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Blown head gasket?

Discussion in 'Technical and Troubleshooting Torque' started by gmawby, Apr 3, 2014.

  1. Hi,
    I rode to work this morning and as I came in to the office car park there was a loud pop, When I stopped a few minutes later there was oil over the front mud guard and oil over the front cylinder of my VT250 spada. There does not seem to be a loss of power , but difficult to tell in the car park. I don't think there are any external oil pipes on the spada but I'll check the manual tonight.

    I'm not sure what happens when a head gasket blows, any advice is most welcome!

  2. First off don't ride with oil all over your bike! If there is no loss in power I doubt it is the head gasket, I think it would more likely be the valve cover gasket. To find out clean up the oil and try to see if there is a slow seep from somewhere. You could even try running the bike and see where the oil is coming from. But before running it make sure the oil level is right you don't want to make the problem worse.
  3. Fork seal bust?
  4. The fact there was a pop suggests you got a pressure built up in the crankcase. So this could be the PCV itself.

    also it probably vents to the airbox, so it could be it got blocked and let go suddenly.

    I too doubt it's the head gasket. Eliminate all else first.
  5. Update,
    I got the bike home this on a borrowed trailer, no problems, then ...... I dropped it getting it off the trailer , broke an indicator , brake lever and foot peg. I'm cursing myself for my stupidity.

    Tomorrow I'll take the tank off and turn it over and see where the oil comes from, take a look at what's in the crank case breather tube, check the coolant for oil, oil for coolant and take it from there. I did price up a gasket just in case and I can get one for under $30.00 but will have to wait for delivery from Melbourne. I've been studying the workshop manual as I've never worked on twin overhead cam before, but, seems reasonable.

    As for the bits I broke today.. there is a breaker in Silverwater who has the parts.

  6. Hi,
    The news is I don't think the head gasket has gone. The cam cover casket has been blown out! See the pic. That suggests that there is pressure building up where there should be none. I'm guessing that a valve is not seating properly. Cam chain is tight and there is no obvious debris. I'll check the valve clearances and turn the engine over slowly and make sure everything goes up and down. Any other suggestions most welcome.

  7. Nice problem solving there. I think a dodgy valve makes sense. Could it be pressure in the crank case coming up the oil passageways?

    You might be able to just replace the valve cover gasket and thats the end of it.
  8. Hi,
    I turned the engine over by hand, checked the valve clearances and they are spot on, the timing is perfect i.e the timing marks line up. I'll check the crank case breather for blockages and get a new gasket and see how it goes.
  9. Wont be a valve. the crankcase should vent somewhere. could be through a PCV. Check this vent line and the PCV first.

    If that's all good, do a compression test. You may have some broken rings. Guessing its the vent line however. Could be really dirty where it goes inot the airbox.
  10. Hi,
    The crank case vents to a small tank which separates the oil from the gases. The gases go back to the air box and the oil collects in a tube which should be emptied periodically. I took all that off and cleaned the tank and tubes but they were not blocked. Also checked the spigot on the crank case and that is not bunged up. It seems that crank case breather system is fine.

    Today I'll buy a compression tester.

  11. Hi,
    I could not buy a compression tester with a 10mm adapter not even from the two motorcycle shops I went to plus SuperCheap, Autobarn etc etc so I've ordered one. The compression test will have to wait. In the interim I've put it back together and ridden it tonight up the freeway and back for an hour and nothing untoward happened!
    I put on some new indicators and I think it's looking quite sexy for an old bike. Shame about the rider!:].

  12. I'm guessing you had a temporary blockage of the vent system that blew out at the same time as the rocker cover gasket.

    Either that or a backfire that somehow pressurise the crankcase.
  13. Hi,
    It blew yesterday when I was coming down from Mt White. I'd ridden about 100k combined road and freeway driving the POP! Riders stopped to help and we "hid" the bike in the bushes. I got a lift home on the back of a Triumph , and as I've not ridden pillion for 30+ years was scary but amazing once I relaxed. Thank you Greg for your kindness.

    Bikes home now and I'm waiting for the compression tester to be delivered.

  14. Hi,
    The compression test was fine , no problems as far as I can tell. I was discussing this with mechanic friend of mine and he had watched the bike as I rode off and he had not noticed any smoke and he concluded there is nothing wrong with the rings/valves. He phone a friend of his who is carb specialist who said that he had seen this problem before and it is most likely due to the carb flooding due to incorrect float height or the petcock leaks. The carb theory is something like this - when the engine is hot and you switch off the engine the excess fuel evaporates and makes its way into the intake. It will eventually condense and seep past valves and rings so over time you get contamination of the oil. I put my nose in the filler spout and is smells of petrol. I've changed the oil and filter, stripped the carb , cleaned the jets ,(some were partially blocked) and more importantly set the float height 6.8mm. One was only 4mm, which is a huge difference. The carb upside down when you set the float height, so the right way up that float would have to rise almost 3mm extra to to close the valve. It's back together now and running.

    He's hoping!!

  15. I don't think the fuel condenses in the oil when engine is stopped.

    More likely that it runs rich, washes oil off the bores and gets blown past the rings. More fuel in oil also reduces ring seal, and you end up with even more crankcase pressure.
  16. oldcorollas,
    this is uncharted waters for me so quite possibly :)
    I took it out this morning and it runs OK..I had to "tickle" the carbs to get the idle right. The throttle free play needs adjusting but I can tinker at my leisure .

    And if the motor cycle Gods smile on me, I'll pass my MOST next week on this bike.

    Here's hoping!!
  17. I've filled a crankcase with petrol with a bad fuel tap and poor seating float needles.
  18. and I too with injectors..
    and also with a pig rich carb on a car, that washed oil off bores and pissed fuel into crankcase past the rings :D

    I meant it doesn't condense from vapour to liquid,
    doesn't happen. fuel that evaporates will stay as vapour because it is a volatile liquid.
    if you lave a cup of petrol outside for a week.. there won't be anything left, and same for vapour in intake. it will slowly diffuse out through air filter
  19. ahh yes, I agree. I thought the condensation explanation was a stretch too.

    So I've lost track of this thread a bit. Where are we at?

    It could be a bad tap and/or carbie. The" pop" could be a backfire.

    The thing that puzzles me is it happened after running for a while. So this doesn't suggest an overnight leak. From memory, a backfire on a closing throttle actually indicated leanness, but that's usually more of a burble than a single "bang".

    So this makes me wonder if it's an exhaust leak or an intake leak on the engine side of the carbie.