So I decided to not tear the engine down again.

NPR states in the piston ring manual:

Quote

NPR manufacturers each piston ring gap with the correct OEM specification for each individual engine. There is no need, nor do we recommend that you alter them in anyway as this might void our warranty. Also note these end gaps are set at

exact bore dimensions.

Update! The engine is running ?  Got A/F ratio dialed in pretty well (using a wideband probe). Timing set to 16° BTDC initial, around 35° maximum mechanical advance. 

Only issues I'm still fighting with: When shutting down the engine, it rattles/shakes a little. Is this something unusual? I don't have another Datsun engine to compare, so I don't know if it is supposed to be like this. 

Besides that, the front nozzle of the SU carb sticks sometimes after the choke has been applied. Cables are greased, so are all pivot points. Should I try to bend something? 

 

Edited July 22, 20186 yr by german240

 I twisted the little flat bar linkage piece that pulls the nozzle down to ensure the linkage mating surfaces were exactly parallel to the attachment points. That allowed the nozzle to return from the choke position easily. Carb. was removed at the time. I doubt that it can be done with the carb installed.

That is an odd sound on shut down.  I wonder if it could be as simple as the noise heard through the carbs with no air filter installed?  Sort of sounds like something is loose?  Is the valve cover nice and snug?

Edited July 22, 20186 yr by siteunseen

So far I haven't found something loose. It's not only a noise but also a visible shaking - maybe a form of dieseling? 

That's weird. I'd have to guess dieseling too. Does the engine rotation reverse in that last split second when it dies??

 If it doesn't, I'd grab my 4' garden hose stethoscope and start probing. It's a great tool for finding noise sources in hard to reach locations.

its still firing.

I'm thinking more and more it is just a resonance during run down. I've heard that many BMW E30/E46 M3 owners experience a similar issue but there's no solution. 

I've switched to colder plugs, high octane gas, played around with ignition timing.. still rattling. My engine features completely different harmonics comparerd to stock (500g less weight per piston assembly!). Therefore, the engine mount stiffness might be not ideal now.. 

If it's a brand new engine it might still be tight.  So right before rotation stops the parts grab and give everything a little shake.  It might get better with time.  Just a guess.

1200 miles later, 3 oil changes, full load up to 6000rpm, everything is fine. The engine pulls really hard! Only issue so far is that the right engine mount already disintegrates (new aftermarket).

I found that SM needles were not sufficient, it leaned out at WOT from 4000rpm on. I switched to RH needles which are slightly richer but leaner during idle. The engine is super responsive and torque, so far I can't justify buying triples!

Timing set to 16° BTDC initial, regular fuel (US: 90 octane).

It's a blast to drive. Thank you guys for your support!

Edited October 4, 20186 yr by german240