Andy FitzGibbon Posted September 30, 2007 Share Posted September 30, 2007 I put my engine back together and the driver's side head gasket apparently didn't seal. The #4 cylinder is showing 95 psi compression (cold) while all others are 140. The car runs but starts burning water when it warms up and the thermostat opens. What are probable causes of the gasket not sealing? I had the heads milled, used FelPro Permatorque gaskets, cleaned the block thoroughly with solvent, and torqued the heads carefully using a clicker wrench. I did not use new head bolts, which I should have, but was in a hurry to get it done (I know, that usually leads to trouble). Any ideas? Thanks, Andy Quote Link to comment Share on other sites More sharing options...
pheonix165 Posted September 30, 2007 Share Posted September 30, 2007 other then the obvious lack of new head bolts...you didn't deck the block. even if it was never overheated the block will still warp over time. i'm guessing you didn't have the heads checked for micro-fractures either... but thats just my .02 bottom line, bad things always happen when your in a hurry Quote Link to comment Share on other sites More sharing options...
Turbone Posted September 30, 2007 Share Posted September 30, 2007 Decking the block isnt usually necessary, I've never heard of a Subaru block thats been warped. What could be the problem is the head bolts. The holes should be cleaned out prior to re-installing. I spray them out with brake cleaner then run the bolts (oiled) in and out a few times to make sure they seat all the way. When they milled the heads, did they say anything about cracks between the valves? Its only a problem if they go up into the exhaust port, where the water jacket is. Quote Link to comment Share on other sites More sharing options...
nipper Posted September 30, 2007 Share Posted September 30, 2007 Decking the block is never really necassary. When doing an aluminum head with an aluminum block, there is no need to replace the head bolts. Reasons for leak: Using non OE gaskets. Felpro is good, but whenever facing a weird or troublesome engine (weird is subaru, who else has two cylinders on each side, troublesome is a dodge neon). Dirty threads as said before. Checking the deck with a steel rule to make sure the cylinder liner did not move. Not having the heads pressure tested. Dirt during assembly. nipper Quote Link to comment Share on other sites More sharing options...
daeron Posted September 30, 2007 Share Posted September 30, 2007 also a possibility that the resulting contact surfaces on the head, or the block, were TOO smooth.. the gasket wants a bit of roughness to seal against. Just figured I would throw that out there too. Quote Link to comment Share on other sites More sharing options...
nipper Posted September 30, 2007 Share Posted September 30, 2007 also a possibility that the resulting contact surfaces on the head, or the block, were TOO smooth.. the gasket wants a bit of roughness to seal against. Just figured I would throw that out there too. The surface finish is critical on mid 90's engines. Its not so critical on older engines, but it is something else to look into. nipper Quote Link to comment Share on other sites More sharing options...
Turbone Posted September 30, 2007 Share Posted September 30, 2007 The surface finish is critical on mid 90's engines. Its not so critical on older engines, but it is something else to look into. nipper Why would it be different? All alum mating surfaces, regardless of year should be the same. I've been told by a couple of shops that alum mating surfaces need to be rough so the gasket material seals properly. Quote Link to comment Share on other sites More sharing options...
nipper Posted September 30, 2007 Share Posted September 30, 2007 Why would it be different?All alum mating surfaces, regardless of year should be the same. I've been told by a couple of shops that alum mating surfaces need to be rough so the gasket material seals properly. http://www.aa1car.com/library/gasket_failure.htm "Improper surface finish is probably the second most common reason for gasket failures, according to McKnight. This includes surfaces that are too rough and surfaces that are not flat." "And never, never use a Scotchbrite abrasive pad to whiz off old gasket residue from a head or block. Abrasives can leave low spots on the surface that will prevent the head gasket from sealing," I have never ever heard that about the surface finish at anytime anywhere, including my engine design class, and all the TSB's in the past 15 years. Thats one machine shop i would never take an aluminum head to. nipper 1 Quote Link to comment Share on other sites More sharing options...
Turbone Posted October 1, 2007 Share Posted October 1, 2007 Ok, let me rephrase that. The mating surface cannot be smooth or to rough:rolleyes: If you look at the stock mating surfaces, you can see the mill marks on them. When you have a head shaved/milled, etc, you end up with a surface that is OEM(supposed to). If you clean the surface(s), you should not use abrasives(sanders, anglegrinders, etc). But I cant see how using scotchbrite pads will take off enough of the surface to cause low spots. I did make the mistake of being to aggresive with a pad on my little angle grinder and paid for that. I had the heads milled soon after and learned from that mistake. But I have used a scotchbrite pad by hand and have had no problems with sealing since. I will try to be more discriptive/detailed in my postings in the future;) Quote Link to comment Share on other sites More sharing options...
daeron Posted October 1, 2007 Share Posted October 1, 2007 Ok, let me rephrase that. The mating surface cannot be smooth or to rough:rolleyes: That was also my impression; obviously you dont want a surface comparable to a four day stubble, or sixty grit emery cloth.. but you dont want it smooth as silk, either; there needs to be SOME surface adhesion for the gasket to seat properly. Quote Link to comment Share on other sites More sharing options...
nipper Posted October 1, 2007 Share Posted October 1, 2007 http://www.aa1car.com/library/ar996.htm how smooth is too smooth. Just for the record, gaskets so all their sealing at the edges. Everything else is for locationof holes and the gaskets. It was an education (and very frustrating when i had to mfg and design limited run gaskets). Made one amazed that some of these things actually worked at all nipper Quote Link to comment Share on other sites More sharing options...
Andy FitzGibbon Posted October 1, 2007 Author Share Posted October 1, 2007 Thanks for all the opinions. I will try all this stuff when I tear it back down to redo it. I'm leaning towards it being bolts/bolt holes. I did clean out the bolt holes but will do it again and make sure they're really clean. I will also use new bolts. Thanks again, Andy Quote Link to comment Share on other sites More sharing options...
walczyk Posted March 23, 2011 Share Posted March 23, 2011 You seem to be misinformed. The surfaces of new blocks and heads are completely flat (to the naked eye and to touch) or any difference is less than 0.001 inches, and that is the ideal surface to reattach a cylinder head. When you talk about adhering, it seems like you're talking about the gasket falling off because of gravity before you torque it. I can list many other reasons, but you should stop thinking that a surface could be too uniform for a gasket to work properly. Quote Link to comment Share on other sites More sharing options...
naru Posted March 29, 2011 Share Posted March 29, 2011 You seem to be misinformed. The surfaces of new blocks and heads are completely flat (to the naked eye and to touch) or any difference is less than 0.001 inches, and that is the ideal surface to reattach a cylinder head. When you talk about adhering, it seems like you're talking about the gasket falling off because of gravity before you torque it. I can list many other reasons, but you should stop thinking that a surface could be too uniform for a gasket to work properly. "Though most gasket manufacturers do not specify a minimum smoothness spec for aluminum heads that have MLS head gaskets, they do recommend a minimum of 30 RA for engines with aluminum or cast iron heads and a nonasbestos or graphite head gasket. The reason for doing so is because soft-faced head gaskets require a certain amount of lateral support from the head and block." You should read the link.Quite good. http://www.aa1car.com/library/ar996.htm Quote Link to comment Share on other sites More sharing options...
Petersubaru Posted March 31, 2011 Share Posted March 31, 2011 maybe your heads are not flat..I feel for you..a real pain to redo..drove my unit 30 mi and then came the white smoke...the heads were milled and pressure checked ( I hope )..long story short, I took the heads to another shop, and out comes the big heavy straight edge and feeler gauges between .002 - .006 were slipping under the bar in various spots..the machinist said he had no answer as to why the heads were so wavy..not unless the previous place used a hand held belt sander... Quote Link to comment Share on other sites More sharing options...
Crazyeights Posted March 31, 2011 Share Posted March 31, 2011 (edited) So, is there a general consensus at to what the proper method is to prep (Subaru) blocks for new head gaskets? Most of the head gaskets I have done over the years at work have been on iron block - aluminum head engines. On the last performance EA81 I did, the machinist took about .003" off of the deck to "clean and square up the surface" and another .020" from the heads to help raise compression. So far it's been great. I am getting ready to put rebuilt heads back on my EJ22 and I was a wondering about methods of cleaning the block surface. Edited March 31, 2011 by Crazyeights Quote Link to comment Share on other sites More sharing options...
MilesFox Posted March 31, 2011 Share Posted March 31, 2011 Turbone has the most valid advice. The rest of you are speculating things that never occur. Original eom gaskets are graphie faced, same with exhaust and intake. The aluminum will squeeze down with the torque sequence. The graphite gasket allows for expansion of the head under such torque. The fl-pro gaskets have been alright for me. I never mill the heads, just clean them off with a razor and carb cleaner, and brass wheel for tougher spots. I would advise you to see if the freeze plugs are present(singe to took it to a machinist. This can be inspected by just removing the valve cover. I also agree with turbone about the oiling of the bolts to get a proper torque. I have seen carbon and rust on bolts. I used gunk and moved the bolt back and forth, and cleaned out with carb cleaner. I wish you could still get the victor reinz gasket, as they were oem with a fuji mark. Felpro supplies genuine grommets and with ea82, and genuine HG for 2.5 engine. Suppose milling the heads took some of it flexibility away and is now bowed at the edges with the torque introduced. Otherwise, you may just have a bad intake gasket. I have done a million ea82 headgaskets, so this is where i am coming from. Quote Link to comment Share on other sites More sharing options...
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