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Old 08-18-2010, 09:31 PM
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Valve Lapping

Hey all I have a 350 in my jeep and have a small exhaust seat leak on my number 5 exhaust valve. I was wondering if anyone has ever lapped a valve without removing the head from the engine. I have small hands and can get the valve down far enough to be able to get the compound on and wiped off. I was going to use a drill attatched to the valve stem on a low speed. Just wanted opinions if its feasible or if anyone has any insight they can give. I havent ran a leak down test to find the precentage but have hooked compressed air and can barely hear and feel air coming around the seat. thanks everyone!

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Old 08-18-2010, 11:12 PM
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Cunferferth,

Boy you are going way back here. Lapping a valve to a seat requires that the valve turns clockwise then counter-clockwise. Then lift the valve off of the seat then do the left- right twist and so on. So just spinning the valve will not do so much. Besides you will never get the lapping compound off of all the parts with the engine still assembled.

I would put a shim under the spring and put it back together and run it a while. The extra pressure will cause the valve to hammer the seat and it may stop the slight leak. This is just a quick fix. If you want the valve to stop leaking, I think I would pull the head and grind the valve and seat again and then you know it is correct.

Good Luck
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Old 08-19-2010, 05:37 AM
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I know the technique, I should be able to use the drill and go forward and reverse and be able to tap the valve up and down. Getting the compound out is my only worry. I can use the air to blow out what I can't wipe off. Being the exhaust valve I feel it won't suck it back into the engine. This is my last resort to get by taking the head off being I just got the motor back together less than 500 miles ago. I guess my first order is to get a leak down tester, what's the maximum leak percentage I can get away with? Thanks
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Old 08-19-2010, 05:46 AM
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If you need to re- lap that valve the only way to do it is pull the head, if not you will be doing the complete rebuild again as there is no way to keep compound and micro shavings from falling down on the piston. Instant cyl. destruction with compound in that hole may as well pour sand in the oil pan.
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Old 08-19-2010, 06:56 AM
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Quote:
Originally Posted by Cunferferth
Hey all I have a 350 in my jeep and have a small exhaust seat leak on my number 5 exhaust valve. I was wondering if anyone has ever lapped a valve without removing the head from the engine. I have small hands and can get the valve down far enough to be able to get the compound on and wiped off. I was going to use a drill attatched to the valve stem on a low speed. Just wanted opinions if its feasible or if anyone has any insight they can give. I havent ran a leak down test to find the precentage but have hooked compressed air and can barely hear and feel air coming around the seat. thanks everyone!
No, the compound in the engine will be catastrophic. Pull the head and fix it
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Old 08-19-2010, 06:56 AM
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Bummer! Thanks for the info! I have the fel pro metal shim gasket..think I can reuse it?
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Old 08-19-2010, 07:19 AM
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Quote:
Originally Posted by Cunferferth
Bummer! Thanks for the info! I have the fel pro metal shim gasket..think I can reuse it?
no.

If you can actaully hear air escaping you need the seat and valve cut- or a new set of heads.
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Old 08-19-2010, 07:29 AM
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Quote:
Originally Posted by Cunferferth
Bummer! Thanks for the info! I have the fel pro metal shim gasket..think I can reuse it?
I wouldn't bother taking the chance- they're dirt cheap and for the work involved to redo it if/when it leaks isn't worth the possible savings, IMHO.
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Old 08-19-2010, 07:51 AM
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I can't hear the air escaping I can feel it and can only hear it when I stick my finger in the exhaust port over the area it's leaking..I'm gonna just pull the head and do it the right way..wanted to go around that but it's my only choice
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Old 08-19-2010, 07:55 AM
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Quote:
Originally Posted by Cunferferth
I know the technique, I should be able to use the drill and go forward and reverse and be able to tap the valve up and down. Getting the compound out is my only worry. I can use the air to blow out what I can't wipe off. Being the exhaust valve I feel it won't suck it back into the engine. This is my last resort to get by taking the head off being I just got the motor back together less than 500 miles ago. I guess my first order is to get a leak down tester, what's the maximum leak percentage I can get away with? Thanks
BTW . You can't get away with ANY leakage past a valve for very long . No percentage is acceptable .
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Old 08-19-2010, 08:08 AM
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It's just weird though because on a compression test #5 cylinder is the one leaking but it read 180psi along with 1,3, and 7
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Old 08-19-2010, 08:14 AM
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Quote:
Originally Posted by Cunferferth
It's just weird though because on a compression test #5 cylinder is the one leaking but it read 180psi along with 1,3, and 7
If you just have a slight leak on the valve seat it probably wouldn't show up in a compression test . Go ahead and pressurize the #5 cyl . Are you sure the lifter isn't adjusted too tight ? If you have ANY leakage past the valve you will have to pull the head to fix it . If you continue to run it , you run the risk of ruining the valve and the seat to where a regrind won't be enough .
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