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I got my new Mopar OEM plastic valve cover for Daisy today. My 87 original Jeep that I am trying to keep original. My OMIX valve cover that I got was a disaster. It simply should have fit but I recognized many differences on the way and thought I had it all covered. Well. Not quite. The new cover has shorter bolts on one side, my original had longer shoulder bolts. No big deal until I realized that the new cover is for 5/16 bolts and the old cover and my cylinder head use 1/4 inch threads. I have the skills for sure to upgrade the bolt holes, etc. but the OMIX valve cover bolt holes are just too far off to make me comfy. It is a POS. I am not modifying if not necessary to make this fit. Sure, I could grind it and use 1/4 bolts, drill the head and use 5/16 bolts. Whatever.

So I found what seems like the last OEM Mopar valve cover on the planet a couple of years later on Fleabay. It was listed for an AMC Eagle. It arrived today and it is for sure the correct cover. But..... The two baffles that go inside the cover surrounding the PCV and CCV grommets have obviously become unbonded from the cover. It is somewhat of defective cover. I will take it though. This particular cover is made of unobtanium.

I am looking for suggestions to bonding these plastic parts together and making it last. I am not expert as to if it is poly this or that plastic. I know for sure though that bonding plastic parts together can be very iffy. Lots of products just do not work. Especially when subjected to heat. I have found little success at this in the past. Most stuff just does not work. I do not want baffles breaking loose and creating havoc with my valve train parts.

Looking for solid suggestions.

Help.
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I've only ever had to "bond" plastic parts together on the outside of an engine. I've always used urethane when doing that.

Other then that I would attempt at drilling and maybe riveting it in place if possible.

Good luck what ever you figure out thou.
 

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Discussion Starter · #3 ·
No. Drilling is not possible. It has to stick from the get go.
 

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With the heat that will be involved epoxy or Lab Metal seems to be the logical answer. You would want to super clean and scuff the surface beforehand. Perhaps create a small lip on the studs to prevent the parts from falling in the event the bond should ever fail.
 

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I am not a plastics engineer or expert. But I have experienced a lot of bonding failures and successes in my 65 years. On well prepped plastic surfaces of all kinds I have never had a failure with E6000 medium viscosity industrial strength adhesive. I have a lot of faith in JB Weld too but I am not sure about that inside a valve cover on plastic.
 

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No expert...

But I don't think epoxies are gonna work long-term in this case. You're better off doing a plastic weld. As long as the baffles are made of the same type of plastic as the valve cover.

Then you can use some axle washers on the little plastic studs (or heat them and mash them down?) to make sure it really stays on.
 

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I have never tried this but for the price you could get it and do a few practice runs with it.
 
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That Q bond looks like an awesome product. Not sure if it can handle the oils and things that'll get splashed on it. It's rated over 350 degrees though.
I've used it and it worked really well, but yeah I don't know about oil exposure etc.

I think I'd try to find one of those plastic welders with the little wavy stud things that melt the two pieces together then you clip the wavy stud part off.
 

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If a bolt is not acceptable (I’d do that) don’t those baffles mount on the little domed toys in there?
I’d melt them after thee baffles are located me lad. I wouldn’t use any sealant or adhesive, either, but I would use two-part paste epoxy as a double whammy
 

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I'm guessing you are way overthinking this, they were obviously attached with a minor bit of adhesive, a decent adhesive rtv, and for insurance I'd take a soldering iron and melt the locating tabs into it a bit, and call it good

Hoss
 

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Discussion Starter · #19 ·
Thanks for all the great suggestions. One of the things that troubled me is that I do not know what type of plastic it is. Polyethylene and Polypropylene are very difficult to bond. The JB weld product specifically states that it does not adhere to these products. There is a chance that the valve cover is a vinyl product when I researched it further. I just do not know. I did come up with a loctite product that seems to bond more plastics than most. It was easily available locally so I will give it a shot. I have had epic failures gluing plastic engine parts in the past but yet had great successes at times.


I had thought of plastic welding the posts that locate it to the cover as additional insurance and many of you suggested this. They barely stick up proud past the baffle itself but they do by a slight amount. I have a power probe butane soldering iron that has a wide variety of tips in it. A couple of them are meant for cutting plastics, etc. Once I get it bonded with something that I feel works, hopefully the loctite does the trick, I will melt the posts over and also melt the baffle a bit into them.

I picked up the loctite stuff at HomoDepot tonight on the way home from our run group. I threw the soldering iron in the truck today. I will give it a shot tomorrow and report back.
 

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Update. I scuffed the surfaces to be bonded with 120 grit. I cleaned them with Acetone. I have alcohols and stuff, the Acetone was the first thing that I found. I used the loctite activator pen. Applied the loctite glue which is basically super glue but there are different types and speeds and viscosities. It bonded and stuck with authority right away. I am impressed with the product. I believe that it would work on its own.

The locating studs do stand a little proud. I will do a little plastic welding this weekend with my solder iron and plastic melting specific tip. The shop is cold right now so the cover bonding was done in the house to make sure that the temp is ok. We have had overnight temps in the 30s already. Usually that is not a big deal for shop temps but the pool install caused us to mark out the propane line to the shop, have it disconnected and capped off. The pool goes over the line and I have no idea if they hit it when excavating or not. We are having updated line installed to the pole barn ( it ended up being smaller than it should be for the btu furnace in the shop and the length of run) with a T to the pool heater. It will not be done until Oct 20th. So. I did it in the house to be sure of temps and cure time.

I am very confident of this bond. I for sure have enough of the little studs sticking up to make a plastic weld for insurance.



So far...... really good. Will
 
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