valve guides or seals
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From: Toronto ON
valve guides or seals
I'm trying to determine whether I need positive seals or if valve guides are worn. I have the blue smoke on start-up but, as far as I can tell, it's non-existent when I rev it in park.
Is this test sufficient to distinguish between these two faults?
Is this test sufficient to distinguish between these two faults?
Intermediate
Joined: Apr 2004
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From: South Lyon MI
IT can be both
When getting a puff of blue smoke in the exhaust is a sign of oil getting into the cylinder and burning. The cause can be the valve seal or it can be the seat. If you have the time you can check the valves by making sure the valve is closed exhaust or intake and use air pressure and monitor to see if you loose any psi. It will take time and some equipment. It is cheaper to check this first. If the valve seals are bad you need to either take the head off and replace them or it can be done on the car but it is tricky and not for the first time mechanic.
I have done it both ways. Try the pressure loss first.
I have done it both ways. Try the pressure loss first.
Burning Brakes
Joined: Aug 2004
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From: Dunstable MA
St. Jude Donor '05
Okay, I'm confused. 
If you lose pressure it's the seats, right? But what about the question regarding whether it's the seals or the guides? I've read the tech tip on replacing the seals and it doesn't sound like a terrible job, but my engine has over 150K on it and I was told that the guides could be involved. How do you test for that?? 
If you lose pressure it's the seats, right? But what about the question regarding whether it's the seals or the guides? I've read the tech tip on replacing the seals and it doesn't sound like a terrible job, but my engine has over 150K on it and I was told that the guides could be involved. How do you test for that??
Last edited by Rich Silvestris; Jan 30, 2005 at 09:55 PM.
Team Owner
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From: SE NY
Cruise-In II Veteran
To test the valve guides you need to remove the springs and move the tip of the valve from side to side and measure the deflection. Then compare that with the spec. which on my '88 is .0010"-.0027". For this you will need an accurate dial indicator.
If you have relatively high mileage on the engine I would just replace the lower seals and the upper O-rings with factory new seals. I did this 3yrs ago when I installed RRs and have no smoke at startup with nearly 150k miles on the clock. Over time with heat cycling the seals become brittle; your O-rings will likely crumble in your hands as you remove them.
If you have relatively high mileage on the engine I would just replace the lower seals and the upper O-rings with factory new seals. I did this 3yrs ago when I installed RRs and have no smoke at startup with nearly 150k miles on the clock. Over time with heat cycling the seals become brittle; your O-rings will likely crumble in your hands as you remove them.
Safety Car
Joined: Apr 2004
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From: Lahaina Hi
If it has the stock thermostat and over 150,000 miles , I would say it needs valve seals for sure.
Not that hard to replace.Just removing the egr tube is a pain.
I would check the plugs and see if the oil deposits are aticking to the electrode.
If the car is hard starting you might check out the injectors?
Not that hard to replace.Just removing the egr tube is a pain.
I would check the plugs and see if the oil deposits are aticking to the electrode.
If the car is hard starting you might check out the injectors?
Race Director
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From: The Top of Utah
Originally Posted by 87vetter
When getting a puff of blue smoke in the exhaust is a sign of oil getting into the cylinder and burning. The cause can be the valve seal or it can be the seat.
Originally Posted by 87vetter
If the valve seals are bad you need to either take the head off and replace them or it can be done on the car but it is tricky and not for the first time mechanic.
As to the original question, the seals allow the oil in, and excessive guide clearance lets it pass easier. At 150,000 miles your guides are worn. The question is, how much? New seals will probably help the situation. How long, depends in part, on how bad the guides are. If the guides are loose enough, the seal lip will be pulled away from the valve stem by the valves moving around in the loose guides. The more rigid, positive seals will do a worse job of sealing with worn guides. New seals are a temporary, "quick fix", but you really need to repair the guides, too.
RACE ON!!!
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From: Toronto ON
Originally Posted by CFI-EFI
The more rigid, positive seals will do a worse job of sealing with worn guides. New seals are a temporary, "quick fix", but you really need to repair the guides, too.
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I changed the springs to the LT4s. The seals I removed were positive ones on the intake and simple rings on the exhaust (or is it the other way around?)
I replaced the ring seals (they were extremely brittle and broke off) and put umbrella type on the intake as well as ring-type. The car doesn't smoke any less. I'm thinking I should have used the positive seals?
ALSO, the old springs had a "shedder" on them (metal cap on top), the new ones have none. Could this add to the problem?
The car has 94K clicks on it.
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Race Director
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From: The Top of Utah
The shedder acts as an umbrella for the umbrella seal. New umbrella seals and "O" rings on all 16 valves was the way to go. Often the exhaust valves don't get seals because there is less vacuum at the exhaust valve guide. My guess is that the guides are shot. They are fairly short lived in the SBC. The best way to check them without instruments, is to open the valve slightly, about a 1/4" and rock then sideways in the guide. Sideways, meaning toward and away from the stud. The best results come from grasping the valve at the stem AND at the head. Of course, you can't grab the head of the valve with the cylinder head on. Good guides will barely move. Unfortunately, you have to remove the springs, again, to do this. Also, because the valve has to be off the seat, you will have to have the piston at TDC, in case you slip. All in all, your time is probably better spent just ripping the heads off and sending them out to be cleaned and pressed. Sorry.
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From: SE NY
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To reduce valve train mass & inertia, I tossed the stock tin oil shedders from atop my valve springs when I installed the RRs with new springs & Ti retainers and have had no oil leakage since.
Measurement is the only way to know it the guides are worn to excess. So I would try the OEM type seals on both intake & exhaust (replacing the umbrella types) if you don't have a good dial indicator.
Measurement is the only way to know it the guides are worn to excess. So I would try the OEM type seals on both intake & exhaust (replacing the umbrella types) if you don't have a good dial indicator.
Race Director
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From: The Top of Utah
On my heads, and many others, as reported on this forum, there were no exhaust seals, other than the "O" rings. I would suggest that if he tries resealing rather than repairing the heads, that he use intake seals all the way around.
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From: Toronto ON
Originally Posted by 65Z01
So I would try the OEM type seals on both intake & exhaust (replacing the umbrella types) if you don't have a good dial indicator.
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From: Toronto ON
Originally Posted by 65Z01
So I would try the OEM type seals on both intake & exhaust (replacing the umbrella types) if you don't have a good dial indicator.
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From: SE NY
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Indeed the '85 L98 had exhaust valve "rotators" so the seals on exhaust differed from those on the intake. My '88 L98 had the same OEM seals on intake & exhaust valve stems; I think this setup came with the advent of the Al heads.
It is my understanding that the OEM are the "positive seal" type. They have the white metal band around the rubber.
Besides my OEM seals held up well (except for the O-rings) for over 100k miles so I felt they would be fine for the next 100k or so.
If the LT4 springs are the ovate wire type I don't think the oil shedders will fit and don't believe they are really necessary. In fact these devices were later omitted to lighten up the valve train, which is why I omitted them too.
It sounds like someone was into your valve train and omitted the leals on exhaust; install new OEMs on int & exh and you should be fine. Be sure to clean any debris from the valve guide and lube the seals with some motor oil before installing over the guides.
BTW, you might want to verify that the new springs have enough clearance so as to not touch the lower seal when the valve is fully open.
It is my understanding that the OEM are the "positive seal" type. They have the white metal band around the rubber.
Besides my OEM seals held up well (except for the O-rings) for over 100k miles so I felt they would be fine for the next 100k or so.
If the LT4 springs are the ovate wire type I don't think the oil shedders will fit and don't believe they are really necessary. In fact these devices were later omitted to lighten up the valve train, which is why I omitted them too.
It sounds like someone was into your valve train and omitted the leals on exhaust; install new OEMs on int & exh and you should be fine. Be sure to clean any debris from the valve guide and lube the seals with some motor oil before installing over the guides.
BTW, you might want to verify that the new springs have enough clearance so as to not touch the lower seal when the valve is fully open.
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From: Toronto ON
Originally Posted by 65Z01
BTW, you might want to verify that the new springs have enough clearance so as to not touch the lower seal when the valve is fully open.
What's this mean and how could this adversely affect performance?
Thanks.
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From: SE NY
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When you do any mods to the valve train there are several issue to be adressed, like coil bind and spring clearance.
Each spring has a minimum compressed height, if you exceed that the coils will touch and coil bind will result. This over heats the spring leading to premature failure. You can simply measure the spring height when the valve is fully open and compare with the published numbers for that spring.
It the spring, when compressed, touches the seal it can destroy the seal and interfere with valve control.
When you have the valve cover off you can use a mirror to watch the spring as you manually turn the crank shaft. If the compressed spring contacts the seal you should be able to see it. Also you can measure the top of the seal from the spring seat and then measure the distance from the seat to the bottom of the top coil when compressed.
Comp. Cams has some very good tech articles on their site relating selection and installation to valve trains, cams, and such.
BTW, I see you are up as late as me and I don't think there is a time zone difference.
Each spring has a minimum compressed height, if you exceed that the coils will touch and coil bind will result. This over heats the spring leading to premature failure. You can simply measure the spring height when the valve is fully open and compare with the published numbers for that spring.
It the spring, when compressed, touches the seal it can destroy the seal and interfere with valve control.
When you have the valve cover off you can use a mirror to watch the spring as you manually turn the crank shaft. If the compressed spring contacts the seal you should be able to see it. Also you can measure the top of the seal from the spring seat and then measure the distance from the seat to the bottom of the top coil when compressed.
Comp. Cams has some very good tech articles on their site relating selection and installation to valve trains, cams, and such.
BTW, I see you are up as late as me and I don't think there is a time zone difference.
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From: Toronto ON
Originally Posted by 65Z01
BTW, I see you are up as late as me and I don't think there is a time zone difference.
btw, what do hotter plugs do and, what brand makes "recessed electrode"?
Thanks for all the info. I just have to rip into it, again, and see what I can see! Weather here isn't much different than where you're at, either.
(problem) but don't loose sleep 