Head heating required when changing bronze valve guides?

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HeinzE
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Head heating required when changing bronze valve guides?

Post by HeinzE »

Wonder what the thoughts are about heating aluminum heads when changing bronze guides. I do a lot of work on aluminum heads, and if
they are fitted with cast iron guides I always heat the heads for about 50 minutes at 275deg's for both removal and installation, and from what I've seen, this, or something similar is common practice in most shops. But what if the guides are bronze. Is it still necessary to heat the heads when
when removing the them? Or is the expansion rate of bronze and aluminum so similar that it is not effective? I imagine that it would still be
a good idea to heat the head for guide installation, I'm wondering mainly about during removal.
1980RS
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Re: Head heating required when changing bronze valve guides?

Post by 1980RS »

I have one machinist that just pushes them out and the other guy heats the head, then when he put them in he heats the head and chills the new guide and drops them right in. Both guys do great work.
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Re: Head heating required when changing bronze valve guides?

Post by rebelrouser »

Not an expert by any means, but it depends on how easy they come out. I have a guide tool that fits an air hammer, if I blurp it and the guides move then I take them out cold. If they are stubborn, then I warm the head up a little. Freeze the guides overnight, and warm the head a little to install. I think the main thing is making sure the guide bore is clean, and has no damage, and the interference fit is correct.
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Re: Head heating required when changing bronze valve guides?

Post by BillK »

rebelrouser wrote: Tue May 11, 2021 10:00 am Not an expert by any means, but it depends on how easy they come out. I have a guide tool that fits an air hammer, if I blurp it and the guides move then I take them out cold. If they are stubborn, then I warm the head up a little. Freeze the guides overnight, and warm the head a little to install. I think the main thing is making sure the guide bore is clean, and has no damage, and the interference fit is correct.
I was going to post almost the same exact thing. Only thing additional is if they really feel stubborn I will drill the guides out to a larger ID. That helps relieve some of the pressure getting them out. Depending on how the guide is shaped on the port side I have also cut the top of the guide down flush with the head and then driven them out from the top. That is very rare.
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David Redszus
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Re: Head heating required when changing bronze valve guides?

Post by David Redszus »

The concept of interference fit is a real science.
It will depend on the materials used and the force that is attempting to displace
the guide once installed. The equations used to predict the sizes of bore and guide
are complicated. But basically, it becomes a matter of material strength and
coefficient of thermal expansion.

TE
aluminum 13.1
steel 7.3
cast iron 5.9
alum bronze 9.0
phos bronze 10.0

The amount of interference fit will depend on the materials used.

To prevent galling of the aluminum head during removal or installation, the head should be heated
to about 250F. If possible, the guides can be shrunk using dry ice (grocery store item) and acetone.

When the temperature adjusted sizes are correct, the guides will require little more than finger
push force to install. Once cooled to normal temperature (engine temperature, not room temp),
the guides will be locked in place.

I just went through the process using phos bronze bushings into magnesium.
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Re: Head heating required when changing bronze valve guides?

Post by rebelyell »

I'm neither materials scientist or machinist ... but my first foray into bronze guides and alum heads was nearly 50 years ago. HD panhead(s). I froze the guides in her kitchen fridge & heated the heads in her kitchen stove. As far as the harley was concerned, my work was great. However, I do NOT recommend my specific method ... because the baked oil & carb cleaner in heads stank up the whole house, clothing, bedding etc (long before advent of Febreze) ... HER stove reeked for many uses. Worse was how she "hated" me & for too long. If you haven't already; get your own stove & fridge AND [-X don't use HER Kitchen as a shop! [-X
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Re: Head heating required when changing bronze valve guides?

Post by David Redszus »

rebelyell wrote: Tue May 11, 2021 12:45 pm I'm neither materials scientist or machinist ... but my first foray into bronze guides and alum heads was nearly 50 years ago. HD panhead(s). I froze the guides in her kitchen fridge & heated the heads in her kitchen stove. As far as the harley was concerned, my work was great. However, I do NOT recommend my specific method ... because the baked oil & carb cleaner in heads stank up the whole house, clothing, bedding etc (long before advent of Febreze) ... HER stove reeked for many uses. Worse was how she "hated" me & for too long. If you haven't already; get your own stove & fridge AND [-X don't use HER Kitchen as a shop! [-X
Was that a FIRST wife or later edition? :)
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Re: Head heating required when changing bronze valve guides?

Post by Dave Koehler »

rebelyell wrote: Tue May 11, 2021 12:45 pm I'm neither materials scientist or machinist ... but my first foray into bronze guides and alum heads was nearly 50 years ago. HD panhead(s). I froze the guides in her kitchen fridge & heated the heads in her kitchen stove. As far as the harley was concerned, my work was great. However, I do NOT recommend my specific method ... because the baked oil & carb cleaner in heads stank up the whole house, clothing, bedding etc (long before advent of Febreze) ... HER stove reeked for many uses. Worse was how she "hated" me & for too long. If you haven't already; get your own stove & fridge AND [-X don't use HER Kitchen as a shop! [-X
Did she hold your beer? :lol:
Heck, I get glared at if I leave a bread crumb unattended in her kitchen
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Re: Head heating required when changing bronze valve guides?

Post by Truckedup »

I've changed dozens of bronze guides in aluminum bike heads...Usually a .0015-.002 interference fit. Heat the head to no more than 250F, drive out the guides noticing if they all drive out with about the same effect...With the head reheated if necessary, the room temperature guide go in with a few moderate hammer hits on the driver...I also have a screw guide installer that has seat inserts to install the guide gently, used on some vintage heads...
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Re: Head heating required when changing bronze valve guides?

Post by createaaron »

I press out and press in bronze guides cold. On a refresh of an engine, we media blast the port and around the guides really well before pushing them out, if you don't and you push the guide out with carbon attached to the guide it will destroy the housing bore. Have not encountered a problem doing it this way yet.
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