Fixed Warped Slant (high compression) Head

Discussion in '2-Stroke Engines' started by Skyliner70cc, Sep 29, 2009.

  1. Skyliner70cc

    Skyliner70cc Active Member

    I've had two slant heads (aftermarket, not original engine) not seal properly to the engine. Closer inspection revealed that the heads were slightly warped.

    I then decided to go to a local NAPA machine shop and see what they could do for me. The shop manager said he couldn't help me and suggested I sand the heads on some glass to get them square again. I recalled that previous posters mentioned leveling the head with emery paper on glass but I have no glass in my garage.

    I then went down to my local glass store (City glass) and asked for some scrap glass. A very kind man gave me a nice sheet of glass for free (it wasn't scrap either).

    I then got a multipack of emery paper from harbor freight. I tacked the emery paper to the glass using a spray adhesive and then sanded the block starting with 60 grit paper and finishing with 220 grit paper.

    Total time to sand was about 15 minutes. After smoothing out the slant head, I sprayed some copper gasket spray on the head and reinstalled it onto the engine.

    I'm happy to say everything works as it should and the only leak I had was a blowout on my rear tire on my maiden ride with the fixed slant head. I will repeat this one of my other bikes later this week.

    I'm glad I got off my butt and got some glass and emery paper. Thanks to all who gave this tip before, it works!

    PS: I did use a new head gasket to ensure a good seal.
    Last edited: Sep 29, 2009

  2. Hawaii_Ed

    Hawaii_Ed Member

    ah, cool idea! Will do this soon with mine!
  3. Al.Fisherman

    Al.Fisherman Active Member

    I have done that to both my heads on the HT engines I bought. After receiving them and installed, I replace the cylinder, intake and exhaust studs, and using LockTite. Then lap the head and cylinder. I use DA paper (used in auto body shops) it has a self stick back. Stick one to ANY pane of glass and lap (actually you are milling it) the head. If you use the super thin head gasket from Sick Bike Parts, be careful that you don't take too much off. The piston to spark plug is very close. I've had 1 (on my first one that blew a head gasket) that the piston hit the plug and had to use 1 stock head gasket. Used 1 sheet of 220 grit. Learned this many years ago when I help rebuild Volkswagen engines. They have the same type jug/head set up, only we lapped the cylinder directly in the head with valve grinding compound. Believe it or not...NO head gasket is used.

    By the way the best way to see how much you need to mill is mark/coat both the cylinder and head mating surface with a magic marker of sorts.
    Last edited: Sep 29, 2009
  4. Pablo

    Pablo Motored Bikes Sponsor

    I've come to the conclusion all the slant heads are NOT flat. Mine was not anywhere NEAR flat :ack2:

    Glad you figured out how easy it is. In fact, I'm gonna get set up and take a bunch off my stock head, to get the compression the same as the slant head.

    Anyway the only thing you left out is cleaning it well between grit changes and doing a very thorough cleaning before reassembly. You don't want true grit in your engine!!:shout:
  5. Al.Fisherman

    Al.Fisherman Active Member

    :5: I'd like to think that one wouldn't have to spell out everything word for word., I look at it this way...putting a dirty part on/in a engine is like taking a dump and not cleaning ones self. But then again one never knows.
  6. Pablo

    Pablo Motored Bikes Sponsor

    I just wanted to make that point very clear. Lots of folks doing stuff like this for the very first time.
  7. Fletch

    Fletch Member

    I have a warped slant head on my engine as well, but I'm not sure if I should flatten it because the engine runs well, and there is no fuel leakage or anything like that. I can just see that the head doesn't seat evenly when it is on (the gasket isn't compressed all the way evenly). Should I sand it down? Compression seems really good. With 2 gaskets there is no gap at all. The only issue I have is that the engine rings like a bell, and I was thinking maybe evening the surfaces might help reduce some noise?
  8. Pablo

    Pablo Motored Bikes Sponsor

    If it's not leaking then no need to fix anything.
  9. Fletch

    Fletch Member

    Cool, thanks P
  10. motorpsycho

    motorpsycho Active Member

    you can also put some clay on top of the piston to see how much you can take off the head.
    take the head off, and put a peice of clay on top of the pistion. put the head and gasket back on and torque the nuts. Install the spark plug and rotate the engine one time. when the piston gets to t.d.c. the spark plug will make an impression in the clay and this will tell you how close the spark plug is to the piston. remove the head and look at the clay. do some measuring, and you will get an idea of how much you can take off the head before the spark plug will hit the piston.
  11. Fletch

    Fletch Member

    That's an awesome tip, thanks! I've got a really long plug, so that will come in handy if I take some off the head. Do you think that the non-level head could be causing extra sound because it is vibrating more?