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Thread: Holden 308 H

  1. #1
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    Default Holden 308 H

    Hi guys

    I am thinking of overhauling my cast iron heads. Valve stems are not sealing. Symptoms, vehicle smokes alot on cold startup. After 5 minutes of driving the smoke clears up. May give a puff after standing at lights for a minute when taking off.

    I am in South Africa and Holden parts are not common here but chevy parts are.

    Is fitting K Liners the only way to repair the valve stem bores? Was thinking about thicker valve stems, and then just bore to correct size.

    Can you wise people please give me some advice on the best way forward.

    I also want to use the umbrella seals once the head is done. Which vehicle engine seals can I use? Will the Ford 351 clevland motor valve seals work?

    All advise will be appreciated.

    Thanks in advance

  2. #2
    Sure why not? 76lxhatch's Avatar
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    Yella Terra exchange heads used to be done with 0.005" oversize valve stems, I think you can still get valves with oversized stems but not as common. By the time you still have to ream the existing guides to suit anyway, you're probably still better off with K lining.

    The original o-rings are basically an umbrella type seal, they just reduce the oil dripping down so new o-rings that fit nicely against the retainer would give the same result. If you are talking about using positive seals then anything that suits the valve stem size (OEM is 11/32" if memory serves) and fits the head/clears the spring is fine, aftermarket stuff for small block Chevy usually suits and you can buy matching cutters to machine the outside of the valve guide in the head. Check the clearance at full lift and that the seal is small enough to clear the inside of the valve springs especially if using doubles.

    Your description of the smoke sounds a little excessive for just valve guides? Unless maybe the head was assembled without any seals at all?

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    Sounds like the old girl is getting tired if it smokes taking off. Get a leak down test done to evaluate the bottom end first, could save you tearing it apart twice. Use k line guides and have them machined for a positive valve stem seal. Any competent machine shop would be able to do this.

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    Quote Originally Posted by 76lxhatch View Post
    Yella Terra exchange heads used to be done with 0.005" oversize valve stems, I think you can still get valves with oversized stems but not as common. By the time you still have to ream the existing guides to suit anyway, you're probably still better off with K lining.

    The original o-rings are basically an umbrella type seal, they just reduce the oil dripping down so new o-rings that fit nicely against the retainer would give the same result. If you are talking about using positive seals then anything that suits the valve stem size (OEM is 11/32" if memory serves) and fits the head/clears the spring is fine, aftermarket stuff for small block Chevy usually suits and you can buy matching cutters to machine the outside of the valve guide in the head. Check the clearance at full lift and that the seal is small enough to clear the inside of the valve springs especially if using doubles.

    Your description of the smoke sounds a little excessive for just valve guides? Unless maybe the head was assembled without any seals at all?
    Your memory is good, the stem is indeed 11/32.
    Its interesting you say that the O rings create an umbrella, have never heard anyone say that before, but I understand what you mean with the "cap" over the spring.
    The K liners are rather expensive here which was why I was thinking of matching valves to suit with a thicker stem.
    I assembled the heads so I know there are seals there. And yes I installed the seals correctly, first pushing down the spring and then the seal.

    I would really like to discuss further the smoking issue. You say that it sounds excessive and yes initially it definitely is. If it was a bottom end issue would the smoking not continue. After I drive if I inspect the spark plugs they are nice and clean, light tan, maybe on the lean side.
    My understanding is that if oil is getting past the piston rings it would do it all the time.

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    Quote Originally Posted by AED View Post
    Sounds like the old girl is getting tired if it smokes taking off. Get a leak down test done to evaluate the bottom end first, could save you tearing it apart twice. Use k line guides and have them machined for a positive valve stem seal. Any competent machine shop would be able to do this.
    Some history of this motor, I freshened her up about 2000kms ago. I had the bores measured by an engineer and was told that the wear was so little. As this is a weekend cruiser i decided to just get new standard rings and assemble the motor. Also new standard cam and lifters and all new bearings and seals.

    This motor was stored poorly by the previous owner. (was a runner until previous owner decided to go chev 400 and swapped it. Although under shelter rain water was present in the heads which made it a little rusty. I stripped it down and wire brushed it clean and gave it skim. The valves seemed to have fitted in its bores fairly snug. I did put the valves back in the slot that it came out from.

    I am a backyard mechanic at best and rely on google and books and forums for advice so would really appreciate all advice to determine my problem source.

  6. #6
    Sure why not? 76lxhatch's Avatar
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    The quality and shape of o-rings supplied varies a lot so I guess its still possible that they have failed, but yeah if you assembled it yourself recently that makes it less likely. Sounds like you also did a basic check of the valve guide clearance too, when that's really good you wouldn't get a lot of smoke even without seals (although its probably not that perfect with original guides).

    Any oil getting into the combustion chamber reduces in volume as it gets burned off (unless its a constant flow!) so can act similar to top-end leaks.

    As above I'd do a leak-down test first (maybe warm it up and get the smoke to clear first, a little oil in the cylinder might affect the result), or even just a basic compression test. You could also check the plugs after a brief cold start where its smoking, if its only one or two cylinders this will help you pinpoint the issue. Then remove the rocker covers and get in there with a light and see whether any of the seals are damaged or missing. If/when you get to the point of removing the heads you can check the valve guide clearance more thoroughly and inspect the bores and pistons for any signs of bottom end issues before you commit to spending any more on it.

    I know what you mean by expensive, problem is I don't think the alternatives would be any cheaper if that's what needs doing.

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    Quote Originally Posted by 76lxhatch View Post
    The quality and shape of o-rings supplied varies a lot so I guess its still possible that they have failed, but yeah if you assembled it yourself recently that makes it less likely. Sounds like you also did a basic check of the valve guide clearance too, when that's really good you wouldn't get a lot of smoke even without seals (although its probably not that perfect with original guides).

    Any oil getting into the combustion chamber reduces in volume as it gets burned off (unless its a constant flow!) so can act similar to top-end leaks.

    As above I'd do a leak-down test first (maybe warm it up and get the smoke to clear first, a little oil in the cylinder might affect the result), or even just a basic compression test. You could also check the plugs after a brief cold start where its smoking, if its only one or two cylinders this will help you pinpoint the issue. Then remove the rocker covers and get in there with a light and see whether any of the seals are damaged or missing. If/when you get to the point of removing the heads you can check the valve guide clearance more thoroughly and inspect the bores and pistons for any signs of bottom end issues before you commit to spending any more on it.

    I know what you mean by expensive, problem is I don't think the alternatives would be any cheaper if that's what needs doing.
    Thanks for the comment.
    I did a compression test a few months back and the results were consistent on all cylinders. I don't remember the exact numbers, but they were all very close to each other.

    I have googled the leak down test and I have asked a couple of mechanics about this test and they have not done this before nor do they have the equipment.
    It would appear that in South Africa or in my town its not a common tool or test performed.

    Do you think its worth the trouble trying those umbrella seals that fit over the guide boss? (I have looked at the Ford windsor 351 seals online and looks similar to the seals they sell in Australia for the 308's). Would be too costly to import just those seals.
    Assuming that there is a bit of wear on the guide bore itself? Would it give me temporary relief at least. That way I will know for sure that my issue is with the heads and not the bottom end.

  8. #8
    been here .......too long Smitty2's Avatar
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    .. genuine Holden valve stem seals are all over eBay here
    they could be easily mailed

    https://www.ebay.com.au/itm/Holden-5...kAAOxyPLpRfPFd

    or even the aftermarket ones are reasonably priced

    https://www.ebay.com.au/itm/FLUOROVI...QAAOSwwERbm57F
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  9. #9
    Sure why not? 76lxhatch's Avatar
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    ^ That's reasonably priced...? Yikes!

    Quote Originally Posted by kavesh View Post
    Do you think its worth the trouble trying those umbrella seals that fit over the guide boss?
    Only if it turns out that your guides are in good condition (seems unlikely) and the current seals are the only problem. As a troubleshooting step I guess you could try it and see but it may not achieve anything, or if effective it may accelerate already bad wear on the guides by starving them of lubrication. Definitely don't go machining the outside of the guides before getting them lined if that's on the cards.

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    Sure why not? 76lxhatch's Avatar
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    Just another thought - you don't have something weird going in with the PCV do you? Maybe stuck open and pumping a heap of oil through the intake? Just check the manifold floor under the carb and make sure its not black with oil.

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    Quote Originally Posted by 76lxhatch View Post
    Just another thought - you don't have something weird going in with the PCV do you? Maybe stuck open and pumping a heap of oil through the intake? Just check the manifold floor under the carb and make sure its not black with oil.
    The PCV is not connected or rather its plugged into the valve cover but the hose is not connected to vacuum. I do have a new PCV valve in place. The reason removed from vacuum is because it seemed to smoke more with it connected to vacuum. As a compromise to release pressure from the crankcase I have 3 breather caps. I on each valve cover and 1 o the timing chain riser.

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    Quote Originally Posted by 76lxhatch View Post
    ^ That's reasonably priced...? Yikes!


    Only if it turns out that your guides are in good condition (seems unlikely) and the current seals are the only problem. As a troubleshooting step I guess you could try it and see but it may not achieve anything, or if effective it may accelerate already bad wear on the guides by starving them of lubrication. Definitely don't go machining the outside of the guides before getting them lined if that's on the cards.
    OKay I hear you. So assume I need to fix the guides. Is it an option to use thicker valve stems rather than the K liners?

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    Quote Originally Posted by Smitty2 View Post
    .. genuine Holden valve stem seals are all over eBay here
    they could be easily mailed

    https://www.ebay.com.au/itm/Holden-5...kAAOxyPLpRfPFd


    I have used these and they have not made any difference sadly

    or even the aftermarket ones are reasonably priced

    https://www.ebay.com.au/itm/FLUOROVI...QAAOSwwERbm57F
    These seals I like. I was told by an old school mechanic today that the Ford cleveland 351 seals will work. But they are what he referred to as floating seals, will move with the valve movement.

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    Will a borescope help to determine where the problem may be? look into the plug holes or remove the carb and try and get a look at the bottom of the valves...
    I could borrow one later this week.

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    It doesn't cost much to have the tops of the guide bosses machined for push on seals.

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