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258 valve cover gasket

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amcfitz View Drop Down
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    Posted: Feb/18/2023 at 9:07pm
Hi. I’m having real trouble with my valve cover gasket leaking. I could only find a cork gasket and the large gap between the hood down bolts makes for poor seal. Does anyone know where to get a rubber gasket or a fix for the issue. Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pdok Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2023 at 7:46am
Fel-Pro has a rubber gasket listed for 81-90 year applications, probably for the plastic covers. Not sure if it can retro-fit earlier years. You could pull up a close-up picture and look at the hole patterns to compare to yours.  My guess is the actual bolt holes are OK, but there might be profile differences.

VS50244R

Someone with a later year might be able to comment on crossover.

FYI, there are two thicknesses of fel-pro cork valve cover gaskets.  5/32 and 7/32.

Two problems to watch for. 1) gasket surface on the sheet metal valve cover must be completely flat, especially at the holes. Overtightening bolts deforms the holes downward and they can cut through the cork. 

2) Do not over-torque the bolts.

Cork is pretty good at stopping leaks if conditions are right, but is fragile and relatively short-lived.  I have generally used cork without any "extra" coatings, but you could always use a reasonable amount of sealant to help those long runs between bolt holes, I guess.  Just don't have it squeezing out inside the cover, use only enough to adhere the cork to the valve cover.  And know that it will likely be a pain to remove the crud if you used RTV (which I would not do in that location).

Check the bolts are snug every time you're under the hood. Use some Loctite on them if you like (clean the oil out of the holes first).
76 Grem X 258/904,4.0 head/MPFI, Comp X250H cam, Hughes springs, Clifford header, serpentine swap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2023 at 4:27pm
If it's the plastic cover you may never get it to seal. One of the engineers even stated that AMC knew they were going to have about 20% of those come back for warranty work,  but the savings was worth sealing/replacing them at least once -- warranties were usually four years at the time. After that it wasn't there problem! I forget where I got the info -- I think it's in a book written by an engineer who worked there for several years (don't even know if I still have the book).

The point is, there are metal valve covers made to replace the plastic one. Most require tapping the guide holes in the head around the perimeter. Don't have to drill new ones, just tap existing. You have to buy a valve cover made to replace a plastic cover though. Like this one:
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheCanadianAmerican Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2023 at 6:58pm
use silicone to glue the cork down to the valve cover. A small small amount. Also look around to see if you can get some of those like force spreaders for valve covers. Usually cork works pretty good on non machined surfaces but the area has to be super clean and not too tight 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Feb/20/2023 at 2:07am
It depends on what year you are working on.

Pre-1981 sheet metal valve cover seal best with a thin cork gasket glued to the valve cover (but not the head) with gasket or weatherstrip adhesive that holds it in place and prevents it from squirming out. The cover must be flat and you tighten the bolts with a nut driver. That's as tight as they need to be. You need to occasionally retighten them as the gasket compresses. Failure to do this will allow oil to work under the gasket, and the lubrication will allow the gasket to tear and squish out. Then it must be replaced. 

Post-1981 plastic valve covers should NEVER be sealed with a gasket. The gasket will compress unevenly and warp the cover. It is far better to clean everything fastidiously and paste the cover in place with a fat bead of Permatex Right Stuff sealant. That is how AMC did it originally. The cover is designed to be sealed with sealant, not a gasket. You run the bead of sealant and tighten the cover down immediately. No "let it set overnight then fully tighten it". The bolts are only tightened to "snug". It's barely more than finger tight. I think the official spec is 36 inch-pounds. You are only trying to hold the cover firmly to the head, not compress a gasket. Then you never touch the bolts again because doing so would break the bead of sealant. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Feb/20/2023 at 7:06am
X2 on what FSJunkie says about the plastic cover. It has two screws in the top holding it down, similar to the 195.6 OHV cover (and Gen1 V-8). Any valve cover gasket you find that says for 81-86 models should also state "with aluminum cover", "with steel cover", and/or the manufacturer (like "with Omix Ada Steel Cover"). No gaskets for the plastic cover, RTV (Right Stuff seems to be preferred) only. Another reason it was so cost effective even though AMc knew a lot would fail before the warranty period was up -- easy to reseal and cheap to replace if necessary. Most warp due to heat and over tightening. Keep the engine cool and don't over tighten the hold downs! If it starts to leak pull it off, clean the old RTV off and the surfaces thoroughly with paint thinner/mineral spirits/etc., then reseal.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcfitz Quote  Post ReplyReply Direct Link To This Post Posted: Feb/20/2023 at 8:55pm
Sorry I didn’t include the year of my car. I have a 1975 Hornet. It has the steel valve cover. I will look for the force spreaders. I did exactly what everyone is recommending. I attached the gasket to the valve cover with a thin coating of silicone.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Feb/21/2023 at 6:50am
The steel covers do get warped over time. Look at the screw holes also. They get indented. Take a small hammer and flatten the area around the holes, that helps. The ultimate "fix" is to get a cast aluminum cover, but you probably don't want to spend $350 for one. There are aluminum valve covers for 81-87 models for around $150, but a quick search only turned up one for pre 80 models (the change to plastic occurred in January 1980, so early 80 models have steel, 2/3 of the year models have plastic) -- from PML, around $350.  You can get a new steel one for under $60 though.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2023 at 12:20am
Redoing the valve cover gasket once every five years or 50,000 miles or so is pretty much routine maintenance on these. That's about when the gasket hardens, compresses, or otherwise fails. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcfitz Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2023 at 7:23pm
Thanks for the ideas. The car only has 28,000 origional miles and a new valve cover gasket.
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