Machining out Valve Guides

Stephen Hill

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I plan on removing a couple of bronze valve guides from the head. I want to machine out the valve rather than just pound them out and risk galling the aluminum guide hole. Yeah, I know, everybody has their own ideas on how to remove guides.

I have a decent mill and plan on milling away the top of the guide (the flanged valve spring end). Then remove most of the center of the guide and drive out the rest into the combustion chamber side. I assume this makes more sense than milling the guide from the combustion chamber end of things.

I am wondering about how thin to machine the walls of the guide, and still have something to work against to remove it.

Anybody have experience with this and have a few observations to share?
 
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I'm having a tough time machining the center out of the guides so I can remove them with minimum damage.

I started at the valve end, thinking I would remove the flanged part of the guide. Very difficult to do down in the valve spring pockets, and easy to damage the casting if you try to remove the whole flange.

I rethought the process and tried working from the combustion chamber end, but there is not a lot of points to mount the head so it can be worked on. I am starting to think I should be drilling instead of milling.

Do folks use counterbore style drills, working from the combustion chamber end??
 
I turned up a counter bore tool from silver steel. It took out the cast iron guides to the depth of the head, left enough for a punch to bear against, left a thin shell that collapsed inwards. machined the guide from the combustion chamber end. Depending on the bronze you might have to use a zero cutting rake on the counterbore tool. will post photos of the tool and guide after brekkie
 
Had a talk to engineer mate who does that all the time who advised as follows.

Firstly please don't take this the wrong way but he said you have to know what your doing and be careful otherwise you damage the head which back in the past he has done. You need a very good drill press or proper mill and set it up very carefully.

Secondly the guide material is relevant when selecting cutting tools. Standard cast iron guides are easy.

He uses a mill bit with a lead piece to remove the top of the guide down to the Head. Then a set of drills step by step going as deep as the length of the guide in the head. This leaves material at the button of the guide to punch out with into the combustion chamber. He leaves 1 mm wall thickness. Warms the head and then punches out the remaining guide. The aim is to collapse the guide in the head.
 
You need a tilting table and test indicator to properly locate the guide, machine the flange down to the casting, then use a .375 end mill and plunge down approx .5", the guide will easily pop out the combustion side

Machining out Valve Guides
 
I have done it this way with cast guides. You need a 5/16 core drill bit. Always work from the spring side. Mark the bit with tape so you stop when just below the head casting, .5" sounds about right but intake vs exhaust casting depths are different. Do not go all the way through. You need to leave material at the bottom for the punch. The top “button” of a cast guide will easily break off if the wall is thin enough. Heat head in oven at 350 degrees then drive out. Easy with cast iron guides but a messy job with lubricant and all the shavings.

Haven’t tried it with bronze. I guess it would depend on the type of bronze. I would not want to have to drill through very far in Ampco 45.
 
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FYI…. don’t blast clean the head with the guides out or you’ve ruined the head. Clean before you take them out.
 
dobba99 said:
I turned up a counter bore tool from silver steel. It took out the cast iron guides to the depth of the head, left enough for a punch to bear against, left a thin shell that collapsed inwards. machined the guide from the combustion chamber end. Depending on the bronze you might have to use a zero cutting rake on the counterbore tool. will post photos of the tool and guide after brekkie
Click to expand...
Photos as promised



Used with a hand held pistol drill. Drilled out from the chamber side.
 
Thank you. Lots of good information here. I am working with 850 guides which have the flange at the spring end. It complicates the task since I wanted to drive the valve from the combustion end toward the spring end. And bronze guides, which are harder to machine than cast iron.

I am removing only the intake guides. They are surprisingly clean and I feel ok driving them towards the spring end. With an exhaust valve, it would be better driving them the other way around, as the combustion chamber crap is way more abrasive.

A counterbore drill seems preferable, and that gives me the flexibility of using a drill press. My mill is a square column style, with no knee. Which meant that once I mounted the head on the angle plate, and tilted the head to the side to match the angle of the guides, I lost the Z travel (perpendicular to the table) necessary for tool changes, etc. PITA.

Once more, unto the breach.
 
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Forgive my ignorance, but why would you machine the guides out if you're blasting/cleaning the guide and chamber before removal, and also heating the head to drive them out? If you are doing both those steps, seems that driving out an unmachined guide would come out just as easily, no?

Driving the new ones in require heating, so why not do everything in one fell swoop?

Just the "ounce-of-prevention" approach?
 
Reduces the risk of scoring the guide hole bore, a small score will allow oil to leak down. The scoring risk is reduced by pre cleaning but heating the head to remove guides, which also heat up, needs a higher temp than fitting a cold guide into a hot head.
 
kommando said:
Reduces the risk of scoring the guide hole bore, a small score will allow oil to leak down. The scoring risk is reduced by pre cleaning but heating the head to remove guides, which also heat up, needs a higher temp than fitting a cold guide into a hot head.
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Thanks. I figured as much, just making sure I'm not missing something else.
 
The use of bronze guides needs a different approach to cast iron ones. The coefficient of expansion of the bronze guide is very similar to the aluminium alloy of the head so heating the head to remove said bronze guide will not help, That is why it is best to machine the old guides out. Heat the head and chill the new guides when fitting. The last three cylinder heads i have dealt with (all singles, 2 ES2s and an Ariel) two had bronze guides that had been hammered into the head cold and had come loose the other had cast iron guides that had been treated the same, hammered in cold, the result, the inlet guide fell out on removing the springs. All these heads required setting up and the guide hole reaming true to the seat, then a custom guide (from cast iron) making to suit the hole, fitting (heating the head,chilling the guide),& seat recutting if required.
 
acadian said:
You need a tilting table and test indicator to properly locate the guide, machine the flange down to the casting, then use a .375 end mill and plunge down approx .5", the guide will easily pop out the combustion side

View attachment 107242
Click to expand...
Setting the head up like that you will not be able to check the alignment to the valve seat. Invert the head and set up to the guide hole AND valve seat. Get that alignment correct and seat recutting is not needed or if it is, not by much.
 
The local machine shop said they use a "sleeve lock" on the new guides to ensure they are sealed to the head. The actual product is Loctite 640, which is a high termp high strength sleeve locking compound.

The guide holes in the head I am about to take in look great, and the guides were a tight fit.
Is there any reason to put anything on the new guides before they are installed? If so, what is recommended?
Doesn't high strength high temp loctite seem like a bad idea? How would you ever remove the guides in future?
 
Not normally required if you've got interference. . With 600 series heat the bolt or component with a torch , it will release the loctite .
 
Good to know. I install the guides myself. The guide bores were good so I didn't use any sealant.
Interesting that nowhere did I see a recommendation for any oil or grease on the guide or bore prior to installation.
 
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