High Temp RTV Sil Gasket Maker for Exhaust Manifol

[1993_VG30E_GXE]

Product:
LOCTITE 5920 Copper
High Performance RTV Silicone Gasket Maker
High Temp Resistance: 600°F Intermittent 700°F Intermittent

Could this product IMPEDE the ability of the exhaust manifold gaskets (fiber/metal gasket material) to work properly?

When I re-assemble the engine, i'm concerned the flanges on the exhaust manifolds themselves (not on the heads) may be slightly distorted for flatness, so I was thinking about installing this high temp RTV IN ADDITION (both sides) to the new gasket.

I don't want to risk that puttering leak like before, once I install this thing. Basically I want to do anything possible to ensure as good a seal as I can make, that will last for as long as possible.

 

[sneakboxer]

I used the same stuff on a snowmobile exhaust manifold in the same manor and i had no leaks. I beat on that pretty hard too.
Good luck

 

[mechtech2]

I'd only use it if I had to - special situations.
The regular gasket should not need it.

 

[bdcardinal]

you know you can get the flanges machined right? we do it a lot at work when we do a longblock on a car with iron manifolds.

 

[onion]

Using RTV on exhaust gaskets or AS exhaust gaskets isn't really the 'right' way to do it. Plenty of people will disapprove.

But I've done it several times, and the RTV seems to hold up just fine. It isn't really necessary if your parts are in reasonably good condition, but in my experience, it won't really HURT anything.

 

[1993_VG30E_GXE]

My only concern about getting the manifold flanges machined, is, the header pipe down blow might not line up properly if I change the distance. They don't mention machining those in the service manual.

The head ports and flanges on cylinder head are within flat spec - checked with the 0.005" Feeler gauge and straight edge.

Thanks guys. As your opinions are that it won't HURT anything, I'm going to put it on just in case. The last thing I want is to put it together and have the sound still there.

 

[tom slick]

how much work is it to R&R the manifolds if they don't seal once they are installed?

 

[onion]

Originally Posted By: 1993_VG30E_GXE
My only concern about getting the manifold flanges machined, is, the header pipe down blow might not line up properly if I change the distance. They don't mention machining those in the service manual.

The head ports and flanges on cylinder head are within flat spec - checked with the 0.005" Feeler gauge and straight edge.

Thanks guys. As your opinions are that it won't HURT anything, I'm going to put it on just in case. The last thing I want is to put it together and have the sound still there.



Have you checked the flatness of the manifold sealing surfaces? I agree with others here that IF they aren't sealing because the surface is warped or pitted, then having them machined is the best fix. I wouldn't worry about the flanges not aligning- we're talking about removing maybe .025" of material, depending on how bad the surfaces are. I seriously doubt this would cause you any problem at all.

 

[Vikas]

Is that O2 sensor safe? Remember silicone is an enemy of the O2 sensor.

- Vikas

 

[1993_VG30E_GXE]

Tom: It's bad. To re-do the manifolds it means complete engine removal, which means transmission removal, transferring to a stand, and more costs in gaskets because the plenum has to be removed. In other words, there's no way I would do it. If the sound was still there, I would leave it.

Onion: I'll check that out, what you said. I guess I see your point, it's such a miniscule amount of metal removed, that it should be fine.

That's a good point Vikas, but only if I sloppily put the RTV on, and enough squeesed into the port.

 

[tom slick]

Quote:
Tom: It's bad. To re-do the manifolds it means complete engine removal, which means transmission removal, transferring to a stand, and more costs in gaskets because the plenum has to be removed. In other words, there's no way I would do it. If the sound was still there, I would leave it.


that's what you may have to deal with by not surfacing the manifolds and head surface to make certain you are providing a good sealing surface. Leaky exhaust manifolds will also cause backfires that you'll have to put up with.

 

[onion]

I'm glad that O2 sensor thing was brought up- I didn't think of that (industrial diesels don't commonly have oxygen sensors (yet?), so I usually don't give them much thought). As I understand it, RTV (whether sensor-safe or not) is no longer a danger to the oxygen sensor once it's fully cured and no longer putting off vapors. However, that's under NORMAL circumstances. If you put RTV on the exhaust gaskets, then it will see temperatures well above what it was designed for- and even though, in my experience, it will remain intact... I wonder if hot RTV could put off enough vapors to endanger the oxygen sensor. I have no way of knowing- but now that Vikas brings up the point, I don't think I'd risk it.

So your best option might be to just go with bcardinal's advice: have the manifold surfaces machined if necessary, and install the gaskets dry.

 

[mechtech2]

Certain silicon RTVs for sure can give off silicon which can coat the O2 sensors, and make them faulty or not work at all.
Look on the label or blister pack for 'O2 Safe'.

But in this case, try to get things to line up, be clean and flat, and use the stock type gasket dry.
Those really are your best odds.

 

[440Magnum]

Originally Posted By: 1993_VG30E_GXE
Tom: It's bad. To re-do the manifolds it means complete engine removal, which means transmission removal, transferring to a stand, and more costs in gaskets because the plenum has to be removed. In other words, there's no way I wou


IF its that bad, I'd have the manifolds machined flat. If the manifold isn't too large and unweildy, you can do a decent job yourself by hand-lapping the sealing surface against a piece of sandpaper laid on either a flat machinists table or a piece of plate glass (ordinary window glass isn't flat enough). Other things will work too- just find a very, very flat surface to back up your sandpaper, use fine sandpaper, and then "figure 8" lap the manifold for a few strokes at a time. You can immediately see the high spots that are getting taken down, and you can tell when to quit for minimum removal of material.

I've used very small amounts of "copper" high-temp RTV on exhaust manifolds before, and my experience is that it works OK... for a few months or even years. But it eventually deteriorates under that kind of heat. Exhaust gas temps on gasoline engines are way over 600-700F, so you're depending on conduction back to the heads and cooling system to keep that flange/head joint under 600F. Its going to be marginal in the long run.

 

[1993_VG30E_GXE]

But tom I checked the surface with a machinist level and 0.005" feeler gauge, it's fine.

The problem was the studs snapped, I don't know how - from heat...mind you they were 16 yrs old? When the stud snapped it creates a gap - then the puttering sound after.

And get this, of the 12 studs total (6 front 6 back) only 6 in total were left holding for the past 5 yrs or so.

 

[1993_VG30E_GXE]

How much can I bid to the machine shop(s) for this task? I found some irregularities on the LH side one. I do have those abrasives like the scotch brite attachments for my die grinder - can this fix it or does it need to be decked?