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Thread: Exhaust valve color

  1. #1
    Junior Member Grease Monkey
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    Default Exhaust valve color

    Hi Guys,

    I had to remove the exhaust manifold today on my 1974 18RG that is stuffed into an Austin Healey Bugeye Sprite, and when looking around, I noted the #3 valve was white, while the other 3 ports were a sooty black. My 1st thought was a lean mixture, probably dirt somewhere in the carb. I should note that I've been swapping jet combinations quite frequently while I was tuning it using an O2 sensor. To try and understand this better, I pulled 2 spark plugs so I could relate the differences seen on the valve. I pulled #3 (the white valve), and #4 (which looks identical to number's 1 & 2 with a sooty dark look. You'll have to see the pictures to believe, as both spark plugs look scary similar. I'll admit this is a bit past my experience. The carb is a Solox ADDHE, and all 4 are set up identical down to the screw settings for idle mix. So what's going on here? With everything identical, why is #3 different?

    Sorry, I can not get the pictures to load, never a problem in the past, but who knows. I'll try in the future.

    Checksix
    Checksix
    18RG 59 Bugeye Sprite

  2. #2
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    Default Re: Exhaust valve color

    Possible coolant leak i.e. head gasket. Is the coolant level low or is oily. If you have a compression tester, I would do a quick check. Davew7

  3. #3
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    Default Re: Exhaust valve color

    Quote Originally Posted by davew7 View Post
    Possible coolant leak i.e. head gasket. Is the coolant level low or is oily. If you have a compression tester, I would do a quick check. Davew7
    I remember some time ago a similar look on a different engine and it was antifreeze. I checked my antifreeze and it might be down slightly, but really hard to tell. There is no blow back into the cooling system, and no oily indication at all. I have yet to do a compression check, but I believe it would be okay as this leak is really small, if it is antifreeze as suspected.

    Any other members who might have an opinion as to the cause? I'm on the fence about doing a head gasket as it is quite a lot of work, but if it is the beginning of a leak, it's not likely to get better. I'd just like some better confidence before making such a big step. If I do do a gasket change, how much material can I remove from the head to get an even surface? Is there a way to measure my head to see if it had been decked prior, and what it the limit of removal?

    Checksix
    Checksix
    18RG 59 Bugeye Sprite

  4. #4
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    Default Re: Exhaust valve color

    If the antifreeze is only slightly down and it's not an oily mess, I would just try one of the stop-leak products. It's worth a try. I suggest using a stop leak, that chemically re-acts, when exposed to combustion gases Vs the type that plugs the void.

    Davew7

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    Default Re: Exhaust valve color

    Quote Originally Posted by davew7 View Post
    If the antifreeze is only slightly down and it's not an oily mess, I would just try one of the stop-leak products. It's worth a try. I suggest using a stop leak, that chemically re-acts, when exposed to combustion gases Vs the type that plugs the void.

    Davew7
    I have never heard of the type that reacts to the combustion gasses. Can you suggest one? I'll try to do some research tonight on it as well. Still sitting on the take it apart fence.
    Checksix
    18RG 59 Bugeye Sprite

  6. #6
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Exhaust valve color

    For a small leak I would suggest you try this stuff... check it out before you
    decide what to use. As you suggest, a lot of the widely advertised stop leak products
    are liable to do more harm than good.



    Cheers... jondee86

  7. #7
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    Default Re: Exhaust valve color

    Quote Originally Posted by jondee86 View Post
    For a small leak I would suggest you try this stuff... check it out before you
    decide what to use. As you suggest, a lot of the widely advertised stop leak products
    are liable to do more harm than good.



    Cheers... jondee86
    This was always my go to product in previous problems. My research tonight brought up several products that were supposed to be heat activated. The reviews were really mixed with 10% or more writing negative reviews, mostly complaining that the product stopped up heaters and radiators. I'm leaning more towards fixing it with a gasket replacement but would love to hear actual success / failure stories.

    Can a head be measured to tell how much I can remove to get it flat? I wouldn't mind raising the compression some, so what is the minimum head thickness?
    Checksix
    18RG 59 Bugeye Sprite

  8. #8
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Exhaust valve color

    Quote Originally Posted by checksix View Post
    Can a head be measured to tell how much I can remove to get it flat? I wouldn't
    mind raising the compression some, so what is the minimum head thickness?
    Can't help with how thick the head might have been when new. But generally speaking
    I would get the machine shop to check the head for flatness and only take off the minimum
    required to get it flat and remove any pitting.

    From memory, I think you should be looking for around 0.8mm squish so you will need to
    measure the deck height when the head is off and go from there. Better to use a thinner
    head gasket than to take a lot off the head. Just my 2c

    Cheers... jondee86

  9. #9
    Forum Member 1st year Apprentice
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    Default Re: Exhaust valve color

    An un-cut head will be 116mm (4.566") tall. Ideal squish for a 4AGE is .032 to .038". Every .004" removed from the head surface is about a .5cc volume reduction. A .010" cut is equal to a 1.28cc reduction. I have actually machine the 4AGE head down to within a few thousands of the valve seat. If you want to look at thinner head gaskets I can highly recommend the Cometic MLS gaskets. You should consider adjustable cam gears if you remove more the just a clean up cut on the head. Davew7

  10. #10
    Junior Member Backyard Mechanic
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    Default Re: Exhaust valve color

    Quote Originally Posted by jondee86 View Post
    Can't help with how thick the head might have been when new. But generally speaking
    I would get the machine shop to check the head for flatness and only take off the minimum
    required to get it flat and remove any pitting.

    From memory, I think you should be looking for around 0.8mm squish so you will need to
    measure the deck height when the head is off and go from there. Better to use a thinner
    head gasket than to take a lot off the head. Just my 2c

    Cheers... jondee86
    He speaks the truth....

    Do the compression test. Confirm the health of the Block and the sealing of the head first.

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