I'm in the process of going thru my 340HP and when removing the valve assembly noticed a couple of the adjuster nuts required more effort than the others to remove. It looks as though the threads on these studs are somewhat buggered up. My choice is to R&R both the studs and adjusters. If I remember this correctly (going back +/- 30 years) these are pressed in studs?? My issue back then was the studs pulling out of the head and the fix I used involved a kit where you drilled the valve stem hump and pinned it. Any modern day information on how best to address this and where to find what I need to do so sure would be helpful. Thanks for any thoughts you may have. Chuck (58064)
1962 340 Rocker Arm Studs and Valve Adjusters
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
I'm in the process of going thru my 340HP and when removing the valve assembly noticed a couple of the adjuster nuts required more effort than the others to remove. It looks as though the threads on these studs are somewhat buggered up. My choice is to R&R both the studs and adjusters. If I remember this correctly (going back +/- 30 years) these are pressed in studs?? My issue back then was the studs pulling out of the head and the fix I used involved a kit where you drilled the valve stem hump and pinned it. Any modern day information on how best to address this and where to find what I need to do so sure would be helpful. Thanks for any thoughts you may have. Chuck (58064)
Steve- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
'62 heads have pressed in studs. They are rarely a problem with OE valve springs, but can be trouble if gorilla valve springs are installed.
If there is no evidence of pulling, I think it's fine to leave them be as long as you use OE equivalent valve springs. I recommend Sealed Power VS677, which are equivalent to the second design OE valve spring 3911068 that went into production circa 1966, and it is suitable for all OE cams including all mechanical lifter cams.
If you want insurance, the studs can replaced with screw-in, which requires facing the stud boss and threading the hole, which most machine shops should be able to do.
I've never seen a minimum breakaway torque spec for the rocker nuts, but I recommend no less than 10 lb-ft. If less the nuts can be peened to increase out of round or use a new nut.
Your existing rockers, balls, and pushrods are likely reuseable. Carefully inspect them for galling or excess wear. If wear surfaces are simply burnished, they may be reused, however they must be maintained as matched sets so the original wear surfaces mate again when reinstalled on the engine, but they don't have to go back at the same valve if you use a new cam and lifters.
You have some easy options to get more power and revs from a 327/340. Search 327 LT-1 under my handle, which will also lead you to The Corvette Forum that has more info on this configuration includilng all the system engineering considerations and dyno tests.
If you choose not to massage the heads, and/or install a LT-1 cam, at least replace the rods with Eagle SIR5700. The original rods are weak and subject to failure at the bolt seats, and the $250 for the SIR5700 set is the cheapest insurance you will ever buy.
Duke- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
Duke, just came in from working on the car. My concern was 3 of the adjusting nuts were pretty hard to remove from the rocker arm stud. I was worried the threads on those studs were buggered-up. I tried screwing one of the other adjusting nuts on these studs and you could finger thread them all the way to the bottom. Sooo, I ran a 3/8-24 tap thru the three nuts that were hard to get off, tried them on their original studs and everything is good. I do appreciate you getting back with me and appreciate your feedback. Thanks again- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
If you can use just your fingers to thread the nuts down the studs, they will never hold adjustment. I believe as manufactured the nuts went through a press to make them just slightly out of round, and this is why it should take some torque to run them down the studs.
Loose nuts laying against a hard surface can be whacked with a hammer, which will usually restore friction, but it may take a little practice to not get them too much out of round, which could require excess torque and possibly damage the stud threads.
By running a tap through the threads, you have made them round again, so there probably won't be enough friction to hold position in operation.
Duke- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
If you can use just your fingers to thread the nuts down the studs, they will never hold adjustment. I believe as manufactured the nuts went through a press to make them just slightly out of round, and this is why it should take some torque to run them down the studs.
Loose nuts laying against a hard surface can be whacked with a hammer, which will usually restore friction, but it may take a little practice to not get them too much out of round, which could require excess torque and possibly damage the stud threads.
By running a tap through the threads, you have made them round again, so there probably won't be enough friction to hold position in operation.
Duke
Duke and Chuck-------
He should replace the nuts with brand new nuts and be done with it. If the NEW nuts can be threaded completely down the studs by hand, then the stud(s) also probably need to be replaced. The nuts can be easily obtained in most auto parts stores. If GM is desired, the part number is GM #12557390. Do not use "any old" prevailing torque (lock) nut. Use nuts intended for this, specific purpose.
Hopefully, the stud(s) will not need to be replaced. If they do, there are several ways to go.
Oversize shank, press-in studs are available from GM for stud replacement. Once-upon-a-time there were 2 oversizes available---+.003" and +.013". Only the +.003" remains available under GM #3814692. However, I DECIDEDLY DO NOT recommend this approach.
Second, you can obtain flangeless threaded studs from aftermarket engine parts manufacturers like Pioneer. With these, the existing stud is removed (procedure can be found in the Chevrolet Service Manual), the existing boss drilled and tapped, and the thread-in studs installed. Using this method, the finished product mimics the appearance of the original pressed-in studs.
Third, flanged style threaded studs can be installed. This requires that the stud bosses be machined down and drilled and tapped. The final configuration does not appear, at all, as-original (assuming one cares). In fact, the configuration will be like that GM used for 1970-72 LT-1 and 1973-81 L-82. Stud GM #10168410 can be used.In Appreciation of John Hinckley- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
You guys got me scared! This is a solid lift cam with adjustable valves. The rocker arm adjusting nut has a locking alen screw you tighten down once you have the correct valve lash set. Am I thinking wrong?? According to my service guide you are suppose to adjust these valves like every 10k miles. I wouldn't think you would have to replace the mechanical type locking nut each time you adjust the valves? These are not the the jam nut type. Duke, could you be thinking nuts for a hydraulic lifter application? Please keep me honest and thanks for your input. Chuck (58064).- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
Both mechanical and hydraulic lifter cams used the same slightly out of round nuts. As I said before, I have never seen a minimum breakaway torque for these, but I consider 10 lb-ft as an absolute minimum.
It sounds like you have some kind of aftermarket "locking nut". My suggestion is to buy a new set of OE replacement Sealed Power nuts from any parts store. Test them to have the above minimum torque required to turn them with the threads fully engaged on the stud and go from there.
Send me an email via the TDB, and I'll send you a paper on how to adjust the valves properly. The GM recommendation is to check them every 12K miles, but most will hold good adjustment lmuch onger, especially if you aren't spending a lot of time over 4000 revs.
DukeLast edited by Duke W.; February 6, 2015, 11:52 AM.- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
Chuck,
I think the nuts are the same hydraulic or solid camshaft and do not have any locking screws to deal with. They are simply a interference fit going on the threads.- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
You guys got me scared! This is a solid lift cam with adjustable valves. The rocker arm adjusting nut has a locking alen screw you tighten down once you have the correct valve lash set. Am I thinking wrong?? According to my service guide you are suppose to adjust these valves like every 10k miles. I wouldn't think you would have to replace the mechanical type locking nut each time you adjust the valves? These are not the the jam nut type. Duke, could you be thinking nuts for a hydraulic lifter application? Please keep me honest and thanks for your input. Chuck (58064).
Chuck------
These nuts are absolutely non-original. Only ONE Corvette application from 1955-96 EVER used this style lock nut (often referred to as a "poly lock"). That ONE application was 1996 LT4.
Prevailing torque lock nuts, as I described previously, are preferred over ALL other types.In Appreciation of John Hinckley- Top
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Re: 1962 340 Rocker Arm Studs and Valve Adjusters
Sounds like you have Poly-Locks on your rocker studs.
Typically they stay put but I have seen a few come loose.
If the engine is stock , get a new set of the GM nuts and you should be OK.- Top
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