Roderunner wrote:Interesting project you have happening, I hope that you keep posting updates!
On the possible crank snapping problem, apparently they usually snap off at the front just behind the harmonic balancer, partly because this is where the torsional vibrations are more concentrated. Add in some excess fanbelt tension helped along by the screw in belt tensioner adjuster and the front of the crank gets pre-loaded a tad too heavily in many cases. Excess injection advance which can induce "nailing" (that tapping noise) also magnifies the torsional vibration seen by the crank, so some minor cold engine nailing might be ok, but if you can avoid it....
The other vulnerable spot on a 4 cylinder inline engine is the big end of no. 3 cylinder, as it also gets a much larger dose of these destructive vibrations,at 3000 revs, which leads me to the flywheel....I know that the standard flywheel weighs a lot, but shaving it down contributes to the torsional vibration problem, so unless your building a 1/4 miler I would think twice before losing some weight off it. The 3000 rev. vibration band is a bummer because it's often co-incides with the open road cruise speed, so you could be cruisin along at part throttle and 5 pounds of boost (light load) and have the no. 3 bearing shit itself. (Don't ask me how I know this lol) all for a few pounds worth of flywheel weight!
On the pump plunger, I believe that the Australian 4jg2 engine has a 12 mm pump plunger from the factory, but I can't remember if it was the electronic pump or the pre- electronic pump, it's something that you can chase up if you feel inclined.
In my case the crank snapping may have been caused by a loose harmonic balancer. But as you said, not an uncommon thing in these.
They do cruise a lot better at lower rpm, I changed my diff ratio so sit at around 2400 @100kph. And it makes 1st a bit more usable at the drags.
Seems to be a general no no, advancing the timing in the Isuzu’s. Does make more power, but at a price. I was running more advance than factory, but I was also running water/meth which slows down combustion and peak cylinder pressure. I have actually dropped the compression ratio a little on the rebuilt engine, make things a bit nicer for the high boost.