Broken Valve Spring :-(
Race Director
Joined: May 2000
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The OE cam is 214/218 @ .050", 110/120 C/Ls, 115 LSA, .27143/.28235" lobe lift. The early cam with the groove in the rear journal part number is 3883946, and the later cam without the groove (beginning in '67) is 3983960. Most replacement cams have the groove, and it's my understanding that it's okay to use a grooved cam in '67-up engines.
I don't know who makes a clone, but start with Federal Mogul, and the OE replacement valvesprings should be commonly available from the likes of Sealed Power.
As with other OE engines, but single best modification you can make is to pocket port the heads/port match the heads with multiangle valve seats and a top 30 degree cut on the valve to eliminate the unused portion of the valve seating surface, and leave everything else OE. This will retain the OE idle characteristics, low end torque, but increase top end power about 10 percent and extend the useable rev range by about 500 revs, while retaining OE fuel economy. High overlap cams are gas hogs!
Duke
I don't know who makes a clone, but start with Federal Mogul, and the OE replacement valvesprings should be commonly available from the likes of Sealed Power.
As with other OE engines, but single best modification you can make is to pocket port the heads/port match the heads with multiangle valve seats and a top 30 degree cut on the valve to eliminate the unused portion of the valve seating surface, and leave everything else OE. This will retain the OE idle characteristics, low end torque, but increase top end power about 10 percent and extend the useable rev range by about 500 revs, while retaining OE fuel economy. High overlap cams are gas hogs!
Duke
Racer
Joined: Jun 2006
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The cams fine and doesn't have too much overlap for the timing. If you like the characteristics of the cam and have been happy with it leave it in there if it ain't broke. I personally like long exhaust timing (versus the intake timing) on motors running manifolds particularly when the exhaust is being opened early like this one is. Lots of good advice above relative to checking for any issues (like spinning and moving the valve in the guide to see if it's ok. Valve springs occasionally break but if I had one break this early I'd buy a new set and replace them all.
Moderator
Joined: Jun 1999
Posts: 7,117
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From: Dove Mountain Arizona
Agree, it's not uncommon for one to break, had it happen to me twice. Just stuff a nylon/cotton rope in the plug hole until no more will go in, then rotate engine by hand until the piston jams the rope up to the valves. Remove old spring and install new. Easy to do. Drive it. 
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
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From: Florida
Thanks for all the advice.
There seems to be a variety of opinions.
Unfortunately, I have a day job, and won't be able to get to this right away.
I'll investigate this more as time permits.
I have a couple of gearhead buddies coming over to drink beer (er help me)
I'll try and gather some more info, maybe get the broken spring out, check the valve, etc.
Maybe on Wednesday, unless Ernesto hits the space coast, and I'm inside with the hatches battened down.
Maybe this weekend.
There seems to be a variety of opinions.
Unfortunately, I have a day job, and won't be able to get to this right away.
I'll investigate this more as time permits.
I have a couple of gearhead buddies coming over to drink beer (er help me)
I'll try and gather some more info, maybe get the broken spring out, check the valve, etc.
Maybe on Wednesday, unless Ernesto hits the space coast, and I'm inside with the hatches battened down.
Maybe this weekend.
Safety Car
Joined: Nov 2001
Posts: 4,424
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From: northern CA
Originally Posted by 66427-450
All you say is true, of course.....
But somehow, I don't think too many here are concerned about fuel consumption
But somehow, I don't think too many here are concerned about fuel consumption
Last edited by mrg; Aug 28, 2006 at 07:19 PM.
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Originally Posted by MasterDave
Agree, it's not uncommon for one to break, had it happen to me twice. Just stuff a nylon/cotton rope in the plug hole until no more will go in, then rotate engine by hand until the piston jams the rope up to the valves. Remove old spring and install new. Easy to do. Drive it.
I'd think it wise to make sure a valve is not trying to come open as the piston is coming up with that rope stuffed in there. Might cause other, bigger problems.
Le Mans Master
Joined: Feb 2006
Posts: 6,048
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From: "cutesy" TN
Originally Posted by dknowles67
Oh yeah, it's all numbers matching stuff.
I hate to keep harping on this but you are dealing with closed chamber big block heads. The combustion chamber is not like a small block.
If this was a open chamber NOM I would still not advise you to do this.
There is too much money involved to take short cuts that may save you 200 dollars.
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Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
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From: Florida
Update -
I got the broken spring off, and collected all the pieces.
They all match up, so there are no missing chunks in the engine.
I called the machine shop, and checked my receipts. The machine shop said that they don't necessarily replace the springs, if they check out okay. If they do replace valve springs, they would charge me for it, and it would be on the receipt. There are no valve springs on the receipt.
This car sat from 1974 to 1996 in a garage untouched.
Maybe the springs got replaced between 1967, and 1974, but definitely not since. Yet they checked out okay in 1997.
Sounds like a cam with .500" (int) and .505" (exh) lift is too much for stock GM springs anyway.
I intend to replace all the springs at a minimum.
Does anyone know, can the cam be replaced with the engine still in the car?
(When I put it together, the engine was on a stand)
I got the broken spring off, and collected all the pieces.
They all match up, so there are no missing chunks in the engine.
I called the machine shop, and checked my receipts. The machine shop said that they don't necessarily replace the springs, if they check out okay. If they do replace valve springs, they would charge me for it, and it would be on the receipt. There are no valve springs on the receipt.
This car sat from 1974 to 1996 in a garage untouched.
Maybe the springs got replaced between 1967, and 1974, but definitely not since. Yet they checked out okay in 1997.
Sounds like a cam with .500" (int) and .505" (exh) lift is too much for stock GM springs anyway.
I intend to replace all the springs at a minimum.
Does anyone know, can the cam be replaced with the engine still in the car?
(When I put it together, the engine was on a stand)
Moderator
Joined: Jun 1999
Posts: 7,117
Likes: 51
From: Dove Mountain Arizona
Originally Posted by MikeM
I'd think it wise to make sure a valve is not trying to come open as the piston is coming up with that rope stuffed in there. Might cause other, bigger problems.
Silly boy....of course one needs to back off both the rockers prior to stuffing the rope in so both valves stay shut. Thought we knew this, sorry.
Le Mans Master
Joined: Apr 2001
Posts: 9,556
Likes: 288
From: Granbury Texas
Originally Posted by dknowles67
Update -
I got the broken spring off, and collected all the pieces.
They all match up, so there are no missing chunks in the engine.
I called the machine shop, and checked my receipts. The machine shop said that they don't necessarily replace the springs, if they check out okay. If they do replace valve springs, they would charge me for it, and it would be on the receipt. There are no valve springs on the receipt.
This car sat from 1974 to 1996 in a garage untouched.
Maybe the springs got replaced between 1967, and 1974, but definitely not since. Yet they checked out okay in 1997.
Sounds like a cam with .500" (int) and .505" (exh) lift is too much for stock GM springs anyway.
I intend to replace all the springs at a minimum.
Does anyone know, can the cam be replaced with the engine still in the car?
(When I put it together, the engine was on a stand)
I got the broken spring off, and collected all the pieces.
They all match up, so there are no missing chunks in the engine.
I called the machine shop, and checked my receipts. The machine shop said that they don't necessarily replace the springs, if they check out okay. If they do replace valve springs, they would charge me for it, and it would be on the receipt. There are no valve springs on the receipt.
This car sat from 1974 to 1996 in a garage untouched.
Maybe the springs got replaced between 1967, and 1974, but definitely not since. Yet they checked out okay in 1997.
Sounds like a cam with .500" (int) and .505" (exh) lift is too much for stock GM springs anyway.
I intend to replace all the springs at a minimum.
Does anyone know, can the cam be replaced with the engine still in the car?
(When I put it together, the engine was on a stand)
Sounds like you might potentially have ORIGINAL 40 year old valve springs. As Duke mentioned, the early big block springs FAILED....regularly. I would suggest AT MINIMUM that you replace all of your valve springs with new OEM (or better) valve springs. Oh another thing.....Duke mentioned adding another 500rpm to your usable rev range, The oval port 427s have fragile cast pistons. They break when you rev to 6000 rpm regularly (redline is 6200), so don't even think of adding 500rpm with the cast pistons.
Safety Car
Joined: Mar 2002
Posts: 3,780
Likes: 442
From: Southwest MI
Originally Posted by dknowles67
....
Does anyone know, can the cam be replaced with the engine still in the car?
Does anyone know, can the cam be replaced with the engine still in the car?
I'd highly recommend buying a GM "Chassis Service Manual," and a "Chassis Overhaul Manual" for your year...... between that, and some tips from the guys here, you'll have pretty much all the info you need to service your car.
Glad to hear you're going to replace all the springs... no big deal to select some proper springs, check an intake and exh to ensure the geometry is OK, then replace them.
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
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From: Florida
Originally Posted by 63Corvette
so don't even think of adding 500rpm with the cast pistons.
(I broke 2 or 3 getting them out - pistons had rusted to the block with a 20 year sit)
I have the '67 GM Service Manual - and several other books. Not the same as real experience - but a good investment nonetheless.
I have not made a decision about the cam yet, but I'm keeping my mind open, as I research it more. I'd like to know what I'm getting into.
Le Mans Master
Joined: Apr 2005
Posts: 6,359
Likes: 428
From: Seattle Area WA
According to the Melling catalog, you need to use spring part number 46622 with a spring height of 1.88" with that cam.
OD 1.260"
ID .876"
158 lbs at 1.88"
318 lbs at 1.38"
coil bind 1.2"
6 coils
OD 1.260"
ID .876"
158 lbs at 1.88"
318 lbs at 1.38"
coil bind 1.2"
6 coils
Last edited by Scott Marzahl; Aug 29, 2006 at 07:02 PM.
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Originally Posted by MasterDave
Silly boy....of course one needs to back off both the rockers prior to stuffing the rope in so both valves stay shut. Thought we knew this, sorry.
My comment was a "just in case" the valve with the good spring wasn't backed off. I'm sure you can tell, many have never heard of doing this, let alone take the extra precaution.
Drifting
Joined: Jul 2005
Posts: 1,977
Likes: 195
From: Putnam Valley, New York. Amateur Radio Operator K2NS
Originally Posted by dknowles67
Does anyone know, can the cam be replaced with the engine still in the car?
(When I put it together, the engine was on a stand)
(When I put it together, the engine was on a stand)
If I remember correctly, the "X" bracing forward of the radiator is directly in the way of the cam coming out. You would probably have to remove the engine mount "through bolts", and jack up the engine to clear the "X".
RON
Race Director
Joined: May 2000
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Originally Posted by 63Corvette
Oh another thing.....Duke mentioned adding another 500rpm to your usable rev range, The oval port 427s have fragile cast pistons. They break when you rev to 6000 rpm regularly (redline is 6200), so don't even think of adding 500rpm with the cast pistons.
On a rebuild I would go with hypereutectic replacements. They're stronger than eutectic, but still won't take a lot of abuse (detonation), but should take 6000 revs.
Even the 7100 rev LS7 has hypereutectic cast pistons.
With some head massaging, a L-36 should have a useable rev range to about 6000. I think the early year L-36 tachs were redlined at 6000, but this was cut back to 5600 in later years.
Was that because of piston problems???
Duke
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
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From: Florida
Originally Posted by Scott Marzahl
According to the Melling catalog, you need to use spring part number 46622 with a spring height of 1.88" with that cam.
OD 1.260"
ID .876"
158 lbs at 1.88"
318 lbs at 1.38"
coil bind 1.2"
6 coils
OD 1.260"
ID .876"
158 lbs at 1.88"
318 lbs at 1.38"
coil bind 1.2"
6 coils
Thanks for the reply, but as I read it,
OD = 1.539"
ID 1.125"
<http://www.melling.com/products/melling_catalog.pdf#search=%22melling%20 46622%22>
Looks like you got the cam before it in the table.
"NOTE: ASM. HEIGHT OF 1.88 - MACHINING MAY BE REQUIRED."
Not sure what that means. Doesn't sound good.
Should I be concerned?
Race Director
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OE spring installed height is 1.88", so I don't understand the statement, unless the OD is larger than OE, which does not appear to be the case.
What springs are installed? Is it a spring/damper or dual coil? OE springs often have a color paint splotch ID. That's a start.
Nominal '67 AMA spec data I have for BB valvesprings are 1.09" ID, 100 lb@1.88", 315 lb@1.38", free length 2.09", flat damper, 3.62 coils.
Duke
What springs are installed? Is it a spring/damper or dual coil? OE springs often have a color paint splotch ID. That's a start.
Nominal '67 AMA spec data I have for BB valvesprings are 1.09" ID, 100 lb@1.88", 315 lb@1.38", free length 2.09", flat damper, 3.62 coils.
Duke
Thread Starter
Instructor
Joined: Jan 2005
Posts: 146
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From: Florida
I've decided to replace all the springs just to be safe, at a minimum.
But if you still want to know what springs are installed, they have a round outer spring, and a flat inner spring. I don't know if that is a "spring damper" or "dual coil". No colored paint splotch that I can tell. I do not think they were replaced in '97, so they've been in there since the early 70's, if they are not OE.
But if you still want to know what springs are installed, they have a round outer spring, and a flat inner spring. I don't know if that is a "spring damper" or "dual coil". No colored paint splotch that I can tell. I do not think they were replaced in '97, so they've been in there since the early 70's, if they are not OE.