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Captain Obvious

Complete Misfire on Three Cylinders

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So here's a question for today. If you look closely at this water jacket hole... Up by the timing chain and cylinder one, on the left side of the engine. It's threaded.

The paper towel wad is stuffed into the head bolt hole, and the other hole just goes down into the water jacket. There's a corresponding hole in the gasket and the head. but question is... Why is it threaded?  :
P1150442.JPG

I tried to measure the thread size and didn't come up with anything standard. It's a very loose fit on M10-1.5, but it's not big enough to be M12. So it's either a badly corroded out M10, or it's something unusual.

Any ideas?

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Sometimes people will block holes like that to change or restrict water flow. Could have been flush plugged or sometimes they will flush plug them and then drill a hole for lower flow.

Just a guess...

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rebuilder thought is was a head bolt hole, and chased it.

I agree, we’ve already established the PO wasn’t all that good this would be the most plausible reason.


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3 hours ago, Captain Obvious said:

So here's a question for today. If you look closely at this water jacket hole... Up by the timing chain and cylinder one, on the left side of the engine. It's threaded.

The paper towel wad is stuffed into the head bolt hole, and the other hole just goes down into the water jacket. There's a corresponding hole in the gasket and the head. but question is... Why is it threaded?  :

It's a performance modification, adding an extra head bolt.  The PO is actually an expert in Z engines.

  • Haha 2

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Actually I'm pretty sure those threads are stock from the factory. First off, they are straight and not at some screwed up angle, so I doubt that my PO did it. And second, that same hole is threaded on my F54 block, and I don't think that engine has ever been apart until I did it.

And interestingly enough, the water jacket hole at the rear of both blocks on the same (left) side is threaded as well.

10 hours ago, Patcon said:

Sometimes people will block holes like that to change or restrict water flow.

That's exactly what I was thinking, and actually, why I asked. I've been looking into head gaskets and the 83 gasket uses a smaller hole there than the previous versions. I was thinking I could run a restrictor plug into that threaded hole.

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5 minutes ago, Captain Obvious said:

Actually I'm pretty sure those threads are stock from the factory. First off, they are straight and not at some screwed up angle, so I doubt that my PO did it. And second, that same hole is threaded on my F54 block, and I don't think that engine has ever been apart until I did it.

And interestingly enough, the water jacket hole at the rear of both blocks on the same (left) side is threaded as well.

That's exactly what I was thinking, and actually, why I asked. I've been looking into head gaskets and the 83 gasket uses a smaller hole there than the previous versions. I was thinking I could run a restrictor plug into that threaded hole.

I know this is used sometimes in water jackets and in oil lines sometimes but I don't know enough to speak to when to do it and why.

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30 minutes ago, Captain Obvious said:

Actually I'm pretty sure those threads are stock from the factory. First off, they are straight and not at some screwed up angle, so I doubt that my PO did it. And second, that same hole is threaded on my F54 block, and I don't think that engine has ever been apart until I did it.

Might be for assembly in the factory or servicing.  A lifting bracket might install there.

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So I'm still waiting for alignment dowels and head gasket to get here.

In the meantime, I spent a little time cleaning up the header surfaces where they mate with the head. My PO put on a 6 to 2 header of unknown origin. No idea where he got it. So I'm looking it over and see huge welding goobers inside the tubes and pieces of MIG wire stuck in there from where the guy who welded it got the wire stuck and burned off pieces of it.

Here's the worst. About an inch of wire stuck in there:
P1150455.JPG

I pried it up with a screwdriver:
P1150456.JPG

And pulled it out with a pair of pliers:
P1150458.JPG

And there are other testaments to the workmanship, like this huge goober. It was on the upper side, so I used a little mirror to get a good pic. I stuffed a paper towel down the pipe a little and tried to pry it loose. No joy. I'm leaving it in there:
P1150462.JPG

So today's question(s) is... What welder has so little pride in his work that he'll leave junk like that in there? Is it just me? Are my expectations too high?

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On ‎7‎/‎27‎/‎2019 at 9:30 PM, 240260280 said:

I've seen numbers on the block and on pistons. I think it was how they selected best fits in plant.

I found the numbers on the block. Here's where the "34" pistons live. I got five of these:
P1150466.JPG

 And I got one of these. This is where the "45" piston lives:
P1150467.JPG

I haven't measured the bores to try to figure out a correlation between the actual numbers and the measurements. It's another of those, "because then I would know" issues.  LOL

The "STD" piston lives in one of the number three marked cylinders. I have no doubt it's aftermarket installed by my PO, but I don't know why. No idea what happened that necessitated replacement of one piston. But I do know that the block wasn't bored.

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Do the valves that correspond with the piston you think was replaced look different from the other valves? Maybe a valvetrain issue caused a collision...which caused the head to get worked on but not really rebuilt?

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3 hours ago, Captain Obvious said:

I found the numbers on the block. Here's where the "34" pistons live. I got five of these:

 And I got one of these. This is where the "45" piston lives:

Good.... I was starting to doubt my memory.

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5 hours ago, jonathanrussell said:

Do the valves that correspond with the piston you think was replaced look different from the other valves?

Nope. They all looked like arse. The only one that stood out from the rest was an exhaust valve from a different cylinder. That one looked like bent arse.

Of course, there's no telling if my PO swapped the pistons around. Based on the fact that the "45" piston is in the bore marked "4", I don't think so, but at this point, who knows!!   LOL

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10 minutes ago, Captain Obvious said:

I have all the valves set a little loose 

I may be way off here but will this create a lower compression reading? 

Edited by rcb280z

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I think you're right. I think it will have some tiny impact on the compression and performance numbers as well. But I'm only off by .003 on the intakes and .001 on the exhausts. I'm pretty sure that I'm leaving a tiny bit of performance on the table, but for the first batch of miles, I'm willing to take that tradeoff for the piece of mind.

Of course, I'm not an expert on the topic, but that's what I'm thinking!

Maybe I just need a padded cell:

Iron_Maiden_-_Piece_Of_Mind.jpg

Edited by Captain Obvious
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Thank you. Appreciate the well wishes! It's going to take some time for me to regain confidence in the motor.

Now I have to finish pulling that F54 block.......

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Great job CO, glad she’s back on the road. I know it was a PITA but it’s a labor of love.


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Yeah, definitely a labor of love to put that amount of work into the lowly stock N47. But as you suggested, it was personal. Me against my PO. LOL!

Have to give it some time to wait for potential issues to surface, but I believe I won.   :victorious:

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So one of the closing items to bring up is that I did take some quick and dirty measurements on the valve protrusion while fully open, and according to the numbers, it's definitely an interference design.

The valves stick down about .200 beyond the bottom of the head when they are fully open. I didn't spend a lot of time trying to max out the lift to the thousandth, so it's likely that it's a little more than this. I just eyeballed it as I turned the cam and set the cam where the lift was the greatest. Could be a little more than .200, but it's certainly no less:
P1150476.JPG

And my new (Nissan) head gasket is about .055 thick new (before any compression due to installation torque):
P1150511.JPG

So even if there is no crush on the head gasket thickness, the valves will stick down .145 beyond the bottom of the gasket. And considering the .115 dish depth on the pistons, it's an interference design.

I've got some other closing items to document as I get the time. Things like my flying trapeze head lifting rig that worked out fantastic...

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