87_LG4

So my new cam came with an installation note saying cylinder heads will need machining. After doing a lot of searching on this forum it seems that we're talking about lifter to valve guide clearance. The numbers I've read here suggests that the 081s will only handle lift up to about .470", where as my new cam has .487" lift. This would then indicate that I would need to grind down my valve guides some. As far as I can tell there are two ways of going about this:
1. Get a machine shop to do it for me.
2. Buy my own valve guide grinder and do it myself.

Option one would probably yield the best result, but option two would most likely be a lot cheaper (still not exactly cheap, but cheaper). The valve guide grinder of choice from comp grinds an o.d. of .530". I've measured my stock valve guides to about .550", so that would mean I'd have to get new valve seals, right? I already have a new set of stock replacements, so that would be an added expense. The guide cutter, arbor/pilot and new stem seals totals at about $150 incl. shipping and taxes. But here's the thing, I emailed Comp about my cam lift predicament and here's what they replied:

(My email):
According to the installation notes regarding 08-408-8 XR258HR, my cylinder heads (14101081) requires machining. Would this be about rocker-to-valve-guide clearance? If so, what sort of, and how much machining are we talking? Or is it something else?

(Their reply):
The note is for a vortec style cylinder head. If you were using a vortec head you would need to machine the valve guides.

So what should I do? Does anyone have 100% accurate lift clearance figures for the 081 heads?

Thanks

Damon

With the seal on top of the stock guide boss the bottom of the retainer will touch it at about .470" lift. So your research is valid. Vortecs are about the same clearance-wise. Not sure why they would tell you the difference is Vortec vs. non-Vortec.

One thing you CAN swipe from Vortec heads that can help here is the Vortec-style retainers. They will open up the retainer-to-guide seal clearance by a little less than .050 with no other changes. Please note that ANY time you get rid of the stock exhaust-side rotator/retainers and replace them with standard non-rotator retainers you will need to drop a .060" shim in the exhaust spring pocket to get valve spring installed height back to stock spec.

You can also consider something we call the "ghetto grind." It involves grinding several hundredths off the bottom of the stock retainers to buy you more clearance with the guide/seal.

None of these options will do anything to avoid coil bind in the springs themselves. This is just for getting extra retainer-to-guide seal clearance.

87_LG4

Ghetto grinding sounds like my kinda option. Cheap, easy and effective, and I don't need to grind them that much. 0.060" should be enough, don't you think?
I could easily go as far as 0.080" (.060" and .080" being circa 1.5 and 2 millimeters respectively, as seen in this metric photo)


(I'm naturally assuming we're talking about grinding down this bit shown right here)

Now, are there any drawbacks to this method?

Btw, I also see you mention coil bind, but that shouldn't be a problem when I'm using the recommended springs from comp, should it?

Thank you

Apeiron

Yes, you're weakening the retainer and over time the hammering of the valve will pull the keepers through it and you'll drop the valve.

87_LG4

Then to heck with it, I'll do it right. Next pay check I'll order the guide grinder equipment from comp, along with new stem seals. Which would be better for my application; viton or teflon?

Thank you

Damon

Nothing wrong with the ghetto grind. The keepers are nowhere near the bottom. The reason they're so long is becuase the factory used to use an o-ring that's captured between the retaier and the valve stem (to keep oil from running straight down the stem, but is unneeded when you use positive-style seals that are affixed to the top of the valve guide), and that o-ring is BELOW the keepers/locks. Hence the extra length down there. You won't pull the locks through the retainer by taking a few thou off the bottom of them.

87_LG4

Having taken a closer look at the retainer with keepers installed I've measured it quite exact to be 2.8mm = 0.110" from the bottom of the keeper to the bottom of the retainer. At the moment I have 0.470" of valve guide clearance. Max lift with my new cam is 0.487", so I need to grind the retainer 0.017" + 0.060" for clearance. If we say 0.080" for good measure that equals 2.03mm. So if I grind down 2mm of my retainers I would still have almost one millimeter between the bottom of the keeper and the bottom of the retainer.



By these estimates the ghetto grind should work. Any thoughts?

Thank you

Damon

You are correct, sir.

87_LG4

Thanks for your help on this one. Saves me a lot of dough.

One final question thou. I'll also need to get either screw in or pinned rocker studs. My situation being that there is only one machine shop within reasonable distance and who's prices are unbelievable (reasonable meaning I don't have to spend a fortune shipping my engine cross country to the next shop and unbelievable meaning $6-700 for a 3-angle valve job!) I was wondering if stud pinning was something that I could do myself. Or screw in studs for that matter. How would I go about this? Can I just drill through the stud and hammer a pin through the hole? I read somewhere that to preserve the studs strength you have to drill through the side of the stud and not through it's center, which sounds reasonable. What do you think? Anyone ever done this?

Thank you

Hotrodder

Du kan bytte til skrudde bolter selv, hvis press-in boltene er 3/8" som på vortec toppene. Du trenger dette verktøyet til 29$ for å fjerne press-in boltene og for å entre korrekt med gjengtappen når du gjenger opp igjen hullene for skrudde bolter:
http://www.summitracing.com/parts/CCA-5306/

Og så må du ha en gjengetapp for 7/16-14". Ikke helt kurant i Norge selvsagt, men fullt mulig å få tak i. Prøv f.eks på en Tools forretning.
Hullet for de pressede boltene er 3/8", så gjengetappen passer visstnok perfekt.

English:
You can change to screw in studs in your own garage if the press-in studs are 3/8" like on the Viortec heads. You need the 29$ tool listed abowe and a 7/16-14" tap. The press in studs is 3/8, so the 7/16-14" tap fits right in.

87_LG4

Takk. Har forresten 7/16-14 gjengetapp fra før, så det er ikke noe problem. Du skulle ikke tilfeldigvis vite gjengestørrelsen på press-in boltene, sånn at jeg kan bruke de muttrene jeg har fra før? Ser at Proform har 7/16-14 skru-inn bolter med 7/16-20 og 3/8-24 gjenger på muttersiden. Tror du noen av de kan passe?

English:
Thanks. I already happen to have a 7/16-14 tap, so that's not a problem. You wouldn't happen to know the thread size on the press-in studs, so that I can re-use the nuts I already have? I see Proform has 7/16-14 screw-in studs with 7/16-20 and 3/8-24 thread size on top. Could any those fit my application?

Takk
Thanks

Hotrodder

On this GMPP after market Vortec cylinder head the rocker arm nuts are 3/8-24

http://www.summitracing.com/parts.aspx?sku=nal-12558060

But I would have checked this from other sources as well.

Apeiron

3/8-24 is normal for stock studs.