Author Topic: 302 head rebuild  (Read 3942 times)

GaryL

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302 head rebuild
« on: November 20, 2005, 06:54:14 PM »
The heads are off due to excessive guide clearance on my new 200 mile rebuild (don't ask). I want to make sure they are excactly right this time. The valves and springs are originals. What should I replace these two items with for a stock rebuild. Just go with GM replacements? This is not a race car, just a cruiser. Thanks.
Gary

Lemans Blue X33. DZ, M20, manual steering. Only BU code rear end is original.

JohnZ

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Re: 302 head rebuild
« Reply #1 on: November 21, 2005, 05:03:47 PM »
Assuming you're having new guides installed, your existing valves may be reusable if the stems don't show any wear and show proper guide clearance; if the stems are worn, aftermarket valves may be less costly than GM valves - I don't have those prices handy. The springs are still available from GM - P/N 3911068; they list for $6.70 each, jobber price $5.05, dealer cost $3.84. These springs are 80# closed and 200# open @ 1.25", and are correct for your car - you DON'T need any of the high-pressure aftermarket springs; all GM production solid-lifter small-block cams used the same grocery-getter springs as hydraulic cams did.  :)
'69 Z/28
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GaryL

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Re: 302 head rebuild
« Reply #2 on: November 21, 2005, 09:48:13 PM »
Are the -142 springs OK? they ARE $3.95 EA.
Gary

Lemans Blue X33. DZ, M20, manual steering. Only BU code rear end is original.

JohnZ

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Re: 302 head rebuild
« Reply #3 on: November 22, 2005, 03:40:28 PM »
I wouldn't use them - the -142 springs were designed for use with the -140 "First-Design Off-Road" cam (the over-the-counter race cam for the Trans-Am Camaros), are higher pressure and .040" larger in diameter; they were never installed in any production engine. The 3911068 springs are the correct ones for your application, and are bulletproof.
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GaryL

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Re: 302 head rebuild
« Reply #4 on: November 22, 2005, 10:53:01 PM »
Thanks for the straight scoop John!
Gary

Lemans Blue X33. DZ, M20, manual steering. Only BU code rear end is original.

lynnbilodeau

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Re: 302 head rebuild
« Reply #5 on: July 04, 2012, 08:32:50 PM »
Resurrecting an old thread, but.... the 3911068 spring is still available.  Did the assy line springs on the 69 Z/28 have a white stripe painted down one side?

Fuzzy memories.....

lynnbilodeau

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Re: 302 head rebuild
« Reply #6 on: July 05, 2012, 12:18:12 AM »
Still a litlle confused.  Car Craft Dec. 69 article on how to Z/28 your 283 Chevy states the correct part number for the 302 valve springs was 3735381, also still available.   I know that magazine guys got a lot of facts incorrect.  Which spring is correct?   Anyone know the difference between the two? 

JohnZ

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Re: 302 head rebuild
« Reply #7 on: July 06, 2012, 04:05:28 PM »
Still a litlle confused.  Car Craft Dec. 69 article on how to Z/28 your 283 Chevy states the correct part number for the 302 valve springs was 3735381, also still available.   I know that magazine guys got a lot of facts incorrect.  Which spring is correct?   Anyone know the difference between the two? 

I don't recall the stripe color, but the GM #3911068 spring is EXACTLY the same as the Federal-Mogul/Speed-Pro #VS-677 spring (F-M makes them for GM); the F-M spring is about half the price of the GM spring, for the same identical part.
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lynnbilodeau

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Re: 302 head rebuild
« Reply #8 on: July 09, 2012, 10:41:28 PM »
Thanks John.  Would you be comfortable running that spring with the Comp cams replacement cam that Jerry recommends for 302's?
Very close specs to the old 30 30 cam.

Car would not likely see over 6500 rpm and will have  a rev limiter set at 7000, just to be safe. 

JohnZ

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Re: 302 head rebuild
« Reply #9 on: July 10, 2012, 02:35:38 PM »
Thanks John.  Would you be comfortable running that spring with the Comp cams replacement cam that Jerry recommends for 302's?
Very close specs to the old 30 30 cam.

Car would not likely see over 6500 rpm and will have  a rev limiter set at 7000, just to be safe. 

You should ask Jerry - I'm not familiar with that cam; the only aftermarket "blueprint" cam I know of that's EXACTLY the same as the factory "30-30" cam is the Federal-Mogul/Speed-Pro #CS-118R (cam only) or #KC-118R (cam with lifters). GMPP also used to have a "30-30" cam & lifter kit (GM P/N 12364052) that was made for GM by Crane, and the cam only was Crane #967251.

The original GM cam had "soft-touch" lobe profiles which allowed use of the stock #3911068 springs, but most aftermarket versions were "improved" and required stronger springs, and they closed the intake valve earlier than the GM cam in the quest for more power, which made them more prone to detonation with the stock 11:1 static compression ratio.
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68Zproject

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Re: 302 head rebuild
« Reply #10 on: July 11, 2012, 06:52:28 PM »
The original GM cam had "soft-touch" lobe profiles which allowed use of the stock #3911068 springs, but most aftermarket versions were "improved" and required stronger springs, and they closed the intake valve earlier than the GM cam in the quest for more power, which made them more prone to detonation with the stock 11:1 static compression ratio.

I can vouch for that.
68Z28