Author Topic: Lesson in valving lapping please. (Read 3375 times)

Magpie · « **on:** March 17, 2011, 03:29:22 PM »

Hi guys! I've never lapped a valve in my life, can someone please give me a lesson in how to do this ? I've done a leak down test on the motor and it came out good but I've taken the head apart to have it jet cleaned. I suppose I could have the shop do it but I'd like to try it myself.
Thanks in advance,
Cliff.

Magpie · « **Reply #1 on:** March 17, 2011, 03:42:39 PM »

Sorry, I should have checked You Tube First! There's a bunch of how to videos there I'll have a look at.
Cliff.

cookindaddy · « **Reply #2 on:** March 17, 2011, 03:46:18 PM »

Magpie - if you did a leak down test and it was good, you don't have any problem with the seating of your valves.

Lapping valves is an ancient and venerable art, passed down from father to son (daughter?).

Seriously, it is not difficult and is covered in any basic auto text. You need a stick with a suction cup and a can of lapping compound (usually has coarse and fine grades in opposite ends of the same can). You put some compound on the sealing face of the valve, put it in the head and spin the stick between the palms of your two hands and then pull it out, wipe clean and take a look. You are basically sanding the mating surface between the valve and the head. Switch to the finer compound when you have a nice smooth even gray area where the two meet. Continue until you get tired. Soothing zen work really.

I am sure that others will have a better description. My dad showed me 50 years ago so I am probably out of date....

odiewan · « **Reply #3 on:** March 17, 2011, 03:47:44 PM »

Ok, it's been a while since I lapped in valves but the principle is fairly simple.
What you want to do is take each valve and put some lapping compound on the valve seal are (keep it away from the stem: the part that goes into the valve guide) put the value in the guide as if you were installing it. Then you spin the valve with something like this:
url]http://www.google.com/products/catalog?q=valve+lapping+tool%3F&um=1&ie=UTF-8&cid=8940557591088100578&sa=X&ei=z42CTdrxLIu8sQPT_aWIAg&ved=0CDoQ8wIwAw#[/url]

Basically it's a stick with a suction cup on the end.

Usually there is a course and a fine paste in the compound kit
You spin the valve back and forth with the course, then with the fine.

The other thing I was taught was to check for leaks by using some diesel oil. You put the head together without the camshaft installed so all valves are closed and pour a bit of diesel oil in the intake and exhaust ports and, if you did a good job lapping, the valves will be dry on the combustion chamber side. If you see wetness, well you gotta do it again.

Like I said, it's been a long time since I lapped in valves and it was on a old VW air-cooled engine with pushrod and no OHC. Some other folks here might have more info.

Quote from: Magpie on March 17, 2011, 03:29:22 PM

Hi guys! I've never lapped a valve in my life, can someone please give me a lesson in how to do this ? I've done a leak down test on the motor and it came out good but I've taken the head apart to have it jet cleaned. I suppose I could have the shop do it but I'd like to try it myself.
Thanks in advance,
Cliff.

Magpie · « **Reply #4 on:** March 17, 2011, 06:33:40 PM »

Thanks guys! Great information as usual. I love this place.

Cliff.

mlinder · « **Reply #5 on:** March 17, 2011, 06:46:02 PM »

Remember to only go as far as needed. You can get overzealous and recess the valves too far.

brianzenk · « **Reply #6 on:** March 17, 2011, 07:01:42 PM »

I watched this video and lapped the valves on my c70
1982 Honda Passport the next day.

mystic_1 · « **Reply #7 on:** March 18, 2011, 08:11:41 AM »

Quote from: mlinder on March 17, 2011, 06:46:02 PM

Remember to only go as far as needed. You can get overzealous and recess the valves too far.

Yup, also note that lapping won't remove larger defects but it doesn't sound like you have any.

It doesn't take much lapping at all to clean up the valves. Lap for just a few strokes and then wipe away the compound and examine the valve seat and face. You'll be able to see exactly where your contact area is. Continue lapping a little at a time and checking like this until you've got the contact areas looking nice, but before you've gone too far.

Google around for pics and info as to how the contact area needs to be, basically it shouldn't reach either end of the bevel on the valve face. Defects in the valve seat and face will show up as dark spots in the lapped area.

mystic_1

faux fiddy · « **Reply #8 on:** March 19, 2011, 01:44:57 AM »

I never saw the suction cup and stick. I have slipped a small hose over the end of the valve to use as a way to hold it and spin it in my palms.

dave500 · « **Reply #9 on:** March 19, 2011, 02:32:13 AM »

like tree fiddy i put a short rubber hose on the valve stem but i have it in a variable speed reversible power drill and pull it gently backwards,a few times in each direction,make sure the stem is oiled,do this with the stems removed and use new ones while your at it,you only need to scratch them in if they havent been cut,itll seal a whole lot better.

MRieck · « **Reply #10 on:** March 19, 2011, 05:19:51 AM »

I wouldn't recommend coarse grinding paste like the fella in the video is using.

SohRon · « **Reply #11 on:** March 19, 2011, 07:33:12 AM »

And, as an added benefit, once you get this technique down you'll be able to start a fire using two sticks just like in "Quest For Fire"...

OldSchool_IsCool · « **Reply #12 on:** March 19, 2011, 08:11:10 AM »

I use a conical spring and the T-handle from my tap set. Slip the valve into it's seat, put the spring over the valve stem, apply a little electrical tape to the stem for protection, then clamp the T-handle onto the stem. The spring will press the valve into the seat firmly and evenly. Now, apply a wee bit of lapping compound to the seat, smearing it evenly. From there, simply spin the T-handle a few times in one direction and a few times in the other. Inspect the seat for a nice, even dull gray band all the way around the valve and seat. If it's not even or if you notice scratches or minor pitting, do it again. Repeat until contented.

Magpie · « **Reply #13 on:** March 24, 2011, 01:26:28 PM »

Well guys, I took a deep breath, reviewed your posts and went at it. It looks ok but I'll assemble the valves in the head and check with the diesel oil. thanks for your input and help!
Cliff.

Magpie · « **Reply #14 on:** March 24, 2011, 11:33:12 PM »

Done and no leaks! More pics here http://forums.sohc4.net/index.php?topic=60120.msg969562#msg969562 and scroll to the bottom of page.
Cliff.

mrrch · « **Reply #15 on:** March 25, 2011, 04:43:37 AM »

Now after doing that, wasn't that simple?
Nice feeling to learn a new skill.

ak58lp · « **Reply #16 on:** March 25, 2011, 05:07:55 AM »

Quote from: mrrch on March 25, 2011, 04:43:37 AM

Now after doing that, wasn't that simple?
Nice feeling to learn a new skill.

I just did my this winter and it was very easy. It makes you feel good to know that you didn't need to pay a garage to do this for you. No hidden mystery here.

MRieck · « **Reply #17 on:** March 25, 2011, 05:20:58 AM »

That's an early head you have there

Magpie · « **Reply #18 on:** March 25, 2011, 07:37:51 AM »

It's from a 12/69 build, number 16xxx.
Cliff.

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Author Topic: Lesson in valving lapping please. (Read 3375 times)