mjfawke

Having been through this a few times.... the low point on the cam is sometimes not directly opposite the lobe. To adjust properly, you need to have a play with each lobe to see where the best point for adjustment is. The Nissan method of two setting points tends to make some rockers pretty noisy. You also need to check the clearance after adjustment. Sometimes when doing up the locknut, it will loosen the clearance, sometimes tighten. Doing the adjustment hot is 'best' for accuracy.... but in the real world the engine cools down too quickly. Hot checking for a noisy rocker or two is fine, but you cannot adjust the whole set in the timeframe. Better to set the rockers up cold, and then do a quick once-over when hot. Also, how hot is hot? If you have just done two fast laps, and the engine bay gives off heat like an oven, the clearances will be looser than if you have gone for a gentle drive down to the shops. Set them cold, and adjust if necessary... Also, how good are your feeler gauges? Cheap ones sometimes have raised edges from where they are pressed out and will not give a true reading.

I'd give up on this box. The layshaft bearings are notorious for breaking up, and usually the layshaft gets broken when the bearing fails. The later cases (RB/CA/SR series etc.) run a bigger layshaft bearing to get around this problem - but for the L series boxes, you cannot get a heavy duty bearing, as it is a custom size made specifically for Nissan. Converting to a 280ZX T5 is the best solution.

When a complete RB25DET costs less than a rebuilt L28, why would you go down the L28ET path?

As per the "sticky", the RB26DETT needs a modified oil pickup, so I guess this will be an issue with any of the GTS4 variant engines.

Nope - you need some surface roughness to hold oil while the cam and rocker arm bed in... the same reason that piston skirts are not polished.

You can resurface the arms on wet/dry... approx 280 - 320 grit from memory was what I used last time. You have to be careful to keep them straight, and clean up the tips at the same time. One the engine is running again, watch for scuffing on the lobes and rocker arms. If any start to scuff, pull the rocker arm and clean up lightly again on wet/dry and do the same for the cam. I had a set professionally reconditioned (new are basically NA in Australia), and the stone they used was not - the cam lobes were running on only about half the surface area of the rocker arm. Killed the cam...

There are a few places that have experience with re-tuning these. Basically the ROM is replaced with a socket so you can swap the ROM's. There are a number of ROM editors for the RB series of engines that let you play with the mapping. Real-time editors on the dyno are the better way. AFAIK' date=' the RB25 computers have one-time programmable processors...[/quote'] So, you could reprogram a rb20 ecu to run on an rb25? Yes - but technically you are open to having the book thrown at you by the EPA. Less likely to be picked up at a roadside inspection... but then again, you could just build an Autronic board into the Nissan case - quite common for GroupN rallly where the internals of the computer are free.

There are a few places that have experience with re-tuning these. Basically the ROM is replaced with a socket so you can swap the ROM's. There are a number of ROM editors for the RB series of engines that let you play with the mapping. Real-time editors on the dyno are the better way. AFAIK, the RB25 computers have one-time programmable processors...

L28ET? That would be the P90 head with hydraulic adjusters?

As I have an RB20DET in my 240Z.... The big advantage of the RB20DET is cost. A bare RB20DET is ~ $1300Au, while an RB25DET is ~$3000 Au. I spent the money on fitting the RB20DET, and when it eventually smokes I could drop an RB25DET into the hole and only have to change the computer. I couldn't rebuild an L series for the money it costs to buy a complete low Km RB20DET. As for power - there are at least two cars (not Z's) in Aus getting over 200kw at the wheels on stock internal RB20DET's with reprogrammed factory computers. None of the tuners in Aus will run an RB25DET over 10psi because the computer will detonate the motor. Not an issue in my 1970Z, because I can ditch the factory management, but cars built after 1 Jan 1971 have to use the factory management that matches the engine (in NSW/ACT at least). About the only reason I would go for an RB25DET would be for the Neo motor (206kw from factory).