Broken valve guides

[Domenic T.]

Re: Broken valve guides

Duke,
I would use that method and actually do with aluminum heads. Never measured the temp of the head but was careful not to get it to hot.
Took the guide out of the freezer and pressed it in.
I might add for the sake of this post that if the guide is drilled out it needs to be drilled undersized and finished with a piloted reamer to get the proper seal. The heads I am familiar with offer over sized guides, .005, .010, and I think .015.
Joe, as you said in a prior post, it is important to get the new guide exact or the valve will miss the seat in the head.
I cheat and use my mill to keep them true. Can't see drilling a oval hole out free hand and getting it exact. The press out seats make life easy because the hole is round and centered and with a piloted reamer can be done free hand.
I know both you & Duke know that but thought I would add to what you both said.


Dom

[Roger G.]

Re: Broken valve guides

Here's a NOS BB head I have sitting in the garage (3931063)

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[Joe L.]

Re: Broken valve guides

Thanks for posting the photo. Now the next question is: What is the replacement method? Is the head heated up in an oven? What temperature?

It's easy to replace guides on aluminum heads since the aluminum expands more with temperature than the iron or bronze guides, but if both the head and guide are iron, high temperature may not loosen them up much, so I can imagine that a lot of old guides break trying to extract them and installing new iron guides may result in similar problems.

A shop that specializes in HD diesel engine heads would probably be the best way to go since they should be set-up and experienced replacing valve guides in cast iron heads.

Also as you noted in your email to me, the exhaust guides are "wet", which raises the possibility of leaks, so an experinenced shop is a must.

This reminds me of my Titanic research over the years. Given that the overlapping hull plates of that era had riveted lap joints, I always wondered if some kind of sealer was used, especially considering that the mill finish was not that smooth and the plates would pickup some corrosion sitting in the yard prior to installtion.

Apparently not. If the red hot rivets were installed and peened properly, the plates were pulled together so tight as the rivets cooled and shrunk that leaks were rare. The Titanic had over 3 million rivets, and though not all of them needed to be water tight, a lot did, which made for a lot of potential leak points.

After the rivets cooled, checkers came along and tapped them them with a hammer. The sound told the checker if the rivet was properly installed and tight - a real art and probably a lost one at this point in time.

Duke

Duke------


I've never actually personally replaced these guides. However, it's always been my understanding that the guides are driven or pressed out. I've never heard of any need to heat the head to do this. With a cast iron head I don't think heating would be of much use, anyway.

Attached are photos of big block valve guides. The example on the left is an intake guide. The one on the right is an exhaust guide. The major diameter of the intake guide is 0.620". The exhaust guide major diameter is 0.625". These guides are for cast iron heads only. Guides for aluminum heads are different.



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