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Old 07-04-2008, 06:57 PM
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SBC Holley heads & Comp springs?

I've just acquired a used pair of Holley SysteMAX (68cc/2.02"/1.6"/184cc) heads for my 350. To be honest, because I have domed pistons (0.125" domes), I wasn't confident the chambers would clear the domes @ TDC, but I mocked-up the heads without a gasket tonight and they clear the pistons fine So, now I'm going to need to check for piston-to-valve clearance once I've installed my cam (Comp XE274 hyd flat tappet).

The stock springs in the Holley heads are good for 0.600" lift and exert 132lbs @ 1.780" installed height. Although this is ample for the XE278 cam, the seat pressure has me concerned for cam break-in and ultimate longevity. So, I'm gonna get a set of Comp 981-16 springs (105lbs @ 1.700" installed height) with matched retainers and valve locks. Question is, can I just plug these springs/retainers/locks into the Holley heads, check for coil bind, rocker-to-retainer and p-to-v clearance and go, or do I need to pay special attention to the installed height? If so, what is the best/easiest way to measure installed height?

Thanks,
Ian.

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Old 07-04-2008, 08:51 PM
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Are the Holley springs a dual coil spring? If so, just remove the inner spring to do the break-in rather than buying more parts you don't need.
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Old 07-04-2008, 10:30 PM
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Quote:
what is the best/easiest way to measure installed height?
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Old 07-05-2008, 02:58 AM
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I wouldn't be as concerned with seat pressure as I would about over the nose pressure. I think you're doing the right thing by buying the springs that Comp recommends for that cam, although I'd ask them about using the 26981 beehive spring and matching retainers/locks. Might as well save a little weight if you can.

The 26981 is installed at 1.700" for a seat pressure of 110. The spring rate is 347# per inch and the theoretical valve lift of the XE274 is 0.490". So, 347 times .49 equals 170#. 170 added to the seat pressure of 110 equals an over the nose pressure of 280#. The 26981 will coil bind at 1.115". With an installed height of 1.700 and theoretical valve lift of 0.490", you should be at 1.210" over the nose, leaving you with a cushion of 0.095". If you're using pressed steel rockers, it will be a little more than that because the rockers never come out to 1.5 ratio. They're always a little less. If you're using high-buck aftermarket roller rockers, they will be very close to 1.5, so the 280# over the nose figure and 0.095" coil bind cushion figure will be valid.

Flat tappet cams will generally tolerate pressures up to about 325#, particularly if you are using an oil additive that contains extreme pressure lubricants, so you should be ok.

You can set the installed height with a micrometer like Stroke referred to, or you can do it the down and dirty way. Cut a piece of heavy wire or welding rod to a length of 1.700", as measured with your dial caliper. Lay a head, port side down, on the bench and install the valves, retainers and locks, making sure everything is clean and free of dirt, grit or burrs, particularly the valve heads and seats in the head. Using a heavy grease like wheel bearing grease on the locks, valve stems and inside the retainers will help to hold the whole mess together for checking. Wrap your forefinger and middle finger around the retainers (as if the valve were an arrow and the retainer were the bow string) and pull/twist on them while pushing the head away from you with the other hand. Use your thumb to push down on the tip of the valve stem at the same time. This should get them seated for checking. Hold the checking wire between the head and the valve spring seat of the retainer. If it won't go, then you will either have to machine the valve seats deeper or use another style of retainer that allows more installed height. If you have play between the wire and the edge of the retainer where the spring would sit, measure the play with your feeler gauges. This will be the measurement for shims to put under the springs. Part# 4753 shims come in 0.015", 0.030" and 0.060" thicknesses, so you can get close within 0.0075". Each 0.0075" of shim you use will be equal to 2.6 lbs. (347 times .0075). This ain't rocket science, so shim it accordingly.

If you're gonna be freaked about breakin' in the cam with these springs, then locate an old worn out set of bone stock Chevy springs and assemble the heads with them. I keep a set on the shelf just for that purpose. After the break-in, use this Manley tool to disassemble and reassemble with the Comp springs. You'll need shop air to keep the valves on their seats while you do the change. I have changed them without shop air by turning the crank so that the piston is at top dead center for each cylinder I'm working on.
http://www.jegs.com/i/Manley/660/418...748285%7C10797

Last edited by techinspector1; 07-05-2008 at 01:30 PM.
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Old 07-05-2008, 11:22 AM
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An ancient trick for swapping springs is to feed some clothes line rope into the spark plug hole and roll the piston up towards TDC compression. The rope holds the valves firmly without damage and allows you to peck the retainer if the keepers are stuck without worrying about dropping a valve.
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Old 07-05-2008, 03:09 PM
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Quote:
Originally Posted by techinspector1
I wouldn't be as concerned with seat pressure as I would about over the nose pressure. I think you're doing the right thing by buying the springs that Comp recommends for that cam, although I'd ask them about using the 26981 beehive spring and matching retainers/locks. Might as well save a little weight if you can.

The 26981 is installed at 1.700" for a seat pressure of 110. The spring rate is 347# per inch and the theoretical valve lift of the XE274 is 0.490". So, 347 times .49 equals 170#. 170 added to the seat pressure of 110 equals an over the nose pressure of 280#. The 26981 will coil bind at 1.115". With an installed height of 1.700 and theoretical valve lift of 0.490", you should be at 1.210" over the nose, leaving you with a cushion of 0.095". If you're using pressed steel rockers, it will be a little more than that because the rockers never come out to 1.5 ratio. They're always a little less. If you're using high-buck aftermarket roller rockers, they will be very close to 1.5, so the 280# over the nose figure and 0.095" coil bind cushion figure will be valid.

Flat tappet cams will generally tolerate pressures up to about 325#, particularly if you are using an oil additive that contains extreme pressure lubricants, so you should be ok.

You can set the installed height with a micrometer like Stroke referred to, or you can do it the down and dirty way. Cut a piece of heavy wire or welding rod to a length of 1.700", as measured with your dial caliper. Lay a head, port side down, on the bench and install the valves, retainers and locks, making sure everything is clean and free of dirt, grit or burrs, particularly the valve heads and seats in the head. Using a heavy grease like wheel bearing grease on the locks, valve stems and inside the retainers will help to hold the whole mess together for checking. Wrap your forefinger and middle finger around the retainers (as if the valve were an arrow and the retainer were the bow string) and pull/twist on them while pushing the head away from you with the other hand. Use your thumb to push down on the tip of the valve stem at the same time. This should get them seated for checking. Hold the checking wire between the head and the valve spring seat of the retainer. If it won't go, then you will either have to machine the valve seats deeper or use another style of retainer that allows more installed height. If you have play between the wire and the edge of the retainer where the spring would sit, measure the play with your feeler gauges. This will be the measurement for shims to put under the springs. Part# 4753 shims come in 0.015", 0.030" and 0.060" thicknesses, so you can get close within 0.0075". Each 0.0075" of shim you use will be equal to 2.6 lbs. (347 times .0075). This ain't rocket science, so shim it accordingly.

If you're gonna be freaked about breakin' in the cam with these springs, then locate an old worn out set of bone stock Chevy springs and assemble the heads with them. I keep a set on the shelf just for that purpose. After the break-in, use this Manley tool to disassemble and reassemble with the Comp springs. You'll need shop air to keep the valves on their seats while you do the change. I have changed them without shop air by turning the crank so that the piston is at top dead center for each cylinder I'm working on.
http://www.jegs.com/i/Manley/660/418...748285%7C10797
Wow, thanks very much for all that detailed info. I really appreciate it. Some interesting and useful calculations there.

Hopefully, the installed height will work-out without needing to shim. The Holley springs have an installed height of 1.780", so I don't think I'll be needing to machine the spring seats. Took me a while to picture what you were saying with mocking-up the retainers and locks without the springs installed and holding the retainer like a bow, but now I've got it

Re. cam break-in, I don't wanna get into swapping springs in-situ as I don't have a compressor to provide an air supply and I don't want to risk dropping a valve. Also, I don't have any weak springs around anyway. The Comp 981-16 springs should be OK and I'll be using ZDDP additive (or the Comp Cams equivalent oil additive) in the engine oil for break-in. I'll be using Torco MPZ cam lube on the cam lobes (simply because I can't get a hold of moly paste over here). Torco MPZ seems to have a good reputation, so hopefully that'll be at least as good as regular moly paste.

I have Valvoline 20W/50 VR-1 ready to go, but I was thinking of using 15W/40 diesel oil (SL/CH-4) instead. What do you think? In either case, I'll be adding the ZDDP or Comp Cams additive in addition.
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Old 07-05-2008, 08:25 PM
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I don't know what the Torco MPZ is, but if it's black and you have to gouge it out of the container with your finger, then it's probably the right stuff. Any time you buy a cam, the grinder always includes the black molybdenum disulphide heavy grease along with the cam. I'm serious now, sit down with the cam on your lap and massage this heavy black grease into the pores of the metal. Listen to your daddy.
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Old 07-06-2008, 06:19 AM
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Quote:
Originally Posted by techinspector1
I don't know what the Torco MPZ is, but if it's black and you have to gouge it out of the container with your finger, then it's probably the right stuff. Any time you buy a cam, the grinder always includes the black molybdenum disulphide heavy grease along with the cam. I'm serious now, sit down with the cam on your lap and massage this heavy black grease into the pores of the metal. Listen to your daddy.
I don't think Comp Cams supply black moly disulpshide with their cams(?)
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Old 07-06-2008, 07:18 AM
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Quote:
Originally Posted by techinspector1
I don't know what the Torco MPZ is, but if it's black and you have to gouge it out of the container with your finger, then it's probably the right stuff. Any time you buy a cam, the grinder always includes the black molybdenum disulphide heavy grease along with the cam. I'm serious now, sit down with the cam on your lap and massage this heavy black grease into the pores of the metal. Listen to your daddy.
Summit tends to remove stuff like that when being shipped overseas.
Hazzard

"An ancient trick for swapping springs is to feed some clothes line rope into the spark plug hole and roll the piston up towards TDC compression. The rope holds the valves firmly without damage and allows you to peck the retainer if the keepers are stuck without worrying about dropping a valve."


Thatīs worked perfectly for me four times now when doing valve seals.
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