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Leon's Other 260Z


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Thanks Steve. Everything is a learning experience so I'm staying positive. Just as I was getting comfortable with the valvetrain, I get this kick in the rear! I wonder why it failed. I plan to pop the head off and inspect it as soon as I can.

 

The contemplation comes from the fact that this was the first motor I've assembled and I did it pretty hastily! The transmission syncros have seen better days as well. I'm going to have to decide whether this will be a quick (ha!) head job or if I'm going to pull everything and reassess. I know that rabbit hole all too well so I may consider buying a head that's already done. Rebello is nearby so that may be a good option. I also have a nice, complete E31 in storage that I can throw on if I really want to. Decisions, decisions...

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Bought this guy off of z240 (thanks Jim!) just before I made the valve guide discovery. I'd been planning to grab a 123ignition unit for a while now and got lucky with the timing ( :)) of Jim deciding to upgrade to the Bluetooth version.

 

post-3287-0-65860900-1465013683_thumb.jpg

 

Had time to take off the manifolds after work today so progress is being made. I can't have this thing sit again, hoping to have it ready by mid-July.

 

I'm considering doing a few things while it's apart, like refining the fuel system, re-doing my carb linkage, and replacing the radiator (which I dinged when I left a wrench on the crank pulley and started it...).

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Looks like it's time for another round of, "damn, I f***ed up!"

 

Pulled the head after work today:

 

post-3287-0-20012100-1465456476_thumb.jpg

 

Turns out an L24 gasket doesn't work on an L28... :huh:

 

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Another example of why rushing is bad. I'm guessing the gasket is for an L24/L26 as it protrudes into the combustion chamber in certain parts of the bore after being crushed. I didn't see evidence of valves hitting the gasket but I haven't taken a close enough look yet as I just pulled it tonight. Planning to get an OEM L28 headgasket if they're still available.

 

In related news, I spoke with Dave Rebello about the head and am planning to drop it off at the shop on Saturday for repairs and some minor port-work. :)

post-3287-0-76575100-1465456493_thumb.jpg

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Great pictures! We have been using felpro gaskets for years now. I think rock auto has them.

 

Good news is it will fix your combustion flow issues ( no overlap ) bad news is it will reduce your compression ratio due to the fact it is bigger than the opening.

 

i think I have a compressed (used) gasket I am happy to mail to you so you can measure the final compressed piston area

 

Good luck!

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Thanks Jim. I really appreciate the offer, I think you may have even sent me some used gaskets in the past for this same purpose! If I go with OEM, my compressed thickness should stay the same which would mean my piston-to-head and piston-to-valve clearances shouldn't change either. Just have to make sure to get an L28 gasket this time... :) I finished disassembling the head last night and will be dropping it off at Rebello tomorrow.

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The head is in Dave's hands, had a great conversation with him this morning. It's mid-season and man that shop is packed!

 

The #1 valve guide was completely destroyed and the rest of the exhaust guides were on their way, very loose. Dave blamed the SI valves and possibly the valve stem seals so we're doing new Nissan exhaust valves, custom Supertech intakes, and different valve stem seals. Also getting some port-work done while we're at it. Should be fun once I get it back on the road!

 

Edit: we did some calculations and realized that my compression ratio is close to 11:1 and not below 10:1, like I had thought!  :shock: This is based on 44cc combustion chamber, pistons .020" above deck, and .020" piston-to-head clearance. Looking forward to getting this setup dialed in!

Edited by Leon
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Hi Leon, 

 

I just read through from start to finish.  Really nice car you were able to get from your prof.  I was a member of the Virginia Tech FSAE team in 90 and 91. Ah, the good ol' days.  Had to LOL at the advice you got to do whatever it takes to finish the car before you got married.  I did that over a period of year and a half and she bailed on me.   :wacko:   

 

Sorry to see you are having multiple problems with the head, but thanks for sharing.  I came across SI valves as a potential source a while back and now I have more information I wouldn't otherwise have.  

 

Sounds like with Dave fixing things up, you'll be at the end of your issues.  

 

Garrett

Edited by inline6
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So you are saying you used an early HG that had oval shaped holes and you came up short on the top and bottom. It's not easy to see the oval shape unless you are looking for it. You throw that 31 on there and your CR is going to take another jump!

Were you using a 1mm gasket ?

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Hi Leon, 

 

I just read through from start to finish.  Really nice car you were able to get from your prof.  I was a member of the Virginia Tech FSAE team in 90 and 91. Ah, the good ol' days.  Had to LOL at the advice you got to do whatever it takes to finish the car before you got married.  I did that over a period of year and a half and she bailed on me.   :wacko:   

 

Sorry to see you are having multiple problems with the head, but thanks for sharing.  I came across SI valves as a potential source a while back and now I have more information I wouldn't otherwise have.  

 

Sounds like with Dave fixing things up, you'll be at the end of your issues.  

 

Garrett

 

Thanks Garrett, means a lot that you took the time to do so! Good ol' days indeed, wish I could go back in time and do it all over again but better. :)

 

Hey, at least you had more quality time to spend on the Z! I have to be so thankful to my wife for putting up with me, she's the whole reason I got my first 240Z. Without her, I may have been stuck working on some shitty 944.

 

My philosophy on this project, or any project, is to do the best I can but to also not be scared to try things out and "learn by doing". Mistakes and failures are not a negative but a learning experience. Frankly I've been expecting issues to pop up as it's the first motor I've ever built and the first go-around is never perfect (something my mom had to teach me every time I'd throw a tantrum after breaking whatever Lego model I was building). I've learned tremendously from the mistakes I've made so far which ensures that I won't make them again. It's my pleasure to share what I can as I've learned an incredible amount of information from the many experienced and generous people here.

 

Plus, this gives me an excuse to have a head build by Dave... :D

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So you are saying you used an early HG that had oval shaped holes and you came up short on the top and bottom. It's not easy to see the oval shape unless you are looking for it. You throw that 31 on there and your CR is going to take another jump!

Were you using a 1mm gasket ?

 

I used an L24 head gasket on an L28 bottom end! :bonk: I admitted it to Dave and he showed me an easy way to visually tell between the two: the OEM L24 HG oil feed hole is round and L28 HG oil feed hole is oval. Another one of those mistakes that I definitely won't repeat again!

 

Not sure what size the E31 chambers are but will definitely stick to the P90 at this point. Not that I have a knock sensor in the block but surprisingly I didn't hear much in the way of knock in the 1500mi that I put on the engine. Dave indicated that with the right build and tuning, 11:1 comp can be okay to run on pump gas.

 

I was using an OEM head gasket which compresses TO roughly 1mm. I'd like to repeat the test that I screwed up when first assembling the motor: with a dial indicator mounted to the block, measure head height with no gasket installed vs a compressed head gasket. That will give me a more-or-less exact figure of the true compressed gasket thickness. I plan to use an OEM L28 head gasket because this motor isn't that special in the sense that the pistons are stock replacements and pop out of the deck as much as a stock piston would, i.e. as Nissan designed it. I ran it by Dave and he says he uses OEM head gaskets in many of his builds, although he is not fully on board with how much Nissan designed the pistons to pop out of the deck.

 

Looking back at the previous measurements, my piston-to-head clearance is 0.017". I did not see any signs of the pistons hitting the head, although I don't think I ever spun it to 7000RPM. I'll be able to re-measure that once I get a compressed gasket thickness, as I know the pistons are 0.021" proud of the deck.

 

Time for some more learn-by-doing... ;)

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  • 2 months later...

Long-story-short, the head is finally done and I will be picking it up on Saturday. Dave also port-matched the intake and pinned it to the head. He doesn't use gaskets on pinned manifolds so I'm considering what I'd like to do here. I can goop it and slap on the manifolds but that would suck to clean up upon the next removal (seems to happen more often than I'd like). Otherwise, I can port-match the gasket, drill holes for the pins, and use the gasket.

 

Hoping to begin reassembly this weekend!

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If you don't want to try port matching the gasket, you could try what is demonstrated in the Ztherapy video where he talks about making gaskets for SU insulators.

 

He basically Slabs some silicon between two layers of siran wrap, then places the spacers on tops and loads them with weight. This makes a silicon gasket after a coue days of drying. Clean it up with a razor and your gtg. Beats fiddling with a gasket if you ask me.

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If you don't want to try port matching the gasket, you could try what is demonstrated in the Ztherapy video where he talks about making gaskets for SU insulators.

 

He basically Slabs some silicon between two layers of siran wrap, then places the spacers on tops and loads them with weight. This makes a silicon gasket after a coue days of drying. Clean it up with a razor and your gtg. Beats fiddling with a gasket if you ask me.

 

Very ingenuitive! I'll think about doing something like that, thanks.

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Picked up the goods this morning. Rebello re-cut the seats, installed new valves+guides+seals, and did a street port.

 

post-3287-0-00937500-1473565532_thumb.jpg

 

Dave mentioned that this casting was better than most so minimal intake port cleanup was necessary. Intake valves are Supertech, with an undercut valve stem for slightly less restriction.

 

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The exhaust ports, on the other hand, were pretty worked over...

 

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Dave also hogged the crap out of the TWM manifold which he said didn't line up very well with the ports. I had carb-matched it previously but he finished the job! The manifold is pinned to the head for alignment, you can barely tell where the manifold ends and the port starts. The cut-out for the injectors kind-of gives it away. :P

 

post-3287-0-10915100-1473565860_thumb.jpg

 

Hoping to find time after work next week to piece it together!

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Glad to see this progressing. It seems you were having similar problems as I was.

 

Do you have any photos of how the manifold is pinned? I'm thinking maybe this is something I should do as well.

 

It's essentially two socket head cap screws threaded into the head, with holes cut accordingly in the manifold. I can take some photos tonight. :)

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Oh my, having the intake manifold pinned to the head, and that port match is just absolutely stunning. If I didn't know any better, I would have thought the intake port never ended!  :lol:  :lol:

 

And that's a good tip about the difference between the L24 and L28 HG. Would come in handy in the event the wrong HG is sent to me, and I have something like an E31 on an F54 brewing.

 

Question about the head cap screws for your intake manifold pin, it's not *that* deep into the head is it? Guessing it's something like just a few mm thread lengths in, or somewhere similar? That pin definitely piqued my interest, if it means that the ports would be aligned with close to 100% certainty

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Haha yeah, I would imagine they're relatively short! It's something I'm actually thinking of doing in the future when I start to become really serious with the engine. Funny enough, I found myself grabbing a complete E31 head not too long ago. Still deciding whether to hold off the head for when I acquire an F54 block, or just slap it on my existing L24 block. Decisions, decisions.

On that note, I'm living a lot closer to you these days. As a matter of fact, I just live a couple of minutes away from Yoshi, and I see him nearly every week. So seeing the car is actually a pretty good possibility  :lol:

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