Where do you measure the rod bolts on a z?

We are rebuilding a motor for our z, and want to put ARP rod bolts in it, but I'm not sure if the motor we are rebuilding has 8mm or 9mm rod bolts in it. Am I correct in that the rods themselves are different, meaning you cannot use the 9mm bolts in a rod that originally had the 8mm bolts? If I am correct is the bolt diameter the measurement of the diameter of the threads, or the diameter of the neck or head of the bolt. I'm 99% sure it's the threads you measure, but just wanted to be positive before I ordered the ARP set. Also I'm curious what type/brand of rings you guys prefer for your Datsun motors. We are using Deves rings, but wanted to know everybodies opinion on this. We have sourced the usual reference material for the build, but any IT specific rebuild tips would be appreciated as well. Thank you in advance for advice.


Chris

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Originally Posted by spawpoet

...is the bolt diameter the measurement of the diameter of the threads, or the diameter of the neck or head of the bolt....

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Threaded hardware diameters are the "major diameter", at the outside of the threads.

I don't know your "L" engines specifically, but unless it's got some kind of "never used anywhere else rod magic", the hardware is not interchangeable; you must use the correct fastener. You should also resize the big end when you replace rod bolts. - GA

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Am I correct in that the rods themselves are different, meaning you cannot use the 9mm bolts in a rod that originally had the 8mm bolts?

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You are correct. You need the rods and caps out of a 1973 L24 engine. OEM Nissan rings are pretty damn good for an IT build.

"Threaded hardware diameters are the "major diameter", at the outside of the threads."

Thank you Greg. I had thought it was the outside of the threads, and that's what made sense to me, but I don't think I have ever read that specifically. As for the reason for the confusion on what size to bolts use, early z's came with 8mm bolts which can be a liabilty while later z's came with 9mm bolts. I'm not sure which my motor has which is why I needed to verify the measurement. As long as I get the correct size the ARP bolts will be direct fit.

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Originally Posted by betamotorsports

You are correct. You need the rods and caps out of a 1973 L24 engine. OEM Nissan rings are pretty damn good for an IT build.

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Thank you John. I wasn't sure what year they went to the bigger bolt. Also what do you think of the Deves rings??

Chris: I'm almost sure ARP makes bolts specifically for this application. I took pictures of all the packages (showing the part numbers) when Bob first got the parts. I'll look when I get home and see if I can get you a P/N. Failing that, I'll call Bob and ask him. I need to get ahold of him anyhow.

I've got the part numbers for the ARP bolts Andy, but I've gotta figure out whether to get the 8mm or 9mm rod bolts. The 240's came with 8mm bolts through 1972, then they switched to a 9mm bolt. I'm not sure which size the rods we are going to use are. I DO need your machinists number though. I'll shoot you an e-mail tonight or in the am.

By all means, if you have and can use the 8mm rods then do so. They are lighter than the 9mm later rods and will give you more horsies! And if you are going with the ARP bolts you don't have to worry about the 8mm parts failing. I've been using them for more than a decade and have never had a bottom end failure.

Also, the Deves rings are a good choice.

I was wondering, if you use ARP rod bolts on a rebuild, and you pull the bottom end to replace or check bearings, can you reuse them without worry or should they be replaced?

Thanks!
hoop

I'll second Steve's suggestions of Deves rings. Total Seal is extremely good too. You might have to mix and match rings from different sources to get the best hp/sealing combination....

I think all 260Zs have 9mm pieces so I've got no choice.

hoop, at the power levels and RPM we're dealing with I think you can use them forever. Be different, in my opinion, if we were in the 250-300+ range and over 8000 RPM, but for the IT builds we are far from that (I hope).

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Originally Posted by Ron Earp

hoop, at the power levels and RPM we're dealing with I think you can use them forever. Be different, in my opinion, if we were in the 250-300+ range and over 8000 RPM, but for the IT builds we are far from that (I hope).

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Ron,

That's what I thought. However, you know how powerfull the Honda is... I might be at the limit :rolleyes: with my winter upgrades.

hoop

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Originally Posted by Parrish57

By all means, if you have and can use the 8mm rods then do so. They are lighter than the 9mm later rods and will give you more horsies! And if you are going with the ARP bolts you don't have to worry about the 8mm parts failing. I've been using them for more than a decade and have never had a bottom end failure.

Also, the Deves rings are a good choice.

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Steve, I thought that might be the case with the smaller bolts. Obviously the ARP's 8mm will be much stronger than the stock bolts, and as you said it's a little less rotating mass in the assembly. This isn't going to be our "hot" motor anyway, so I just want to upgrade from stock to ARP whether they are 8mm or 9mm. We WILL seek out 8mm sized rods though when we build our full race motor. Thank you for the info Steve. It's good to know that someone has run the smaller bolts for years in IT without a problem.

chris

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Originally Posted by Ron Earp

I'll second Steve's suggestions of Deves rings. Total Seal is extremely good too. You might have to mix and match rings from different sources to get the best hp/sealing combination....

I think all 260Zs have 9mm pieces so I've got no choice.

hoop, at the power levels and RPM we're dealing with I think you can use them forever. Be different, in my opinion, if we were in the 250-300+ range and over 8000 RPM, but for the IT builds we are far from that (I hope).

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Ron, I had heard mix & match on the rings was the way to go. I'd imagine Total Seal for the top sealing ring, and then lower drag rings (Deves??) for the second compression, and oil rings. Is that the hot trick?? Won't really matter for us at the moment anyway as I find the Total Seal a little pricy for our budget for this motor which is really being set-up as our second motor. We want it to be reliable above and beyond everything else, and power is a secondary consideration.