Engine Trouble Mods for easier starting.

Discussion in '2-Stroke Engines' started by jefuchs, Jan 11, 2013.

  1. jefuchs

    jefuchs Member

    As I posted earlier this week, I finally got my bike running, after much more work than I would have anticipated. Since then, we've had tropical storm conditions, so I have only run the motor that one time.

    But I thought I'd share some of the work that went into getting it going.

    First, due to my physical limitations, I needed a smaller chainwheel to make the bike easier to pedal. You'll never get the motor running if you're struggling just to pedal the bike. After a lot of searching, all I could find was a chainwheel that fit my bike, but not my chain, and a chainring that fit my chain, but not my bike. So I bolted the two together, and it seems to work pretty well. I'm considering this a prototype, as the two should probably be welded together if I decide to keep it.

    Next, I added a decompression valve to the motor. This really works great. I had never heard of decompression valves until I saw a post about them on this forum. My chainsaw is electric, so I never had a need to know about them.

    Third (and I hope this is temporary), I took a tube from a WD-40 can, and bent it 90 degrees with a little heat, and glued it into my air filter cover so I can spray starter fluid without removing the cover. I'm hoping I will only rarely need this.

    My brand new bike looks really beat up in the pics, and yes, I scraped it up a bit in the process, but the flash on my camera makes it look a lot worse than it is. With a little touch up, it'll look good again.

    Attached Files:

  2. Fabian

    Fabian Well-Known Member

    Jeff, can you 'please' tell us your story on how you machined the cylinder head to accept the decompression valve, in every tiny detail.
    Can you please take the cylinder head off your bike and show us what the decompression valve looks like from the combustion chamber side.

    I'm really keen to attach a decompression valve to my engine, but nothing shows how it's done like a photo tutorial on the subject. Maybe you can make a complete new thread on this subject, because it's a needed level of technology, especially for those with a high compression (slant) cylinder head, and using a SickBikeparts shift kit, where pedal start is the only method; bump start not being a possibility.
    Last edited: Jan 11, 2013
  3. V 35

    V 35 Member

    Old European motorcycles often used compression releases, usually found on big singles. Larger small engines [ 4 cycle ]
    use a bump on cam to bleed off compression, when the engine runs, the bump passes by so quickly that the valve does not open.
    Others use a cam that retards during cranking, advances during running at higher RPM .
  4. jefuchs

    jefuchs Member

    Fabian, I'll give you the short version now, and the longer version after I take the head off (which I need to do, keep reading) and take pictures.

    I put the head on my drill press, angled at 30 degrees so that it was perpendicular to the drilling line. Then instead of a drill bit I used a 1/2" plunge router bit to remove the fin that was in the way. This had to be done in stages, because I needed to remove more than the half inch of fin that could be cut in one pass of the router bit. I used the router bit because it was what I had. A larger forstner might have been better. This was used only to remove the fin, and to remove a little bit more, to provide a flat surface on the curved part. I DID NOT use it to drill a hole.

    I bought a valve on eBay, and took it to the hardware store and matched it to a thread tapping bit (M10 x 1.0). Then I drilled the correct size hole, and tapped the threads.

    Of course, it wasn't that simple. I'll go into more detail later.

    While the valve does a great job, my motor still is not running. This is crazy, but even with the head bolted town tight, I could see daylight between the head and the head gasket. A clear sign that something was wrong. I added a second gasket, but still, this should not have happened, as it was designed to fail right out of the box.

    I don't understand how the motor ran (if only briefly) with this ill-fitting gasket, but I still cannot get it to run with the two stacked ones either. I bought a tube of gasket maker, and will see if that helps. Getting this thing running has turned into a monster headache. I need to re-read this forum's posting rules and see if cussing is allowed, because these things make me want to cuss a lot, and it would be unfair to restrain me.
  5. Fabian

    Fabian Well-Known Member

    Ahhh, so you are talking about using the scientific method of operation: a hammer in one hand and a bunch of swear words in the other!!!

    Can't wait for your extended explanation and photos of the decompression valve modification.
  6. BigBlue

    BigBlue Active Member


    Get rid of those acorn nuts and buy some shouldered grade 8 or higher hex nuts. You may not be getting proper torque with those acorn nuts, causing improper head sealing, especially now that you have a compression release valve. Also make sure you are using a torque wrench. 8mm nuts are torqued 120 to 175 INCH POUNDS - NOT FOOT POUNDS. 6mm nuts are torqued 60- 70 INCH POUNDS - NOT FOOT POUNDS. BE AWARE OF THE DIFFERENCE and know how to properly use a torque wrench.

    Also replace those studs. Use Loctite on studs only. The stock studs may not be bottomed out or may be different lengths. It is possible that you may have unscrewed the studs when removing the acorn nuts.

    You might want to use some Permatex gasket sealer on the head gaskets.

    Good Luck,

    AKA: BigBlue
  7. Fabian

    Fabian Well-Known Member


    The acorn nuts may be bottoming out, preventing proper clamping force on the cylinder head and the stud heights may be at different lengths, further compounding the issues of incorrect clamping force.
  8. jefuchs

    jefuchs Member

    Every tube of gasket sealer in the local auto parts store says not to use it on head gaskets. Even the store staff couldn't find a sealer that claimed it could be used for head gaskets.

    I did buy some gasket material, though, and I'll just make my own. The cork material should compress into a nice seal.

    Also, I got a torque wrench from Harbor Freight. Weather is so bad now, I'm staying indoors. I'm retired, so there's no rush to do stuff in bad weather, when good weather is certain to come soon enough.