rabidrabbit001 wrote:4jg1t and 4jg2t from what I can tell have the same crankshaft and rods.
I don't know how Isuzu balanced these engines in their manufacturing plant, maybe they weigh the pistons to get matched sets, or maybe they just drill some holes into the flywheel. That's what we're up against when modifying unusual brands/models. If this were a small block Chev or ford engine there would be 10 guys who could pass on this type of information, not to mention at least 10 books on how to hotrod them too.
BUT, where is the fun in doing what 500,000 other guys have already done!
Unfortunately (or fortunately depending on how you look at it) fooling around with the isuzu diesel engine is fraught with apparently unsolvable problems which really try out ones mechanical aptitude (and attitude), I usually get beaten by the tough technical questions, not finding out the answers until the particular engine/vehicle is passed on to the next owner when I upgrade to something more powerful and reliable. (That's why I purchased the Isuzu)
I only offer the harmonics theory as a possible contributor to the valve gear noise, probably because I destroyed 3 sets of conrod bearings in my last diesel performance build because no-one (including myself) had a clue as to what was happening in the engine via crankshaft harmonics. While I'm ranting (I've been drinking lots of bourbon today), did you peeps know that a 4 cylinder inline engine has a bad vibration band at 3000 and 6000 revs...which is concentrated onto the no.3 bearing, well, now you do, so if you can avoid it don't run your hopped up engine at 3000 revs for an extended period of time (like at cruise speed), also don't shave the flywheel for the same reason- vibration is satan's spanner!
Maybe the gearnoise that you can hear is at the normal sound level, and the change from belt drive to gear drive has made the gear whine more noticable. I can't hear the gear drive noise when I listen to my 4jg2 at idle or at any revs for that matter, but my hearing is a bit dull these days, all I hear is some mild combustion knock at idle, and the fan when it is engaged. I did a short video of my engine running, and posted it on you tube so that you can compare it with yours, Maybe the insulated cover over the geardrive muffles the noise a bit ( that's what it is there for so I think that's a reasonable assumption). This video makes the engine sound louder than what it is when the hood is closed, at 100 km/h I can't hear the engine at all over the tyres and wind noise. The buffeting noise in the vid is the fan engaged, and it dis-engages toward the end of the vid.
https://youtu.be/6Xg1pLmCDSY