36 or so crank. I have no idea as to if there are any counterweight or other "fitment" issues if one was going to rework the mains and run the later crank.

I've not built early 21 stud engines, so I can't recommend exactly what the process is - though I've seen some custom seal plates/work done on the rear main caps to handle it.

[Bored&Stroked]

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Also, given the dimensions that Frank showed (the lower deck height), this would put the piston crown further up or out of the bore as compared to a later block (if there is truly .008 to .013 deck height differences).

Just wanted to make sure we're all thinking the same.

[Yoyodyne]

Thanks Frank. I can't read much on that print, but I do see the 10.437 deck height.


I'm making an assumption about the the piston compression height by assuming the pistons I have are close to nominal, since they are all the same within .005. Are there any prints in existence for those pistons, to know what they are intended to be from Ford?


Cutting the deck to 10.437 and making the stroke 3.7500 would still leave my pistons .036 below the block deck.
Adding .020 to the stroke would still make it .026.



Looks like without custom pistons the fix is to profile the heads. At least I can do that here.
How deep can I make valve reliefs in stock ford heads?

[Bored&Stroked]

Just to let yah know, I have called Ross directly and they will move the piston pin for a fair price - just not sure they make 221 sized pistons.

[frnkeore]

As I said, in my first post, if you use a crank, with the 2.139 rod journal, you can offset grind and adjust the stroke, for any deck clearance you need.

MY intent is to offset the crank to give .020, above the deck and the std Victor, .060 head gasket.

The increased stroke, also gives a higher CR.

[Yoyodyne]

Originally Posted by frnkeore

As I said, in my first post, if you use a crank, with the 2.139 rod journal, you can offset grind and adjust the stroke, for any deck clearance you need.

MY intent is to offset the crank to give .020, above the deck and the std Victor, .060 head gasket.

The increased stroke, also gives a higher CR.

There's no 2.139 crank that drops into a 36LB. At least that's my understanding. I was going to do that to fix a 37 block that has .015 oversize saddles, convert it to 59a bearings and put a 4.125 offset ground Merc crank in it. But that conversion is not real simple and not in the cards for this motor.

[frnkeore]

So, your saying that there is more to it than grinding the mains to 2.399 and using the later seal?

If I need to know, because that is what I intend to do with my '37 block.

[Brian]

Frank, With the 2.449 [std] journaled cranks, the front and centre main journals, whilst being.100" larger in dia than the 36 LB crank, are shorter....so, when you whittle them down to 2.399", you'll also need to widen them so they will indeed drop into the 36 block. Then you need to put a spacer behind the crank timing gear in order it will line up with the camgear. The snout of the larger crank is also longer and larger dia, so use later pulley or machine to suit the 36 crank.

[frnkeore]

Thank you, Brian.

That's all doable, I was going to rough the mains down anyway for the crank grinder. I'll just measure the main to main distance and machine that too.

[Mart]

This is an interesting thread. Lots of tech gems trickling out here.
Mart.

[Bored&Stroked]

While the crank work will be a bit expensive, it will probably be less than a custom set of pistons. So if it was mine, I'd explore with my local machine shop (somebody who is expert on crankshaft work) - what this crank work would cost. It is very important for the quench/squish to be about .040, so an offset crank grind back to 2" rod journals would enable you to achieve the exact stroke you'll need (given the pistons you have). Let us know what you find.

Also, this approach would create the least number of "bastardized" parts (versus screwing with the heads - which I wouldn't do for multiple reasons).

BTW: If you need this type of crank work done and don't have a trustworthy local crank shop, let me know - can probably get this done for you at Fowlers in Columbus. This is where all my machine work is done and their crank guy "Dennis" is second to none. Let me know if I can help . . .

Also, I have a couple "spare" later 239 cranks - so you wouldn't have to ship or deliver one both directions. In a perfect world, I would prefer to have the short-block to mock everything up. This is the best way to prevent any potential unforeseen circumstances . . . as we all know that crap happens!

[Yoyodyne]

Thanks for the offers, Frank and Dale, you are both generous.


Dale - Why wouldn't you recommend changing the heads?

[Bored&Stroked]

Originally Posted by Yoyodyne

Thanks for the offers, Frank and Dale, you are both generous.


Dale - Why wouldn't you recommend changing the heads?

It is just a very strange way to deal with quench issues. Also, imagine the next guy that takes the engine apart . . . would be one big "What the heck is this?" type of moment. It will make any future head work a real PITA - as you can no longer deck the head in any normal fashion.

But, it is your engine and you obviously have the skills and equipment to do such a job. And obviously it doesn't cost you anything to use this approach

[Yoyodyne]

Originally Posted by Bored&Stroked

It is just a very strange way to deal with quench issues. Also, imagine the next guy that takes the engine apart . . . would be one big "What the heck is this?" type of moment. It will make any future head work a real PITA - as you can no longer deck the head in any normal fashion.

But, it is your engine and you obviously have the skills and equipment to do such a job. And obviously it doesn't cost you anything to use this approach

I get that, I really do. But I gave up caring about the "weird" factor on my own stuff long ago. Iron heads are cheap, about $25 each, I can test with iron heads without much risk. Worst case, bolt stock heads on and it's a normal 36 engine. I already have the gasket pattern digitized, I could do this in a week of evenings if I needed to. I think the hardest part might be preparing the heads properly to clamp them down parallel to the table. The alternative is waiting for pistons, or waiting for a crank to be done, and nothing outsourced seems to be going quickly lately. Modifying the heads is going to be way more entertaining for me than waiting for parts would be. (When your only tool is a hammer, everything looks like nail, right?)
If I hurt a custom piston, then I'm waiting for more to be made, if I hurt a special crank, I'm in more trouble. If I hurt a head I made, I make another. If someone else is working on it they would have the same problems plus I won't be around to care.
Plus this way I can easily experiment with how close I can get the pistons to the head if I want to. I cut my engine teeth on '70s Modified eliminator SBCs that often had the pistons touching the heads at 10k+. (I don't anticipate that sort of thing to happen, but this is a what-if post, right?)

I'm sort of surprised this deck height issue on flat tops hasn't been discussed here before. Seems like everything else has been...

This is not a done deal yet of course, but it's how I'm leaning unless I run into something that stops me.
Thanks for the input!

[Bored&Stroked]

Would be nice to do it on a CNC - but as you mentioned, the hardest part is getting the deck surface parallel to the machine and holding the thing down. You might consider making a big plate to mount the head on - with stand-offs for some studs to set the height and make it parallel and then 4 threaded locations where you could put bolts through the spark plug holes.

[21stud]

Good thread, much valuable knowledge here!

This just show how many ways there is to correct loose factory fit.
Worst thing will be decking the block. so thin already.

[frnkeore]

I'm sort of surprised this deck height issue on flat tops hasn't been discussed here before. Seems like everything else has been...

I have explained my use of a 2.139 crank pin and offset grinding, to set the deck clearance, in at least one other thread on this forum.

I've also (in the same thread, I think) talked about the limitation on boring the 21 stud engines, because of the lower center stud location (the reason Ford changed to 24 studs) and that the factory, nominal OD of 3.38 for the cylinder walls.

[frnkeore]

A couple of other things that might help, regarding Ford factory specs, is that the nominal, specified deck thickness of the 21 stud block, is .25 and I'm attaching the head bolt pattern for the block. I've added the blue lines to make the pattern clear. Holes that are not at the blue line intersections, aren't head bolt holes
Edit:
All the hole locations are the same as the 24 stud engines, except the lower bolt holes, at are on the center line of the cylinder.

One other thing, while the nominal cylinder wall diameter is 3.38, it is a little thicker, between cylinders at 3.40, specified as a 1.70 from the center line of the cylinder.

Core shift, of course, can effect the actual cylinder thickness.