Hey fellas, I had a machinist look at a set of heads that I wanted him to do a valve job on and he said the heads were junk becuase someone had replaced the guides improperly. He explained that the new replacment guides should not be exposed to the coolant in the water jacket of the head. Honestly I dont know enough about the replacment procedure but I understood the original guides are cast in place and that new guides would bore out the old guides and new guides are pressed in. should the new guides be exposed to the coolant in the heads and how would I tell if they are? I've done an internet search and am still not clear on this. BTW, I'm taking the heads to another shop this week to get a second opinion. thanks Charlie
Charlie : Please, Keep us posted in detail with what the next shop says, as I've not previously heard that particular reason used to explain why a set of heads were 'junk', & I'm curious to find out how 'water-jacket-coolant' damages replacement valve guides so that I can avoid similar damage to my own heads in the future. Does this damage only happen to BBC heads, or are other types of heads also vulnerable?
I ran a set of 781 heads on one of my previous built big blocks. From the factory they were in the water jackets. They are good heads to use for mild performance but beware, there are some idiosyncrasies to deal with. http://speedtalk.com/forum/viewtopic.php?f=1&t=4563
Dr, I'll let you know what the next shop says. EL, thanks for the link I'm going to have to study that a bit to fully understand what's being described in it but it appears that the ex guides are in the coolant...but not the int.
The guides are pressed in, then machined. They're thick wall iron. Usually, the worn guides are left in place, and bored out for bronze sleeves or some such. I've had a few replaced, it's usually not a big deal. But without knowing all the details of what the machinist found, it's hard to say whether he's right or wrong.
Its been quiet awhile since I have done this, but I know the guides press in , there is a certin direction they have to be pressed out,so not to crack the head, I will call a machinest friend and find out ,then post
The very first BBC heads,, The guides were not on center with the seat,, when pressed out and a new guide pressed in you were in big trouble. The guide is exposed to water because it is bored through two surfaces. It was recomended to insert liners in the original guide. GM corrected the misalignment issue around 67 or 68 I haven't pushed any guides out of any late heads. Also if my memory is correct the guides had to be driven out from the chamber (seat) side,, there was a slight difference in the guide O.D. from spring seat to chamber to aid in alignment when installing the guide.
Hey guys just a quick update. I took my heads to a respected machine shop here in the east bay and they saw nothing wrong with the way the guides were done or anything else wrong with the heads. the guides on the exhaust go through the water jacket and the guides are tapered as described above. I'm going to go ahead and get larger valve installed along with a good valve job and hardened seats.
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