Actual Blown Headgasket

Discussion in 'Motorized Bicycle General Discussion' started by Junster, May 29, 2010.

  1. Junster

    Junster New Member

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    Hi, I was all mad and about to dis on Opti-2 oil. I rebuilt the top end of my bike because of a scored cylinder the end of last year. I had about 2000 miles on the zoom 80 motor. I switched to Opti-2 oil from the breakin and broke in the new top end as fast and hard as it would go. I have about 500 on the rebuild and the other day I was going wide open and I heard something happen. Lost some power and the bike became really hard to start. I figured the oil had failed and the top end was gone. Just took it apart and the pic is what I found. Inside of my cylinder is smooth as glass and slippery to feel but the plug is dry chocolate. The Opti-2 is working great, maybe so good that the compression did this because I hadn't checked my headbolts for a bit and they were a little loose. Posted this cause I really didn't think these motors had the power to blow a alum headgasket. Once again I was wrong.

    headgasket.JPG
     
  2. Dave31

    Dave31 Moderator
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    Wow, I have never seen that on these motors. Thanks for sharing with us.
     
  3. bairdco

    bairdco a guy who makes cool bikes

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    if your head bolts were a little loose, that was probably it. the hot gases will exploit any tiny opening and attack it till it fails.

    lucky that's all that happened, though.
     
  4. Junster

    Junster New Member

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    Ya Fairracing I've had head gaskets leak, everyone has. This was the first one I ever saw really blow. Never expected it till I pulled the head. It's funny to I put a yamaha enduro 60 tank I got off ebay on my bike a few weeks ago and put a couple Harley stickers on it. I have had more ppl ask me if it's a antique Harley than you'd believe.

    HDbike.JPG
     
  5. Junster

    Junster New Member

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    UPDATE; I couldn't stand to wait for a new head gasket. I went to the hardware store and bought a short piece of alum. dryer vent. After destroying a couple attempts with a drill I finally used my air grinder with a 3/4" sanding drum and sanded out a very nice round hole for the cylinder (used the bottom of a caulking tube to mark the hole just the right size). I have a extra bottom gasket I keep just for marking the bolt pattern. Again punched the holes small with a drill then with a pointed grinding bit relieved them out to the right size. Coat of spray copper head gasket sealer on both sides and good to go. Oh while the head was off I lapped it in again on a piece of glass. This is the second time. It was heat warped again. Took about 3 minutes to get it flat. I'll be buying a billet head from Pirate Cycles as soon as Jim resupply's them.
     
  6. Patr1ck

    Patr1ck New Member

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    How do you do this lapping on a piece of glass thing?

    Pat
     
  7. omegaunderground

    omegaunderground New Member

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    Very lucky it was an easy fix Junster, my engine came with no head gasket installed.... But came with 2 "spare" head gaskets haha. I did not realize it was missing and did not have a problem at all but once I noticed it was missing I put one in ASAP.
     
  8. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    My head is leaking again TOO. This is the cause. My slant head and vigorous lapping has increased my compression greatly. The price to pay I guess, but my head was NO WHERE NEAR FLAT AS RECEIVED.

    For the fellow who asked:

    One piece of flat glass 12"x12" or whatever.
    A plywood surface or towel on concrete outside (work surface that you can get wet and dirty)
    Various grades of wet/dry sandpaper (rougher for material removal) all the way up to 1200 for real smoothing.
    Water.

    Set your glass on a towel, lay the sandpaper on the glass, get the whole affair wet. Then rub the mating surface of the head in a circular pattern as required while holding it as flat as possible. Progress up to finer grades of paper and clean the whole affair at each grit change.When complete, wash the head very well. You don't want grit in your engine.
     
  9. bairdco

    bairdco a guy who makes cool bikes

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    to add to Pablo's instructions, turn the head a few times while doing this, i mean how you're holding it. like, if you've got your fingers on all the bolt holes and you're pressing down, rotate the head so your fingers are on a different set of bolt holes every so often.

    this way you'll keep an even pressure on it, and won't end up sanding it on an angle.

    also, i just use masking tape and tape a piece of 600 grit down to a piece of glass, and use that. on a Grubee head, there's circular marks from where the factory surfaced it, and i keep sanding till they're gone.

    you can lap it a little just to create a smooth mating surface, or a lot to increase compression. just don't go overboard, it doesn't take a lot. a coupla millimeters is enough.

    another thing to keep in mind, is higher compression makes it harder to start, meaning more pedaling.

    one more thing. my head is lapped about as much as possible, and the compression is way more than stock, and i've been beating the he11 outta my motor for 6 months, and a few thousand miles with no problems. i guess it's a hit or miss situation.
     
    #9 bairdco, May 30, 2010
    Last edited: May 30, 2010
  10. K.i.p

    K.i.p New Member

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    The correct way to lap is in a figure eight pattern. 300 grit should handle the whole process. You will get a 10 micro finish no problem even dry. Wet sanding and going for a mirror finish is just gilding the lily. Hey knock yourself out if it makes you feel good but I prefer to work smart not hard. Wet sanding is generally only a cosmetic process.

    If you have a nice cross hatch that feels smooth when you run a finger nail over it your there. Running a graphite pencil tip over a surface is another improvised test for micro finish.
     
  11. Fabian

    Fabian New Member

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    quite possible that the engine was running on the lean side to put so much heat into the gasket.

    I've done 6,000 kilometers (3,700 miles) and i've reused the same head gasket 5 times, with no heat related problems.
    I'm surprised at how well those aluminium gaskets seal, even when they are reused multiple times.

    Having said that, the gasket does ooze filthy black goo, but no more than the base gasket or the case gasket.

    Fabian
     
  12. Junster

    Junster New Member

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    The only reason most of us use wet paper is it doesn't plug up as quickly as dry paper does. With the paper very wet it sticks to the glass well enough you don't need to fasten it down. I generally use 220 then 400. I do a little polishing but just to the combustion chamber with Mothers polish. I think it helps keep carbon from sticking as quickly but it's probably not really doing anything. I use a piece of scrap 1/4" thick glass from a local glass place. Thinner glass can be flexed.
     

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