Valve Guides

[FelicityRebuild]

I've read that Don doesn't recommend replacing valve guides unless absolutely necessary, I'm curious why? I have 2 guides that need replacing, 1 actually broke as I was removing the valves (I admit I may have gotten a bit overzelous with this particular valve), and the other is fused to the valve, but for the one to break like it did, it appeared to be metal fatigue. I was thinking I'd just replace them all to be safe, and for $9 it seemed worth it until I read not to. So why not?

[hanleyclifford]

valve guides

Good question - why not? If you broke a guide removing a valve, it's a good bet you should replace them all. You can get them from MM, and driver and reamers from the Goodson catalogue. Its easy to do the job yourself, then you'll know exactly what you've got. I can get you the Goodson numbers if you like.

[FelicityRebuild]

Silly me.

I found the goodson website. Thanks. Never knew that company existed. Now the big question is what size driver? Silly me. I was just going to use a phillips head screwdriver and a hammer.

[hanleyclifford]

driving valve guides

I found the goodson website. Thanks. Never knew that company existed. Now the big question is what size driver? Silly me. I was just going to use a phillips head screwdriver and a hammer.

If you have not done this before, here are a few suggestions. Use the correct tool. I have GP-431 from Goodson. Before you begin make note of the position of the guides in the block so you will get exactly back to it. In driving the guides use heavy ball peen with short, square, moderate and accurate strikes. After all the new ones are in, ream to the tolerance of your choice. Read Don Moyer's thoughts on this first. I use a .314 from Goodson
Good driving!

[thatch]

Good advice

Matt,
hanleyclifford is spot on with his valve guide installing technique.
I recently replaced all 8 in my spare A4 and the process went very smoothly. Whoever does the seat cutting for your valves will be thrilled to have an accurate hole to alleign his cutter to.
Tom

[FelicityRebuild]

Thanks for the tips. I'm pretty sure I'm going to replace the guides, but this raises a stupid newbie question. How necessary is it to re-cut the valve seats? Mine are pretty clean and don't seem to need a re-cutting. Is it something I can do myself provided I can find the valve seat cutting tool? Can I get away with what's there now?

[hanleyclifford]

valve seats

The question is a good one, not stupid. I never recut valve seats unless there has been a bent valve or other issue requiring it. If everything looks good, just lap the valves in using an appropriate pumice. Everytime you grind valve seats, you are losing material which should not be done routinely.

[FelicityRebuild]

Good.

I was hoping for that answer. The valve seat question was the only thing now stopping me from replacing the guides. I can now click on 'submit' and get my order in. Thanks all.

[thatch]

Fun stuff

Matt,
After you have replaced the valve guides and cleaned or replaced the necessary valves there are a couple of tests you can do to decide if lapping or cutting is the way to go on your seats. While I agree that lapping is the way to go on these engines, trying to lap several thousants of a inch of seat material away is a very long ordeal. The old worn guides allowed the valves to live at what was not a perfect 90 degree angle so the seat was not wearing evenly around it's circumference. Marking the seat with a felt marker and then rotating the new or cleaned valve in it's new position will quickly show any high or low spots. Once you have found the low spots you can use a feeler guage to measure how much material will need to be removed. Using a drag method, where you insert the feeler guage between the seat and valve and then "drag" the guage out while putting pressure on the valve face, will give you a fairly good measure of how much material needs to be removed.
Tom

[67c&ccorv]

I've read that Don doesn't recommend replacing valve guides unless absolutely necessary, I'm curious why? I have 2 guides that need replacing, 1 actually broke as I was removing the valves (I admit I may have gotten a bit overzelous with this particular valve), and the other is fused to the valve, but for the one to break like it did, it appeared to be metal fatigue. I was thinking I'd just replace them all to be safe, and for $9 it seemed worth it until I read not to. So why not?

Unless you are experienced at this sort of work I would not recommend it for an amature. I am not saying that an amature enthusiast can't do a good job but I am saying that this sort of job requires knowledge, experience and training.

Anyone can get in there with a ball peen and drift and knock guides out and back in but there is a lot more too it than that!

The fitting of valve guides to the cylinder head (or in our case the A-4 block) is a undertaking that requires the ability to work with torlerances in the order of 3 decimal places and an understanding of the machining process and techniques involved.

Why not pull the block, send it to Moyer and have them do the work for you? It will cost more money than DIY but in the long run will save you the expense and frustration having your motor konk out at the worst possible moment and the misery of pulling a motor twice to do something that only needs to be done once.

FWIW the valve guide is made of cast iron - pretty easy to bust one if the right force in the wrong direction is applied!

Cheers!

[lat 64]

Hi,
The hazard with just lapping your valve seats after replacing the guides is that the new guides will never be in exactly the same concentric circle as the old guides. At least most of the time.
If the valves are new, this will be even more apparent.
If your use the old valves with some wear on the stems then you might get away with it(not my recommendation of course).
You can test the seat with lapping compound. See my drawing, the seat on the left is concentric, the right one is not. This is also a good way to check your work even if you do cut new seats.

Russ

[hanleyclifford]

concentricity

Hi,
The hazard with just lapping your valve seats after replacing the guides is that the new guides will never be in exactly the same concentric circle as the old guides. At least most of the time.
If the valves are new, this will be even more apparent.
If your use the old valves with some wear on the stems then you might get away with it(not my recommendation of course).
You can test the seat with lapping compound. See my drawing, the seat on the left is concentric, the right one is not. This is also a good way to check your work even if you do cut new seats.

Russ

Russ, I have to agree with your method for checking to see that valve and seat are finished and mated correctly. However, I disagree with the statement that " new guides will never be in exactly the same concentric circle as the old ones". Assuming that the block is not damaged, and the guides, old and new, were machined correctly any loss of concentricity will be due to wear of the old guides. It is possible that a previous cutting of the valve seats without replacing the guides could lead to a loss of concentricity, but this is the fault of the now less than concentric seat with respect to the guide. But of course the result is the same and new valves and guides will bring the deviation to light. For this reason valve seats should not be machined if the guides have gone out of tolerance. I think we would agree that in the case under discussion, after the guides have been changed and reamed and any new valves fitted, your test should be performed to see if cutting is required.

[lat 64]

Russ, I have to agree with your method for checking to see that valve and seat are finished and mated correctly. However, I disagree with the statement that " new guides will never be in exactly the same concentric circle as the old ones". Assuming that the block is not damaged, and the guides, old and new, were machined correctly any loss of concentricity will be due to wear of the old guides. It is possible that a previous cutting of the valve seats without replacing the guides could lead to a loss of concentricity, but this is the fault of the now less than concentric seat with respect to the guide. But of course the result is the same and new valves and guides will bring the deviation to light. For this reason valve seats should not be machined if the guides have gone out of tolerance. I think we would agree that in the case under discussion, after the guides have been changed and reamed and any new valves fitted, your test should be performed to see if cutting is required.

Hanley,
I think your right about the new guides can be concentric with the old seats. Never is a word that should never be used. I just did not want a beginner to assume all is well, and pop the new valves in without checking the seat contact. Most of the stuff I fixed(in my previous life), was old chev small blocks and they were so worn we nearly replaced everything. These little flatheads are like gems in comparison.
Back in the day I have seen too many warped heads and green castings, so I don't assume anything. Aluminum was the worst, but that is not an issue here.
I should add that we used an El Marko brand marking pen to sue as "bluing" to watch seat width as we ground them, and regular bluing to check each seat for fit.
To be sure cut or grind new seats only when necessary

Cheers,
Russ

[hanleyclifford]

valve job recap

Felicity rebuild - Assuming that you have decided to go ahead with replacing all your guides, and now that we have all chased this thing around the barn a few times, maybe we can set up a recommended sequence for you. First, install the new guides. Second, ream to desired tolerance. Third, designate all valves to respective holes, including new ones if applicable. Fourth, test each valve to its seat using the method described by Russ. Fifth, grind seats that are too far out of concentric or too worn to be lapped properly. Some body please make addition or correction if I've left anything out.

[67c&ccorv]

Russ, I have to agree with your method for checking to see that valve and seat are finished and mated correctly. However, I disagree with the statement that " new guides will never be in exactly the same concentric circle as the old ones". Assuming that the block is not damaged, and the guides, old and new, were machined correctly any loss of concentricity will be due to wear of the old guides. It is possible that a previous cutting of the valve seats without replacing the guides could lead to a loss of concentricity, but this is the fault of the now less than concentric seat with respect to the guide. But of course the result is the same and new valves and guides will bring the deviation to light. For this reason valve seats should not be machined if the guides have gone out of tolerance. I think we would agree that in the case under discussion, after the guides have been changed and reamed and any new valves fitted, your test should be performed to see if cutting is required.

1.) The old adage used to be if new valves are installed then new guides should be also - unless the bore of the guide has almost nil or acceptable wear. High quality bore measuring tools and the ability to compute the tolerances is a must.

2.) Valve guides are an interference press fit within the block (or cylinder head). Whenever they are drifted out with a hammer and drift (especially without properly heating the surrounding block material) you can guarenttee that the removal process will have modified the concentricity of the valve guide bore by loss of bore material along with the guide. Same thing when the new guide is installed - drifting it in without heating the guide bore and freezing the guide itself will cause loss of concentricity. (It should really be done with a tool that can hydraulically press the guide into the block.)

3.) Often the removal process so enlargens the valve guide bore in the block that a oversize hole must be drilled and an oversized valve guide installed - that is why they make replacement valve guides in various oversizes.

4.) Valves, valve guides, seats and valve geometry are some of the most precise and highly stressed components installed in an engine - even our A-4's.

That is why I suggest leaving the work to those who have the expertise and the tools to do the job properly.