valve guide boss: HOW MUCH?

[LameHoof65]

I have read that you can grind the bosses pretty much to the bottom of the bowls without compromising the head integrity or put too much of a strain on the valve stems. Right now I have them cleaned out and all the sharp edges removed, should I go farther?

 

[Stubby]

I have seen them streamlined to an airfoil shape and I have seen them totaly removed on some heads. Either way you can creat a problem for your machinest. The overall length needs to be considered and the guide work needs to be done first. If you are using .500 od guides and the boss is too thin they can crack and pieces of cast iron will be ingested.
If you are using thin wall guides like Kline you can gring them more.
Work with your machinest and think of longevity and perf. You must find a balance you can live with for as long as want the head to last.

 

[rickwrench]

With the intake guide, I've seen quite a few performance heads that have the guides or guide boss cut back to the chamber wall. The valve will wear out the remaining guide bore quite a bit faster than a full length guide but otherwise no short term problems. How long often do you plan to pull the head off? If it's for pure street use, and you never plan on taking the head off, just taper and slim the intake guide/boss.
On the exhaust side, bullet/taper the end, and otherwise leave it alone. It shields the stem from the exhaust gas blast and provides an escape route for heat absorbed by the valve.
Don't use stem seals on the exhaust side either. I see this all the time. There isn't any vacuum in the exhaust port sucking oil through the guide, just a little rocker splash on the stem tops, and that oil is also cooling the exhaust valve.
I found stem seals on the exhaust valves in one of the Falcons I bought, I promptly removed them and the increase in oil consumption was... nothing.
Rick

 

[LameHoof65]

I'll just stop where I am right now. Tomorrow I will begin with the combustion chambers. The guys who cleaned and magnafluxed my head said all I really needed to do was lap the valve seats. I thought I would clean the bowls up first, and it is a good thing I did because I barely but did tap the seat on one exhaust and one intake, it is real hard to see it. You can't feel it with a finger swipe, but I can see it. Never done valve lapping before, but I watched a friend do it once. What kind of lapping compound do I need and where can I get it? He used an egg beater type thing, but I have seen the ones that you just spin back and forth in your hand, where would I get something like that?

 

[addo]

The race-spec SP heads had about 100 thou removed off the guide boss in addition to it being bullet-shaped. Roller rockers eliminate the side -load wear that Rick points out.

 

[LameHoof65]

Yea, too bad I can't afford the rr's right now. whoa is me..... At any rate I think that I will leave enough meet to get me through for awhile. And did I read it right that you don't need valve stem seals on the exhaust valves? The head I just had cleaned up had a leaky exhaust valve and it had a ton of crud on it.

 

[Anonymous]

Use a "gentle" teardrop" shape, and you'll be fine. If you are going to use bronze valve guides, have them "bulleted" to reduce obstruction. Even if you are not using roller rockers, a gentle street cam will put less stress on the valve guide than a more aggresive profile. Paying close attention to valvetrain geometry will also help to compensate for the lack of support on the guide.
When you use the teardrop shape method, you might enlarge the port at that point to compensate for the restriction. IMHO, just smoothing down the whole area will pay dividends without the need of going crazy, or sacrificing valve guide life. After all, these are cast iron heads. If you look at the AL SCP heads, you'll notice that we use a fairly large boss, that's there to improve valve guide support, compensated by a carefully designed shape. The tendency on race heads nowadays is to achieve reliability, because at 8000 rpms, roller rockers or not, if you risk failure, you'll loose the race.