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valve stem seals?

Discussion in 'The Garage' started by shaun89, Oct 18, 2006.

  1. shaun89

    shaun89 1/2 ton status

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    i need to replace my valve stem seals and i thought it would be a one type thing to buy, but there are many different sizes....is there any way to tell which ones u need?:confused:
     
  2. sweetk30

    sweetk30 professional hooker Premium Member

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    for the engine valve steam seals get the umbrella and stay away from the oring style thay suck .
     
  3. jdemaris

    jdemaris Registered Member

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    There are three basic types that I know of. On some equipment, no seals are used at all when the engine is new. The mindset being that a little oil leakage is good for the valve-stems. With autos on the road, with current emmissions laws - now the seals must tight.
    So, with engines like Chevy -built pre-emmissions - just a o-ring on the intake valve retainer was used - and none on the exhaust. Once those engines got a few miles on them - the valve-stems leaked and the engines smoked. So - we'd install the valve-stem "umbrella" seals. They usually stick tight to the valve stem and travel up and down when the valve opens and closes. Umbrella seals work "good enough" but are not positive seals suitable for meeting modern emmissions laws.
    The usual standard now - for valve-stem sealing is the stationary seal. It clamps tight onto the top of the valve guide and has a teflon wear-surface in its bore that the valve stem travels through. Many types of industrial equipment have used these since the early 1960s. But, on most car engines - built in the 60s or early 70s - these seals won't fit without doing some machining on the tops of the vavle-guides. Perfect Circle used to sell a little cutter for machining the tops of valve-guides for their stationary seals. Now - I suppose - that just about all modern engines come from the factory with the stationary seals- and the valve guides are already machined.
    To answer your question about what type you need? You can put unbrella seals in along with the original o-rings and it will probably be fine. They won't seal as tight as the stationary seals - but not enough so you'd notice. Umbrellas don't have as long a life span either -but again - this may not matter. And of course, you can install the stationary seals - they will last longer - but may take a little more work to put in.
     
  4. shaun89

    shaun89 1/2 ton status

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    damn...u no a lot john. thanks, i think im gonna go with the umbrella seals...they seem easier plus i dont think my engine will outlast them....this makes it much easier now. i just need to pick up that pump for the spark plug holes...thanks again:bow:
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    rope trick...

    I use nylon rope --stuffed into the spark plug holes,to hold the valves shut--you stuff about a foot of nylon cord like they use on a lawnmower motor's pull starter,and crank it over by hand until the piston contacts the rope,pressing it against the valves and holding them shut--no chance of "losing" a valve if air pressure drops,or you accidentally push the valve down!..

    You need at least 100 psi to use the air fitting to hold valves shut--and pray they STAY closed,and the piston doesn't drop to BDC ,as they often do when the air is applied!..I "lost" a few valves using compressed air to hold them shut,they had burnt spots that leaked the air out!--had to pull the heads to get the valve "back",and it needed a new one anyway,since it was burnt...:(

    I just assume pull off the heads now,when doing valve stem seals..often,the valves and guides need work too by then,not just the seals..after having one motor blow a head gasket about 2 weeks after putting in the valve stem seals (my back was STILL sore from bending over the engine a whole day!),I decided I'll just pull the heads off next time I do valve stem seals..then all you have to do is pray the RINGS don't start passing oil,now that the valves are tight and "fresh"!...had more than one motor start smoking BAD after a valve job--sometimes its best to run them as is,if you don't want to rebuild a motor completely...:doah:
     
  6. stockk5

    stockk5 1/2 ton status Premium Member

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    rope eh?....that sounds pretty good, maybe ill do that...i no doing more is better but its a DD and i cant keep it off the road for more then 2 days...but thanks for the tips man! ill try that
     
  7. jdemaris

    jdemaris Registered Member

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    If the valves and cylinders are in pretty good shape, you don't need all that much air. The pressure has little to do with it - it's the amount of flow. But - if some of the valve-retainers are stuck tight - then the high-pressure helps a lot. Sometimes you have to rap them with a hammer to shock them loose - if they are split keepers. Pin keepers are never a problem. Simple math - you must pump in at least as much - as - is leaking out.
    I've done many engines - probably hundreds over the years and never had a valve drop. If you were really worried, you could just put the cylinder being worked on, on top-dead-center of its compression stroke - and then - the valves could only go in a little and stop at the piston. If that is done, you have to make sure the engine is locked - because air-pressure will want to push the piston back down to the bottom. Back in the 60s and early 70s - when I was a gas-station mechanic and grease-monkey - our most common repair was small block chevy valve-seals - along with bad cams and lifters and fail plastic timing chain gears..
    I once was asked to help a friend put valve-seals in his 1965 Ford truck with a 240 cube six-cylinder. It had 200K miles on it at the time. The catch was - he had no air-compressor. So, I'd stop by on lunch-hours with a five-gallon air-storage tank. I'd hook it to one cylinder and work as fast as I could -trying to get the two valves done before the tank went empty. On one cylinder, the tank ran out - and the valves did not drop until pressure was zero. I then - gently put Vise-grips on both valve stems. Came back the next day with more air and finished.
     
  8. Thunder

    Thunder 3/4 ton status

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    I have always used the "Indian rope trick" as described above to replace valve seals. Dont have to hassle with the compressor/air and all that other stuff. Always worked for me. But I like to keep things simple.
     

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