Complete Misfire on Three Cylinders

[siteunseen]

4 hours ago, 240260280 said:

 

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. 

[Zed Head]

4 hours ago, Dave WM said:

how do folks store complete heads? 

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

[Captain Obvious]

Head is off, and by some incredible stroke of luck.... No contact between pistons and valves!! 

So I don't know if the engine isn't interference (with the dished pistons), or if I just got lucky and the rear half of the camshaft just happened to stop in a position where none of the valves were open enough to cause a problem, but whatever the reason, I'm thankful for small victories.

Here's a pic of the valves from one of the rear cylinders. They all look like this. No clean spots and no hint of collision:

My beautiful camshaft. The rear portion spun really easily in the two rear journals. I just slipped it out the rear of the head:

The front portion of the camshaft spins relatively easily, but not as easy as the rear half. There is also one part of the front half rotation where it gets a little tighter. Not so tight that I can't turn it by hand, but to my calibrated hands, it's a little tighter in one spot then the rest. I wouldn't be surprised if there's some sort of alignment issue with the cam journals that was stressing the shaft for the past five years.

Here's the break area. I don't have any of the typical beach marks of a gradual failure. It looks like it was a one time catastrophic snap:

I took the front half out to get a better pic. Here's another close-up:

Next chance I get, I'm going to put the front portion of the cam back in and see if I can loosen up the front towers and get them aligned better. I suspect that if I loosen them up and tighten them down again evenly I might be able to get rid of the rotational tight spot. Just to see if I can.

[Dave WM]

JB weld?

[Av8ferg]

CO, looks like a classic brittle fracture. Mechanism of failure on a brittle fracture is typically a flaw or crack somewhere in the material. Looking at the photo I think I see where the stress riser was located and likely the source of the fracture. I see a small
nick in the edge of the cam
and then corresponding V shaped initial failure area. Do you think the CAM has been damaged at some point causing the initial stress riser.
Great news your valves are good. So now what, have your decided what level of rebuild you’re going to pursue?


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[jwtaylor]

I noticed that also.  It looks like the fracture runs all the way though to the oil passage to me.

[240260280]

Looks fine to me.  I have a 3 cylinder Honda Insight so I am partial to unbalanced, low power engines.

[Captain Obvious]

SMOKING GUN!!! 

So I was messing with trying to align the cam towers by loosening them a little bit and trying to get the cam to spin smooth, but #3 kept giving me trouble. Just didn't feel right. So I decided to pull it off completely and see what I could see. And.......

Here's what my Previous Owner put in there on one side to "align" the tower to the head:

And it gets worse... Notice that since that threaded "thing" is so crappy, it caused the other side alignment ring to be so far off that he had to use the cam tower bolts to jack the tower down (because it was out of alignment). it caught the alignment ring on the other side and pinched it in the gap and smashed it. Here's what used to be the precision alignment ring:

The ring got smashed and actually extruded a tongue of material out into the seam between the tower and the head. Pulling that damaged ring out, you can see the dent it left in the aluminum head:

At first, I thought that threaded thing was a Helicoil or something, but it was just a short stub of bolt that he drilled out. I guess he lost or mangled the original alignment ring and made that instead. Here's the two pieces that were "aligning" my #3 tower:

Previous Owner strikes again!!!

It's beyond me how you can't tell that something doesn't feel right as you need a wrench to crank that tower down into place and crushing that alignment ring in the process. I know the hobby is filled with people of varying skill levels, but this surprises even me.

[Captain Obvious]

So, as a follow up to the above, I pulled all the cam towers off and found all sorts of other issues as well. Less severe than the above, but I also found:

• Screwdriver pry marks (and corresponding burrs kicked up) at the seam between the towers and the head because he had a hard time getting the towers off.
• Small flakes of aluminum smashed between the towers and the head. Presumably little pieces of material scraped off with the screwdriver used above.
• Small chunks of carbon junk smashed between the towers and the head.
• Burrs kicked up on the alignment rings from using pliers to pull them out of place. And one of them was ovalized a little bit from too much force with the pliers.

So just as a quick test to see if it was possible... I carefully dressed all the mating surfaces to remove the burrs on the head, the towers, and the (salvageable) alignment rings and put everything back together. I got it to the point where the towers properly sit flush against the head and I can align them so that the two parts of the cam spin easily with two fingers. I haven't tried it with a complete cam, but it looks like this head may actually be salvageable.

So... Long story short. my PO's workmanship strikes again. Not enough cleanliness, attention to detail, and understanding of what's important. Please step away from the motor, sir. Just walk away.

Anybody got a Nissan "A" grind cam laying around they would part with? I think that would be my fastest route to getting back on the road for the rest of this summer.

[Dave WM]

 

[Av8ferg]

Holy Smokes...I wonder how many miles it made it with that bastardized repair. So where did all these metal fragments go? I’m assuming they were flushed in the oil system. Do you need a new head?



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[Zed Head]

3 hours ago, Captain Obvious said:

Anybody got a Nissan "A" grind cam laying around they would part with? I think that would be my fastest route to getting back on the road for the rest of this summer.

You could also use an F grind internally oiled.  I think that there's a also a K out there, from the ZX's.  The specs are all similar, you could probably use any cam and not notice a big difference.  The atlanticz table is close, but the FSM specs show some small differences.  

http://www.atlanticz.ca/zclub/techtips/cam/index.htm