Captain Obvious

Complete Misfire on Three Cylinders

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Drive 5 hours and bring your bug repellant


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Metal fatigue is a whole different world than metal strength.  If the cam towers were off a little bit that small bending motion could fatigue the shaft over a few billion revs.

Turning the back half by hand/wrench might show if a valve is bent.  Might help with planning the repair, if you want to do it all in a short time.

On the other hand, you could just unplug the back three injectors and drive it that way while you pick up parts.  

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15 hours ago, Captain Obvious said:

Sorry guys. I was trying to be cute and I guess the issue doesn't come across so obviously in the video. That's what I get for holding my antique crappy  camera in one hand and reaching in with my other hand to crank the engine.

Seriously? It was totally obvious (Captain) that the back half of the cam wasn't turning! Three seconds in I was shouting "WHAT??" I have never seen that...

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18 hours ago, Captain Obvious said:

That's what I get for holding my antique crappy  camera in one hand and reaching in with my other hand to crank the engine.

That's what she said. LOL

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11 hours ago, Dave WM said:

CO, do you have a spare camshaft that you can install? just want to know if there is ANY binding that you can detect.

No, I do not. The one in there is an "A" grind from 1977. I've got an F54/P79 combo here from an 83. That might be the same cam, but if I'm going into that motor, it's for the intention of dropping it in where my existing motor is.

9 hours ago, Av8ferg said:

I’m pulling that N42 head next time I’m away for work. There are 2 N47’s in that yard. Meet me there and we’ll pull them both. $70

LOL. Maybe I will! Bug spray and sunscreen!

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7 hours ago, cgsheen1 said:

Three seconds in I was shouting "WHAT??"

First time I hit the key, I just wanted to see everything rock around like it's supposed to. It was so striking that I had to do it again. I was like "Wait.... What???" I was stunned. Took a couple seconds to sink in, and then I was really bummed.

So what are the prospects for bent valves? Is the L28 an interference engine?

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32 minutes ago, Captain Obvious said:

So what are the prospects for bent valves? Is the L28 an interference engine?

Nissan implies that it is.  Are you planning to pull the head or just go ahead and swap engines?  Did you look for stuck valves?  Seems like if the shaft broke in the wrong spot a valve would have got bumped.  Don't forget, we love destruction, even though it means more work for you, so take more pictures.  Weren't you getting bored anyway...?

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I haven't decided what path forward I'm going to take, but whatever that path, I will be sure to take pics.

I did not look for stuck valves. I haven't done anything else beyond that short video clip other than go out to the driveway and open the hood on the 83 and look inside.

I was NOT getting bored. I'm so backed up with car work at this point that one more thing is absolutely not desired at this point. In fact... I'm cleaning up after dinner last night and the hot water coming out of the tap is way hotter than usual. Dangerously scalding hot. Take a look a the water heater and it's got water dripping from somewhere out the top. Not good... I killed the breaker.

SWMBO isn't going to appreciate cold showers. Especially if I'm out in the driveway working on my car.   :facepalm:  Anyone want to help me wrestle a water heater down into the basement? I'm getting too old for this crap.

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3 hours ago, Captain Obvious said:

I haven't decided what path forward I'm going to take, but whatever that path, I will be sure to take pics.

I did not look for stuck valves. I haven't done anything else beyond that short video clip other than go out to the driveway and open the hood on the 83 and look inside.

I was NOT getting bored. I'm so backed up with car work at this point that one more thing is absolutely not desired at this point.

That does suck then.  The quick and dirty fix, if no valves are bent, might be a cam shaft swap.  I think.  Slide the old parts out and the new parts in.  Might as well loosen or remove the towers then use the tap, rotate, and tighten method to be sure it spins free.  If you brought the rocker arms over with the camshaft, it might not even know it's in a different engine.

I've looked at a bunch of cam specs and they're all about the same.  I think the ZX's were probably changed for better emissions, nothing dramatic.  After the mid-70's, most changes were about emissions.

It would be an interesting challenge, to see if you could make the swap without destroying another camshaft.  The key to finishing it is to avoid the while-I'm-heres.

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I’m gonna guess that there is likely some valve damage considering you drove it for awhile to get home but maybe I’m wrong. I think it’s a head removal anyways s time will tell. I fully expect a detailed report post removal.

I know you got car issues besides the Z, hope you get some free time to hash them all out.


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I think it depends on how fast the broken piece stopped spinning and how extended the open valves are.  Inspection will tell.

The back cam tower could be removed and the broken half lifted out, I think.  That might be fun.

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On 5/15/2019 at 9:54 PM, S30Driver said:

Wow. must have been weakened from those 10,000 rpm shift points of your spirited driving .LOL

Only thing I can think of is a bearing froze after the break or a flaw in the metal that decided that was the time to let go.

 

 

Atlanta in Zup's car? LOL

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Maybe the cam had been dropped at one time and was cracked - and it finally gave out. 

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18 hours ago, siteunseen said:

Atlanta in Zup's car? LOL

Shhhhhhh.....     LOL

Zed Head, I could take the back half of the cam out easy. Maybe I'll do that (if I can sneak some time in the garage when I "should be working on other things")

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Update on my dead engine project...

I made a rocker removal tool. After multiple failures and spending waaaaaay too much time on it, I finally hit on a geometry that worked:
P1150149.JPG

I took the rockers out so I could turn the cam without having to worry about valve positions, etc. I put the engine on #1 TDC before taking stuff apart so I knew where everything was. Way easier to spin the engine over with the plugs out and all the rockers removed.

Then I made a cam chain wedge tool. My tool is about an inch longer than average because that's just how I roll. I wanted to get the tool down as deep as possible to assure it was holding the tensioner shoe back. I also came up with a (yet to be fully tested and therefore potentially stupid) removal plan. That's the screw on the front and the metal removal handle:
P1150166.JPG

Since the tool is longer than most, I had to remove the cam gear bolt to get the tool into place. Being careful not to knock the gear off the end of the cam (not really a difficult task), I took out the bolt, slipped the tool into place, and then put the bolt back in until I was sure the tool was fully seated in place and holding the chain:

Here's some pics of that whole process Bolt out just long enough to get the tool to clear the bolt head:
P1150167.JPG

Then get the bolt back in place for now:
P1150169.JPG

And here's the tool fully installed wedged into place:
P1150170.JPG

And here's how the removal tool is supposed to work:
P1150171.JPG

Hook the screw head with the hole in the metal handle:
P1150172.JPG

And pull the wedge back out:
P1150173.JPG

Worked in test. We'll find out later if it works as well in real practice.

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Sorry to hear that CO! I’ll be the first to admit I didn’t for a moment imagine camshaft failure was the root cause! (And I didn’t watch the vid)

My initial thought after cam shaft discovery was that I hope you didn’t bend valves!!

I know some engines have a non-interference set up with dished pistons etc. Do you have access to a borescope to be able to look through the plug holes and check for marks on rear 3 pistons? Would hate to see you install new cam and have a bent valve to a “paper clip being bent back and forth a thousand times” trick and kill the head.

Good luck!!

Ps. Loving the home made tool!

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Thanks for the compassion. The general consensus is that the design IS an interference engine. So if that's true, depending on where the cam stopped, there may be some significant carnage. I should know for sure very soon.

I don't have a borescope, but I did pull the plugs and have a peek in the holes. I see some stuff in there that doesn't look right. Can't tell if it's evidence of a collision or what, but something in there is weird.

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The machine shop broke the cam on this car when replacing it. I did not see the cam but I suspect removing cam towers with the rockers not removed is one way to do it.

 

 

DSC03390.JPG

DSC03401.JPG

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how do folks store complete heads? I have my spare N42 complete (valves/cam) with the valve cover on and a 2X6 on the bottom tied together with some strapping. I positioned the camshaft to a point where only 2 valves were opened. On those two I removed the rocker/lash pad, tagged and bagged them, left them inside under the valve cover, then return the camshaft to the point where no valves were opened before strapping the 2X6 to the bottom.

Edited by Dave WM

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I pulled and labeled the rockers, lash pads, springs, and valves. Left the cam in. The head now rests on a flat piece of wood awaiting the resurrection.

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3 hours ago, Dave WM said:

how do folks store complete heads? I have my spare N42 complete (valves/cam) with the valve cover on and a 2X6 on the bottom tied together with some strapping. I positioned the camshaft to a point where only 2 valves were opened. On those two I removed the rocker/lash pad, tagged and bagged them, left them inside under the valve cover, then return the camshaft to the point where no valves were opened before strapping the 2X6 to the bottom.

I bought my N42 from a local machine shop that had it after the owner never came back to get it.  They'd had it for 10 years inside a plastic bag with about an inch of styrofoam on the bottom protecting those 2 valves.  I've got 3 or 4 heads stored on top of a piece of foil faced insulation with valve covers on each.

Image result for Foam Board Insulation

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4 hours ago, 240260280 said:

 

DSC03401.JPG

That looks just like my first Z!  A '76 with Western aluminium wheels.

That's the one with the stuck wiper vane in the AFM I got for $1,000 back in 1986.  Cranked and idled fine but wouldn't take any more fuel.  Took it to a mechanic and in 30 minutes he had it running like new.  Charged me $20. 

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4 hours ago, Dave WM said:

how do folks store complete heads? 

I stored mine standing on end.  Takes up less space too.

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