Plug Well Seals

[DeepPower]

Time to do the plug well seals on my '89 SHO - again!

I had done the seals 75K miles ago, carefully and methodically. Is there a recommended procedure for doing the plug well seals? Can anyone tell me the best quality seals I should get?

 

[Devin]

http://www.shopowered.com/html/maintain/maintain_60k_upper_1p.htm

I doubt there is really more than one source of plug well seals for this engine, even if they are branded differently. For what it is worth I used felpro.

 

[luigisho]

If you can find oem seals those are best. The Felpro seals are good if you can locate those. No experience with the others. 75k isn't that bad for those seals considering the heat cycles.
You can ref the seal replacement here as part of the upper 60k write up
http://web.archive.org/web/20110506202226/http://www.shophoenixproject.com/upper60k/upper60k.htm

 

[SHOdded]

I thought Scott (sdpatt) had found some generic o-rings that will work also? Anyway, here's one of his posts on the subject of replacement:
http://www.shoforum.com/index.php?threads/oil-around-spark-plugs.15979/#post-130417

 

[rubydist]

in my experience, they tend not to leak between the seal and the cover, but between the seal and the head. I have taken to using some high-temp rtv there when I assemble them - that seemed to me to extend the "dry" period somewhat.

 

[Off Road SHO]

You will never have to replace the plug well seals again if you stop the REASON they are leaking. Get rid of the vacuum in the plug well and it won't suck oil in. I can hear you all thinking now, "I don't have vacuum in my plug wells". Yes you do. The plug well on the Yamaha is a sealed unit, with the seal on the bottom and the spark plug boot on top. When the air in there heats up to 160 degrees, it expands and the overpressure forces some out through the spark plug boot. When the engine cools down, the air cools down and shrinks, causing a slight vacuum in the well. The spark plug boot at the valve cover seals so well that the only other place it can get air is from under the plug well seal at the bottom, which is surrounded by hot thin oil. All of the buggy guys that used this engine figured this out right away.

There are several ways you can address this vacuum problem:

1) Use different spark plug wires that don't use the valve cover seal.

2) If you insist on using the Ford spark plug wires, slip a small piece of plastic cable tie in between the boot and valve cover when pushing the boot on the final 3/4". This allows a microscopic path for air to go in and out easily.

3) Heat up an ice pic and melt a tiny hole in the silicone boot, also providing an escape path for the air.

Get rid of the vacuum America!
H&R Block voice\off

Tom

 

[DeepPower]

You will never have to replace the plug well seals again if you stop the REASON they are leaking. Get rid of the vacuum in the plug well and it won't suck oil in. I can hear you all thinking now, "I don't have vacuum in my plug wells". Yes you do. The plug well on the Yamaha is a sealed unit, with the seal on the bottom and the spark plug boot on top. When the air in there heats up to 160 degrees, it expands and the overpressure forces some out through the spark plug boot. When the engine cools down, the air cools down and shrinks, causing a slight vacuum in the well. The spark plug boot at the valve cover seals so well that the only other place it can get air is from under the plug well seal at the bottom, which is surrounded by hot thin oil. All of the buggy guys that used this engine figured this out right away.

There are several ways you can address this vacuum problem:

1) Use different spark plug wires that don't use the valve cover seal.

2) If you insist on using the Ford spark plug wires, slip a small piece of plastic cable tie in between the boot and valve cover when pushing the boot on the final 3/4". This allows a microscopic path for air to go in and out easily.

3) Heat up an ice pic and melt a tiny hole in the silicone boot, also providing an escape path for the air.

Interesting take on this and it makes perfect sense. Yes, as the engnine cools it will want to suck air in and if the plug wells are sealed, it will pull it from the gasket.

Isn't there a danger that rain water will get into the spark plug wells? Many of us saw that problem when using the wrong plugs that are too tall for the plug wire boot to seal.

I've been looking at this from the plug end, I'm looking at specialized gasket material that can be used between the spark plug and the valve cover, to be used either with, or to replace, the plug compression washer.

 

[luigisho]

Great info Tom. I am waiting to hear about water as well. I suppose the small size of the hole could mitigate this?

 

[SHOdded]

Isn't there a danger that rain water will get into the spark plug wells?

Maybe you can make snorkel tubes sticking out of the OEM boots, kinda like carb velocity stacks

 

[rubydist]

maybe that is why I haven't had that much of a problem - most of the aftermarket wires don't fit to the valve cover very well, so there is no chance for vacuum there... at the same time, there is plenty of opportunity to get water and dirt in...

 

[Off Road SHO]

Water will evaporate out of the well within 10 minutes of driving. If you get so much water under your hood that it fills a well, don't worry because the engine will have already ingested water through the intake and be hydrolocked. Temporary water in your plugwells will be the least of your problems.

Also keep in mind that a rotating engine produces a positive pressure in the crankcase and since they are connected to each other, the underside of the valve covers. It is the PCV system on engines that allow that built up pressure to never happen. On the Yamaha, the crankcase and valve covers are "sucked on" by the throttle body, by way of the oil separator passageway up the back of the block and through the oil separator can in the V of the block and then through a 1/2" diameter hose into the bottom of the throttle body. If that gets clogged up with condensed oil vapors, the engine can no longer suck out the over pressure and the over pressure will take the next easiest routes, like front and rear main seals, valve cover gaskets and plug well seals.

Tom

 

[DeepPower]

Water will evaporate out of the well within 10 minutes of driving. If you get so much water under your hood that it fills a well, don't worry because the engine will have already ingested water through the intake and be hydrolocked. Temporary water in your plugwells will be the least of your problems.

Um, that's not the experience many of us here have had.

I once tried non-Motorcaft plugs, I think they were Bosch, and because they were taller than Motorcraft plugs by a very tiny amount, the plug wires didn't seat properly against the valve covers. Not enough that you could visually see, but in the rain I got water in the plug wells that did not evaporate. It was especially bad after going through a car wash.
So please count me as skeptical of your claim about venting the spark plug wells.

 

[itwonder]

Um, that's not the experience many of us here have had.

I once tried non-Motorcaft plugs, I think they were Bosch, and because they were taller than Motorcraft plugs by a very tiny amount, the plug wires didn't seat properly against the valve covers. Not enough that you could visually see, but in the rain I got water in the plug wells that did not evaporate. It was especially bad after going through a car wash.
So please count me as skeptical of your claim about venting the spark plug wells.

I think what Tom is saying is either use proper fitting top seals (he's suggesting with a tiny vent), or use wires that have no top seal at all. A poorly fitting top seal is the worst case, and I can vouch for your comment; those close off the top just well enough that water tends to not evaporate out even with engine heat. It's amazing how long it will stay in there. Tom's thought of using no top seal at all is an interesting one. Rigged that way, any water that goes down the tube should evaporate out pretty quickly, like a stove *** with no top vs. a top. Not sure how that will work out on a street car vs. a race car, but I may try it if my present wires wear out before the car does.

In any event, I'm with rubydist's advice in post #5. The best thing you can do is to use a little high-quality RTV on both sides of the plug well seal when you install them. Works much better than dry! IIRC, I used the gray when I did mine last time; same stuff you use at the corners of the valve cover gaskets.

 

[DeepPower]

Tom's thought of using no top seal at all is an interesting one. Rigged that way, any water that goes down the tube should evaporate out pretty quickly, like a stove *** with no top vs. a top. Not sure how that will work out on a street car vs. a race car, but I may try it if my present wires wear out before the car does.

Okay, you try it and tell us how it works out. Let us know what happens in a car wash.

In any event, I'm with rubydist's advice in post #5. The best thing you can do is to use a little high-quality RTV on both sides of the plug well seal when you install them. Works much better than dry! IIRC, I used the gray when I did mine last time; same stuff you use at the corners of the valve cover gaskets.

I agree. Actually the Motorcraft plugs use aluminum crush washers, which are the worst material one can use for a sealing gasket in this situation. The best would be copper crush washers. I've already bought some 14mm black fiber high temp crush washers and I'm going to try one on one of my leaky plug wells, and a 14mm copper crush washer on another. @itwonder can try no top seal (just cut away the boot seal) and we will report back.

 

[Off Road SHO]

Deep Power,

I think you mis-understood what it wonder was talking about in regards to adding silicone to the plug well seal. It's made out of rubber (Viton I believe) and is fitted to the bottom of the spark plug wells on the valve cover.

I know the SPARK PLUGS use crushable aluminum sealing washers, which are very good for the SHO's aluminum head. That sealing washer has nothing to do with keeping oil out of the plug wells, rather it is for sealing the spark plug to head.

And after the car wash, if there is water sitting in the little indentation in the valve cover where the top spark pluge wire boot seals, as the air inside the well cools down, it will suck that water into the well and not let it evaporate.

Tom

 

[DeepPower]

I know the SPARK PLUGS use crushable aluminum sealing washers, which are very good for the SHO's aluminum head. That sealing washer has nothing to do with keeping oil out of the plug wells, rather it is for sealing the spark plug to head.

I'm sorry but that is incorrect. One purpose of the crush washer is act as a gasket, providing a gaseous seal between the spark plug bottom and the cylinder head cover. It is a one-time-use item that compresses to conform to the spark plug well and the cylinder head cover to make a seal.

Just because the cylinder head cover is aluminum doesn't mean the crush washer must be aluminum. Unfortunately, after much research I've found that aluminum is a lousy material for this application. Aluminum doesn't crush well, it leaves gaps. So using an aluminum crush washer against an aluminum cylinder head cover is compounding problems. Remember, the issue here is that oil is obviously seeping past the aluminum crush washer. That in an of itself tells us that the crush washer is not doing it's job in this application. And if oil is getting past, then it is definitely failing in it's main job to prevent gases from escaping.

Because copper is such a soft metal, it is the best material for a crush washer. That is why copper crush washers are used for hydraulic fittings such as brake linings.

http://scegaskets.com/wp_super_faq/whats-what-the-facts-of-gasket-materials/
"Solid copper is capable of sealing more combustion pressure than the other two [steel & aluminum] metal head gaskets"
"Copper gaskets offer the most options to the engine builder for bore & thickness combinations and the material is malleable allowing it to conform well."

I am going to do some testing, and I believe we will find that copper crush washers will solve the problem of oil in the plug wells. However, I'm concerned that with an aluminum cylinder head cover, with a copper crush washer, against a steel spark plug creates some problems. Dissimilar metals under stress generate heat at the point where they meet. Now, in the intense heat of a spark plug well this shouldn't matter. But it can also generate a minute electric charge (think thermocouple) that might degrade the copper crush washer over time. So I'm going to put my EE degree to work and see what the math says about this.

EDIT 4/5/2015: Corrected "valve cover" to "cylinder head cover".

 

[Off Road SHO]

Holy cow, where did you get your information?

"I'm sorry but that is incorrect. One purpose of the crush washer is act as a gasket, providing a gaseous seal between the spark plug bottom and the valve cover. It is a one-time-use item that compresses to conform to the spark plug well and the valve cover to make a seal."

??? Really? The spark plug doesn't even touch the valve cover.

"Remember, the issue here is that oil is obviously seeping past the aluminum crush washer. "

No it isn't. Who told you that?

Tom

 

[itwonder]

I'm sorry but that is incorrect. One purpose of the crush washer is act as a gasket, providing a gaseous seal between the spark plug bottom and the valve cover. It is a one-time-use item that compresses to conform to the spark plug well and the valve cover to make a seal.

Nope, you've got it wrong. The lower section of the spark plug tubes on the SHO are integral to the cylinder heads. About halfway up, there is a gasketed joint where the tube changes from being part of the head to part of the valve cover. The spark plug crush washer touches only the cylinder head. I think you are confusing the SHO engine with other hemispherical combustion chamber engine designs where the spark plug tubes are sealed by the spark plug at the bottom; the infamous Chrysler 426 hemi being one that comes to mind.

 

[rubydist]

back to the topic and reality here for a moment:

my experience is that with no seals on the plug wires to keep water and debris out of the plug well, or with really crappy sealing plug wires, a drive in a rainstorm will allow water into the plug wells much faster than it can evaporate out, quickly resulting in an engine running on 3 cylinders rather than 6. that approach may work in the desert on buggies, but it is not recommended for daily drivers in the rest of the world.

 

[Devin]

This has been a known issue for years due to knock-off wires with crappy seals (and badly installed wires of any brand). Anecdotally I've not seen any issues with proper sealing wires at all when dealing with water ingress. Of course neither properly fitting wires not the spark plug seals have anything with do with the valve cover plug well seals, which should be installed properly with a small amount of RTV.