cylnder head laping/ flating

rich4240

New Member
Jun 6, 2012
55
0
0
lefroy
I have been meaning to put together a quick tutorial on how to flat lap a cylinder head since the question does get asked on occasion. Tonight I finally did just that. Some may remember the 3hp Briggs I found a while back. It's been sitting on the work bench partially disassembled, so I figured what better candidate. This procedure is general in that it applies to OHV heads as well. Without further ado...

Materials:
- Wet/dry sandpaper sheets, at least 400 grit.
- Masking tape.
- Layout fluid like Dykem if you have it or a permanent marker if you don't.
- Soapy water. Light oil can be used too, but it's much messier, so I don't recommend it.
- Gloves. Okay, and safety goggles.

1.) You'll need a clean flat surface, the more precise the better. I have a real granite surface plate at my disposal that is flat to ±0.00006". For the purposes of this tutorial, a piece of decent window glass will suffice. I have even resorted to a polished concrete floor for quick 'n' dirty work. Tape the corners of your sandpaper down like this

2.) Put a little soapy water on the sandpaper. This keeps the paper from loading up and makes it last a bit longer:


3.)Make sure the head is completely clean with no gasket residue. You can put layout fluid/marker on the gasket surface now or wait until the next step. Put the head on the wet sandpaper and make a few swipes in a figure-8 motion, NOT a circle. Keep the pressure as even across the part as you can:

4.) Have a quick look for high and low spots. Here you can see the high spots are mostly around the head bolt holes:put the layout fluid/marker on there if you haven't yet:

5.) Use some more elbow grease. Rotate the part occasionally as you lap it. Check progress as you go. Low spots will still have color like this:

Keep lapping until you are comfortable that they are gone.

6.) Finish up with a relatively fine paper. Like I said before, 400 is probably a good minimum grit. I started with 400 and went directly to 1000. This is why I recommend using gloves:

7.) This is what I ended up with. Almost all of the hills and valleys are gone and the gasket has an RA more than fit for even a copper gasket:

see next post for step by step pics

brnot
 
Last edited:

2door

Moderator
Staff member
Sep 15, 2008
16,335
141
63
Littleton, Colorado
Rich,
Very nicely done. Thank you for your efforts. This should be shared with everyone who asks about blown or leaking head gaskets. I will add that the exact same procedure should also be applied to intake and exhaust manifold flanges, especially on the Chinese 2stroke engines.

Tom
 

GearNut

Active Member
Aug 19, 2009
5,104
7
38
San Diego, Kaliforgnia
Very nice tutorial, rich4240!
I hope that the photos can be matched up to the text in a more flowing manner, and that this thread be made as a sticky in the troubleshooting section or perhaps the high performance section.
This is really good information that answers a frequently asked question and is also a frequently recommended procedure to beginners.
 

rich4240

New Member
Jun 6, 2012
55
0
0
lefroy
fixed the post the best i could removed the pics in first post and put them in a second post and labled each pic to help it flow the best i could, its deflenty something every one should do between unflat cylnders and heads and unevenly torked parts it the #1 reason for blowen head gaskets

also how would we goabout makeing this a sticky

Very nice tutorial, rich4240!
I hope that the photos can be matched up to the text in a more flowing manner, and that this thread be made as a sticky in the troubleshooting section or perhaps the high performance section.
This is really good information that answers a frequently asked question and is also a frequently recommended procedure to beginners.
 
Last edited:

GearNut

Active Member
Aug 19, 2009
5,104
7
38
San Diego, Kaliforgnia
I have been meaning to put together a quick tutorial on how to flat lap a cylinder head since the question does get asked on occasion. Tonight I finally did just that. Some may remember the 3hp Briggs I found a while back. It's been sitting on the work bench partially disassembled, so I figured what better candidate. This procedure is general in that it applies to OHV heads as well. Without further ado...

Materials:
- Wet/dry sandpaper sheets, at least 400 grit.
- Masking tape.
- Layout fluid like Dykem if you have it or a permanent marker if you don't.
- Soapy water. Light oil can be used too, but it's much messier, so I don't recommend it.
- Gloves. Okay, and safety goggles.

1.) You'll need a clean flat surface, the more precise the better. I have a real granite surface plate at my disposal that is flat to ±0.00006". For the purposes of this tutorial, a piece of decent window glass will suffice. I have even resorted to a polished concrete floor for quick 'n' dirty work. Tape the corners of your sandpaper down like this


2.) Put a little soapy water on the sandpaper. This keeps the paper from loading up and makes it last a bit longer:



3.)Make sure the head is completely clean with no gasket residue. You can put layout fluid/marker on the gasket surface now or wait until the next step. Put the head on the wet sandpaper and make a few swipes in a figure-8 motion, NOT a circle. Keep the pressure as even across the part as you can:



4.) Have a quick look for high and low spots. Here you can see the high spots are mostly around the head bolt holes:put the layout fluid/marker on there if you haven't yet:


5.) Use some more elbow grease. Rotate the part occasionally as you lap it. Check progress as you go. Low spots will still have color like this:

Keep lapping until you are comfortable that they are gone.

6.) Finish up with a relatively fine paper. Like I said before, 400 is probably a good minimum grit. I started with 400 and went directly to 1000. This is why I recommend using gloves:

7.) This is what I ended up with. Almost all of the hills and valleys are gone and the gasket has an RA more than fit for even a copper gasket:

see next post for step by step pics

brnot
This is what I did with a little reply editing.
It will only allow 5 images per post unless an admin or paul allows more.
I hope that they can clean it up for you and allow all the photos. You have made a really good tutorial!
They can delete this post to remove any unnecessary clutter if I am cluttering things up too much.
 
Last edited:

rich4240

New Member
Jun 6, 2012
55
0
0
lefroy
One thing to add is don't worry about wreaking you wife's marble or granet conter top unless you start trying to sand the part with out the sand paper. Don't laff at that I know a guy who f***ed his wife's counter and had to sell his toys to buy a new one because he for got sandpaper