Guest LIghtningZ Posted June 17, 2002 Share Posted June 17, 2002 Just got done reading the thread that Bang posted about head probs, i just found out yesterday that i have a stuck (Read, bent)valve in my 75' 280 all stock. this car has to get running as is it will be my only means of transport for a while i was told that taking the cam from a 260Z and putting it in a 280F.I. should wake it up? also thinking about finding a maxima head for my engine or is this going to develop to much compression? I'm a compression fiend. but i dont blow the lower end until i secure a S.B.C for transplant... I hope that DAW and the rest of you guys can come to my rescue!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
DAW Posted June 17, 2002 Share Posted June 17, 2002 The Maxima head is not going to raise the compression too high on your '75 L28 block as it has dished top pistons and 8.3:1 c.r. the Maxima head may take you up to about 9.5:1 which is unlikely to ping on premium gas and you should definitely notice an increase in performance. However, ideally the intake valves from the L28 head should be swapped into the Maxima head (44mm vs 42mm) for better breathing at high rpms. I'm not sure about the cam specs re L26 vs L28 but an L26 cam could only be directly swapped into a '75-'76 L28 head (N42) as they have the oil rail systems. The early style cam towers & oil rail would have to be transferred to an N47 type head to run the early style cam from a 240-260Z. That shouldn't be any big deal but I don't know if there's any advantage with a 260 cam. I looked up in factory manuals the specs on '72 240Z and '77 280Z and the durations and cam timing specs are the same, with the 280Z cam lobes having slightly more lift. So if the 260Z cam is the same as the 240Z, you might be actually decreasing performance. DAW Quote Link to comment Share on other sites More sharing options...
Guest LIghtningZ Posted June 17, 2002 Share Posted June 17, 2002 Your the man DAW!!! Quote Link to comment Share on other sites More sharing options...
Guest bang847 Posted June 17, 2002 Share Posted June 17, 2002 DAW is the man... Hey whats your name? so I can thank you on a more personal level.. Also I am intrested in your history with the L block... where did you get all the know-how? Again thanks to DAW... Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted June 17, 2002 Share Posted June 17, 2002 Hey DAW do you have the spec's on the turbo cams too? I need them, 81 auto to be exact. The easiest way to get your car running is to either swap the head, or swap the valve. Either way would work. Just be sure to get the timing chain secured properly before taking the timing gear off, or you will be uttering more obsenities. Quote Link to comment Share on other sites More sharing options...
Guest LIghtningZ Posted June 17, 2002 Share Posted June 17, 2002 Hey DAW you said i should swap the intake valves will those just drop in or do i have get them machind open for the bigger valves? hopefully it will just be a matter of getting out my valve spring compressor. what sagely advise do you have for me wise one in the ways of the L6!!! P.S. hey Tim240Z im going to play dumb and ask if you have specs for you Y-shaped chain retainer?? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted June 17, 2002 Share Posted June 17, 2002 LZ, no specs off the top of my head, but if you take the valve cover off and look at the gap between the 2 sides of the chain, it will be very obvious what size it needs to be. I just cut a piece of 1x3 with a jigsaw to the right size/shape. Tim Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted June 17, 2002 Share Posted June 17, 2002 http://geocities.com/zgarage2001/head.html Read this, it has the mod info you need. BTW, I thought the wood was supposed to be 1x2. As a tip, after you have completed the swap, and the timing gear is back on and the bolt is tight, if the wood is difficult to remove, put the car in 5th gear and bump it forward a little. This should loosen everything up so the wood comes right out. Good luck with it. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 17, 2002 Share Posted June 17, 2002 I gave up on wedgeing the timing chain to hold it in place while removing the head because this method would only work about half the time with me. I have done about 30 heads on L20 B engines.. I take out the radiator, loosen up the and remove the oil pan to timing cover bolts and remove the timing chain cover and basically tear down about everything.I then can align the timing chain to the proper bright links locations to the crank and timing chain sprocket and properly adjust the chain for slack. A lot of work but when I point the timing light on the marker, I know it is not off by little if any.To get that back on the road, I would lap in a used valve with lapping compound, suction cup and drill.If the valve seat or valve has low spots that cannot be lapped out, this problem will become evident after a few minutes of vigorous lapping Take off all the rocker arms and flip the head over with all the valves closed and fill the upside down chambers with solvent and see which valves leak.Remove and inspect the leaky valves.Since you live in Sacremento, I can send you a used valve(s) from a 280 Z head if you pay shipping. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted June 17, 2002 Share Posted June 17, 2002 You must not be holding your mouth just right.... Actually, for everyone's info, there is a tensioner with a limiter on it, and you can order it from Nissan. Part Number is 13070-N7120. It costs 84 beans, which is cheap compared to the frustration of having to mess with taking the front cover off. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted June 17, 2002 Share Posted June 17, 2002 Aw,,,that's just making life too easy!!!! cheatin' I say!! Thanks for the info! Tim Quote Link to comment Share on other sites More sharing options...
DAW Posted June 17, 2002 Share Posted June 17, 2002 Some repair manuals actually give the dimensions of the piece of wood to cut to block the timing chain from slacking when you remove the valve timing sprocket. I don't have them in front of me but it's basically a 2" wide, 3/4" thick x 6" long block of wood from which you cut away a triangular section. The resultant piece is 2" wide at the top and extending down about 2.5" at which point it tapers down to about 1" wide at the tip. Very important: drill a hole in the upper portion of the block and thread some electrical wire or a wire coat hangar or a big zip-tie through it and tie it, leaving a tail of about 8"; you're going to have to remove the block once you've reinstalled the timing sprocket and there won't be room in there for hands. Let's see, there were a lot of questions...if you put L28 intake valves into the N47 L24 Maxima head it will require new L28 intake valve seats installed. The site referenced above re Nissan head mods is great, lots of info there. The N47 Maxima head is sort of a hybrid of the L28 N47 head and the L28 P79 head (except it has smaller, L24 intake valves). The P79 mod/shave/shim/valve exchange makes sense except I think it is far less expensive to have L28 seats installed in the Maxima head, L28 int. valves, and use an L28 cam (from an N47 or P79 head). As to the turbo cam specs, I don't have them but there was very recently a parallel thread which discussed them re one year having 10 degrees retarded cam timing but otherwise the same lift & duration. An OEM turbo cam generally won't produce as much power in a na engine as the OEM na cam will; at least that's what I gather, and putting a high perf. cam designed for a na engine into a turbo engine may make less power than the OEM turbo cam. DAW Quote Link to comment Share on other sites More sharing options...
Guest LIghtningZ Posted June 18, 2002 Share Posted June 18, 2002 Thanks DAW i owe you big time i've already found a P79 head (It pays to have a kid brother that works in a wrecking yard!!) so i guess i should just be able to swap over my cam and towers and also intake valves to get this combo to work?? I really wont make my move until i get your blessing... I really cant afford to screw up!!! Quote Link to comment Share on other sites More sharing options...
Guest LIghtningZ Posted June 18, 2002 Share Posted June 18, 2002 Okay, okay so from what ive been told the timing chain can be a pain due the chain tensioner and the timing itself so how exactly do i keep the chain from falling loose and remove the head by the way DAW what casting #'s and parts should i remove/look for??? looked at my head for a casting # and found N42? pretty sure this head isn't O.G. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted June 18, 2002 Share Posted June 18, 2002 LZ, Cut a piece of wood into a "Y" shape and tie a piece of string to the top. Then, pull up on the chain to get as much slack out of it as possible and then jam the Y-wood in between the 2 sides of the chain, ie forcing the tensioner back into its housing. Jam it in there good, because if it slips out, off comes the oil pan and front cover....or about 3 hours with a couple of long screwdrivers to get the tensioner and spring back in....I've done that twice....no fun. Tim BTW, MSA and Victoria British both sell a plastic pice to wedge in there if you want something purdy. Quote Link to comment Share on other sites More sharing options...
DAW Posted June 18, 2002 Share Posted June 18, 2002 Do not put a P79 head on a dished-piston L28 block unless you're going to supercharge or forced induction. For a na engine you'd be going from bad to much worse because the P79 would drop the c.r. below 8:1 vs the N42 head you removed. The P79 would be good for you only if you have the .080" surface cut done and all the associated alterations described in the P79 article/site. A P79 head will be from a non-turbo '80-'83 280ZX and these use a flat-top piston because they moved the volume (10.9cc) from the earlier style dish-top and put it up into the roof of the chamber (most of it anyway, they were able to bump compression a bit due to the better chamber design). DAW Quote Link to comment Share on other sites More sharing options...
denny411 Posted June 19, 2002 Share Posted June 19, 2002 If you need an n42 I have 1 left Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted June 19, 2002 Share Posted June 19, 2002 Mill the P79 about 75 to 80 thousandths, shim the cam towers. Good compression will be the result. Quote Link to comment Share on other sites More sharing options...
katman Posted June 19, 2002 Share Posted June 19, 2002 Originally posted by Lockjaw:Mill the P79 about 75 to 80 thousandths, shim the cam towers. Good compression will be the result. As well as bad cam geometry. Don't forget to change the rocker guides (lash pads) when you shim towers. Quote Link to comment Share on other sites More sharing options...
DAW Posted June 19, 2002 Share Posted June 19, 2002 No. That's the point of swapping the all of the valves from an earlier (N42 or N47 280Z) head as part of this conversion. The valve geometry is put back into the ball park at least because the earlier valves are approximately the same length longer as the amount the cam is raised by the shimming and surfacing. Look back at the article for the details. I haven't personally tried it but on paper it makes sense and the author says it worked well in his car. DAW Quote Link to comment Share on other sites More sharing options...
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