Can you tell if the valve guides are in the block correctly without pulling the head? I just bought a used 25 V-Twin engine that had to badly bent push rods (2) in which I replaced. After reading some, I read that overheating can cause the valve guides to move in the head. I didn't pull the head, only the bottom end and cleaned the crankcase and put it back together. I replaced 2 push rods and adjusted the valves. It seems to run fine but after reading about overheating it made me think before I go further. When I removed the top plastic covers it looked like either mice had a home or somehow was swamped with grass clippings, worst than I have ever seen on anything. That what makes me believe it may have over heated at some point. The valves were free to push open by hand but in my way of thinking if the guide moved toward the spring it would cause extra pressure causing the push rod to bend. I did start it and it seems to run fine but only ran it for maybe a few minutes. Your thoughts???? In reading this to myself I don't think the spring tension would change unless the valve spring cap bottoms on the guide. Again any ones thoughts???
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V-twin Valve Guides
- Thread starter Budd4U
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Export threadYou are correct when the head overheats the guides move up inside the springs toward the spring cap and keeper until the rocker arm tries to push the valve open and the valve stem cap hits the rocker and the push rod bends. In some cases the valve guide will move up to within 1/4 inch of the valve stem cap. Compare the height of the valve guides in the head and it should be easy to spot if one has moved since both guides should be the same height. Exhaust valve guide will be the one to move which would be the valve closest to the muffler exhaust pipes.
I took the valve cover off and then hand turned the engine until the rocker arm was at it's max travel and then tryed to push the valve open even wider and I can by hand. I did this on all of the valves and they all traveled further by pushing with my fingers. So I believe the valve caps are not bottoming on the valve guides. I didn't take the valve springs off to look at it but I think with the extra travel they will be okay. Your thoughts? It runs great...You are correct when the head overheats the guides move up inside the springs toward the spring cap and keeper until the rocker arm tries to push the valve open and the valve stem cap hits the rocker and the push rod bends. In some cases the valve guide will move up to within 1/4 inch of the valve stem cap. Compare the height of the valve guides in the head and it should be easy to spot if one has moved since both guides should be the same height. Exhaust valve guide will be the one to move which would be the valve closest to the muffler exhaust pipes.
You should be able to compare the height of the guides without removing the springs or even the rockers. But if they have started to move they will continue to move even after the overheating issue is resolved.
Tinkerer200
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Valve guides should not extend more than 1/8" above the head casting. From what you say about the conditions under the cooling shroud, I suspect heat has caused the valve guides to slip regardless of what you say about being able to push the valve further and bent push rods are a further indication. While B&S says the only cure for slipped valve guides is new heads, I do have a permanent fix along with others furnished to me with permission to share. Address below, put in proper format and remind me the engine model and the problem.
Walt Conner
wconner5 at frontier dot com
Walt Conner
wconner5 at frontier dot com