Valve guide boss cracked

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4spdragtop

4spdragtop

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Doing my DIY port and gasket match and spotted this on #4 intake. I read that you can take the boss and valve guide down about a 1/4"? I dont know if that will get rid of crack or not. Suggestions?
Thanks
Steve

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Machine it down until the crack is gone. It will be fine.
 
I have cut some down shorter for flow benefits, no real problem at all if you are running roller tip rockers. The 273 type rockers tend to pull the valve sideways and the shorter the guide the faster they ware, you have to realize that you cut the top down for more lift so they can be a 1/2" shorter before you know it.
 
1/4" would be no problem like I said the shorter the guide the faster they ware.
 
If it would fit, I have done worse things with a Dremel tool with a fiber cut off wheel, but I think standard professional procedure is a die grinder with a carbide cutter.
 
Thanks Brian, I plan on running 273 adjustable.
Why would the guides wear faster being shorter?
Thanks!
brian6pac said:
I have cut some down shorter for flow benefits, no real problem at all if you are running roller tip rockers. The 273 type rockers tend to pull the valve sideways and the shorter the guide the faster they ware, you have to realize that you cut the top down for more lift so they can be a 1/2" shorter before you know it.
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That crack won’t bother anything.
It’s not uncommon for the boss to crack when installing 1/2” guides, as your heads have.

Just continue on like it’s not even there.
 
As long as it doesn't migrate... Shorter guides wear faster because there is less area to deal with side loading imposed by the rubbing action of the rockers. Roller rockers will do this as well, but maybe not as fast? At the risk of bench racing again (winter is killing me!) I am skeptical of how much value a rollerized rocker really has. I am not as wildly optimistic about the outcome as the aftermarket would have us to believe about roller rockers, although I would use them myself. I believe most gains in rockers are from an improvement in strength/flex resistance and harmonics. There are people a whole lot more experienced than I on this topic on here though, and many new factory engines use rollers, but the rocker anges/etc. are engineered with this in mind ahead of time. In this case it's usually not just an add on/improvement to an existing design.
 
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4spdragtop said:
Doing my DIY port and gasket match and spotted this on #4 intake. I read that you can take the boss and valve guide down about a 1/4"? I dont know if that will get rid of crack or not. Suggestions?
Thanks
Steve

View attachment 1715283402

View attachment 1715283403
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Hey Steve,

That crack looks to be all the way through the casting. If you just leave it, Temps/vibrations etc .. will cause it to spread even further, maybe even change direction the same way a crack in a windshield can migrate all over the place. The real fix is to drill or grind out the crack completely and fill it . Find a shop that can do cast iron welding and fix it properly. Or, just find another head.
My approach to problems like this has always been... "How bad do you want to take it all apart again to do it the second time? "
 
stixx said:
Here we go with another full set of opinions on the same topic. . :)
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Yup! That's what the site's for! Discussions and opinions. It would be pretty boring on here if nobody answered a question or offered any insight.
 
You may to get some bright light and and a dental type mirror and inspect it as close as possible, maybe even probe it out with a pick to see how far the crack runs. Usually, these stop right in the thick part of the guide on each side But being I don't see any of it on the roof of the port is a pretty good sign that it hasn't migrated towards water yet. As long as it's not in the roof it is probable it hasn't made it any farther through the guide. I would go ahead and cut the guide down, I really think you'll be able to cut that one out before it gets into the damage point.
 
Fully agree, basically. But it doesn't make life easier for the OP. His options range from zero to a few hundred $.
I'd go with this one "That crack won’t bother anything." (PRH)
 
Correct on all counts! “If it doesn’t migrate” is a gamble I don’t like taking either. However, the cracks through the seats between the valves of 302/308 heads are a prime example here. Those make me even more nervous but a pressure test it the go/no-go gauge for those. It’s rare for them to fail once they stop migrating in most cases because your just not pushing the casting to its limit. Now start adding in things like race gas compression, triple valvesprings with dampers, etc. etc. Well, you’re throwing good money after bad because you will get more with a good set of aftermarket heads to start with for the same amount and not be pushing everything as hard.
 
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I can tall you that another head is cheaper than getting that one repaired if you want it done right.

 
stixx said:
Fully agree, basically. But it doesn't make life easier for the OP. His options range from zero to a few hundred $.
I'd go with this one "That crack won’t bother anything." (PRH)
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In perfect hindsight, if PRH says it, I wouldn’t give it a second thought... no substitute for experience!
 
I'll try to sneak a mirror in there.
Side note, while looking for carbide bur, I'm reading thru ads and "they" say single cut burrs are for iron, double cut are for aluminum? Insight into this? Burrs are crazy expensive here.
Thanks!
nm9stheham said:
Mirror....
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