Mismatched heads and block on 40-72

[jbento]

Well after I finally got the "right" spark plugs for the 40-72 and guess what:  THEY DON'T FIT!!!!

So I can only assume that the heads are NOT the ones that came with the original block.

Now, the original block had a couple of cracks in it, so some of you may remember that I ended up replacing it a number of years back (this project started about 8 years ago).  So for the record, the block I am using has the number "8418042*", identifying it as  coming from a 1946 Series 62.  Same block excepting for some minor grinding work to get the starter to fit.  which it now does nicely.

The heads have the following numbers on them"322 625     346 670". Same numbers on both heads.  And instead of having the 10mm spark plug opening that the original heads would have had, they have 14mm openings.  So here are my questions:

1) What engine did these heads come off of? 
2) Given the block (from a 46-62), what is the correct spark plug to use?

Any other interesting tidbits or questions would be appreciated as well.

Many many thanks!

[Bob Hoffmann CLC#96]

Joe, the MPB shows those as the correct heads, even though they don't match. Go figure. Also, many mechanics of the day hated the "peanut" plugs as they were called. They bored them to 14MM. HTH, Bob

[jbento]

Thanks Bob!

I am assuming that when you say "correct" that you mean to the original 40-72 block.

The thought crossed my mind that someone maybe bored the openings to 14mm.  Couldn't think of a reason they would need to though.  The dilemma that poses is that the original AC Delco 104 plug (now a delco M8) has a 1/4 inch reach.  No 14mm plug I could find has less than a slightly more than 1/2 reach.  This brings up 2 distinct issues:

1) I need to make sure that I clear the valves.  And given that the position of the spark is different;
2) What is the proper gap setting (assuming that it may be different).

Would an ACDelco R45S plug work?  And yes, the system is still 6v +ground.

Thanks!

Joe

[Steve Passmore]

Hi Joe.
Cant you just put your original 1940 heads back on?

Boring out these plugs for the larger size was and still is a very common practice in my country as there was a time when these 10mm plugs were nearly impossible to get without shipping them from the US, and when these cars were still clunkers back in the 50s and 60s no one would ever bother doing that, far better to have a size that you can buy from the shelf.

I have several heads here with the holes bored out to 14mm and I have a 47 engine that was run with them, the plugs never hit the valves as there are some very short reach 14mm out there, J-6 and J-8 are 3/8" reach, also  UJ-10Y  12Y and 18Y, so too are
J-11Y and J-13Y, these may not be the proper heat range for your car but I ran my 41 Cadillac for years on very short reach 14mm because that too had been bored out, it ran fine but may not do for your countries temperatures.    It was strange how Cadillac had 14mm on the earlier engines anyway and I think the gap is more or less the same regardless. (25)

Your other solution is to find another pair of heads if you wanted to keep it original,, I should be surprised if they used a "series" specific head on these cars, Iv never come across it unless Bob knows better, you just have to find 1940 heads,  real easy in your country.
Steve

[Warren Rauch]

   The heads you have were most likely bored out. But there is a possibility that the right one is from a 37-38 Lasalle or 38 series 75, they did have those casting numbers and 14 mm plugs. The left head  only had 346 670 (42 book or is this a replacement part allready). The  meaning of the numbers is engine cubic inches followed by compression ratio.  The compression ratio was changed to 7.25:1 in 1941 thru 1948 on all engines ( they reduced the gap from the piston to top of the compession chamber).
   The spark plugs for 1938 were AC45 ,with optional numbers of 44 or 46. ( when engines get older it is recogmended that you use a hotter plug that will burn a little oil   ie. replace a 45 with a 46 or higher ( AC# 41 thru 49 are same plugs with different heat ranges) Since a higher heat range is accomplished by extending the electrode further into the compression chamber ( closer to the top of the piston) you don't want to go any hotter that is needed.
   Since you have mismatched  parts I would be very careful . Maybe  rotate one piston to top dead center and measure the clearance before trying a plug. They did used ("R") resistor plugs for cars with radios in1938,so that should be alright. THe "S" on the end of the number may have to do with how the plug seats on the head. Some have a tappered surface, you will need a flat surface and a gasket to fit your head. The plug gap in 1938 was .025 -.027 " Warren

[Steve Passmore]

Thats interesting what you say about compression ratios Warren, I had believed this for many years as the reason that Cadillac was able to up the BHP however, I now own engines from 1936, 37, 39, 43 (wartime) 46 and 47 and I have tested each and every one with a vernier looking for the higher compression ratio and all heads are identical measurements top of compression chamber to piston, so how were these higher ratios attained?
Steve

[Warren Rauch]

 I have always thought the heads were used to change the compression ratio as well. They used compression ratios of 7.25 on all the 43,46 and 47. But the older engines should be 6.70 for series 75  and 6.25 for   most v8 's and LaSalle 36, 37 and 39.I don't know where you are from,but one of your posts implies it isn't the USA.  If your gas would have been low in octane, they sold a shim  part# 1421930 to go on with the head gasket . This lowered the compression ratio so the engines could use lower octane gas.Warren

[Steve Passmore]

Gas octane would not have been an issue with the head shims in relation to ratio Warran as all my engines except one I have brought over from the USA myself, the odd one came from a car sold new here in England in 1939 and the combustion chamber is the same anyway.
Steve

[Doug Houston]

Cadillac used LaSalle heads on the 75 series cars, and probably the 70 and the 72. This gave the engines a slightly higher compression ratio. So, the heads on the 40-72 could have had the 322 Cu. In notations on nthem. The '41 heads would have had: 346-725 on them. Those  heads were used across the board through '48.

I'd recommend that you try to get a couple of '41-48 heads, put them on the car, and drive away contented. You already have a postwar block on the car, which is still a correct original engine, so if you can find a couple of heads for it, go for them. The big thing against 10 MM plugs is that they're delicate, and you can break them off at the cylinder head without trying.

The reason that the 10 MM plugs were used on Cadillac, Packard, Chevrolet and Buick (that I know for sure) was that the plugs could cool better, the gap being closer to the mass of the head. It worked well on everything but Buick.It was one of their major disasters in 1941, along with the compound carburetion. Buick service published a procedure for drilling out the plug holes, re-tapping them for 14 MM plugs. In the Buicks, the 10 MM plugs cooled too well, and fouled right and left. There was no other way out than opening up the plug holes.

I have a service head on my '41 Chevrolet, that has 14 MM plugs on it. The original head had 10 MM plugs. Nobody ever had trouble, but Buick, and did they ever!

[jbento]

Thanks all!

It seems my heading might be a bit incorrect.  So let me understand what I have heard so far:

1) these are likely the original heads ('40 block), but drilled out (as was relatively common at the time).
2) The heads will work on the '46 block.

I have no desire to change these heads if they work.  If all I need to do is find the correct 14mm plug that will work, I am good with that.

Is there a compelling reason I would need/want to switch heads?

And what is the "Best" plug I would want to use given the set up I currently have?

Lastly, I am still a bit confussed about the numbers.  Let me be clear, the numbers are on BOTH heads, going from left to right, in a single line, spaced much like I have typed below

                          322 625              346  670

So what do these mean?

[harry s]

Joe, Those numbers indicate the compression ratio if that head is used on a 322 cubic inch engine or a 346 cubic inch engine.

[Steve Passmore]

Do you mean Joe that you have ALL these numbers on BOTH heads???   That would be confusing.                               
Steve

[Otto Skorzeny]

Where's the confusion, Steve? I think harry s has it right.

[Steve Passmore]

Hi Otto
How can the compression ratio change just by fitting the head to a different engine?? as far as I know all pistons are flat and stop level with the top of the block, or is that different on La Salle, never had a 322 engine apart.
Steve

[Otto Skorzeny]

The 322 and 346 obviously have different bores and strokes. I would assume that the two different engines had different compression ratios. I think the numbers just inform the mechanic that the head is correct for both a 346 w/ 6.7:1  and  a 322 w/ 6.35:1

I don't think he meant that it would alter the compression ratio just that those are the stats of the engine the heads will fit.

[Steve Passmore]

Then we are back to the same question Otto, how is a different ratio attained if not through the head differences? Warren and Doug both think the heads change the ratios.  Bore and stoke would have no affect on this, it must be the cubic dimension of the gap that's left after top dead centre surly??  Does the La Salle have a dished piston perhaps giving that lower reading?
Steve

[harry s]

The difference in the compression ratio of the two engines is due to the bore difference. The larger bore in the 346 compresses a greater volume of air into the same amount of space in the combustion chamber. The stroke is the same on both engines.

[Warren Rauch]

 There is no problem having 2 compression ratios with the same heads.The Lasalle has a smaller bore than the Cadillac, but they both use the same rods(so the stroke is the same).  The volume compressed by the piston varies (346/8 -322/8 =3.0 cubic inches). Since the volume in the head cavity remains the same , A smaller amount of gas compressed into it will result in a smaller compression ratio.
 This does not explain how the 41 up engines have a higher compression ratio.The claim that the cavity in the head is the same as the older engines must be wrong. If the thickness of the cavity is indeed unchanged , then the cavity must be shrunk some other way. Warren

[Brad Ipsen CLC #737]

This is a little off subject but another very interesting fact is the LaSalle piston weighs the same as the Cadillac pistion even though the piston is smaller by 1/8 inch.  Cadillac made the wrist pin in the LaSalle piston heavier so both wrist pin/piston assembles weigh the same.  This then made the crankshaft balance weights exactly the same between the two engines and are interchangable.

[Steve Passmore]

There is no problem having 2 compression ratios with the same heads.The Lasalle has a smaller bore than the Cadillac, but they both use the same rods(so the stroke is the same).  The volume compressed by the piston varies (346/8 -322/8 =3.0 cubic inches). Since the volume in the head cavity remains the same , A smaller amount of gas compressed into it will result in a smaller compression ratio.
 This does not explain how the 41 up engines have a higher compression ratio.The claim that the cavity in the head is the same as the older engines must be wrong. If the thickness of the cavity is indeed unchanged , then the cavity must be shrunk some other way. Warren

This does not explain also what Doug said, that the La Salle head was used on 75 series cars to gain a higher compression ratio.