nonhog

Curious about smoothing the valve guide boss. I've read its a good idea to grind it smooth(eliminate) then have a thick walled guide installed. Seem's logical to me. Input welcome.

Also when having heads done, valve grind, assembled etc. Should I only have the outer springs installed to be easy on the cam during break in?

Its a Jm20/22 cam with 361/007 springs.(I can confirm spring#'s tonight)

Thoughts?
thanks in advance.

Warhead

Smoothed?
It's more about stem/guide clearance. Most high mileage heads have much too much stem/guide clearance, the best long lasting method is to drill out the guide and either install iron or bronze guides. Also available are thin wall bronze guide liners, they have to be installed in a specific manner.

ANY new guide will have to be sized for an Oldsmobile valve (.3427 dia stem) because most are made for the Chevy/Pontiac .341 stem. Please use positive seals, as opposed to the factory umbrella's.
Part of the deal.

If you plan on running stout springs, yeah.
Need to know the pressures at whatever your installed height may be.

If you are less than 100# seat, and less than 250# over the nose I say no, but you need to break in the cam for 20 min, before you let it down to idle.
If you ramp the pressures up, you might want to. Never a bad idea, just a bit of work.
Make sure you use the recommended break in lube on any new cam and lifters.
You probably know most of that, anyway.

Jim

nonhog

Smoothing for better flow/power. I'll have the machinist take care of the stem/guide clearance.
When doing the clean up porting instead of tear dropping the boss, actually remove it.

70Post

Jim---When Nonhog says "smoothed" he means the part of the cast in guide boss or bump that protrudes down into the port pocket. From your answer it looks like you thought he was talking about the guide walls up inside the guide where the valve stem passes through.

Yes, taking down the guide boss seems to be pretty common on ported heads. A lot of them seem to leave a bit of a bump or protrusion/raised area but still, a lot of the fairly massive guide "bump" seems to be removed.

cutlassefi

But I wouldn't recommend removing the guide boss on the exhaust side. The stem will run run hot due to the fact you'll have very little area for the transfer of the heat. I'd just smooth that one.

Jmo.

nonhog

Thanks guys, my goal besides better power is being hands on for some reason I love the idea of doing what I can. If its value is small all I'm out is time. And I do have an idea how tedious it can be. I've smoothed exhaust manifolds before.
I am smart enough not to hog anything out. Thanks cutlassefi for the exhaust boss suggestion.
Still studyiing the bowl area as to how to attack that clean up.
Some great pictures on a porting thread elsewhere on this site.
I'd much rather spend time for small gains by being conservative than screw up a set of heads.

Run to Rund

I wouldn't shorten the guide. The valve guides last a lot longer if they give more support to the valve stem.

nonhog

Food for thought(thanks, thats why I start threads)

So I've read up on valve size and feel I should go with 2.07 intake but what about exhaust valves? Go to 1.71?
general rule of thumb?
some good prices on 2.07/1.71 Ferrea valves on E-bay right now.

Warhead

Smoothed-- just have not heard many people use that term for grinding, porting, or for any real amount of metal removal. However, that term does lead to the final finish of the port, many people want a rough finish, I don't follow that school of thought. I like the though of removing the boss, just make sure every port is identical as possible.

Most Chevy aftermarket heads shorten the guide bosses toward the roof with no detrimental effects, with an increase in port flow. Machine shops regularly shorten the guide tops when they machine for positive seals.
There is a lot of factors in guide wear. Material of guide, clearance, lift, geometry, spring pressure, oiling, etc. Bronze is much, much more forgiving than iron guides in HP applications.

We went to 1.71 exhausts on one engine, did not see any real gains from it. Those valves will get real close, and with your mild build, you don't leave any room for larger intakes if you want to step up later.

Jim