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For any used Pioneer 1000 check the date of manufactur sticker on the frame for any 2017 or older model for being built August 2017 or after. Those have the updated clutch cover from the factory which provides a 7x more robust system to prevent clutch overheating and failure. Older models are eligible for the product update campaign that ends in about 60 days. There is a cast in bump on the updated clutch cover housing that indicates it is the revised part. Read thread in forum for Clutch Update Campaign and it has photos showing what to look for. Link below
ITS OFFICIAL. Honda has finally released the UPDATE CAMPAIGN set to fix all the issues many of us have been having with the clutches. Who is eligible for this update? ALL 2016 Pioneer 1000's are eligible. ALL 2017 Pioneer 1000's are eligible. 2018's are expected to come with this...
hondasxs.com
That said, I would personally stay away from any unit with internal gear reduction and or portals. You have no way of knowing if everything will hold up. Where I ride in East TN, portals have proven to be very unreliable in this terrain. That's not to mention if or how much the machine has been submerged with potential unseen engine damage.
Definitely check steering rack for excess movement, usually due to large tires, portals, exerting undue stress on steering components.
Check all fluids, front and rear differentials- any sign of milky water contamination. Are they full, how dirty or clean does the oil appear? If full, oil should weep out of fill holes when cap is removed.
Sub transmission oil, dipstick under seat, check for oil condition and any milky water contamination.
Engine oil, start machine, let idle for about 5 minutes and turn off, after 2 minutes check dipstick level behind drivers seat under bed for correct level and signs of water contamination. Also smell the oil, is there a burnt smell indicating clutches have been slipped and overstressed from large tires and deep mud, occurring when stuck and hammering machine in reverse most often culprit. Is engine oil very black and feel slightly gritty, also sign of clutch wear from above.
If every single fluid looks brand new it can mean it has been well maintained or covering up being submerged in water and fluids have been flushed, unless done multiple times usually still have trace indicators of water contamination.
Check A-Arms and frame tab mounts for signs of paint cracks at welds and welds themselves, looking for any signs of being re-welded, out not square side to side.
Drive it, does it track straight or pull to one side, could be uneven tire pressure or tweaked suspension components.
Look under machine, any signs of frame damage from smashing rocks, including frame hitting engine cases. Look for signs of JB weld to hide any leaks/ cracks in engine cases and differential cases on very bottom.