I was wondering about when converting a factory head to screw in studs, is it mandatory to machine the rocker pad surface for the thickness of the guide plates? I just wondered why- figuring you would have to use a custom pushrod anyway and if that .100 or so thickness made a difference?

 

You need to mill the "pads" to do the best job, it's really the only 100% correct way to go in my opinion to end up with some 7/16" bottom threads!

Regardless of your rocker choice you should be checking for the accurate pushrod length anyway!

Thank, Gary in N.Y.

P.S. Here's a link with some info about roller rocker installations! They will fit with OEM covers and single-thick V/C gaskets.

https://classicoldsmobile.com/forums...questions.html

 

The problem isn't just the pushrod length, it's also the geometry of the rocker on the valve tip. If the rocker is up too high (as it would need to be if you didn't machine the head) then the rocker tip would be too far inboard on the valve stem, resulting in side loads on the valve and even possibly running off the edge if the geometry is too far off.

 

Fwiw I didn't mill my pads. The geometry was not too far off to be honest . Not perfect but it was slightly off center on the valve stem but it didn't sweep across . Been running the same setup for many years with no issues. I'm running a pushrod that's on the ragged edge of making the rocker arm bind on the stud. If I could get it to drop another .050 like milling the pads it would be perfect but I found a pushrod that was .050 taller to avoid binding it up during valve lash . If I lash it past half a turn the rocker arms will bind up but at half a turn I'm at .040 preload so it's good. Not the best case scenario but I spent a lot of time making sure I could get it damn near perfect without milling the pads and what I ended up with was a pattern slightly off center.

 

I didn't mill mine either, I honestly didn't even know people were doing that. I just bought an adjustable pushrod to check geometry and see what length pushrods I'd need. Came out with pretty nice geometry

 

It's common to mill the pad when running stock valve lengths with roller rockers. They always end up to short and the geometry is way off. Most aftermarket Olds valves are .100" longer than stock with the exception of the off the shelf Ferea valves. Those do not require the pad to be milled in most cases. Don't forget, most guys that are rebuilding OE heads also mill them. That also comes into play with the rocker geometry as well as different thickness gaskets and deck height. You always need to check with an adjustable pushrod to establish correct length, but the rocker placement over the valve is not effected by push rod lenth.

 

I think the slotted rocker arms like the roller tips are affected slightly . When i did my original measuring i was still running the roller tips. The longer the pushrod length the closer to the exhaust side of the cylinder head the pattern would be in my experience. Although it does have a ball to pivot on i think the slot allows it to move slightly off center when compare to a roller rocker where its fixed in the center and it could not creep from that center point. The area the pivot ball sits on isnt exactly round either kind of an ovalish shape. I might add it wasnt anything extreme but if i where to describe it. The pattern i ended up with would be one pattern line over center towards the exhaust side. When i set up the checker to the length pushrods i had it would put it almost 2 of those lines past the centerline towards the exhaust side .

 

Actually, most are stock-ish length that I have seen.

 

Hmmm yes it is, that's why you check it.

 

Idk much about valvetrain but that's the impression I had/have. When I was building my 350 I checked with stock rods and my contact was off center seemingly a decent ways so I bought an adjustable pushrod tool and was able to bring the contact very close to riding across the center of the stem.

 

Cutlassefi is correct. The tip of the rocker arm will change where it locates on the valve tip by changing pushrod length.

The most important aspect is that there is very little sweep across the valve tip, not necessarily where it locates on the valve tip. This can be done during mockup up and using a sharpie marker on the end of the valve tip. Coat it real well and run the rocker arm through its cycle. Take the rocker off and it will show you where the "sweep" occurs on the valve tip. Less sweep will be easier on your valve guides.

 

What is the best way, or what method does the machine shop use to drill out the 5/16 holes and tap? Bridgeport?

 

I use a Bridgeport to drill and tap studs. That would be the most accurate way so as not to have the studs (once installed) make the head look like a porcupine.

I have in a time of need drilled and tapped by hand. They came out straight as an arrow but that was going from 5/16" to 3/8". The 5/16" hole allowed the drill size (which was 5/16") to follow closely. If you drilled in steps I bet you could get it dead on by hand, but I still wouldn't recommend it.

 

If you cut apart a head, you will find that they aren't very thick in that area. Don't mill more than necessary.

 

X2 with Run to Rund, be careful not to cut too much. I have successfully drilled and tapped Olds heads for studs with a drill press. I have also been successful with using the thinner 1/16" thick guide plates and not cutting anything from the pads. If you can still find them, Pontiac used a 1/16" thick guide plate on their 400 and 455 engines (5/16" pushrod). They can be sectioned apart and used on the Olds head with a screw in rocker stud and any aftermarket rocker.

 

X2 with 67OAI


Ray