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462624 head #

 
h_friesen
V-6 Camaros rule!
Posts: 51
Joined: 11/08
Posted: 01/22/09 04:46 PM

hey guys i just bought a set of heads with the casting number 462624, seller swears up and down they arent cracked not sure what too make of this... any help?  

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Pontiacman2
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Posts: 8956
Joined: 09/08
Posted: 01/23/09 02:09 PM

explain are you having trouble with the heads or what.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

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chevman24
I have an SS396 tatoo
Posts: 430
Joined: 08/08
Posted: 01/23/09 03:07 PM

You got ripped off.Those are crack prone heads. They were used 76-87 with 1.94/1.50 or 2.02/1.60 size valves with 76 cc chambers.  

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h_friesen
V-6 Camaros rule!
Posts: 51
Joined: 11/08
Posted: 01/23/09 06:10 PM

i see  the exhaust ports are right next too each other and its a lightweight casting making them crack prone or what?  

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chevman24
I have an SS396 tatoo
Posts: 430
Joined: 08/08
Posted: 01/24/09 03:45 PM

On all small block chevy heads the 3,5 and 4,6 exhaust ports are next to each other. With exception to the LS series engines. So thats not the cause. Its not specific in the booklet as to why these are weak castings but i would assume it would have something to do with the casting process or the iron they used to cast them with. If you used them in normal operating engines they would probobly be fine just not in a race or high performance car.  

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BigChevyFTW
I love my Chevy Chevette!
Posts: 18
Joined: 06/11
Posted: 10/15/11 07:58 PM

just to explain why these heads are prone to cracking on the exhaust seat is because, "they have heat crossovers in the exhaust ports' add in that extra heat and thin casting and crack-ola! however, if you have a set that is not cracked and is a used set, think of it this was. they're now stronger then before because they have went thru alot of heat cycles. there is a company out there that uses these same heads on 383 engines that put out 375 hp  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/15/11 09:15 PM

it really critical with these and almost every other head and engine .. to run a proper temp thermostat..

why...

the heads are longer than they are wide... they expand length wise... when brought up from room temp to operating temp..

when they cool off after you turn off the engine.. this is one thermal cycle....


with a thermostat maintaining the in block and head temps at a mostly stable temp....


without a thermostat...   as you idle.. the temp builds up to the high end of the temp range...   when you are starting to drive.. the ram air through the radiator cools the engine off..  under high loads or at high speeds..  the engine again starts building heat as the coolant flow through the cooling system is so fast.. the ram air thought the radiator does not stay there long enough to loose heat.. so you have a runaway cooling system...

all this temp fluctuation expands and contracts the head many more times than normal...


~~~~~~~~~~~~~~~

there is also the inner block pressure created by the water pump trying to force water through the much too small bypass when the thermostat is installed properly.. ... this raises the in block and in head coolant pressure

one pound of additional pressure increases the boiling point of coolant 3F...  this keeps the HOT spots where the castings are exposed to exhaust and combustion temps from boiling the coolant away like streams of bubbles from hot spots in the bottom of a sauce pan boiling water on a stove..

so.. having a properly   spec'd thermostat..   50 % to 70 % coolant to water blend..  and a 13 or 16 pound radiator cap that actually does hold pressure...  


one last thing..  the vacuum operated  trap door in the right hand exhaust..    its spring loaded in the closed position..

no vacuum.. trap door closed...  exhaust is diverted through the crossover increasing the heat and causing expansion where it was not designed to be..

the trap door is vacuum controlled..  the ported vacuum switches usually allow the trap door to get full manifold vacuum when the coolant temp reaches 105F..   thats luke warm..    many use a thermal vacuum switch in the side of the air cleaner .. that nobody ever hooks back up properly...   all of these will cause the trap door in the exhaust to stay close and melt things like the carb base gaskets..  

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tuffnuff
Moderator
Posts: 7841
Joined: 12/09
Posted: 10/15/11 11:26 PM

Icon QuoteBigChevyFTW:
just to explain why these heads are prone to cracking on the exhaust seat is because, "they have heat crossovers in the exhaust ports' add in that extra heat and thin casting and crack-ola! however, if you have a set that is not cracked and is a used set, think of it this was. they're now stronger then before because they have went thru alot of heat cycles. there is a company out there that uses these same heads on 383 engines that put out 375 hp

The 624 is a light weight version of the 882 head.,. one of the worst that GM produced and not intended for high performance use.
There are better heads out there.

Headgide1

Key Cast Marks Cast Nos. Description

A Rectangle 460 ‘55 & up 265/283 low comp (8:1) 1.72/1.50 valves

B Narrow triangle over rectangle 520, 896 ‘58 & up 283 PowerPak/’57-’60 Fuel Inj.,9.25:1 CR, 1.72/1.50 valves, 59cc chamber; could be good replacement on late 305 but no accessory bosses.

C Vertical bar over rectangle 997 ‘57 Corvette 270HP, 9.5:1 CR, chamber similar to PowerPak but with sharp corners in plug shroud area

D 2 vert bars over rect 997 ‘56 Corvette 2X4 bbl, 283; ‘58 pass car FI; chamber same as ‘57 270HP Corvette

E, F Large “camel humps” 291, 461, 461X, 462 Original hi-perf or “fuelie” heads; chamber sizes are 62-64cc; both 1.94/1.50 & 2.02/1.60 valve versions available; 291 on 327’s thr ‘68; 291 have temp sender hole; 462 don't

G Left-facing right triangle 041 ‘69-’70 350/300HP, accessory bolt holes, most have 1.94/1.50 valves

H Small “camel humps” 186, 492 Later hi-perf or “fuelie” heads, some 186 (‘69 & later) & all 492 have accessory bolt holes; 1.94/1.50 or 2.02/1.60 valves; 64cc chambers; ‘70 LT1/Z28 use 492; avail as PN3987376

I Large triangle over rectangle (“crown”) 882 Large chamber (76cc), hardened exhaust valve seats, compromised intake port(‘71-’76 350/400cid), best of lightweight heads

J NONE 113 ‘86-’90 Corvette/ present 350-HO aluminum, no exhaust heat, 58cc chamber, 1.94/1.50 valves, centerbolt valve covers; good street head, ‘88-on have raised D ex port, 3/8 screw-in studs

K 3 right-facing “stairs” (“bench” on intake runner) 487 ‘71-’76 76cc, best large-chamber head; 1.94/1.50 & 2.02/1.60 valves available; latter machined for screw-in studs & guideplates

L Right-facing “bench” 993 Common big-chamber head, not a lightweight casting; sim to 487; may have steam holes

M One triangle 882 Alternative marking for 882; see I, above

N 2 triangles 624 Late-model lightweight casting version of 882

O “Saddle” and vertical bar 416 Late-model 305, conventional valve covers, intake port not restricted; lightweight; 57cc chamb

P Double (Captain’s) bars 193 Mid-’80’s style centerbolt cover with restrictive vane cast in intake port (hi-swirl); not recommended for high-performance applications.

Top Ten Production Chevy SB Cylinder Heads

No’s 1-6 are small-chamber, hi-comp and must have dished pistons to get comp below 10.5:1. No’s 1-7 have nonhardened exhaust valve seats which must be replaced for use with unleaded fuel.

No’s 1-6 are small-chamber, hi-comp and must have dished pistons to get comp below 10.5:1. No’s 1-7 have nonhardened exhaust valve seats which must be replaced for use with unleaded fuel.

Rank Cast # Good Points Bad Points

1 3782461X Hi comp (57.5cc), best ports of any OEM production cast-iron head, intake runner vol 170-180cc No accessory bolt holes, rare, likely to be cracked, 2.02/1.60 versions very rare

2 3991492 ‘70 hi-comp (61.2cc), good ports, acc bolt holes, 2.02/1.60 valve versions have screw-in studs & gplates Close proximity of water jacket to spring pocket on 492s cast prior to 1972 req special seat cutter if using larger springs

3 3890462 Ports similar to 461, but better comb chamber shape More common than 461-461X, but still rare; no acc bolt holes

4 3782461 Similar to 461X but with smaller intake ports Rare, probably cracked, no acc bolt holes

5 3927186 ‘64-’70, av chamb vol 64cc, ‘69-’70 have acc bolt holes Rare, valvespring seats close to water jackets

6 3947041 ‘69 350/300 HP, good chamb (similar to 462), acc bolt holes Very rare, valvespring seats close to water jacket

7 3932441 ‘69-’70, large chambers (73cc), some have steam holes for 400 blocks, ports decent, accessory bolt holes No 2.02/1.60 valve versions from factory

8 3973487 ‘71, 76cc, like 441 but better chamb, hard seats, acc bolt holes Big chamb needs domed pistons to get hi-comp

9 3998993 ‘71-’76 US/ ‘85-’88 Mexico, similar to 487, widely available Big chamb needs domed pistons to get hi-comp

10 332882 ‘71-’76, 350/400, big chamb, acc bolt holes, hard seats Changed intake ports, become worse, BEST of the worst

11 462624 ‘76-’78, 305, 58cc chamb, 1.84/1.50 valves, hardened seats, accessory bolt holes, best of the 305 heads 1.84/1.50 valves and ports too small for large cid; accepts 1.94/1.60 valves & seats

Casting no’s. & Date codes are cast on top of head (under valve cover) between second & third rocker arms from left.
First letter (A through M) is month (Jan through Dec)(I not used), one or two digits for day of month, one digit for last digit of year cast.
Lightweight castings (not for hi-perf use) have “scalloped” edge below exhaust ports; regular have straight edge.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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tuffnuff
Moderator
Posts: 7841
Joined: 12/09
Posted: 10/15/11 11:41 PM

I just noticed.,. this thread is almost 3 years old.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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tuffnuff
Moderator
Posts: 7841
Joined: 12/09
Posted: 10/16/11 12:29 AM

Icon Quoteh_friesen:
i see  the exhaust ports are right next too each other and its a lightweight casting making them crack prone or what?

All Gen1 SB's have the center exhaust ports side by side.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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Pontiacman2
Moderator
Posts: 8956
Joined: 09/08
Posted: 10/16/11 09:56 AM

Icon Quotetuffnuff:
I just noticed.,. this thread is almost 3 years old.

Smile


+1 That happens from time to time someone revives a old dead thread. Grin  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

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jat70
I love my Chevy Chevette!
Posts: 1
Joined: 12/11
Posted: 12/07/11 02:46 PM

I’m glad this was revived, as I was just offered a set of 624’s.  I imagine I would be forgiven for hijacking this thread, given it’s age.  Wink  My car had 3970126’s and apparently they’re no good.  I was quoted $300 to rebuild prior to discovering this. The machine shop, in trying to get the car running again inexpensively, offered me a set of 624’s, freshened up, for the same $300.  I don’t race the car or run it hard.  It’s a sbc car that I take to car shows/cruise nights.  I’m told if I don’t overheat it, these heads will be fine, and it seems I can’t beat the cost.  Is it a mistake, even at $300, if I’m just trying to get 4-5 years of summer driving out of it?  My thought is maybe get another shop to look at my 126’s at some point.  

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Ravoll
I love my Chevy Chevette!
Posts: 2
Joined: 01/12
Posted: 01/01/12 03:16 AM

Me Too,

First an introduction cause I'm new to this forum.
Name: Alan
Age: 46
I'm Ex-Military (U.S. ARMY),born and raised in South Texas,currently residing in Germany.

Have a 1979 Corvette with cracked 462624's.Just bought a brand new pair that were taking off a crate engine (Hecho Mexico models).
Bought em  before I read that these are crack prone.I noticed that these new heads have pressed in exhaust seats rather than the typical "ground in to the casting" setup.Will they still be prone to cracking,or is this a modern fix?
Will be running a mild cam with 105lbs of seat pressure.  
The older I get,the faster I was.

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BuzzLOL
I have an SS396 tatoo
Posts: 380
Joined: 12/10
Posted: 01/07/12 05:50 PM

.. The heads should last indefinitely if whenever you get a cooling system leak, you stop driving the car and get it fixed before the engine ever overheats... GM does a grueling endurance test on all its products and they last well under normal operating conditions...

.. The hardened Stellite exhaust seats are mainly to give longer seat wear life with no lead gas than just case hardening the cast iron... the press in seats actually make the heads more crack prone because the iron around them is now thinner, but GM prolly made the iron head castings thicker in that area to compensate, and, as I said, this new design would also have to pass endurance tests... so they should last indefinitely... just shut the engine down at any sign of abnormal coolant loss and/or overheating...

.. I'm Randy, U.S.Army 1970-'71, Vietnam veteran, DaNang area... signal/communications corp... my brother served in Germany because I was already in a combat zone... Toledo, Ohio... putting a 500HP SBC 405" in '86 Monte Carlo LS... hopping up a TPI 350" in '87 GTA, 305" into '77 Pontiac Astre Formula wagon, 215" aluminum V8 into '75 MG Midget, 425HP 351W in 19' ski boat, also have an '85 Fiero...  

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Ravoll
I love my Chevy Chevette!
Posts: 2
Joined: 01/12
Posted: 01/08/12 09:33 AM

Thanks Randy,
Now I can sleep better knowing that I did'nt spend money on stuff that will be busted next week.
When I bought the Vette last year Feb.,it had just been imported from Cali.Contacted the person on the cali title.Turns out he was the original owner,and was told the motor had never been opened.As far as overheating,the raditor did leak and I ended up replacing it last summer.even leaking it never ran over 220°F in city traffic.For a 32 year old motor that was never opened,it ran great.No telling how long the heads were cracked I guess.Probably never would have noticed had I not decided to tear it down.
Anyway Thanks
Alan

P.S. :
I did notice thought that the seats for the exhaust valve springs are machined farther down than on the cracked heads.  
The older I get,the faster I was.

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