Salvaging the warped P79 head

[madkaw]

I have turned into the Datsun tutor for a young lad(17”) Alex that has bought a 81zx project. The motor was half apart and the guy he bought it from was not the wrench on this car , just an owner . Anyways , the block and head were together in the car , but no induction or exhaust - that was all laying in the car . Dirty valve train like the valve cover was off for a long time . It’s been sitting for years . Took the head off to inspect and clean . Mating surface was flat . Cam is a CWC core and seems to be a stock replacement . Engine did turn over fine . 
He brought me the head and I broke it down to be cleaned and to do anything else necessary for him to have a runner . I sent it to the machine shop and told them to check it out . Valve tips looked molested already like someone already did a valve job. 
 Got it back from the machine shop and they had taken .007 off the mating surface to clean up pitting and did a valve job . I started reassembly to check wipe patterns and I couldn’t get the cam in . I admit that when I took the head apart I did the quick and easy and removed towers and cam all at the same time , so I probably missed the cam was binding . Got out my straight edge out and found the top surface out of flat . This is where I realized I was dealing with a previously warped head . Shame on me and the machinist for not checking for time . In all fairness , who know if this shop ever saw an old Datsun head . 
 What to do now . The kid had.230$ in this head that the cam won’t turn . Took it back and head top surface skimmed . He said he took .017 off the middle and .002 off the sides? Not sure how he come up with that , but it’s flat and the cam turns perfectly . A quick wipe check showed the wipe pattern that will work , actually pretty well centered . I imagine that was because they dressed the tips of the valves . I also questioned the tipping of the valves and they assured me that they didn’t go too far which would compromise the hardness level. 
So what happens to the combustion chambers ? It’s been shaved , so what’s the CR now ? How far off will they be from each other since the head had been warped ? See my findings . I guess I have some grinding to do 

[madkaw]

Just now, madkaw said:

I have turned into the Datsun tutor for a young lad(17”) Alex that has bought a 81zx project. The motor was half apart and the guy he bought it from was not the wrench on this car , just an owner . Anyways , the block and head were together in the car , but no induction or exhaust - that was all laying in the car . Dirty valve train like the valve cover was off for a long time . It’s been sitting for years . Took the head off to inspect and clean . Mating surface was flat . Cam is a CWC core and seems to be a stock replacement . Engine did turn over fine . 
He brought me the head and I broke it down to be cleaned and to do anything else necessary for him to have a runner . I sent it to the machine shop and told them to check it out . Valve tips looked molested already like someone already did a valve job. 
 Got it back from the machine shop and they had taken .007 off the mating surface to clean up pitting and did a valve job . I started reassembly to check wipe patterns and I couldn’t get the cam in . I admit that when I took the head apart I did the quick and easy and removed towers and cam all at the same time , so I probably missed the cam was binding . Got out my straight edge out and found the top surface out of flat . This is where I realized I was dealing with a previously warped head . Shame on me and the machinist for not checking for time . In all fairness , who know if this shop ever saw an old Datsun head . 
 What to do now . The kid had.230$ in this head that the cam won’t turn . Took it back and head top surface skimmed . He said he took .017 off the middle and .002 off the sides? Not sure how he come up with that , but it’s flat and the cam turns perfectly . A quick wipe check showed the wipe pattern that will work , actually pretty well centered . I imagine that was because they dressed the tips of the valves . I also questioned the tipping of the valves and they assured me that they didn’t go too far which would compromise the hardness level. 
So what happens to the combustion chambers ? It’s been shaved , so what’s the CR now ? How far off will they be from each other since the head had been warped ? See my findings . I guess I have some grinding to do .

 

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[Patcon]

1.6cc

Thats pretty substantial

[Zed Head]

I've wondered what happens to the valve angles.  Their center lines moved with the warpage but aren't corrected by the shaving.  So the tips of the valves will not be parallel with the rocker arm tips.  The arms can twist as they move so it probably works out.  If they skimmed the valve heads that will make them parallel but they'll have a slight side to side movement as they move up and down.  Just one of those odd things to consider. 

So you're going to remove combustion chamber material from the small volume chambers to match them up?  Make them all 54.8 CC?

Edited November 27, 2020 by Zed Head

[madkaw]

1 minute ago, Zed Head said:

I've wondered what happens to the valve angles.  Their center lines moved with the warpage but aren't corrected by the shaving.  So the tips of the valves will not be parallel with the rocker arm tips.  The arms can twist as they move so it probably works out.  If they skimmed the valve heads that will make them parallel but they'll have a slight side to side movement as they move up and down.  Just one of those odd things to consider. 

So you're going to remove combustion chamber material from the small volume chambers to match them up?  Make them all 54.8 CC?

Correct on all statements as far as I can tell . It’s a budget build and I am presenting it that way to the kid . It should work out well enough to get him going . Over time there might be some wear issues , but I bet it will fair decently well. I will open up the small chambers to even it up. He has a complete running spare 83 ZX , but it’s so rusty it’s a hazard . It’s engine runs but has busted exhaust studs and whatever other unknowns for a 300$ car . I told him the next engine build can be better . 

[madkaw]

29 minutes ago, Patcon said:

1.6cc

Thats pretty substantial

It’s enough to fix for sure . I thought sharing numbers would be beneficial. to see the outcome of shaving a warped head