Re: Re: Crawler Undercarriage

Subject: Re: Re: Re: Crawler Undercarriage

Comments:
: Stan, : I really appreciated your thorough answer! : That really helped! I am trying to buy a : older crawler/dozer (JD 420, 430), and I am : very ignorant in this area. : (I would respond to directly if I had your email : address. My email address is: : tickle@eng.mc.xerox.com. Would you mind if I had : more crawler related questions?) : Thanks very much, : Terry : : Terry, : : A crawler has pads mounted on large chains. : : The chains are driven by a sprocket on the rear : : and run under rollers at the bottom of the : : carraige. There is a large idler wheel at the : : front of the carriage, and possibly an upper : : roller or two (depending on the track length). : : The sprocket pulls the chain up at the rear : : and sends it to the idler at the front, where it : : is laid on the ground. : : All that said, there are hardened bushings in the : : track chains, along with hardened pins.The pins : : and bushings wear over time, as they are not : : lubricated and are operated in the abrasive dirt : : (or worse, acidic manure). There is always some : : form of track tightenermechanism at the front of : : the carraige that allows the large front idler to : : be adjusted forward. This allows the chain to be : : tightened to compensate for the pin & bushing : : wear. If the chains are not kept tight, the track : : is likely to be thrown off during a turn. : : OK, when someone quotes an undercarraige : : percentage, they are usually referring to the : : amount of tightening adjuster travel left. This : : will give you an idea as to how much work you : : might expect to obtain before having to replace : : the pins & bushings in the track chains. : : Stan

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