78 280zcar Posted April 24, 2006 Share Posted April 24, 2006 I posted this on classiczcars but need somemore opinions. I just yesterday put flat top pistons from an F54 block into my N42 block. The pistons go over the deck about .021", is this normally how the F54 has them in there, I am going to put a P79 head on it that has not been shaved or anything like that! Also which year head gasket should I buy, 81 zx or 78 Z? Quote Link to comment Share on other sites More sharing options...
mentallylost Posted April 24, 2006 Share Posted April 24, 2006 Yep, it's right about .021 above the surface of the block. I was alittle nervous seeing that the P79 doesn't have round combustion chambers for the piston to clear into. I am running a F54 block and a shaved and shimmed .080 P79 head. I am using a felpro head gasket for a 83 model L28 and the thing that I don't like about it is that there are 2 coolant passages blocked by the gasket. I ended up using a hole punch to free the passages. I don't know if the 78 model head gasket has the 2 passages blocked. Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 24, 2006 Author Share Posted April 24, 2006 Right on so it is suppose to be that way! I thought I would have to end up getting an F54 block. About the coolant holes I know there is one extra coolant passage in the P79 head and I wasnt to sure about what gasket to get, the extra hole should be plugged up by the head gasket if there is no hole in the block for it, right?. Is there a difference in the thickness of the 81, 82 and 78 head gaskets? Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 24, 2006 Author Share Posted April 24, 2006 Also do I have to get different spark plugs, I have NGK spark plugs for a 78 do I have to get them for an 81-83 ZX? Thanks Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 24, 2006 Share Posted April 24, 2006 Mentallylost, I started a thread about L28 head gaskets a while back covering the same issue about coolant passage covers. While its probably fine for a lot of people, covering two BOTH coolant passages on the manifold side of the head was enough to blow two of my head gaskets, both around the cylinders where the passages were blocked (don't remember details atm). Also the manifold side of my pistons was slightly discoloured brown, I'm not sure what that means. After replacing the gasket with a proper L28ET one (PN 11044-P7911) which doesn't block passages I've had no further issues. Something to keep in mind I suppose. Dave PS. Other thread: http://forums.hybridz.org/showthread.php?t=108626 Quote Link to comment Share on other sites More sharing options...
mentallylost Posted April 24, 2006 Share Posted April 24, 2006 The felpro headgasket that I ended up using was a result of a cheaper headgasket (I don't remember the brand) that blew from the blocked passage between cyl's #5 + #6. I was more than a little upset with myself. I know better that ot use cheap stuff. And my motor had less than 100 miles on the rebuild. So when I bought the felpro and saw that the same coolant passages were blocked again, I pulled out a hole punch to free the passages. And just to be sure that I didn't weaken the gasket too much, I spayed both sides of the gasket with a can of copper gasket spray from Napa. So yes, I do recommend clearing the passages. Either by finding the correct OEM gasket P/N 11044-P7911 , or punching the gasket with a hole punch. But you are right Dave, the OEM gasket would have been the better way to go. I just was not in the mood for another run to the local Nissan dealership. Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 24, 2006 Author Share Posted April 24, 2006 I dont have an F54 block though that actually has the extra passage in it, I am using an N42 block that doesnt have the passage! I am using an N42 with a P79 head! Do I still need to break a hole in the head gasket if there is no hole in the block? Quote Link to comment Share on other sites More sharing options...
mentallylost Posted April 24, 2006 Share Posted April 24, 2006 No, if there is no passage in the block then leave the gasket intact. However if there is an open passage in the head with no place for the coolant to go, then you may want tap some threads in the passage and use a pipe plug to block it. I have never done this before, but maybe someone else with this head/block combination has? Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 24, 2006 Author Share Posted April 24, 2006 Now that is something I have never done to a head. Wouldnt a pipe plug block the coolant flow though? And cant I just put the gasket on and the coolant should just pass to the next hole? Hopefully! Quote Link to comment Share on other sites More sharing options...
mentallylost Posted April 25, 2006 Share Posted April 25, 2006 Wouldnt a pipe plug block the coolant flow though? And cant I just put the gasket on and the coolant should just pass to the next hole? I thought that you said that the block does not have the coolant passage and that the head did. If there is no passage in the block and there is in the head, then there is no next hole for the coolant to pass. Blocking the passage out of the head will then just keep the coolant pressure from being applied to the gasket. The coolant will still travel through the head and block and pass through the other passages. Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 25, 2006 Author Share Posted April 25, 2006 Yes that is what I said, there is no coolant holes on the block to match up for the two extra holes on the head. maybe I should just take it to a machine shop and see what they can do! Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted April 25, 2006 Author Share Posted April 25, 2006 How big are those holes and what size tap and plugs should I use. I found these plugs on ebay they also have 1/2" plugs! http://cgi.ebay.com/ebaymotors/Moroso-Pipe-Plugs-3-8-NPT-Chrome-Plated-39152_W0QQitemZ8045861047QQcategoryZ46098QQssPageNameZWD1VQQrdZ1QQcmdZViewItem Quote Link to comment Share on other sites More sharing options...
mentallylost Posted April 25, 2006 Share Posted April 25, 2006 The coolant passages on the P79 are 7/16 diameter so I would tap it out to 1/2 and just match the threads to the plug. Quote Link to comment Share on other sites More sharing options...
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