Since it's easier to ask someone who has already tried it first instead of actually going out to the garage, pulling a valve cover and installing a polylock on a rocker, will polylocks fit under the OEM Z/28 style finned aluminum valve covers or are the polylocks too tall thereby requiring I swap my covers out for taller covers? I'd prefer to use polylocks instead of the OEM jam nut on the rockers, but I really want to keep my valve covers. I've also thought about roller rockers with polylocks, but again, same question as I hate to use lock nuts on new roller rockers. I hope one of you guys have already tried this. Thanks.
Will Polylocks fit under OEM Valve Covers?
ctcz28
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Since it's easier to ask someone who has already tried it first instead of actually going out to the garage, pulling a valve cover and installing a polylock on a rocker, will polylocks fit under the OEM Z/28 style finned aluminum valve covers or are the polylocks too tall thereby requiring I swap my covers out for taller covers? I'd prefer to use polylocks instead of the OEM jam nut on the rockers, but I really want to keep my valve covers. I've also thought about roller rockers with polylocks, but again, same question as I hate to use lock nuts on new roller rockers. I hope one of you guys have already tried this. Thanks.
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They sell both short and long locks. If you have drippers the short locks will slightly be rubbing on some drippers. If you have no drippers then buy the short ones. But if you have stacked or a thick cover gasket then you may be ok. My covers are crap so I knocked off the drippers.
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I'm using these.
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Short I'm using.
I'm using these.
Short I'm using.
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I have AFR heads and ARP rocker studs as well as OEM covers. I use the 4601 comp nut with their pro magnum rockers. I try to get the nut down as far as I can on the stud shank and the nut set screw as high up into the top of the nut barrel.
When I can't get that nut down far enough, I use the short Crower poly nuts. I don't like the rocker arm trunion bottom to be in any threaded section due to possible flexing. Because I run tall springs and valves, I run higher spring pressure than most guys, 155# closed.
Something you might check while sorting these nuts out is your rocker arm geometry .
I ended up running a shorter pushrod to correct my valve tip pattern. But you may not need this but should be checked. There is a topic on this subject on this site if interested.
When I can't get that nut down far enough, I use the short Crower poly nuts. I don't like the rocker arm trunion bottom to be in any threaded section due to possible flexing. Because I run tall springs and valves, I run higher spring pressure than most guys, 155# closed.
Something you might check while sorting these nuts out is your rocker arm geometry .
I ended up running a shorter pushrod to correct my valve tip pattern. But you may not need this but should be checked. There is a topic on this subject on this site if interested.
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Don't use Polly locks with stock rocker studs. Stock studs are not machined flat on top, the nut can tilt to one side when tightened & the uneven stress split the nut along the thread. It happened repeatedly on a friends race car, small block with BB 7/16" GM studs. Some brands of rockers use a thinner wall nut than others. I know an engine builder who spot faces the GM studs on a valve grinder machine, but ARP stuff isn't that expensive and it's ready to go.
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As Mark posted above Comp Cams sells a short Poly-Lock for use under stock valve covers. I used them on my 406 in conjunction with blue Moroso permanent steel core rubber valve cover gaskets (I also used ARP 7/16 inch rocker studs and Comp Cam's chrome-moly 1.6:1 ratio roller rockers). They fit under a stock seven rib Corvette Z/28 cast aluminum valve cover.
Of course I also ran bigger 3/8th inch chrome moly push rods that require a new set of hardened guide plates with a wider slot, but I had to remove the old 5/16th inch plates any way when I installed the new ARP rocker studs so there is no extra work involved. Did I mention I replaced the valve springs with the stiffer solid roller ones to match Lunati's cam recommendation from PAC, and chrome moly valve spring retainers (because you can not run titanium on the street for spring retainers or valves as they will fail even with lash caps).
When you buy roller rockers Comp, Lunati, Crane, Isky, and every one else ship them tall poly locks: normally only used with a stud girdle. It is because they are too tall that they interfere with a stock height valve cover that people assume you have to buy and run tall valve covers if you have roller rockers. You don't, you just have to buy the correct parts,
An added expense I know, but then again so does Comp-Cam, and all of the rest of the cam grinders as they made this into a business decision to generate more revenue. This is because if you were going to actually run a stud girdle you wouldn't do it; you would buy shaft mounted roller rockers such as sold by Jessel or BD. Though personally I have been running a stud girdle in my big blocks for years as I don't rev my engine to 11,600 RPM any more, the way they did it in NHRA's Pro Stock class (or did before EFI and the rule changes limiting them to only 10,000 RPM) If you rev to the moon then yes I would use shaft mounted rockers as well, but this was a simple street motor.
My Photobucket account isn't responding, so I will have to post pictures illustrating the parts later.
Big Dave
Of course I also ran bigger 3/8th inch chrome moly push rods that require a new set of hardened guide plates with a wider slot, but I had to remove the old 5/16th inch plates any way when I installed the new ARP rocker studs so there is no extra work involved. Did I mention I replaced the valve springs with the stiffer solid roller ones to match Lunati's cam recommendation from PAC, and chrome moly valve spring retainers (because you can not run titanium on the street for spring retainers or valves as they will fail even with lash caps).
When you buy roller rockers Comp, Lunati, Crane, Isky, and every one else ship them tall poly locks: normally only used with a stud girdle. It is because they are too tall that they interfere with a stock height valve cover that people assume you have to buy and run tall valve covers if you have roller rockers. You don't, you just have to buy the correct parts,
An added expense I know, but then again so does Comp-Cam, and all of the rest of the cam grinders as they made this into a business decision to generate more revenue. This is because if you were going to actually run a stud girdle you wouldn't do it; you would buy shaft mounted roller rockers such as sold by Jessel or BD. Though personally I have been running a stud girdle in my big blocks for years as I don't rev my engine to 11,600 RPM any more, the way they did it in NHRA's Pro Stock class (or did before EFI and the rule changes limiting them to only 10,000 RPM) If you rev to the moon then yes I would use shaft mounted rockers as well, but this was a simple street motor.
My Photobucket account isn't responding, so I will have to post pictures illustrating the parts later.
Big Dave
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After fighting it tooth and nail I was able to recover two pictures from my PhotoBucket account (It keeps jumping back to the top of the hierarchical menus), and it takes forever to scroll through the pictures)
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Big Dave
Big Dave
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Aftermarket heads have higher gasket sealing surfaces for more room. I have a buddy with a stock iron headed Z/28 and he switched to roller rockers with polly locks. He had to buy spacers to clear them with the GM aluminum valve covers. I don't think he trimmed the drippers. If I remember right, he bought aluminum adapters to go from 4 bolt covers to two bolt, then trimmed away the two bolt part of it so he just used them as spacers.
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Thanks for the feedback, you guys pointed out some things I did not even think about, like how the top of the stock rocker studs aren't milled flat. I see that Big Dave's are ARP and flat on top. I guess now I will have to go pull the cover and take a look. I'm using the blue FelPro gaskets with the crush (prevention) washers and they give a bit of extra room. Can't say as I remember if my covers have drippers, I think not however. This all started with my discovery of a set of polylocks I picked up many many years ago, but never put in and forgot about. I'm afraid that they may be the wrong size and thread pitch, but again, I'll have to pull the covers to find out. New rocker studs, geez, more cost, it just never ends does it? I've still got the stock rockers, those rollers look great, but I wonder if they're worth the cost, I mean, would I notice any difference in how the motor runs or sounds? One final question, assuming that the rocker studs are available in several sizes where the polylock threads on, does it matter whether I get a 3/8 or 7/16 or whatever thread matches the tops of the stock studs or can I buy new studs to match my polylocks so I don't need to buy a new set of those too? I'm also asuming my studs thread in and aren't pressed in. Thanks again, I really appreciate the input.
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There is the matter of the twenty to twenty five horsepower lost to parasitic drag with the stock stamped steel and ball compared with a roller rocker. This number was determined with a Spintron and the discrepancy in lost power is reflected in changes in spring pressure and RPM (the faster you spin it the less time there is for oil to penetrate into the gap lubricate the parts). So there is a difference, though you are correct there is no gain in horsepower in terms of making it; just the ability to recover some horsepower that was lost to friction.
Big Dave
Big Dave
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Yes Dave but that would only be at the higher RPM range that for a street car you'll probably rarely see.
I'd like to open this topic up again.
I have a 70 Z28 like Mark's in post #2 and would like to set my valvetrain up like he has done in the photos above, but without spacers or double thick gaskets.
I would also like to keep the dippers on the covers. Where do the short 4601 polylocks hit on the covers? Would it help if the polylocks were reduced a bit in height or diameter? I have access to a surface grinder and it would not be an issue to spin the diameter down where the nut flats are or to reduce the height a bit. How much would it take to not have to run spacers or double gaskets etc? Is it even close or out of the question?
I have a 70 Z28 like Mark's in post #2 and would like to set my valvetrain up like he has done in the photos above, but without spacers or double thick gaskets.
I would also like to keep the dippers on the covers. Where do the short 4601 polylocks hit on the covers? Would it help if the polylocks were reduced a bit in height or diameter? I have access to a surface grinder and it would not be an issue to spin the diameter down where the nut flats are or to reduce the height a bit. How much would it take to not have to run spacers or double gaskets etc? Is it even close or out of the question?
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Why don't you lay a strip of play doh or strip chalk over each stud nut and find out where the hitting point is? You could trim each dripper to a point . Leave cover drippers dry to get a good impression.
I use the same cover but Crower short nuts and have no issues with standard cork cover gasket but it may be that because I use AFR heads that seem to have a taller cover rail. This may be a standard on aftermarket heads.
I use the same cover but Crower short nuts and have no issues with standard cork cover gasket but it may be that because I use AFR heads that seem to have a taller cover rail. This may be a standard on aftermarket heads.
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You do not need drippers with Poly-Locks. The poly-locks sit up high enough to obstruct the squirting oil to flow over the bearings rollers on the nose and to cool the springs. I would grind the drippers off of the underside of the valve cover; as not even a white gloved judge is going to take the car apart to check.
Shortening (squaring the top of the stud) reduces it's over all length which could affect push rod length and valve train geometry. Stock stamped steel rockers suffer from variances in the length of the slot which affects available lift, variances in ratio which affects valve lift between cylinders, and from friction due to the steel rubbing on steel (oil is not force fed as in engine bearings), and stock rockers relies upon reduced spring pressure while the valve are on their seat to lubricate the trunion. Reduced spring pressure doesn't support high RPM operation as it promotes valve float. There are a lot of reasons to utilize a roller rocker.
If you do not want to grind the drippers off of a set of vintage stock cast valve covers there are reproductions available. I use cast valve covers to obtain better sealing of the valve covers that is not offered by tissue thin Moroso stamped aluminum covers that are easily bent out of shape (and leak) even when proper bolt torque is applied (I have to rely upon Corvair hold downs to seal the valve covers). I do use the bright blue Moroso valve cover gaskets as they are nearly infinitely reusable soft silicone rubber gaskets with a steel inner core that uses stand offs at the bolt holes to prevent deforming under excess torque to seal the oil in the valve covers.
I tend to follow GM engineers lead for a lot of the parts that I use; but I am not married to the idea: as if there is a valid justification for going with a better engineered part I will use it instead. GM engineers were often hamstrung by the bean counters who over ruled many engineering choices just so that GM could make money. (shocking! I know ... but cheap cork gaskets where used instead of the better rubber ones offered by OEM vendors just to save money). You can make your own decision as to which parts you choose to use unless you are hamstrung by the compulsion to do what the factory did just for the sake of originality.
Big Dave
Shortening (squaring the top of the stud) reduces it's over all length which could affect push rod length and valve train geometry. Stock stamped steel rockers suffer from variances in the length of the slot which affects available lift, variances in ratio which affects valve lift between cylinders, and from friction due to the steel rubbing on steel (oil is not force fed as in engine bearings), and stock rockers relies upon reduced spring pressure while the valve are on their seat to lubricate the trunion. Reduced spring pressure doesn't support high RPM operation as it promotes valve float. There are a lot of reasons to utilize a roller rocker.
If you do not want to grind the drippers off of a set of vintage stock cast valve covers there are reproductions available. I use cast valve covers to obtain better sealing of the valve covers that is not offered by tissue thin Moroso stamped aluminum covers that are easily bent out of shape (and leak) even when proper bolt torque is applied (I have to rely upon Corvair hold downs to seal the valve covers). I do use the bright blue Moroso valve cover gaskets as they are nearly infinitely reusable soft silicone rubber gaskets with a steel inner core that uses stand offs at the bolt holes to prevent deforming under excess torque to seal the oil in the valve covers.
I tend to follow GM engineers lead for a lot of the parts that I use; but I am not married to the idea: as if there is a valid justification for going with a better engineered part I will use it instead. GM engineers were often hamstrung by the bean counters who over ruled many engineering choices just so that GM could make money. (shocking! I know ... but cheap cork gaskets where used instead of the better rubber ones offered by OEM vendors just to save money). You can make your own decision as to which parts you choose to use unless you are hamstrung by the compulsion to do what the factory did just for the sake of originality.
Big Dave
Thanks for the quick replies.
I can't as of yet do the play-do thing (I actually like silly putty...but everybody has their favorite) as I am at the reassembly phase and haven't made the purchase of the poly locks and rocker arms as I was basing the purchase on if it was even possible to use the upgrades based on the mods required.
I wasn't going to mod the stud, but the poly lock if it was pretty close to working. If it comes down to a 1/16 or 1/8 inch, I'll do it. If its a 1/4 inch or more I may just go with stock interference fit nuts. If it is the size of the poly lock at the wrench flats area that is hitting the dippers of valve cover, I can machine this down a bit. I think the set screw will be supported just fine with as little as 1/8 wall thickness beyond the major diameter of the threads. I realize that the wrench flats will be very small at this point, but how much torque is required when the set screw is broken lose to adjust the lock?
Not sure I follow you on the top of the stud thing effecting the geometry. Reducing its height shouldn't effect the valvetrain geometry. Its just hanging out in the breeze so to speak (picture the threads above an interference nut..they really don't do anything). Until the height drops below to the point where it isn't engaging the nut enough to provide enough pull strength and the nut or stud strips out due to pressure from the rocker arm, it is just theoretical excess metal. Now, if you were to cut the stud down to the point that you had to use short pushrods, that's another thing altogether. I wouldn't do that.
I can't as of yet do the play-do thing (I actually like silly putty...but everybody has their favorite) as I am at the reassembly phase and haven't made the purchase of the poly locks and rocker arms as I was basing the purchase on if it was even possible to use the upgrades based on the mods required.
I wasn't going to mod the stud, but the poly lock if it was pretty close to working. If it comes down to a 1/16 or 1/8 inch, I'll do it. If its a 1/4 inch or more I may just go with stock interference fit nuts. If it is the size of the poly lock at the wrench flats area that is hitting the dippers of valve cover, I can machine this down a bit. I think the set screw will be supported just fine with as little as 1/8 wall thickness beyond the major diameter of the threads. I realize that the wrench flats will be very small at this point, but how much torque is required when the set screw is broken lose to adjust the lock?
Not sure I follow you on the top of the stud thing effecting the geometry. Reducing its height shouldn't effect the valvetrain geometry. Its just hanging out in the breeze so to speak (picture the threads above an interference nut..they really don't do anything). Until the height drops below to the point where it isn't engaging the nut enough to provide enough pull strength and the nut or stud strips out due to pressure from the rocker arm, it is just theoretical excess metal. Now, if you were to cut the stud down to the point that you had to use short pushrods, that's another thing altogether. I wouldn't do that.
I agree with everything you said as far as the GM engineer constraints. I am by and large building the engine for my requirements rather than a judge, but I also don't want to kill the value of a matching numbers engine. Bolt-on upper valve train mods are good, but I am staying away from things like double springs and things that require machine work. Example is I went with a Scat lower end (forged crank and rods) as the original crank was cracked and the pink rods were of course old and had been reconditioned twice already. I went to rev it up from time to time without worry. Going with the original '178 cam.
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