1970 472 ci engine heads

[Philippe M. Ruel]

A friend of mine has a 1970 De Ville convertible, with a 472 engine. A head gasket has blown, and it appears that heads are warped and gasket contact surface has become rough.

The question is, what is factory head height, and how much may be grinded from there ? He doesn't have a shop manual, and I cannot find these specifications in my Chilton's auto repair manuals.

Thank you

[bill henry]

well i dont know the original cc of the heads you can cut off whatever it takes to clean up as long as you then cut the intake manifold . this will also raise your compression ratio . your machinist will know how to do it

[TJ Hopland]

I dont have a number for you but I have never heard of anyone having a problem doing a normal clean up on any of the big cad heads.  Problems could be if it has been done before or several times before.  These motors were not known for head gasket problems so you would have to wonder if there is somethig wrong that caused this. Any idea if it has been apart before?

The 68-73 472/500's would have come with the 'small' 76cc chamber heads.  68-70's were 'high' 10.25 or 10.5 :1, Im thinking the early ones were 10.5 and the 70 was 10.25 but I could be wrong.  In 71 Gm made em drop to 8.5:1 so they did it with some huge dishes in the pistons.  In 74 they gave up and designed new heads with a 'large' 120cc chamber to work with more standard looking flatter pistons.  The 74 472 had true flat top pistons.  If his 70 doesnt have the smog rails cast into the head they may be worth a few extra bucks to some of the hardcore performance guys because they are a couple of pounds lighter than the other heads and without the smog rail they have a bit more metal in them in critical areas for serious porting.  In a fairly stock engine the only thing to worry about is the chamber size so you get the compression you are going for.  There are casting numbers in the center of the head on the top near the valve springs.  Ending 250 & 902 are the common 76cc. 950 are the non smog 76's.   493 and 552 are the later 120's.

[Brett]

I always think what I will do if my engine blows in my 71 Fleetwood so this is good information. Does this mean that the best (read most powerful, highest compression) 472/500s in stock form are from 1970 model year? And 472/500 heads are interchangeable?
If that is the case...RockAuto has the 950 casting heads for $218 plus a $45 core (surely cheaper than sending old ones back) remanufactured by Marshall.  It is part H2446
'cast 950, 902 with air'

I would post a link but (I am not familiar with web terminology ) Rockauto is in 'real time' so you need to scroll through....check it out for yourselves and please let me know what you think...

I could obtain a Marshall part # G5000C which is a reman 500 specd for a 70 Eldorado, it says Block 200,300, 238 and Head #950, 902 Valley Pan Gasket Not supplied with engine...


what do you think of this? What does 902 mean? what are the block 200,300, 238 casting numbers?

[TJ Hopland]

The 472 & 500 heads are the same except for cc's which changed in 74 and subtle changes like the smog rail.  The 425 and 368 heads will bolt on but there are minor issues that need to be dealt with and some question if the ports are large enough to breathe properly on the larger motors (472/500).  The differnce between a 472 and 500 are crank and pistons otherwise they are the same.  The 68&9 blocks need some minor work to clear the 500 crank and have minor oil problems for extreme performance applications. From the factory the 70 eldo 500 had the most torque and HP.  The 68-69-70 472's were close.  In 71 GM made em drop the compression so the 500 became more like the earlier 472's. Unless you are going for a 600+ horse motor (which would easily cost $5K) there is no reason you need to start with a '70. If you find a 70 you could sell or trade it to some hardcore person that needs it, you may even get lucky and they will trade you some recently rebuilt stuff. If you are going to rebuild one the more common pistons will give you high compression with the earlier 76cc heads and low compression with the later 120cc heads. The large dished factory pistons are getting harder to find which is what you need to make low compression with the early heads.    The cam and timing is where most of the power went over the years, the rest of the changes dont amount to much for fairly stock applications.  Any of the big motors rebuilt with an updated cam and some tweaks to the ignition system will give you more than enough power to move a caddy around and smoke the tires if you want to.  If you want more power just get out your wallet and there are vendors that will give you as much power as you can afford.  I just rebuilt a motor for my 73 eldo.  I picked up a used set of large chamber heads cheaper than it would have cost me to find the stock pistons becuase I wanted a low compression motor so I didnt have to worry about finding (and payin) for high octane gas.  My old tired motor could smoke the tires so I didnt think I would need any more power.

[Philippe M. Ruel]

Thanks for the information. This 472 has flat pistons (not "dished") so I guess it is the factory engine of this 1970 car.

The problem is, the heads have already been ground in the past, and my friend doesn't know how much can be ground again before pistons meet valves, or he needs to use 108 or so octane fuel because of a too high compression ratio.

Second-hand heads for these engines are not too easy to find here in Europe, whether small or large chambers, and shipping cost from the USA for such heavy parts is unaffordable, compared to the value of this particular "running-as-is" car.

[The Tassie Devil(le)]

G'day Philippe,

The best way, and the only way to see how much material has been removed from the Head Surface is to check the Combustion Chamber size against the Original Specifications, by "cc'ing" each chamber.

If the heads have only been surfaced via normal "cleaning-up" processes performed during basic reconditioning, then I don't think you will have much to worry about.

If you still aren't sure whether the Pistons will clear the heads, then simply measure the distance between the piston at Top Dead Centre "TDC" and the surface of the Block.   If there is a Positive measurement there, then in no way will the piston hit the head, no matter how many thousands of revolutions the crankshaft is doing.

If you are concerned about valve to piston clearance, all you need to do is put a couple of blobs of plasticine on the Piston top of one piston, below where the valves might hit, wipe some grease on the bottoms of the valves and then put on the head, pushrods and valve gear for that one cylinder, give it two rotations of the crankshaft by hand, and then remove the head and measure the thickness of the plasticine that is still stuck to the piston top.   Greasing one side will allow the Plasticine to stay stuck to the Piston so you can tell which piece is which if they come loose.

Plus, a '70 engine will require the premium'est fuel that you can get for it.


Bruce.

[bill henry]

if your engine has true flat top pistons it is a 74 the 70 model had a peanut shaped valve relief in the top of the piston.also if the heads you have were only ground i would not worry because you cannot remove much stock like that. heads are usually cut on a mill if they need more than a few thousands of an inch to clean up

[Philippe M. Ruel]

The shop guy finally estimated he has to grind about 8/100 mm (3 thousandths inch) from the warped heads, which is not soooo much.

The exhaust manifold looked more like a banana, he will remove 3/10 mm (1 hundredth inch) from the heads, exhaust side, and 1.8 mm (7 hundredths inch, yes you read it) from one of the manifolds. Now my friend knows why he burned so many exhaust manifold gaskets, they were barely held between manifold and head.

Thanks for your answers and advice.

[bill henry]

philippe after you have your exhaust manifolds planed you do not need to and should not use an exhaust gasket . the 472 never came with them from the factory and the are mainly used as a crutch for warped manifolds .

[35-709]

philippe after you have your exhaust manifolds planed you do not need to and should not use an exhaust gasket . the 472 never came with them from the factory and the are mainly used as a crutch for warped manifolds .

FWIW,
I am no engine expert, but not using exhaust gaskets on an overhaul or a job such as Phillipe's friend is doing goes against everything I have ever been told by those who ARE engine experts.  There is really no reason NOT to use them.

[bill henry]

well you may be right but in my own experiance with both caddys and chevys unless you tighten the cast iron manifold up perfectly  and evenly the gasket will blow out in short order or you will crack the manifold  and if your machine work is done right it should seal perfectly with no gasket just like it did from the factory.but hey thats just me i have a hard time keeping header gaskets from blowing out!

[TJ Hopland]

My 2 cents on the exhaust topic.  I have not tried gaskets on a fresh machined head and manifold so I dont know how long they last or dont last.  On the fresh machined stuff I have put them together without a gasket and not had any problems.

[Glen]

Torque on the exhaust manifold bolts is important.  The manifolds are designed to slide on the head as they expand and contract as their temperature changes.  I believe the torque is 35 lb/ft.  If they are torqued too high they are then pinned to the head and could crack from the heat. 

I also recommend using a high temp anti seize on the mating surfaces and the bolts.