I am working on a set of Pontiac heads and I made the mistake of letting my mind wander while cleaning parts. I got to wondering about the various methods of repairing worn valve guides; the advantages or disadvantages of each method. All of the engines that I have worked on (even the traditional ones) have steel valve stems running in cast iron valve guides. They seem to work well and last a long time. Back in the day when they wore out the typical quick repair was to knurl the guide and press it back to the original size. I've done it (and still have the knurling tools) and it seemed to work OK. Another method was to ream the guides oversize and install oversize stem valves. I don't know anyone who actually did this; possibly due to the cost of new valves. In most cases the valve guides were drilled/reamed out and new guides pressed in. I see that new guides come in two flavors cast iron or bronze. So finally to my question: which is better and why? Are there other methods that are better? A related thought is that in the dark ages in High School auto shop we used a piloted drill bit to remove the old guide. It occurs to me that using a hand held drill motor isn't the most accurate way to locate a hole. How critical is the positioning of the guide in relation to the rest of the head? Sorry for the ramble but parts cleaner sometimes goes to my head, Norm
Just my opinion. Knurling is a waste of time. Oversize valve stems work fine in a non-performance situation and are often used by large rebuilding firms. Bronze and cast iron guides both work well. Most of my circle track friend prefer cast iron. The pilot deal works amazingly well but is not as good as a quality seat-guide machine. Pete
Well valve seats are ground guide centric. if you get the guide off center you are going to have to cut a bunch of the seat out. Back in the dark ages I used oversized valve stems to save a set of heads more then once. After the guides have been knurled you have no other real option and usually by the time the guides go the second time it is time to replace the valves. I have even been known to take valves (used or new) and modify the stems to fit the heads. Some heads were just worth too much to toss. These days I put a bronze liner in the guide when I can. You punch the guide out if you need to, you p*** a knurling tool through the original guide then slide the liner in and use a knurl to press it into the knurled guide. Then ream to size and you are golden. The down side to bronze guides is that they are hard on the valve stem. Most of the time people don't keep the car that long but I have pulled some heads down with bronze guides that I had to replace the valves because of worn stems.
Valve guide wear is very significantly curtailed by installing roller tip rocker arm. No matter how well you get the geometry standard tips push the valve sideways. Oh, the subject, I like the bronze guides. One more thing on roller tip rockers; if you can get them on a shaft and elimate guides that too is better.
Bronze and cast iron both good, bronze is better if lubricated but iron will work ok without lubrication. They run the valves right in the head on a lot of engines so it must be ok. The new guide does not have to be totally accurate because you are going to cut a new seat off the new guide.
I'd say having the guide replaced with the proper size guide be it cast or bronze would be the wise move. I have done a lot knurled guides in the past and while it works you don't tend to get high mileage out of heads you do that on. I worked in a local cylinder head shop 20 something years ago that replaced the guides with undersize guides and then turned the valve stems down undersize and used special keepers. They were a royal pain in the **** for the next guy who worked on those heads with undersize guides and valve stems though. There are lots of ways to get the job done some just work a bit better and last a lot longer than others.
"The down side to bronze guides is that they are hard on the valve stem. Most of the time people don't keep the car that long but I have pulled some heads down with bronze guides that I had to replace the valves because of worn stems." That surprises me. I would have thought that the bronze being softer than the steel it would wear out first. The bronze guides are easier to put in than the cast iron guides. Every time I put in a cast iron guide I cringed expecting the head casting to break. That never happened but I cringed anyway. I understand that the valve seat locates off of the guide. Is there any advantage to intentionally moving the guide? I'm thinking that if the guide isn't properly oriented that could screw up the way the rocker operates the valve; forcing it side to side for example. Oh well more random thoughts. Sometimes it don't pay to look at things too closely.
Friction coefficient. The bronze doesn't wear and the steel does because of friction coefficient. it is a matter of physics I think.
There are bronze liners available , my local machine shop uses them & reports good results...tooling is not horribly expensive & they install easily.. dave
Either click on reply and it comes up automatically as a quote, or if you want a multi quote, you click on quote,(as many as you want to quote)then click on reply on one that you are also going to quote. There will bean insert quote ****on on the bottom left put your curser where you want your quotes to land then click on the insert ****on and follow the instructions. Give it a whirl you can always delete it after if you don't like it.
They used to put offset guides in the head to move the valve over, so they could put in larger valves. This was done years ago before aftermarket heads.
Now that makes a lot of sense. Naturally there is a limit to how far you can go before bad things start to happen. I can also see where the roller tip rockers would limit the side thrust forces on the guide. Thanks to all for the interesting exercise. It seems like there is a lot of effort in getting the rotating ***embly just so but I don't hear so much about the valve train. I think that I will go out and inhale some more parts cleaner, Norm
these old kits are still out there , an easy HOME based way to repair replace v/guides. http://www.ebay.com/itm/KL-K-LINE-1...626492?hash=item51e7d1a27c:g:SsoAAOSwYSlXhTKQ .502 bronze or cast would be a mach shop route... although if the guides HAVE been replaced before by a machine shop , you can get a air driver (or hand ) driver and replace then at HOME. KNURlizing can/might hold for a few thousand miles its a bandaid/temporary for a genuine repair. For YOUR application i'd stay with cast.
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