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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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top end rebuild, valve, valve guide, valve seal

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  #1  
Old 14th November 2018
T_worth T_worth is offline
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Default Bad Exhaust Valve Seal

I did a top end rebuild a few weeks ago due to either worn rings or seals, so I replaced both to play it safe. I used the Cometic top end rebuild kit C9763. For the valve seals; I cleaned the heads, lapped the valves and reassembled.....and now I have an oil leak from the front exhaust valve seal. Luckily, my other seals are okay.

https://ibb.co/emtYx0

I'm kicking myself now because I gambled and skipped the steps in measuring the valve-to-guide clearance and honing the valve guide (cause I didn't have the right tools). I'm hoping I just damaged the new seal when installing it instead of the valve stem/guide being worn. Now that I learned my lesson, I'm going to order the proper tools and tear into the front cylinder head and do the job correctly.

A guy at my garage said I should have polished my valve stem before reinstalling. Does anyone have any tips on doing that? I read putting it in a drill and sanding with fine grit. Any other things or tips to look out for would be appreciated so that I don't have to do this a 3rd time.

Thanks guys!
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  #2  
Old 14th November 2018
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aswracing aswracing is offline
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The stem seals that come in that kit are really easy to drive on too far, which causes them to leak because the top of the guide ends up interfering with the seal area.
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  #3  
Old 14th November 2018
T_worth T_worth is offline
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Ah. that is very likely. It was my first time installing seals, so I wasn't sure how to install them. The seal should be pressed down enough to meet the shoulder correct?

Pushing them down with my thumb didn't seem to push them down enough because the rubber would expand/bend and I was worried the tiny spring would pop off. In the end, I used a socket to tap the seal down. Perhaps I did tap it down too far
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  #4  
Old 14th November 2018
T_worth T_worth is offline
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once the seals are installed, is there a measurement that I should check from tip of valve stem (by the keepers) to top of valve oil seal?
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