Captain Obvious

Complete Misfire on Three Cylinders

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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:
P1150205.JPG

My beautiful camshaft. The rear portion spun really easily in the two rear journals. I just slipped it out the rear of the head:
P1150194.JPG

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:
P1150195.JPG

I took the front half out to get a better pic. Here's another close-up:
P1150213.JPG

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.

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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? 5cebd8ad898650f8f1600f3402df43b6.jpg


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

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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:
P1150221.JPG

P1150220.JPG

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:
P1150223.JPG

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:
P1150228.JPG

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:
P1150229.JPG

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.

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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.

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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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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

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And...when finding a cam...unless you want to fiddle with lash pads and geometry, you will want to find an uncut original cam with original base circle. This all assumes your cam is the original base circle and your lash pads are original.

Is your cylinder head an N47?

 

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@Captain ObviousI have an A cam that I think was from an N47. I acquired it by itself without a head at some point though. It has oil holes in the lobes. Lobes are clean as are bearing surfaces. 2nd lobe from sprocket measures appx 1.585 which is the same as a low mileage n42 A cam I have on a head that I know has never been rebuilt, nor cam cut. So, if your cam is uncut and you have original lash pads, should slide right in...assuming you are able to sort out the cam tower mounting mess.

If you would like to have this cam, message me with your address and I will ship it to you.

See two photos.

 

 

20190709_141117 (Medium).jpg

20190709_141123 (Medium).jpg

Edited by jonathanrussell
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7 hours ago, jonathanrussell said:

I have an A cam that I think was from an N47. 2nd lobe from sprocket measures appx 1.585

If you would like to have this cam, message me with your address and I will ship it to you.

Wowsers!! Yes, that's exactly what I have now. Both pieces. Haha!!

I measured my lobes at 1.585, so the same as what you have there. I'd love to have it! Thank you so much for the offer!!

PM on it's way!    :beer:

Edited by Captain Obvious
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I'm not sure if my PO had my head planed as part of the "work" he did to the engine. I took a quick look through the FSM and I didn't find a spec for the overall thickness of the head when new. Is that number known?

I measured my head thickness at 4.255 in (108 mm)*.

Anyone know if that's factory original thickness, or if it's had material removed?

* I didn't clean the head well before that measurement, so I could be off a couple thousandths.

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I have a new in box, never been built E88 head...so it is perfectly clean. When I measure with my digital caliper, it reads 4.247. So, if you are getting a bit of a higher reading...due to cleanliness....I would say you have an uncut head.

On page 55 of the Honsowetz book, he says 4.218 which is incorrect. I hand wrote in the book 4.248...which I probably found researching online. So, I would say my measurement is close. I may have been pressing a bit hard for the measurement. On further research, apparently I have the 1st edition of the How to Modify book. I see something that says the 2nd edition shows 4.248.

FYI, I measured my "new" head again and 4.248 seems more correct- pressing too hard to get 4.247.

Edited by jonathanrussell
added Honsowetz info

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So with the incredibly generous help from @jonathanrussell, I've got a replacement cam on the way. Since they are both factory grinds, I'm hoping his cam is a drop-in.... errr.... slide-in replacement for what I have now. So with his help, I'm not out of the woods, but I should be a lot closer to the tree-line than I was before.

This people here on this forum are fantastic!      :love:

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11 hours ago, jonathanrussell said:

I have a new in box, never been built E88 head...so it is perfectly clean. When I measure with my digital caliper, it reads 4.247. So, if you are getting a bit of a higher reading...due to cleanliness....I would say you have an uncut head.

I will get a better measurement on the head thickness once I get things cleaned up. But even though I took just a quick check, I don't think I've got eight thousandths of grime on my head. There might be a little error in my 4.255 measurement, but just a couple thousandths. Plus or minus two thousandths maybe? Probably not eight.

So either they made the N47 head thicker than the E88, or I'm thinking your E88 has been cut.

Anyway, when I get things cleaned up a little more, I'll take a more reliable reading.

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Someone correct me but...my recollection is that all L6 heads, well certainly in my mind the ones used with S30 cars have the same thickness measurement....uncut.

Also, I have found it pretty difficult to get to this number without a perfectly clean head. 70 thou doesn't sound that unrealistic on a less than clean head.

Edited by jonathanrussell

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Everything I've seen suggests 108 mm as the number.  Metric, of course.  From a manufacturing perspective I don't think t's a high accuracy, precise dimension.  Valve lash adjustment can take up quite a bit of error/range.  Might be that a half mm either way was acceptable during manufacturing.,

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Well I don't have an explanation for why your E88 is different than my N47, but I do stand by my numbers.

I cleaned off the measuring surfaces and even broke out the big guns. More accurate than the springy calipers for things like this. I don't know the last time this ol' girl saw the light of day, but she's still got it where it counts:
P1150232.JPG

Installed the correct anvil, checked her against the measurement standard rod, and then rechecked the head. I get the same thing I got before. About 4.254 inches or about 108 mm.
P1150235.JPG

So I don't know if they changed the head thickness over the years, or if yours has been cut.

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23 minutes ago, Zed Head said:

From a manufacturing perspective I don't think t's a high accuracy, precise dimension. 

Even though functionally it's not critical, It would be highly un-Japanese to not control that dimension from the factory. These things are running down the assembly line and IMHO it would be extremely unlikely that they were not all peas in a pod to within a thousandth or so.

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I didn't say it was uncontrolled.  I said the spec. was set wide.  It' not economical to set a tight tolerance where it's not necessary.

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So I started stripping the valves out of the head. Next chance I get, I'll post up some pics of my home-brewed valve tool, but in the meantime.....

So I'm taking the valves out, and here's the springs from a couple of the valves. I never even knew the springs had a variable pitch and a "proper direction" to them, and apparently neither did my PO. The retainer caps are at the top for both of these, but the pitch direction is different between the two:
P1150231.JPG

I'm not sure how much difference it makes in the grand scheme of things, but just another detail that was missed.

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What's the backstory on the car?  I wonder how deep the PO got in to the engine.

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