Datsun Roadster Forum-311s.org

I would like data on the frequency of factory rod bolt failure on the U20 engine. I am going to get a spare set of rods resized, and keep reading about how "you should always change your rod bolts", or, ARP is necessary". What is the reality? Has anyone here, under driving conditions up to the factory redline, and short periods up to that point, suffered a rod bolt failure? I mean not sustained 8k running, and not racing.
Knowing how overbuilt these engines are, I would be surprised to learn that the rod bolts would not be equally overbuilt. Personal knowledge is best, or knowing of a situation personally. I have a friend with 8 of these cars, 30+ years working on them, who has not ever seen it happen. Enlighten me. Maybe this should be a poll? Thx Pat

I don't recall changing out my rod bolts in several builds, but may have at one time.

That's the kind of info I'm looking for. Can you re-use them, do they stretch, or what are your experiences. I'm thinking they would be fine, as they are not TTY bolts. I guess I'm mythbusting. Thanks greg. Pat

The only issue with U20 rod bolts is not knowing what a PO has done.

If the bolts have never been over stressed, they are likely fine. You probably do not need ARP bolts.

Of course you probably can't know the history or if they have been over torqued or stretched.

U20 rod bolts pretty much never fail except maybe under extreme race use and even then probably secondary to a bearing failure or other abuse.

If there is any rust on a rod bolt(any rod bolt), throw it away.

If you never want to think/worry about it, use the ARP's, otherwise the stock bolts are fine.

Thanks, Jim. I'm guessing there won't be many people who've had factory rod bolt failures. I like to know the facts, so that's why I asked. Pat

unklpat wrote: Thu May 20, 2021 11:15 pm Thanks, Jim. I'm guessing there won't be many people who've had factory rod bolt failures. I like to know the facts, so that's why I asked. Pat

Nope. The R16 rod/bolt failures are MUCH more common, but again it’s usually secondary to a bearing failure due to the #2or3 rod starving for oil. That isn’t a common issue with U20 cranks.

And with U20 cranks, #3 is the first rod beaing that starves for oil, in my experience. Pat

I have no experience with a U20 and am learning the R16. However, if you can take a new nut and hand thread it all the way down the bolt with no issues, then you know that it has not undergone inelastic deformation (stretched and not rebound to normal dimension), nor suffered damage to the threads. A bolt's maximum allowable torque is set at 75% its tensile strength to prevent stretch, but that does not mean that you should torque one to that number. You just should never exceed that number.

If the rod bolt stretches, does the nut also? Let's say the rod bolt/nut was over torqued, or used over multiple re-builds, wouldn't the last 1/4" of the rod bolt feel different when spinning the nut on by hand? If those threads are exposed during normal use, then they can't be stretched, right? I'm surprised at the lack of responses to the original question. No one has ever had or seen a failure on a nissan rod bolt? Pat