Originally Posted by dhanushs
Most of the times, axle u joints give away. If you have lockers, then while powering up over huge boulders, the short side shaft itself breaks. Neatly.
Not a stock rig eric. We are talking about engine swaps. And, its not 2 passengers. A fully prepped up vehicle will mean, you have 4-5 people standing on your front bumper. I'm saying, when you get more torque, keep it light to reduce failures. Keep the torque requirement minimum.
Hey Danush, appreciate all your clarifications. I meant that two passengers would be the equivalent of the heavier engine alone, all other things being equal. This could be the proverbial "straw that broke the camel's back" of course.
And definitely lockers introduce a whole different thing into it, since over large boulders or really any high-grip uneven surface, you will have tyres on either side that might WANT to move at different rotational speeds (what a differential would normally allow for), but they can't, if tyres on opposing sides are both getting good grip - so ultimately either the traction has to give way at a very high threshold, or a component has to break. In that scenario, I see your point - bigger tyres add grip, and higher weight from any source increases downforce (and thus traction) on those tyres, so no surprise that axles / u-joints and other stuff will start breaking then, unless correspondingly upgraded. We're not supposed to engage 4x4 when on pavement, etc - same sort of thing there, as there's no differential action between front / rear drive systems and windup (due to differing amounts of ground covered) becomes an issue - and there again, if traction doesn't give way, a component will.
Lots of ways this could be entertainingly further analyzed...
1) Suppose a particular engine, heavier and higher-torque (I think the Scorpio engine was being questioned orginally?), besides being more drivable on-road, could power me through a lot more tight spots in my sort of off-road use than the original Peugeot engine; Hence I'm getting stuck a lot less. Then maybe I'd ask whether I really needed the winch and the larger front bumper structure required to hold it at all. That omission offsets the heavier engine weight, and the net effect might be that I actually have a more powerful, capable vehicle off-road / on-road, that's not necessarily more prone to breakages (and less prone to getting stuck) than a Peugeot-equipped rig weighed down with a bunch of extra stuff ahead of the bumper. Hmmm...???
2) Or, for that matter, I keep the lighter Peugeot but install lockers and similarly drop the winch. I get through more tight spots with the extra grip, and the "locker" load described earlier is minimized since there's less downforce on my tyres.
3) Or else: If the function of reduced breakages you've wisely recommended is the avoidance of excess weight, thus limiting the downforce on the tyres and thus limiting maximum traction (which reduces torsional loads on my drivetrain components)... then for certain types of offroad uses (surfaces), I could just as easily swap in a heavier, more powerful engine, but move to equally tall (for ground clearance) but skinnier tyres (less maximum grip), so that my overall torsional forces on axles will be the same!!!
Like most things, multiple options and compromises. If I want zero compromises, then I'll need to strengthen every "weak" link progressively, simultaneously trying not to add too much weight (and then my bank balance is certainly compromised!).
Thanks for taking the time to reply, and that more than once. Mind you, though I relatively recently own a 4x4, I'm certainly nothing like an off-roader, so am not speaking from that sort of experience. You guys have lived it.
Guess what made me raise the question it is that, well, our Marshal (and all the dozens / hundreds of 4x4 Bolero Campers / pickups in use up here, which are sometimes very heavily loaded besides) use the same Dana 44 stuff as all these MM340's, etc, and both the weight of the DI over the axles and the weight of the entire vehicles are much, much higher (likely higher than an offroad-ready 340/540), and yet in normal 4x4 use breakages are pretty uncommon. Wonder what the net downforce / available grip / torsional loads with our heavy Marshal & DI engine sitting on 6.00x16 skinnys is, compared to that available on a prepped 340's...hmmm...
Of course, I'd think lockers, especially in combination with huge tyres, certainly compound the critical stresses, and "real" offroad use will exploit every weak link in a system.
I do wonder whether, if the U-joints are the main weakness (apart from shafts themselves, if huge boulders are an aim), they should automatically be upgraded in cases of larger tyres/lockers. What are the options here? I mean, if the main argument against an engine swap is essentially that my u-joints won't hold, then that might be relatively easy to rectify, so long as someone is not intending much rock-crawling???
Your Nissan-powered rig must be a complete blast to drive... something I can only dream of... and you must've put a LOT of work into it - stop in if you're ever in H.P.