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Old 07-13-2016, 05:33 PM   #1
Jeff Stout
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Default Question on lapping valves

This is on a Harley. I ported a set of heads ( getting ready for stock eliminator LOL). Replaced the valve guides and reamed to .002 to .003 stem clearance. Using old valves and cut face to 45 degree with a 30 degree under cut. Went to head with a kwik way and cut seat to 33-45-65 degree. Lapped valve and checked with flashlight through port and can see light past seat and valve face. Without valve spring and just the weight of valve. After about 4 attempts I no longer see light passing through. I faced new stones a couple times to make sure they were correct. Valve isn't bent. I don't have a way to check seat to guide but guides have a lip and bottom out in head properly I believe. I guess my question is do you need to lap along time to get a 100% seal around seat and valve face? I know its not a class motor but you guys give good honest help. Thanks Jeff
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Old 07-13-2016, 05:56 PM   #2
Billy Nees
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Default Re: Question on lapping valves

I know that I'll probably catch a bunch of crap for saying this but "valve seal is overrated!"
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Old 07-13-2016, 09:05 PM   #3
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Default Re: Question on lapping valves

Jeff,
Harleys have very short valve guides and they never go in exactly concentric to the previous guide or the seat. You always have to recut the seat. Have you checked your pilot to see if maybe it isn't bent a little ? Put it in the guide and touch the seat. Then put some dykem on the seat, turn the pilot 180 degrees and touch the seat again. It should touch right up. If it doesn't your pilot could be bent.

You can do the same thing to check your valve grinder. Chuck a valve up and grind it, then turn it 180 degrees in the chuck and grind it again. It should touch right up.

I always lightly lap valves just to make sure they are hitting the seat all the way around. I use 320 grit lapping compound. If the seat and guide are concentric and your pilot isn't bent or flexing, you should be able to lap the valve in and see a pattern with very little pressure.
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Old 07-14-2016, 07:52 AM   #4
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Default Re: Question on lapping valves

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Originally Posted by Billy Nees View Post
I know that I'll probably catch a bunch of crap for saying this but "valve seal is overrated!"
Billy, Would you grace us with your knowledge?

Rick Thomason
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Old 07-14-2016, 12:00 PM   #5
Jeff Stout
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Default Re: Question on lapping valves

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Originally Posted by BillK View Post
Jeff,
Harleys have very short valve guides and they never go in exactly concentric to the previous guide or the seat. You always have to recut the seat. Have you checked your pilot to see if maybe it isn't bent a little ? Put it in the guide and touch the seat. Then put some dykem on the seat, turn the pilot 180 degrees and touch the seat again. It should touch right up. If it doesn't your pilot could be bent.

You can do the same thing to check your valve grinder. Chuck a valve up and grind it, then turn it 180 degrees in the chuck and grind it again. It should touch right up.

I always lightly lap valves just to make sure they are hitting the seat all the way around. I use 320 grit lapping compound. If the seat and guide are concentric and your pilot isn't bent or flexing, you should be able to lap the valve in and see a pattern with very little pressure.
I will check pilot the way you suggested. It is a brand new one because of the size but doesnt mean its correct. I did the turning valve 180 in valve grinder and it checked good.
I went and did the exhaust valve yesterday and only took 2 times to get no light to shine through. Im going to do the other head and watch carefully how seat grinder is contacting seat with some bluing. Thanks for advice. Jeff
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Old 07-15-2016, 12:01 AM   #6
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Default Re: Question on lapping valves

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Originally Posted by Jeff Stout View Post
This is on a Harley. I ported a set of heads ( getting ready for stock eliminator LOL). Replaced the valve guides and reamed to .002 to .003 stem clearance. Using old valves and cut face to 45 degree with a 30 degree under cut. Went to head with a kwik way and cut seat to 33-45-65 degree. Lapped valve and checked with flashlight through port and can see light past seat and valve face. Without valve spring and just the weight of valve. After about 4 attempts I no longer see light passing through. I faced new stones a couple times to make sure they were correct. Valve isn't bent. I don't have a way to check seat to guide but guides have a lip and bottom out in head properly I believe. I guess my question is do you need to lap along time to get a 100% seal around seat and valve face? I know its not a class motor but you guys give good honest help. Thanks Jeff
The guide has to be round and strait, that means reaming it undersize then honing it to size, then your seat can be gound or cut and should come in. When you drop the valve on the seat you tap the center of the valve head with your index finger, if you feel any movement its not right.

Last edited by HP HUNTER; 07-15-2016 at 12:04 AM.
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Old 07-15-2016, 02:00 PM   #7
Mike Taylor 3601
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Default Re: Question on lapping valves

When lap valve if valve is good will have ring all the way around valve, if it does valve is good,seat can be off and valve will lap in,it will contact highest spot on seat and leave ring all the way around valve.
seat should have ring all the way around seat 360*,if doesn't seat needs to be cut or ground so you have 45* all the way around, will most likely end up wide on one side narrow on other,then take 30* and 60* and narrow 45 until it is even width all the way around,probably .075-.100'' wide.
Should be able to lap valve about 30 seconds by hand and it have rings all the way around valve and seat,when correct. Can use machinist dye/layout fluid if needed to see better.

Billy,
I agree with you most of the time,but I half way disagree on this,exhaust get away with a little leak,intake not gonna get away with much of a leak,with out blowing fuel back up the runners.
Or is there more to your comment,like buddy of mine that worked on mowers,came in one day while I was putting seats in a Briggs twin,common for them to fall out,he told me electronic ignition caused that,???? he said when had points,got a set yearly,got all grass cleaned out of cooling fins,electronic doesn't get cleaned out so runs hot seats fall out,LOL
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Old 07-15-2016, 02:15 PM   #8
Jeff Stout
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Default Re: Question on lapping valves

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Originally Posted by Mike Taylor 3601 View Post
When lap valve if valve is good will have ring all the way around valve, if it does valve is good,seat can be off and valve will lap in,it will contact highest spot on seat and leave ring all the way around valve.
seat should have ring all the way around seat 360*,if doesn't seat needs to be cut or ground so you have 45* all the way around, will most likely end up wide on one side narrow on other,then take 30* and 60* and narrow 45 until it is even width all the way around,probably .075-.100'' wide.
Should be able to lap valve about 30 seconds by hand and it have rings all the way around valve and seat,when correct. Can use machinist dye/layout fluid if needed to see better.

Billy,
I agree with you most of the time,but I half way disagree on this,exhaust get away with a little leak,intake not gonna get away with much of a leak,with out blowing fuel back up the runners.
Or is there more to your comment,like buddy of mine that worked on mowers,came in one day while I was putting seats in a Briggs twin,common for them to fall out,he told me electronic ignition caused that,???? he said when had points,got a set yearly,got all grass cleaned out of cooling fins,electronic doesn't get cleaned out so runs hot seats fall out,LOL
Mike Taylor 3601
I think this was more my problem. I went and cleaned up Intake seat again and lapped valve and cleaned up in one pass. Just finished second head and paid attention to margin by bluing seat before grinding and these valves lapped with one shot each.
Thanks for all input I think they look pretty good now. Jeff
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