Plenum Port + Standard Gaskets = Bad Idea

[gbmidyear66]

I completed a top end Port in March and have been driving my Z as a Daily driver since (well I also sold my SUV and am waiting for my new one to arrive).

Car has been running great - but in the last week I'm getting a vacuum leak sound and I'm leaking a small amount of antifreeze from the Passenger IH plug (3rd #$%^& time I have tried to seal it with gasket cement).

When I put it back together in March I used a set of standard thickness gaskets I had purchased some time back - I trimmed them to the opening of the port. When I took her apart tonight - the gaskets had literally been sucked inward from the vacuum . I guess trimming them was a bad idea..... Luckily LGAFF (who did my port) had sent me along a new set of the thicker gaskets. I put those in tonight - I hope this is a permanent fix.

I liberally wrapped the leaky IH plug with teflon tape this time - hope this does the trick.

She's running smooth and quiet again.....

[carter200]

When it's apart again check the straightness of the IH to make sure it's flat. Sounds warped to me............

[LGAFF]

Carter, no welding on these or anything only Powdercoating.....as the parts were factory PC'd would not think warping would be an issue

[LGAFF]

if the plenum if only leaking around the one runner, I would think the issue is coolant getting under the gasket, not warping....try the tape, and recessing the allen head then covering with RVT

[gbmidyear66]

No - its not related to the coolant. The pic of the side I attached (which was worse than the other side) was the side that WASN'T leaking coolant.

Thinking about this more - I am wondering if I created the problem myself.... I glued the gaskets to the Plenum using contact cement, then applied a coat of motor oil to the mating side (since I was sure I'd be going back in again at some point!). I wonder if adding the coat of oil was a bad idea - clearly it will reduce the binding of the gasket to the IH surface?

The gaskets you sent Lee were about 3 times the tickness and didn't need to be trimmed - I am hoping the increased structural rigidity of these gaskets will be sufficient for them not to collapse like the std thickness ones did.

[mike100]

I recently pulled my plenum for a similar reason...no vacuum leaks, but I had cranckcase vent oil seeping across the gasket and oozing out of the side. It bothered me enough to redo it.

Basically I had used rtv silicone gasket seal around the water port and a very thin film around the crankcase breather ports. I think the sealer was so thin it cured before I had a chance to torque the bolts which may have left an uneven texture allowing the oil to weep across the gasket surface.

Following Jerry's advice, I used the brown Permatex aviation form-a-gasket style sealer which doesn't harden up right away. He also sent me the thicker gaskets which I think I prefer, if for anything, they seem less likely to tear.

[mike100]

Another factor that may have contributed is if the gaskets got moved around too much while you assemble the plenum top.

I use M6 all thread studs in the 4 corners of the i/h mounting holes. they are only an inch long and act as a guide to drop the plenum on, plus hold the gaskets from moving around.

[rhipsher]

Another factor that may have contributed is if the gaskets got moved around too much while you assemble the plenum top.

I use M6 all thread studs in the 4 corners of the i/h mounting holes. they are only an inch long and act as a guide to drop the plenum on, plus hold the gaskets from moving around. I'm thinking the same thing. The glue may have dried before you got the gasket in place and it got fugley. I've never used glue before. I've heard of people using a thin coat of grease to help increase the sealing but not oil.

[rhipsher]

Of course the other method of coolant block off is the finolic plenum spacers that don't have the coolant holes in them. I personally like the idea of just tapping a thread in the coolant hole to block it of myself. Using the spacers is more work and you have to cut 4 gaskets instead of two. But it's always worked very well for me.
I just go down to the auto parts store and just buy a sheet of .062 thick Felpro gasket materiel and I use .048 thick for my throttle body after I top end ported my car. And just use the spacers to trace out the pattern. But I also have the spacers marked face 1-2-3-4 so they go back on the same way I blended them to the plenum and IH housings.
http://i301.photobucket.com/albums/nn63/keeno1970/2011-10-01_13-12-33_841.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/2011-10-01_14-02-07_393.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/2011-10-01_14-57-36_625.jpg

[gbmidyear66]

Another factor that may have contributed is if the gaskets got moved around too much while you assemble the plenum top.

I use M6 all thread studs in the 4 corners of the i/h mounting holes. they are only an inch long and act as a guide to drop the plenum on, plus hold the gaskets from moving around.

I glued the gaskets (last time and this time) to the plenum. There is no chance the gaskets moved during assembly. You can see the glue residue in my photo. I guess this raises the question of whether the contact cement was a good idea ( I got the idea as a recommendation from somewhere else - can't recall where)

[rhipsher]

I would not use glue for the simple fact that I'd hate having to scrape it off every time I put new gaskets on. What a pain in the butt.

[gbmidyear66]

Those fenolic spacers are interesting (might have to look at that if my gasket problem returns)... I heard a rumour that the cooler Plenum/air temp is worth 20HP?

[Kevin]

Those fenolic spacers are interesting (might have to look at that if my gasket problem returns)... I heard a rumour that the cooler Plenum/air temp is worth 20HP?

i've got a bridge i'd like to sell ya

[GOLDCYLON]

Those fenolic spacers are interesting (might have to look at that if my gasket problem returns)... I heard a rumour that the cooler Plenum/air temp is worth 20HP?


Only pointed downhill on a 60 degree slope. In Short Hell no...

[rhipsher]

They do make the plenum much cooler. But not 20 hp cooler.

[carter200]

Of course the other method of coolant block off is the finolic plenum spacers that don't have the coolant holes in them. I personally like the idea of just tapping a thread in the coolant hole to block it of myself. Using the spacers is more work and you have to cut 4 gaskets instead of two. But it's always worked very well for me.
I just go down to the auto parts store and just buy a sheet of .062 thick Felpro gasket materiel and I use .048 thick for my throttle body after I top end ported my car. And just use the spacers to trace out the pattern. But I also have the spacers marked face 1-2-3-4 so they go back on the same way I blended them to the plenum and IH housings.
http://i301.photobucket.com/albums/nn63/keeno1970/2011-10-01_13-12-33_841.jpg



Rick,
Is that a pubic hair on the top drawing left side port? You guys must be getting slopping in your shop again ;)

[carter200]

Carter, no welding on these or anything only Powdercoating.....as the parts were factory PC'd would not think warping would be an issue

Lee,
You know that checking relieves all doubt. We can only be guessing till the tale of the straight edge is told. Not pointing any fingers just stating what "I" would do.
You do great work and you would NOT have let anything like this slip past you :cheers:

[HAWAIIZR-1]

Wow, that is interesting. Because both heads and plenum are ported on mine and I trimmed to match and although very thin in the middle and no glue or adhesive never had a problem like that. I blocked off and bypassed the coolant so that may have helped. I trimmed OEM gaskets though. Glad to hear you got it resolved.

[LGAFF]

I just want to make sure its right, I am not a PC expert.....so if there is a chance they are warping want to know how to avoid it, etc

Lee,
You know that checking relieves all doubt. We can only be guessing till the tale of the straight edge is told. Not pointing any fingers just stating what "I" would do.
You do great work and you would NOT have let anything like this slip past you :cheers:

[rhipsher]

Rick,
Is that a pubic hair on the top drawing left side port? You guys must be getting slopping in your shop again ;) No! It's one of my big black butt hairs.

[carter200]

No! It's one of my big black butt hairs.

Obama......You are such a kidder :p

[gbmidyear66]

Before I ported the top end, I had a problem with the TB and the secondaries did not seal. I could not get the engine to idle below about 850 RPM (with A/C On).

Now - it idles right down at 650 (so I'm sure vacuum pressure is higher) AND the gaskets were thinned to accommodate the port - so they are definitely dealing with a higher vac pressure and have less meat to them.

Next time its apart (hopefully not soon) I will check the planarity of the IH and Plenum faces and let you know Lee.

[rhipsher]

Obama......You are such a kidder :p Hey I shed allot. What can I say. Saloma lake loka.:D