Loud tapping noise, ideas?

[redroadster]

Use of this oil if not recommended may cause damage to your engine
( last qt of 20w50 I used stated in this in the print )

[Gregs672000]

So good news... the piston is salvageable and will only require a slightly thicker pin and some machine work. Gonna do all four the same just to be sure. I have to source the pins however, but I'm willing to do that. My shop guy said he had not seen a broken pin in 10 years... usually everything else breaks before the pin itself. He looked it over and could see the failing/fracture points that occurred over time. We'll be checking the rod for bend etc as the cause is unknown at this time, but it looks like I was lucky and fortunate to have had forged pistons as a cast one, while certainly fine in most circumstances, would probably have not survived and taken the whole motor with it. Whew.

Datsun down for a few weeks... bummer, but workable.

[Habitat.pat]

Great news!

[Gregs672000]

So, warnings to other do it yourself engine builders... check you wrist pins carefully if you are reusing them! I was looking more closely at a "good" pin and saw that it was cracked in two places (!). This is not something I have ever seen mentioned in rebuilding engines beyond making sure they had no play on the piston or on the rod itself, and no binding of course... never to look for hairline cracks. And yes, this is a higher compression motor but certainly not a race engine or highly abused. Beware and learn from my mistakes!

[JT68]

Greg, as you say the likelihood of it being "because you used 20/50" is absurdly low. As you 100% correctly said earlier, correlation doesn't imply a causal relationship. If one did a careful analysis, I'm quite certain the probability of that type pin failure would be essentially the same whether it was 30wt, 10w40, or 20/w50 and would be ultra low. Oil viscosity isn't the cause. Next we'll be arguing about flat earth....Millions of Nissan engines ran on 20/50 for decades/zillions of miles w/o wrist pin failures.


Pin fit has always been a critical specification for IC engines.


Pin failures are extremely rare except in turbo/super charged/drag racing motors. So the fact that it happened in your normally aspirated street engine points to either bad setup or Random Component Failure or excessive stress. The probability of RCF piston pin failure is ultra low, so it points to bad setup or also the possibility that those components had too much previous abuse-that sounds more likely.

I would not advise re-using the Arias pistons yet again and trying to cobble together a bigger pin. There are many reasons not to do that.

[david premo]

I would bet the pin was bad before it ever went into use and it was just waiting to fail.
Dave

[redroadster]

Then would not my 30w60 oil be even better?
What keeps the crank and rod and cams from seizing ? , it's a day 1 engine test. Question
Also does your 20w50 go thinner or thicker ?

[Gregs672000]

Thanks for the input all. I think the pins had seen many miles, possibly over 100k as I've run these pistons in two motors, and in a different set of pistons before then. The pin manufacturer I spoke to today (Trend Performance) was familiar with the Nissan pin and indicated they were not considered that strong and may have seemed good (tight, no scuffing etc) but were tired. The machine shop measured the piston and examined the overall condition and found it showed minor for and aft rocking due to the pin fracture but very little scuffing, and I have no cylinder wall damage. Even though the pin was fractured it was still in there but allowed the piston to rock just enough to create the tapping noise I heard. The stock pin is 22mm and the oversize pin I've sourced (which is much stronger material) is 22.0726mm, so that's all the more that's needed to repair the bore for the pin in the piston. New rod bushings are on the way and will be honed to match. All rods will be inspected for bend, but the only rod bearing showing unbalanced wear was #3 and reflected the damaged pin bore. All the other rod bearings looked great but will be replaced. Honestly, the pistons look great other than the one pin bore, and it's just scored, not distorted. They are good to go.

No, I think the pins were just worn out, and it's my own lack of knowledge that probably led to this. I knew enough to make sure they were tight etc, but I doubt I examined them closely for signs of stress or fracture, as I did not appreciate how stressed they are, and nobody had ever emphasized them as something that can fail... my bad. That's how you learn sometimes.

Regarding stressd parts, it made me think back to when I had a pilot bushing problem that caused the crank to eat the thrust bearing due to constant pressure and then eventually damaged the crank. That engine saw a lot of miles. I wonder if the pins were stressed due to the forward pressure. Different crank now, different block, same pins and rods.

[Gregs672000]

OK, so it's been over a month, but I'm happy to say The Bitch is Back! Just got back from putting 12 miles on the repaired/refreshed engine. Took longer than I had hoped due to a lost order, then an incorrect shipping address (!), but I just birthed the baby a couple hours ago i.e. I finished assembling the motor early this afternoon and fired it off for the first time. Always a tense moment, but there was no drama and it fired on the second turn. It burned the crap off the header and exhaust that always gets on it, had no leaks, no bad sounds, no tailpipe smoke and off we went down the road to start seating the rings. After a couple miles to confirm I hadn't done anything stupid, I increased the rpms and before long it was saying "I'm good" so a few gentle runs to 6000+ rpms had me smiling again. I've always heard and followed the advice to "break it in like you're going to drive it" once you are comfortable it's not going to come apart or spin a bearing, so that is and will be the plan. It has new slightly oversize pistons pins, new Total Seal rings (reused the oil control as they said they were fine with the low miles they had), honed of course, new rod bearings, the Isky cam back in place (yeah!), and I cleaned and lapped the valves just because. I rechecked the clearance for the valves and the block just to be sure, but the absence of any tapping sound is confirmation and music to my ears!

All in all, I was very lucky to have avoided catastrophic failure, and despite having missed a month and a half of summer driving I feel fortunate... she's back together (right this time), there's still some time to drive, and it didn't break the bank. My machine shop guy was great, and he turned parts around for me in record time.

Hopefully in the next few days I will be 100% sure I can say "Ah, that's all behind me now...". And there's still some time left in the season to schedule some dyno tuning! Onward!

[Habitat.pat]

Great news! Glad it went as comparatively easy. Go have some fun before the weather cools off!

Peace, Pat

[nismou20]

Congrats Greg, I know that feeling of victory! All that stress gone after that moment of truth. Enjoy the ride!