I replaced the intake manifold gasket on my internally oil-leaking recently rebuilt 1970 LS-5 engine. Now it only leaks 3/4 of a quart in 300 miles which is still unacceptable as a daily driver. Also, I have now noticed a puff of smoke during start-up after a 5-10 minute shutdown on a warm engine. Seems to me like valve seals are leaking. I am going to talk with my engine rebuilder about doing this and ask him to do a leak-down test. Can valve seals be successfully changed without removing the heads?
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Tony -
Re: Leaky LS-5 Intake Update
Tony-----
First off, a cylinder leak down test will do nothing to assess the condition of valve guides or valve seals. A leakdown test will allow you to assess the condition of valves, piston compression rings, and, to some degree, head gasket compression seal. It is also not effective at assessing the condition or effectiveness of installed piston oil control rings.
Valve seals can be easily changed without removing the heads by any one of several methods. I prefer using compressed air to pressurize the cylinder, holding the valves closed. Then, using a special tool which mounts on the rocker arm stud, you can compress the valve spring and remove the valve spring and retainer. These kits which include the tool and the compression fitting for the spark plug hole are easily available from auto parts stores at a nominal cost.
If valve guides are bad, simple replacement of valve seals will be a futile effort. Also, on a stock big block, the valve seals are of the umbrella design; they are NOT a positive seal (e.g. "Perfect Circle" teflon seals). It is very hard for these seals to be "bad" in a recently rebuilt engine. It is possible, however, that a positive-type seal was installed. Personally, I don't like the all-Teflon type positive seals; I prefer the Viton type if a positive seal is going to be used.
Check with your engine builder regarding three things, in particular: first, did he replace the valve guides and, if so, what type did he use? Second, did he replace the valves or did he check them for stem wear to confirm that they were within acceptable limits? Third, what type of valve seal did he use? Those are the important factors to consider if valve guides/seals are to be considered suspect in this problem.
If your engine builder installed new valve guides (preferably, cast iron type or, alternatively, silicon-bronze thick wall type), if he replaced all the intake valves or checked them for serviceability, and if he installed a quality valve seal of almost whatever type, THEN VALVE SEALS/GUIDES ARE NOT YOUR PROBLEM. If he didn't do all of these things, then valve guide/seals MIGHT be your problem. I doubt it, though, because this problem sounds all to familiar to me.
Also, bear in mind that if your intake ports were wet with oil all the way to the interface of the intake manifold, valve guide/seals COULD NOT BE RESPONSIBLE for oil getting to this point. Among other things, the induction airflow is in the opposite direction.In Appreciation of John Hinckley -
Re: Leaky LS-5 Intake Update
Joe,
I don't know if my rebuilder replaced the valve guides for sure but I suspect that he did. I will verify this. I will also verify what type of valve seals were installed. I do know that he did install new valves as the old ones were burnt and I have them in storage. I do also remember that the same valve springs were reused but they were all checked first and were within the specs to be reused.
Are there any other tests that I should be aware of that might point to where the oil is going?TonyComment
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Re: Leaky LS-5 Intake Update
Tony-----
Were all the valves replaced? Usually, it's the exhaust valves that most often suffer from "burning" and, assuming that you have any problem at all with vales/guides/seals, it will be the intake valves only that will be involved as far as the oil consumption issue is concerned.
In any event, find out what was done to the guides, what valves were replaced, and what valve seals were used. I think that it will put the "oil-leakage-past- valve-guide" issue "to bed".
As far as tests to determine where the oil is going, I wish I knew of one. As I mentioned previously, I devoted years to analyzing this problem and never solved it. I hope that you do, though, so that I can benefit from your success.In Appreciation of John HinckleyComment
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Re: Leaky LS-5 Intake Update
Yes, Joe, all the valves were replaced. I hope I can solve this problem as well. I'll keep you informed as I work to resolve it.TonyComment
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