Blown Head Gasket

Discussion in '2-Stroke Engines' started by Timbone, Apr 22, 2016.

  1. Timbone

    Timbone Active Member

    Was cruising into work a few mornings ago and while climbing a short steep hill I suddenly lost power and the engine would no longer run, forcing me to pedal in the final 4 miles.

    Before attempting the return ride, I re torqued the head bolts (they were a bit loose) and checked the spark plug for gap. For about 3 miles, I kept working to get things running, checking every system of the bike. Electrics were good. Throttle cable was operating nicely and the jet was clean. No problems with the choke. But by this time, I had noticed blowback from the cylinder head.

    Finally, I removed the head. Bam! Saw the problem: aluminum gasket was deformed badly with the rearward facing part blown loose. Blowback was shooting straight backwards past the cinder head.

    I removed the old gasket and tried to run without it. No way. But I stopped at a hardware store and bought a roll of Teflon tape. I pulled out a small stretch of tape, folded it in half and rolled it into a string that I carefully roped around the the top of the cylinder. I clamped the head back down and it actually worked! I made it home!

    It was far from perfect as I still had leakage and loss of power. I thought I would make the gasket thicker. It worked for a second and then POP! - it blew the gasket out of the back! Looked like a piece of graffiti sticking out.

    I've examined the head and the top of the jug. The top looks pretty flat to my 50+ year old eye. The head itself may be a bit warped, with a high spot that would face directly rearward. I did some very light sanding to smooth out any rough spots that might make that part higher but, honestly, it's hRd to see exactly where I need to sand.

    I am gonna spend $9 on a copper piece that I will cut to replace the old messed up gasket. But it will sicken me to go to that effort just to see the thing get destroyed. Are there any clues I can find that will allow me some idea if I am in a workable condition here?
     

  2. crassius

    crassius Well-Known Member

    make sure torque is actually being applied to head rather than just causing binding of studs into acorn nuts (add more flat washers if needed)

    a disposable aluminum roasting pan makes a good gasket
     
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  3. Frankfort MB's

    Frankfort MB's Well-Known Member

    How many gaskets could you make out of that copper peice? You can buy 5 head gaskets already cut copper for like 15$, I've rode for about almost 750 miles without a single problem from my copper gasket (knock on wood) ;)
     
  4. Timbone

    Timbone Active Member

    Who is the vendor?
     
  5. Frankfort MB's

    Frankfort MB's Well-Known Member

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  6. 45u

    45u Active Member

    Here is the sellers web site. The owner I think his name is Matt is a great guy and if you call and leave a message he will call you back. I have bought quite a few things from him both on eBay and his site I have no complaints.

    https://bicyclemotorworks.com/
     
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  7. Frankfort MB's

    Frankfort MB's Well-Known Member

    I've bought everything you could imagine from them, on the east coast it is one of the best places to buy from
     
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  8. Timbone

    Timbone Active Member

    I made a new gasket out of .025 thick copper. The bike startted right up and it runs, but there is big blowback straight back OVER the new gasket, And there is a little leakage front center, over the gasket. There's nothing on the head that looks strange or way outta whack. And I think the torque on the head nuts are good.

    Any suggestions?

    Again this is a stock cylinder head with no modifications.
     
  9. Frankfort MB's

    Frankfort MB's Well-Known Member

    I would try and plane your head and make sure everything is flat
     
  10. 45u

    45u Active Member

    Did you make sure the gasket does not have a burrs on it or rough cuts? You can all so try and anneal the gasket. That is one thing good about copper gaskets you can anneal them and use them over and over. All so make sure the head and cylinder gasket surface is not warped.
     
  11. 45u

    45u Active Member

    You can mill the head and top of cylinder by using a flat piece of glass on a flat surface with some fine lapping compound. You can all so use the glass to check the head and top of cylinder with a feeler gauge.
     
  12. crassius

    crassius Well-Known Member

    Did the compression ring of the head cut a clean groove in the copper? That sharp cut is what forms the seal, so if the copper was too hard, it may have failed to seal.

    Did you look carefully to be sure the head isn't cracked?
     
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  13. 45u

    45u Active Member

    This is why you anneal copper gaskets.
     
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  14. Timbone

    Timbone Active Member

    There was no marking at all into the copper. I am gonna put a torch to this gasket in minutes! Thanks, guys!
     
  15. Frankfort MB's

    Frankfort MB's Well-Known Member

    Can you use copper sealant? Or rtv sealant? Seems like it could hold these little motors, One of my buddies used it everywhere on a drag car making 900hp and it works well
     
  16. 45u

    45u Active Member



    This is what is called annealing and been doing it to motorcycle copper head gaskets for 40 plus years. You need to let it get glowing red and let it cool. This swells the copper up and makes the gasket softer. You do not have to get the whole gasket glowing at once just try to get every part of the gasket to glow.
     
  17. Timbone

    Timbone Active Member

    OK. I am rolling again!

    I annealed the gasket. Being a pyromaniac, it was fun. Got it as hot as I dared and let it air cool. I could tell the difference.

    Replaced the gasket and the cylinder head, clamped it down tight and I got running again. But still, a significant leak directly backwards. No go.

    I took the head off my last engine, clamped it down on the new gasket for a test. This thing is in excellent condition with just a bit of carbonization in the combustion area. The bike took off and runs great now. Obviously, the problem is with the cylinder head. I am gonna run like this until there's some kind of problem.

    Here are pics:

    The blown out part of the gasket (left side) is actually the rear. The leakage was towards the intake.

    I can't see any kind of problem with this cylinder head. The leak is on the left side in the picture, which while on the jug aligns with the spark plug hole and back towards the intake.

    Any of you experts see something here?

    Thanks to all for the great advice and counsel!

    =Timbonius=
     

    Attached Files:

  18. crassius

    crassius Well-Known Member

    can't really tell from a pic, but I'd guess that head was seriously warped
     
  19. Frankfort MB's

    Frankfort MB's Well-Known Member

    Glad you got it running! I've had that same thing happen before as well as a cracked head not fun trying to ride a bicycle without a motor for fat old me :)
     
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  20. 45u

    45u Active Member

    I have found with the aluminum gaskets every time you stop from riding and let cool the torque is off. This is because aluminum gets hot then cools the aluminum gasket expends and contracts so much. I did try just re-torquing but after a gallon of gas did not change. I do recommend with a copper gasket to re-torque after 20 to 50 miles.

    Timbon you can fix your other head like I mention above.
    Glade you got back running wish I could ride mine. Nothing wrong problem is I just got out of the hospital Tuesday. But I have drive my rig (motorcycle with sidecar).
     
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