Author Topic: 186 heads - rocker arm studs  (Read 4827 times)

vabeach56wagon

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186 heads - rocker arm studs
« on: November 14, 2019, 03:44:04 PM »
Please spare me the effort of removing a valve cover: are the 186 heads equipped with screw-in rocker arm studs? Memory fails me.

Mine are Dec 1 68 and Dec 2 68...




Thanks

paul

bertfam

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Re: 186 heads - rocker arm studs
« Reply #1 on: November 14, 2019, 03:54:00 PM »
No. Screw in studs didn't start until late 1969 (the 1970 model year).

Ed
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william

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Re: 186 heads - rocker arm studs
« Reply #2 on: November 14, 2019, 03:54:45 PM »
They weren't built with them but they were often added.
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69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #3 on: November 14, 2019, 03:55:05 PM »
I believe the 186 heads were equipped with 'screw in rocker stud' beginning with the 1970 model year.  Before 1970, 186 heads had press in studs.

Note:  Anyone rebuilding their '68 or '69 186 heads who want to keep their heads appearing stock (press in) but use screw in studs should be aware that machine shops have access to rocker studs that screw in but without the integrated 'nut'.. so it would appear to be press in but would be screw in...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
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vabeach56wagon

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Re: 186 heads - rocker arm studs
« Reply #4 on: November 14, 2019, 04:48:34 PM »
Thanks for the response...that helps in the planning/budgeting of the build.

We'll machine the bosses for the studs plus an extra 1/8" for the pushrod guide plates - and elongating the pushrod slots in the heads slightly.

This block is a July 25 stamped DZ. Ours is a June 18 car. Does anybody have a good block with an April or May casting and DZ stamping? As long as the engine is out, may as well find a more realistic date. I DO NOT RESTAMP and will always disclose the reality of the car, i.e. the M22 is an all-new transmission built by Riverside Gear in Eaton Rapids, Mi and stamped to match this car.

All Corvettes I've done have been matching numbers cars and any restamped elements (including blocks) were always disclosed to the buyers.





Do internal improvements to a DZ engine impact the perceived value of the car?

paul

Stingr69

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Re: 186 heads - rocker arm studs
« Reply #5 on: November 15, 2019, 04:04:16 PM »


Note:  Anyone rebuilding their '68 or '69 186 heads who want to keep their heads appearing stock (press in) but use screw in studs should be aware that machine shops have access to rocker studs that screw in but without the integrated 'nut'.. so it would appear to be press in but would be screw in...


I considered doing that myself but the more I dug into it, the less exciting it was.  Seems they can be failure prone at the stud boss.  I actually bought a set of those replacement threaded studs but decided against using them.  Chose to go with the known better option of milling the boss and using a stud with a hex base with the guide plate and push rod hole enlargement.  It is much more robust that way.

If anybody wants to try a set you can have them for the cost of postage.  I will not use them.

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #6 on: November 15, 2019, 05:25:13 PM »


Note:  Anyone rebuilding their '68 or '69 186 heads who want to keep their heads appearing stock (press in) but use screw in studs should be aware that machine shops have access to rocker studs that screw in but without the integrated 'nut'.. so it would appear to be press in but would be screw in...


I considered doing that myself but the more I dug into it, the less exciting it was.  Seems they can be failure prone at the stud boss.  I actually bought a set of those replacement threaded studs but decided against using them.  Chose to go with the known better option of milling the boss and using a stud with a hex base with the guide plate and push rod hole enlargement.  It is much more robust that way.

If anybody wants to try a set you can have them for the cost of postage.  I will not use them.

WHY would this type of screw in studs be more prone to breakage at the boss than the original press in studs?   

When I purchased my Z28 back in '76, one of the heads had a 'poorly welded' stud and a poorly welded valve cover (where the original press in stud had come loose and broke the valve cover as well.   Back then, when I rebuilt the engine, I replaced the heads with angle plug heads (good screw in studs) and a new valve cover (but I still have that 'welded up one' as a reminder.. :)     When I pulled the motor (many years later), I sold the angle plug heads and after that found good dated '69  186 heads for rebuilding and using on my engine.   I was 'torn' between the originality of the press in studs and the strength advantage of the '70 type screw in studs, so I 'compromised' and had my head shop install the 'stock looking' screw in studs.  I really don't expect I will drive the same way when I put it back on the road as I did in the 1970's... :)
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

william

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Re: 186 heads - rocker arm studs
« Reply #7 on: November 15, 2019, 06:02:41 PM »
Press-in studs don't break; the press-fit can loosen over time and the stud lifts. Makes some racket and can ruin the valve; if on an exhaust valve it will pop back through the carb. I have heard that hot-tanking heads can compromise the press-fit. I bought a Z/28 in the '70s with freshly rebuilt heads and it pulled a stud a few weeks later. The simple fix is to re-seat the stud; drill and pin it. That works ok but I have heard the stud boss may eventually crack and break.

Were I to ever have another 302 rebuilt, I would never use press-in studs.
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70z28lt1

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Re: 186 heads - rocker arm studs
« Reply #8 on: November 15, 2019, 06:09:43 PM »
Just like many things the answer is "it depends" on the type of screw in stud.  Rocker studs have 3/8-24 fine threads for the nut.  With replacement screw in studs that do not require the head to be milled, the part that threads into the head is usually 7/16-14.  The minor diameter (root of the thread) for 7/16-14 is 0.3499 in diameter.  This is less than the 3/8 diameter of the stud between the 3/8-24 and where it meets the head casting boss.  So the weakest spot in now the minor diameter of the 7/16-14 thread.  With a screw in stud that has a flange and the head is milled there is a generous fillet that transitions to the hex to tighten down against the machined head.  This is MUCH stronger than the aforementioned replacement thread in studs.  This also results in a more stable valvetrain.  It's hard to tell, but when the valve opens the stud actually flexes back and forth a small amount. You lose a bit of lift due to this.  Hence the need for shaft mounted rockers and stud girdles when high lifts and heavy springs are used.
Maybe a better way for you is to have the standard press-in studs machined for pins to prevent the studs from backing out.  The pins are generally 3/32 to 1/8 in diameter and the head is cross drilled about mid-way down the head casting boss and the pins are then pressed in.  This can't be seen and prevents the stud from backing out.  Not many do this as the real, machined screw-in studs are better than this so most racers don't bother with pinning the stock studs.

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #9 on: November 15, 2019, 07:37:30 PM »
For racing purposes, there's no discussion... that's the topics over in TC.    Here in TC, we discuss originality (for the most part).. keeping cars original (or at least original looking). 

PS.  I don't think many of us with original 69 Z28s are going racing with them nowadays.. :)
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

70z28lt1

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Re: 186 heads - rocker arm studs
« Reply #10 on: November 15, 2019, 08:37:03 PM »
I believe the 186 heads were equipped with 'screw in rocker stud' beginning with the 1970 model year.  Before 1970, 186 heads had press in studs.

For dates, keep in mind the heads that used the screw-in studs in 70 were only on the LT-1 Corvette and the 1970 Z28.  Both of the those had late intros in January of 70, so in reality there would be very few true '69 dated '186 heads out there with screw-in studs.  Most heads and blocks only pre-date the build of the engine by 2 or 3 weeks generally.

z28z11

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Re: 186 heads - rocker arm studs
« Reply #11 on: November 15, 2019, 09:06:18 PM »
I believe one of the problems using the screw in stud without the hex may stem (pardon the pun) from the smaller diameter stud (as was mentioned before), but also the fact there is no radius to re-inforce the stud instead of creating a built-in stress riser at the smallest diameter of the 60 degree V thread profile. Hex head studs have a generous root radius at the bottom of the upper stud, which can withstand a long slot rocker and high lift cam, plus heavy spring pressure that puts a lot of force on the stud during any kind of rpm (much less a solid lift camshaft motor). Probably why big blocks have screw-in studs (which are also compromised by the mounting angles of the studs themselves).

I have a spare set of 186 heads that I picked up a long time ago, screw-in studs already in place - I've been considering using them rather than alter my originals by pinning, or drilling/tapping. Remember, they're only originals once, as some of us are quick to point out.

Regards,
Steve

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1969 Z28 X77/M20/VE3 LeMans/W
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69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #12 on: November 15, 2019, 10:42:46 PM »
I believe one of the problems using the screw in stud without the hex may stem (pardon the pun) from the smaller diameter stud (as was mentioned before), ...


The screw in stud (that I referenced) is the same diameter shaft as the original press in studs with the ONLY difference being the 'fine' threads cut in on the bottom so it screws into the head boss.
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

vabeach56wagon

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Re: 186 heads - rocker arm studs
« Reply #13 on: November 16, 2019, 02:43:37 AM »
For racing purposes, there's no discussion... that's the topics over in TC.    Here in TC, we discuss originality (for the most part).. keeping cars original (or at least original looking). 

PS.  I don't think many of us with original 69 Z28s are going racing with them nowadays.. :)

In your experience, do internal engine modifications to improve performance and longevity impact the value of an original engine in an original car? That would include the aforementioned screw-in studs, pushrod guide plates, stainless valves, matched ports, blueprinted cams, etc.?

paul

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #14 on: November 16, 2019, 05:03:14 AM »
I think it depends on the prospective buyer as to $value$; for some it would (if the seller is honest).

For judging purposes, if the judges can't see it, hear it, or 'sense' it, then it isn't modified... :)    (The owner isn't obligated to 'tell all' when his car is being judged..  :)

Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan