Captain Obvious

F54/P79 Swap Project

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    A while ago, I picked up an 83 ZX non-turbo and (with my recent calamity with my Z motor*), I've been working on pulling the motor with the intention of moving over into my 1977 Z. It's a stock F54/P79 combo and I'm not going to do a big time rebuild at this time, but I do want to do some clean-up and maybe some easy low hanging fruit improvements. I'm no engine expert and I'm going to have some questions for the collective along the way.

    I think there was a slight head gasket issue with the engine, so one of the things I wanted to do was replace that. Here's where I am right now. Head is off and block is stripped ready to be pulled from the donor car:
    P1150102.JPG

    So my first question is.... After I pull the block and have it on the engine stand, I have aspirations of removing the freeze plugs and sticking a power washer into all the block orifices and blasting out as much crud as I can. Anyone want to talk me into or out of that plan? Is the installation of new freeze plugs a straight forward and reliable process? I've never messed with them in the past.

    *https://www.classiczcars.com/forums/topic/62173-complete-misfire-on-three-cylinders/#comments

     

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    if you are going thru the effort, I would take it to a shop and have it hot tanked. Unscrew the block drain and check out the crud. But I guess that ups the ante a lot as far as having to tear it down. OK strike that comment about the hot tank idea.

    Edited by Dave WM

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    Yeah, I have no reason to believe there is anything wrong with the bottom end and I'm reluctant to pull the pistons and crank. I was going to pull and replace the oil pan gasket because the old one is seeping a little, but other than that, I was hoping to not mess with the bottom end.

    Oil pressure was great and no unusual noises from the lower end. I was hoping to let it be.

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    I'm doing the exact same transplant at the moment. The pressure wash wont clear out the inside of the engine, either have it hot tanked or baked. I just had mine baked then shot peened. Did a 40 thou over bore and some new flat top pistons. Check inside the block to make sure there are no stray freeze plugs that the last rebuilder pushed in and didn't retrieve, I found one in mine. I went with brass plugs when I replaced them.

    Roo

    1973 240Z

    1970 240Z

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    You aught to be able to turn the freeze plugs out and with the head off blow the majority of the block clean. I know Rossiz did something similar and said he was surprised at the amount of gunk that came out.

    The freeze plugs can be difficult to get out. I have struggled to get them turned sometimes but a fabricator at your level will grind out some interesting little widget to make it easy peasy!

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    If you've got it that far stripped, I'd always clean it and put new bearings in, give it a hone and new rings.
    It's fun!

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    When you do the freeze plugs tap it in on one side only, you want it to pivot on the center, once you can get a pair of Visegrips on the lip pull it out.  Set your pressure washer nozzle to the needle setting, all kinds of crap will come out and get everywhere so if you are going to keep the pistons, rods and crank in make sure they are sealed off.  But it is just as easy to pull all that stuff and then you can clean them, check the measurements and inspect the bearing wear.

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    4 hours ago, jonbill said:

    If you've got it that far stripped, I'd always clean it and put new bearings in, give it a hone and new rings.
    It's fun!

    Absolutely......and maybe a .040 overbore with new flat tops. Don’t stop there, go ahead and shave the P79 .080 and jack up the cam towers and valve springs using the early longer 280 swirl valves. Don’t forget to ship the old cam to Isky to make her a .490 lift stage III.    It’s fun!

     

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    Thanks for the input everyone. All that sounds like fun, but in the cause of expediency, I'm really hoping to leave the crank and pistons in for now.

    Diseazd, Question for you while you're here... I remember talking to you in Atlanta (over drinks and pool) about that .080 cut off the P79 head. So how far can I cut the head before I need to shim the cam towers? Do you know how much change can the chain tensioner account for before needing to mitigate with shims?

     

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    Core plugs.

    My thought on the coolant passage flushing is that you're just blowing out stuff that settled in a dead zone.  No flow.

    You should get the "How to Rebuild.." book.  Lots of good stuff in it.  Also, ponder what, exactly, happens when a head is milled.  Bottom alone, or top and bottom.  What about cam tower alignment if the head is warped? Aren't they out of alignment also?

    https://www.thezstore.com/page/TZS/PROD/10-1151

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    9 hours ago, Captain Obvious said:

    Thanks for the input everyone. All that sounds like fun, but in the cause of expediency, I'm really hoping to leave the crank and pistons in for now.

    Diseazd, Question for you while you're here... I remember talking to you in Atlanta (over drinks and pool) about that .080 cut off the P79 head. So how far can I cut the head before I need to shim the cam towers? Do you know how much change can the chain tensioner account for before needing to mitigate with shims?

     

    I would suggest as little as possible to clean the head up. I’ve heard .030 inches is about all you can cut without affecting the timing. Maybe someone else knows the exact number. .010 to .015 is where I would try to stop.

    Guy

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    I think that number is in the "Rebuild" book.  Mine is boxed up right now otherwise I'd find the page.

    The MSA page says 7 thousandths, but they don't give a reference for the number.

    image.png

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    I would suggest as little as possible to clean the head up. I’ve heard .030 inches is about all you can cut without affecting the timing. Maybe someone else knows the exact number. .010 to .015 is where I would try to stop.
    Guy
    Any amount you change the cam height affects the timing. Slimming the head a small amount I think advances the timing a small amount. This can be adjusted for with the 3 dowel jokes on the sprocket, or an adjustable sprocket.
    The limit of this is the amount of chain Slack the tensioner can take up which may be somewhere around. 75mm for the standard tensioner.
    Cam tower shims aren't the only remedy for it though - there are alternate tensioners you can get (from Kameari for example) which can handle more Slack in the chain.

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    46 minutes ago, Zed Head said:

    I think that number is in the "Rebuild" book.  Mine is boxed up right now otherwise I'd find the page.

    The MSA page says 7 thousandths, but they don't give a reference for the number.

    image.png

    Page 91...

    image.png

     

    Edited by siteunseen

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    15 hours ago, Captain Obvious said:

    Thanks for the input everyone. All that sounds like fun, but in the cause of expediency, I'm really hoping to leave the crank and pistons in for now.

    Diseazd, Question for you while you're here... I remember talking to you in Atlanta (over drinks and pool) about that .080 cut off the P79 head. So how far can I cut the head before I need to shim the cam towers? Do you know how much change can the chain tensioner account for before needing to mitigate with shims?

     

    I'm sure you've read this before but you know me...flog that dead horse! 

    http://www.datsunzgarage.us/p79/

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    The FSM says that each different alignment hole in the cam sprocket adjusts the cam timing forward by four degrees. To make sure I knew what was going on with that I checked it out using the cam gear.

    Here's a quick sketch I whipped up using the cam gear off my P79 head. I traced the holes and sprocket teeth in the three different positions, and guess what... They are two (cam) degrees apart. That's perfect because two cam degrees is four crank degrees. Note that the direction is backwards because I could get a better registration with the cam gear flipped over, but the delta between the different positions is what's important. Here's what I whipped up:
    P1150111.JPG

    P1150112.JPG

    It would appear from the calculations, that you could take .080 off the head and advance cam the gear to it's next setting and pretty much be exactly back to where you started.

    Probably showing my inexperience, but assuming the tensioner can account for the difference, why can't you just do that instead of different valves and a whole bunch of shims under the springs and cam towers? Seems like the only thing you would need to do is move the cam gear.

    Edited by Captain Obvious
    Included a note about flipping cam gear over for sketch

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    3 hours ago, jonbill said:

     Slimming the head a small amount I think advances the timing a small amount.

    I don't think slimming the head results in advanced timing. I believe removing material from the head results in retarded valve timing. I think about it this way... The distance between the crank and cam got smaller, but the length of chain between the two did not. So the cam will trail the crank by that additional length.

    Did you mean slimming or shimming?   :ph34r:

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    2 hours ago, siteunseen said:

    I'm sure you've read this before but you know me...flog that dead horse! 

    http://www.datsunzgarage.us/p79/

    Great illustration Site.....and I spent hours in Roanoke with the Z Doctor. He built all of my P79 heads....he’s the one that originally came up with the set up. It tricks a P79/P90 into stock chain configuration with a 10:1 c/r. As far as advancing the cam sprocket 4 degrees to make up for an .080 cut without shims Capt., I think if that worked, it would have been done that way. I think Jeff G figured out some offset bushing for the cam sprocket that eliminated shims for his race car. I miss Doc!

    63202280-AF0F-4417-8674-6299D5117B31.jpeg

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    I'm having a machine shop do what is put forth by the Z doctor for my P79 head. I will be leaving the F54 stock except for new seals/water pump and oil pump etc. And of course headers and more exhaust.

    For around $400-500 it seems like a good easy way to get a bit more out of an otherwise stock L28 and remain as reliable(leaving the cam stock for original EFI computer). At least for me, as someone who doesn't have much experience building engines.

    Sent from my N9130 using Tapatalk

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    I would think .080 head thickness reduction would be difficult at best to maintain proper valves timing without shims. First you would be  slotting your chain guides to slide them over enough to make up for the serious chain slack. I wouldn’t trust doing it without shims unless I could degree the cam. The cool part of that p79 trick with the taller valves is I believe you don’t have to mess with lash pad adjustments ( Guy can verify ) if you keep the stock cam or a slightly modified cam. 

    I currently run my E88 with .050 cut off with no shims. I did degree my Isky cam . I am actually running 8 degrees advance on the cam .

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    Right Madkaw......I used Stage III Isky Cams in mine. .160 to .180 lash pads for that set up.

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    I don't think slimming the head results in advanced timing. I believe removing material from the head results in retarded valve timing. I think about it this way... The distance between the crank and cam got smaller, but the length of chain between the two did not. So the cam will trail the crank by that additional length.
    Did you mean slimming or shimming?  
    I meant skimming yeah, I wasn't 100% sure whether it retarded or advanced. Having thought again I agree with you, it'll retard it.

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    Thanks guys. I did some searching around online and the issue with the .080 cut seems to be more about the chain tension, rather than the valve timing. The valve timing can be adjusted using an adjustable pulley or the stock holes as I described, but with that much of a cam drop, the tensioner can't deal with that much slack.

    There are other options to take up the slack, but I haven't gotten to the bottom of the details yet.

    But the bottom line seems to be: Yes... You can relatively easily mitigate the cam timing, but you can't easily mitigate the chain slack.

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    I love your attention to detail Capt.  Did you go to engineering school or just have the knack? That coming from me, who never even reads the instructions! 😬

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    7 hours ago, Diseazd said:

    I love your attention to detail Capt.  Did you go to engineering school or just have the knack? That coming from me, who never even reads the instructions! 😬

    He's a "sparkie" :ph34r:

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