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Old 04-01-2009, 08:07 AM   #1
Scooby Newbie
Member#: 177527
Join Date: Apr 2008
Chapter/Region: W. Canada
Location: Edmonton Canada
2004 STI

Default How to lap valves?

So I got my heads back from the machine shop and they still have very small leaks, I asked if they lapped the valves and was told that they don't do it anymore because it takes to long and the valves will stop leaking when you run the motor. So I need to know how to lap them myself, I got all the tools and lapping compound from NAPA but just need to know if you have to take out the valve seals or oil the stem or what other tricks there are. Any help would be great.

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Old 04-01-2009, 09:47 AM   #2
Scooby Specialist
Member#: 56297
Join Date: Mar 2004
Chapter/Region: Tri-State
Location: Long Island NY
2013 Focus ST
2004 STi MSPT Tuned


I've seen a video on youtube on how to do it, it seems simple to do.
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Old 04-01-2009, 03:46 PM   #3
Team Scream
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Member#: 121532
Join Date: Jul 2006
Chapter/Region: SCIC
06 FXSTi, 06 FXTAT
06 STi Wagon, 99 GF Wagon


Definitely take out the oil seals, and DO NOT use too much compound.
It does not take much nor does it take a lot of work to get them right if the seats and faces were ground properly.

You really want to avoid getting too much compound down in the bowls so that your clean up is easier.

Basically the valve and seat angles will have a shine to them before you start.
You smear a little compound on the valve face all the way around.
Place the valve in the hole, stick your suction cup tool on the top of the valve and starting from the top of your tool you spin back and forth with both hands. As your hands reach the bottom of the tool from the back and forth motion you stop and start at the top again.

Do this 2 or 3 times, then take the valve out, inspect the face of each angle on both the valve and the seat and when you have "matted" the finish evenly you are done with that valve and seat.

If when you take it out and look at the valve/seat they are still shiny or have grind lines in them rinse and repeat until the surface is a matte finish on each angle/face.

The first few rotations of the tool you will feel a gritty grinding sensation which gets less as you continue to rotate.
This is the grit in the compound grinding itself smooth.
You don't feel nearly as much of this when using the fine compound in the 2nd step.

Pretty easy process. take your time, and do not use too much downward pressure while spinning the valve, let the weight of the valve plus the tool be the downward force applied and do this consistently for each valve so you are repeating the process exactly ,.

It is pretty hard to screw up this process.

You will do this in 2 steps.
One is a coarse grit lap (120 grit compound)
Two is the fine grit lap (280 grit compound)

Clean the heads and valves really well when you are done.
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Old 04-01-2009, 04:46 PM   #4
Scooby Specialist
Member#: 112612
Join Date: Apr 2006
Chapter/Region: MWSOC
Location: Appleton,Wisconsin
2010 Legacy 2.5 CBS
2002 Impreza WRX WRB


For the compound I use permatex lapping compound first. Loctite makes an abrasive compound called "clover". I use that last. It does take a while. Afterwards,I hot tank the heads.
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Old 04-01-2009, 10:00 PM   #5
Scooby Specialist
Member#: 2532
Join Date: Sep 2000
Chapter/Region: South East
Location: Orlando, Fl
2001 2.5RS-T


Be aware that some valves are coated to increase their durability. If you lap such a valve you'll cut the coating and the valve will wear out sooner. Most new valves are very good and don't need lapped. Normally I use one of the old valves and lap all the seats using 800 grit clover compound. I'll only use a coarser grade of compound if necessary to get a good seat.
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Old 04-02-2009, 03:55 AM   #6
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Member#: 175435
Join Date: Mar 2008
Chapter/Region: MWSOC
Location: Minneapolis, MN
1986 RX7
Sunrise Red


I watched those videos on youtube and they really helped me understand the process of what is involved. Hey I actually feel like I could do it now, it isn't that hard! All I need is a couple simple tools.

This video explains almost completely how to do it, but of course they went quick and you would take more care on your own motor:
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Old 04-02-2009, 08:13 AM   #7
Scooby Newbie
Member#: 177527
Join Date: Apr 2008
Chapter/Region: W. Canada
Location: Edmonton Canada
2004 STI


Thanks for the help I'm sure that I can do this and not mess anything up. Are the STI valve coated?
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Old 09-03-2015, 11:20 PM   #8
Scooby Newbie
Member#: 171039
Join Date: Feb 2008
Chapter/Region: NESIC
Location: Colchester, Vermont
99 RSTi Type-R LTD
Mystic Blue Pearl


bump from the dead!

Will valve lapping decrease my lash clearance? In other words, would I have to re-shim?
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Old 09-04-2015, 05:42 AM   #9
Scooby Newbie
Member#: 359289
Join Date: Jun 2013
Chapter/Region: International
Location: Germany,Hamburg
2002 WRX STI Prodriv


I did mine a couple of Month ago and yes you have to re-shim...
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