1970

[bcroe]

Check numbers on your car and the engine.  My research says
68-69 blocks were all 472, in 70 all blocks went to a new number
which could support either a 472cu in RWD or 500 Eldo engine. 
The Eldo got the extra inches with a longer stroke crank.  I
believe both used the same number head.  Bruce Roe

[Roman Z]

Bruce, your right. The block cast number is 1495200. Could be either. Research says to check second journal on crank for cast number as well as measuring the stroke.
Thanks again Bruce, your a true professional.

[Roman Z]

Hello Bruce. I've done the research
Block:  1495200
Head:  1602493
Crank: 1496793
Makes it a 1974 500.
The EGR valve should have been a clue I guess.

[bcroe]

Hello Bruce. I've done the research
Block:  1495200
Head:  1602493
Crank: 1496793
Makes it a 1974 500.
The EGR valve should have been a clue I guess.

My understanding is, all 500s have the same block and crank,
variations are in the heads, pistons, and cam.  So is a regular
burning 74 useful, against a best premium burning 70 472? 
What is the head on your 70 472?  Bruce Roe

[Roman Z]

Bruce I don't have my old motor apart yet. I'll get the numbers as soon as I can

[Roman Z]

I'm wondering if I can use the crank out of the 500 in my 472? Will I have the clearance to the valves?

[bcroe]

I'm wondering if I can use the crank out of the 500 in my 472? Will I have the clearance to the valves? 

A 500 version of your engine, same block, was built for the Eldo
starting in 70.  Probably the 472 could be converted to a 500 by
changing to the other crank, rods, and perhaps pistons.  The
outfits that build these engines should have all the details.  I do
know head and piston designs vary so much, you cannot very
freely swap the combinations.  Bruce Roe

[The Tassie Devil(le)]

You do have to change the pistons as the Gudgeon Pin height is different to allow for the extra stroke.

Bruce.

[2manycars]

I'm wondering if I can use the crank out of the 500 in my 472? Will I have the clearance to the valves?

If the 472 and 500 heads were the same in 1970, you can do it, assuming they used the same block. You would need the 500 connecting rods, and pistons, IF the pistons  differ. You need rods and a crank anyway.

[The Tassie Devil(le)]

The 500 Connecting Rods are the same.

Bruce.

[Roman Z]

I know the bore is different by 0.244" So pistons are needed. I'm curious about the heads. Will the piston clear? My heads are 76 and the donor motor is 120.

[The Tassie Devil(le)]

The pistons will not foul the heads, but using flat top 1970 500 pistons in a 76cc head will yield over 10 to 1 compression.   Which is not good for todays' fuel.

I have '70 500 pistons in my '72 Eldo 500 with the higher compression, but I am using Water Injection to control the pre-ignition.

Bruce.

[bcroe]

I know the bore is different by 0.244" So pistons are needed. I'm curious about the heads. Will the piston clear? My heads are 76 and the donor motor is 120. 

My book by Doc Frohmader states all 472s and 500s have a bore
of 4.30in.  Stroke of a 472 is 4.060in, 500 is 4.304in. 

The 500 crank has a longer stroke, so either the pistons or the rods
would have to be different from a 472. 

Bruce Roe

[The Tassie Devil(le)]

The Pistons have differing height of the Gudgeon Pins.   That is that in the 500, the Gudgeon Pins are set higher up in the piston.

Bruce.

[Roman Z]

I'm thoroughly confused. I'm starting over. I have a 1970 Cadillac 472. I purchased a 1974 500. If I take the heads from my old 472 and put them on the 500, why wouldn't that work?
1970 472 heads:
1486250
1497902
1495950

1970 500 heads:
1486250
1497902
1495950
They have the same part numbers.
It was mentioned that if I put my 76cc heads on the newer 500 the compression ratio would be higher than 10:5.1
why would that be?

[bcroe]

All those heads will bolt on.  The problem is that Cad used several
combinations of piston tops and heads to lower the compression from
1970 to 1974.  If you put together a poor combination, the result can
be a ridiculous (high or low) compression ratio.  But I am not the
expert on such things. 

What shape are your 74 heads in? 
Bruce Roe

[The Tassie Devil(le)]

It was mentioned that if I put my 76cc heads on the newer 500 the compression ratio would be higher than 10:5.1    why would that be?   

The later engines used pistons with flat tops, whereas the '71 to '73 ones, used pistons with really deep dishes.

To get the engines to immediately comply with the requirements of the fuel that was to be used after 1970, the makers used the deep-dished pistons from '71, immediately dropped the compression.   Hence it was cheaper to do that than make new cylinder heads as well.

They must have found that the use of these deep dish pistons were not ideal, and that flat-top ones would be better, but to retain the low compression required for the available fuel (Unleaded) redesigned the cylinder heads to be larger.

Bruce.

PS.   I also found out that mixing the heads does not work, as I couldn't get a '71 engine to run right, only to find out that someone has put a '74 head on one side, and the '71 head on the other side.   The car was an import from USA in the 2000's, and the swap had to have been done before it left USA.   This meant that one side was 8.5 to 1, and the other side was something like 6.5 to 1.    Now I have a totally reconditioned 120cc head for sale.

[Roman Z]

Bruce, I don't know the condition of the heads yet. Now I'm wondering which pistons are in the 1970 472. I'll find out this weekend when I tear down the 472.  Maybe there's a combination there to salvage my project.

[The Tassie Devil(le)]

Here is the difference between the 1975 pistons. First picture (Flat-top)  And the Forth picture, the 1972 pistons, (Deep Dish), and the second and third two pictures are of the '71 head, and the '75 head (Combustion Chambers)

Notice the huge volume of the '72 pistons.   

I don't have a picture of the '70 engine parts, but I believe they are like the last picture which I am running in my '72.

Bruce.

PS.   I am tipping the 472 will be similar.

PPS.   My '72 head has larger valves fitted, plus has been planed which is why the valves look different between the two.

PPPS.   To the Members that saw the initial post, I had the wrong picture, so I had to change things around, including the text.

[TJ Hopland]

Do we know we have a head problem?   These engine rarely have head issues other than the umbrella seals falling apart and a carbon/goo build up on the intake valves.   Many times the bottom ends are still good too.   You do see cam and rocker issues but other than that these things tend to hold up pretty well.


74 472 pistons were a true flat top but that was the only year and model.   The other pistons that that went with the 120cc 74-76 heads did have a typical slight dish like in Bruce's photo. 

We assume the massive dish pistons as the 'fix' for the low compression mandate of 71 was because Cadillac assumed and hoped that it was just a temporary limit that would be lifted sooner than later so they didn't want to invest in a new head design.    At one time someone did explain to me why that big a dish is a bad thing and pointed out that no one else ever did it but I didn't understand it then and have forgot it now.   Has to do with flame fronts and turbulence.

From memory if you use the 68-73 76cc heads with the fairly flat pistons you end up around 13:1 which you pretty much need some kind of alcohol to run.   I do remember people trying the 425's 96cc heads with those pistons and having trouble even when running 'race' gas.