Valve stem guide damage
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Joined: May 2011
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From: Morgantown, WV
Valve stem guide damage
Long story short, pulled the head thinking bent valve was my issue, valve is actually fine. but the guide hole is deformed now. Its bigger. I want to know what my options are now. Getting another head isn't one unless i can find one pretty cheap. I'm going to call some machine shops in the area to see what they can do or recommend. If I can fix it myself I will, but if its going to take precision machining and pressing in a sleeve, ill have to leave that to a professional.
Its the exhaust valve for cylinder 7. Im still trying to upload a picture.
Its the exhaust valve for cylinder 7. Im still trying to upload a picture.
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^ Yeah, what he said. But I'll add that diesel valve guides are *really* easy compared to gassers since almost all diesels have perfectly vertical valves.
Precision drill and ream undersize to fit replacement guide. For fleet work if the guide is done precisely enough it can re-enter service without further work. Most machine shops won't like to try to do this since cutting in the seat will guarantee a good fit for the new valve.
Always a good idea to check valve face protrusion. Mostly so that if you have low ones you can replace them to keep your compression ratio where it *should* be. IDI's are high enough compression that relatively subtle changes in valve protrusion can make differences that are worthy of fixing. If you can't bring it to spec with replacement valves, seat work is needed. This kind of thing doesn't show up much in automotive stuff though since they don't see the run time to cause that kind of wear unless something funky has gone on. And of course valve protrusion must have adequate clearance for pistons.
Precision drill and ream undersize to fit replacement guide. For fleet work if the guide is done precisely enough it can re-enter service without further work. Most machine shops won't like to try to do this since cutting in the seat will guarantee a good fit for the new valve.
Always a good idea to check valve face protrusion. Mostly so that if you have low ones you can replace them to keep your compression ratio where it *should* be. IDI's are high enough compression that relatively subtle changes in valve protrusion can make differences that are worthy of fixing. If you can't bring it to spec with replacement valves, seat work is needed. This kind of thing doesn't show up much in automotive stuff though since they don't see the run time to cause that kind of wear unless something funky has gone on. And of course valve protrusion must have adequate clearance for pistons.
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Always a good idea to check valve face protrusion. Mostly so that if you have low ones you can replace them to keep your compression ratio where it *should* be. IDI's are high enough compression that relatively subtle changes in valve protrusion can make differences that are worthy of fixing. If you can't bring it to spec with replacement valves, seat work is needed. This kind of thing doesn't show up much in automotive stuff though since they don't see the run time to cause that kind of wear unless something funky has gone on. And of course valve protrusion must have adequate clearance for pistons.
Valve /sealing/ issues, however...
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Assuming a 21.5 target ratio and 2.33ci combustion chamber volume at tdc, .050" would drop compression ratio by about half a point with a 2" diameter face valve. Not a huge difference, and the wear is split between the seat and valve, so it's not unreasonable to find that kind of wear.
I found similar wear on one exhaust valve seat on an engine that was troublesome to get started. Unfortunately it was on the exhaust side of an iron head and had no seat, so I had to machine and treat a seat, machine the pocket for it and lap in a new valve. With no other changes it fired up easy after that. Looked like a factory machining goof.
The high compression of IDI engines exaggerates even the most modest combustion chamber volume changes.
Now having said that, this was on an IDI three cylinder industrial engine running 22.5:1 compression. Such an issue might never have been noticed on a V8. Perhaps a question of whether one wants good... or good enough. When the head is off is the most excellent time to weigh that option.
I found similar wear on one exhaust valve seat on an engine that was troublesome to get started. Unfortunately it was on the exhaust side of an iron head and had no seat, so I had to machine and treat a seat, machine the pocket for it and lap in a new valve. With no other changes it fired up easy after that. Looked like a factory machining goof.
The high compression of IDI engines exaggerates even the most modest combustion chamber volume changes.
Now having said that, this was on an IDI three cylinder industrial engine running 22.5:1 compression. Such an issue might never have been noticed on a V8. Perhaps a question of whether one wants good... or good enough. When the head is off is the most excellent time to weigh that option.
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Joined: Dec 2011
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Hm, something I just learned from my machine shop:
You can get valves with oversized stems. My own heads which I'm having rebuilt were all worn, and they decided the cheapest way to go was just bore the stems 0.015 over and use 0.015 oversized-stem valves.
This seems like a cheap and easy way to go -- just have your machine shop enlarge the stem and add a single new valve.
You can get valves with oversized stems. My own heads which I'm having rebuilt were all worn, and they decided the cheapest way to go was just bore the stems 0.015 over and use 0.015 oversized-stem valves.
This seems like a cheap and easy way to go -- just have your machine shop enlarge the stem and add a single new valve.
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Joined: Jun 2014
Posts: 221
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Hm, something I just learned from my machine shop:
You can get valves with oversized stems. My own heads which I'm having rebuilt were all worn, and they decided the cheapest way to go was just bore the stems 0.015 over and use 0.015 oversized-stem valves.
This seems like a cheap and easy way to go -- just have your machine shop enlarge the stem and add a single new valve.
You can get valves with oversized stems. My own heads which I'm having rebuilt were all worn, and they decided the cheapest way to go was just bore the stems 0.015 over and use 0.015 oversized-stem valves.
This seems like a cheap and easy way to go -- just have your machine shop enlarge the stem and add a single new valve.
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