Question on installing MHG pertaining to lower timing cover and copper spray.

[icey756]

I recently pulled my engine out and I am installing an HKS MHG. I took my head and block to a machine shop and both are straight and true. The only problem I have is the rear lower timing cover on the block is higher by .002 inches. Its flat for about an inch from the exhaust side but then all the way to the intake side is where it raises a bit. He said the only way he can get it down is by machining the whole block because he has no way of holding just that piece to take that much off. So i just planned on sanding it a bit. I hope that works but im not sure if it will. Any opinions? Also I cant seem to find out what the name is for that copper spray from napa. Supposedly creates a better seal or something i heard. Am i suppose to spray that on the block and head side or just for the block? Also i was wondering if i should get cp piston rings or npc rings. seems that npc stuff might be cheap considering i can get npc rings, pistons, and connecting rods for the same price as the cp rings.

 

[Cyrus]

you should be machining the head and block anyway for a MHG. and when you machine the block, you should machine the rear timing cover at the same time.

problem solved!

also it is called Spray-on Copper Gasket and it is often made by a company called Permatex.

and you should read the sticky in this section about spraying that on MHG's. it is widely considered a no-no.

 

[radiod]

Can't do much more than echo what Cyrus already said. You need to have the head/block machined because the metal head gasket needs a much smoother surface (roughness average/RA value) to seal properly. Some metal head gaskets are more forgiving than others, but you're just asking for troubles if you aren't going to do the proper prep work.

If I remember correctly, the HKS gaskets are ones to need a smoother RA.

Here's the thread that was mentioned about that the copper gasket spray:
http://www.supramania.com/forums/sh...ay-Sealer-on-a-MHG-...Might-Want-to-Read-This

 

[hvyman]

Dont use the copper spray on a new hg.

 

[icey756]

The machine shop checked my head and block and said they were both straight and true other than that cover. I already had to head in once to get machined but i took it off again so thats why i got it checked. I wont use the copper spray but why would i get my block machined if its already straight like the guy said.

 

[RPSil13]

The machine shop checked my head and block and said they were both straight and true other than that cover. I already had to head in once to get machined but i took it off again so thats why i got it checked. I wont use the copper spray but why would i get my block machined if its already straight like the guy said.

bc of roughness average/RA value

 

[icey756]

why would that change at all from the factory? its not like i was making gouges in it or hitting it with a hammer to make it not smooth.

 

[hvyman]

The head and block should be resurfaced to 25ra or better in order for the mhg to properly seal.

Also if the rear timing cover is not machines with the block the hg is not going to deal at all.

 

[radiod]

In other words, the factory machine finish is not smooth enough. There's a LOT more margin for error with a composite (stock) head gasket.

 

[icey756]

how does someone measure the roughness average? And you say it should be machined to at least 25ra or better but ive seen people saying to get it to 15ra or better. The rear timing cover in sanding myself. I honestly dont think that i need to get the block resurfaced just because the "ra" is from the factory. Wouldnt the copper spray just fill in any irregularities anyway? isnt that the point of it? to make sure it seals correctly?

 

[89gte]

The block head, and timing cover need to be resurfaced all at once. The stock head gasket is made out of a composite material that allows for a higher margin of error like others have stated. Metal head gaskets do not have that same margin for error. If you sand that cover yourself, and it is not exactly where it needs to be, you will blow your head gasket, and be in the same position if not worse. I would also be sure that you have selected the correct thickness for your MHG. This sticky at the top of the forum explains it all: http://www.supramania.com/forums/showthread.php?97552-Head-Gasket-thickness-selection. Good luck

 

[hvyman]

Also new from the factory the surface is plenty fine for a mhg. How ever you block is no where near new now and the surface is far from smooth enough for a mhg.

I wouldn't sand the rear timing cover either it's not going to end well.

Your on the cheap path. I don't see it ending well at all.

 

[icey756]

And you would know that my block is no where near what it needs to be now how again? How can the ra on a block change from a factory with out warping? And i also dont understand how my timing cover can be higher on one side and not the other. the block has never been resurfaced so when would that even be off the begin with?

 

[hvyman]

1your block is not new.
2 it's been 20 years since it was.
3 most cars these age have had 3+ head gasket issues.
4 never seen a shop use distilled water which means it has some corrosion all around the cooling system.

Just because the block is not warped doesn't mean the rs is crap. Ra = roughness average. It's how smooth the surface is not how bad it's warped.

A composite gasket doesn't need to be as smooth as it is compressed when it's torqued down.


You can go about it how you wish. We can only tell you how to do it properly. Do what you want it's your car.

 

[3p141592654]

No one knows what your block/head ra is, so go get it measured, then compare what you have to the MHG manufacturer's requirements. This is a simple issue and any competent machine shop can give you the info you need. No guessing is needed.

 

[icey756]

yes but how does a blocks ra get worse with age? Cast iron isnt exactly soft.

 

[3p141592654]

Your head is aluminum, and your block is iron, and they have different coefficients of thermal expansion. That means every time your engine goes through a hot cold cycle the head scrapes across the block because they expand at different rates, The 7M head expands about 0.5mm more in the long direction than the block from cold start to running temp. Over many years that creates wear. Also, the hard metal fire rings on the composite gasket create indentations around each cylinder from the same expansion action. Finally, contrary to what was posted above, the 7M did not come out of teh factory with a finish that was good enough for a MHG. That took alot of manufacturing development in the late 80s before they figured out how to make MHGs work on production engines. The 7M predates that development work.

 

[IJ.]

Electrolysis..

 

[icey756]

Ok I will ask about his ra and see what he can do. Now do i have to get an HKS gasket or can i go with a greddy? HKS as far as i know only offers a 1.2mm and a 2.0mm gasket. Greddy has a 1.5mm. And Titan motorsports has a 1.4 but i havent really heard anything negative or positive about them. Also still dont know about what rings to get. stock bore but i honed them.

 

[radiod]

If I recall correctly, the Titan gaskets are custom Cometic gaskets rebranded. The Titan/Cometic gaskets will do the job just fine and out of the metal head gaskets are the most forgiving (50RA or better as opposed to 25RA or 15RA). The brand isn't going to change much in terms of "gasket performance", but the style of gasket will. The majority that you will find are a "bead" style head gasket, but you will find some more expensive "stopper" style gaskets out there as well. The stopper gaskets are a better design, but much more expensive.

In terms of head gasket thickness, it's easy math.

Amount machined off stock head + amount machined off stock block + 1.3mm (stock gasket compressed thickness) = new headgasket size

If you get a gasket that is thinner than the formula result, you're bumping up compression, if you get one that is thicker, you're making it lower compression. If you don't know what you're doing, use the closest you can find to the formula result.

If you need more than that there's a whole sticky thread devoted to head gasket thickness selection:
http://www.supramania.com/forums/showthread.php?97552-Head-Gasket-thickness-selection

And just in case you're curious, a little comparison of RA values. The left side is 68RA and the right is 24RA. The left is not within spec of a metal head gasket sealing.

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