Lapped my head

Pablo · #1 06-26-2008, 11:53 PM

Did the Norman wet paper, water and dish soap on glass thing.

Took just a few thousands off, maybe about .005"-.008". It 's a bit hard to measure without a proper height gage. I used the butt of a caliper. I took enough material off to eliminate the small dent/gouge shown below. I had only one freak out moment - I thought I sheared a head stud - but it was a loosened stud spinning until seated. Phew.

Anyways it started up like it's usual happy self, runs like a champ. Can't say I felt much power improvement during my short ride, maybe a tiny bit more low end grunt.

Easy Rider · #2 06-27-2008, 02:21 AM

Pablo,
If you want a cheap way to raise your compression, try using a NGK B8HS plug. That's what I did for hundreds of miles on my bike before I sold it. When I last checked it, the plug was in perfect shape and the color was a nice brownish tan color.

Pablo · #3 06-27-2008, 09:34 AM

Pretty quick and easy to lap it. I was mainly doing it to make sure it is flat and remove the factory ding - plus have some relaxation. I run a NGK B7HS
.....and it too seems perfect....I'm really wondering if anything fro B4HS-B8HS will work fine.

jasonh · #4 06-27-2008, 10:00 AM

Have you done any calculations to determine how much you raised the compression?

I'd like to know how a spark plug can raise your compression...maybe the plug is bigger or something?

Oh and I believe that raising the compression should make the motor a tiny bit more efficient. Maybe keep an eye on your fuel consumption?

Pablo · #5 06-27-2008, 10:10 AM

Quote:

Originally Posted by jasonh

Have you done any calculations to determine how much you raised the compression?

I'd like to know how a spark plug can raise your compression...maybe the plug is bigger or something?

Oh and I believe that raising the compression should make the motor a tiny bit more efficient. Maybe keep an eye on your fuel consumption?

I don't know the volumes so I can't calculate it. I colder plug could have more volume at the insulator....

I don't keep track of fuel consumption that closely. I am also under the impression that everything else in good order, raising CR can get a boost to low end torque.

MrLarkins · #6 06-27-2008, 10:59 AM

i've lapped cpu blocks for better heat transfer, but what are the physics behind lapping your cylinder head?

jasonh · #7 06-27-2008, 11:22 AM

shaving a wee bit off the bottom of the head will make your combustion chamber a little bit smaller, thus increasing the compression of the motor. This will give you a little more power, and a little more efficiency.

Plus, making sure it is flat and true will help reduce head gasket leaks.

Pablo · #8 06-27-2008, 11:25 AM

Quote:

Originally Posted by MrLarkins

i've lapped cpu blocks for better heat transfer, but what are the phycis behind lapping your cylinder head?

The physics?
1) Flatter for better seal (not that there was a problem)
2) Smoother for better seal (got rid of some Chinisesisms - see photo)
3) Slight material removal (with a slight compression ratio increase With better fuel air squish, perhaps efficiency improves a tad - as long as there is no pre-detonation.)

Skyliner70cc · #9 06-29-2008, 12:10 AM

From what I've been told by a vendor, you can safely remove 10 thousanths of an inch.

Pablo · #10 06-29-2008, 01:13 AM

Thanks - good input.

I went for a very long ride today after I fixed the fuel valve.....for the first time in a long time the beast just wasn't running right on the way home....sure enough the head nuts needed a lot of turns to get them back to 15 ft pounds. Basically they were loose! I should have retorqued them before my ride :duh: :headslap: