2020 SANY SY18C vs 2021 BOBCAT E20Z — What to Inspect Before Buying a Used Mini Excavator

The machine was already on a trailer, boom was already down and blade is low, and the machine was already sold to us twice as a one owner machine. I was in front of the left track frame kneeling on the heat of the last drive housing; that is what you feel with your palm to tell how recently the machine has been run, the gradient. Two to one temperature difference from the centre to the outer flange. That spread matters.

Let me give you three things that will give the biggest bang for your buck on this class when it comes to repair and how to come up with a price for each; nothing I can possibly tell you about it can beat real hands-on experience, however. It devours the challenge.

Two measurements; the swing cylinder and the travel motor, which cost you the machine.

Beginning at the swing cylinder rod, with your fingers before your eyes.

Starting from the wiper wipes out to where the chrome is, trace your fingers along its length and locate where the surface begins to change, not the scoring but the end of the polish band. That’s the band that a travel sees. A band that ends well short from the gland indicates short and compact movement and a band that extends to the limit of the stroke suggests that under load the arcs would be large. None of these are the default. The important thing is the time that the band stops and the surface transitions from the glass appearance to having a grain to it–the point at which the wiper has been letting abrasive through the surface and the chrome has started to come away at the edge. Chrome lift at rod edge is a decision point, maintenance is not required.

Place your hand over dust seal and keep hand on it while your swing is performed. A film is a film. If a drip was found while watching it, it’s a different story but if the smell is a seep that has been going for a few weeks softening the paint underneath the gland, then add some for that.

The more challenging aspect of the test is the drift, as most people get this wrong. Throw the boom on the side, lift the tracks out of the way and drop the lever with the house perpendicular to the tracks. A house that continues to creep while they’re counting is either a cylinder with a built in bypass, or a slew motor with a worn rotating group; if they’re out on a slope, the two failure conditions are loaded differently, so they can see where the creep is occurring. On a level track and you don’t understand the situation at all except that your machine isn’t sticking.

The travel motor is more readable and is a motor that people tend to overlook. Take the case drain (not reservoir) sample, pour it in a clear cup, turn on the device at its operating temperature for a timed amount, and observe the sample. Volume indicates how far blow is past the rotating group. Colours are an indicator of the heat history. The metallic patina deposits as opposed to floats is a clue that this is the reduction gear contaminating the oil; after seeing it under the flashlight and recognizing that mess you won’t mistake it anymore.

Data sources for the table above:https://parts.cat.com/en/catcorp/product/169-4019

The cup doesn’t sound special to the first-time customer. The man who has replaced a final drive reads a rate at which it fills–but the total is not what is being read–and a cold engine (or machine) reads the same rate as a hot one, because the case drain like blowby information is hidden in a cold engine.

Then walk it. Run straight, hardpack, blade up and look at the track marks the whole distance. It is not necessarily a motor failure if the machine tracks in a perfect straight-line in reverse, but takes a wander in forward – I was caught out on one machine, where the idler frame was bent – I now check the frame before sanitizing the motor!

The pilot circuit is indeed the honest witness on a mini – and there is a mechanical reason.

The pilot hoses run at low pressure and low flow rate make them smaller, more flexible and run through tighter geometry than the working lines: practically everything that gets attached to the upper structure tends to affect them, and the severe irritation from having to rebore them is compounded by their being the cheapest of all things to ignore. A man hurriedly zip ties them to where they’ll reach. A caring man will place them back in the comb.

So read the comb. Check the slew area and the boom foot for where the loom crosses, close inspection of the anti-chafe sleeve, and check the wear on any anti-chafe sleeve to the seemingly age of the machine. There’s fresh sleeve on the sun-bleached panels and a worn seat which sparks up a question that is for you to ask. The best record you will have will be clamp indentations, as rubber has a tendency to “set” and a hose which has spent years in one clamp naturally has a flat where a hose has been re-routed.

Double-check all against dates. Hose date codes are a relative guideline, not an indication; newer than those listed on the build plate may indeed be indicating a standard change out, and witness marks placed on fittings, clamp sets and the presence of the loom in the comb it was built in, will help validate them. If two agree and the codes do not then you have your question.

Order of importance: cheapest to check first, most expensive to get wrong last–you have your inspection swing, travel and loom, and you know you do.

This gen machine’s cluster is a display and the controller is a witness, both of which have a factory built controller that has been counting.

If a dealer-level read and/or Service-tool read are there, then the time in the record is the deciding time; it will be the delta (difference, not absolute!) between that and the displayed time that is the entire conversation. I have personally witnessed tiny works of integrity in cluster replaces following a broken lens. I’ve witnessed those holes that weren’t truthful. What you want to determine is if the story has form or not.

There are 3 (OK, there are four, but we’ll trim all but 3) reasonable conditions under which you can discount that risk. One owner, with continuous service documentation for the machine and not a pile of general machine service documents. A dealer trade history that shows the unit. Original cluster with the cosmetic age of the cab, same sun fading on the lens, legends in a worn area where thumbs go and dust down in a matching seam as other surrounding components. If a cluster appears newer than the panel in which it is housed then it is asking, rather than a judgement.

Wear doesn’t reset. That’s the property that you are benefiting from.

Integrate the bucket linkage pin, measured at the wear band and at the unworn shoulder and you end up with a ratio of load cycles and not calendar time, the very thing the display touts as measuring. Then, check out the boss. Ovality detects a “step” at the end of the grease channel and at the start of the unworn bore that can be felt with a fingernail, and exceeds any paint or decal for an hourly proxy.

Read the linkage, like a clock. Then assemble a triangle with these parameters in it: hours, linkage wear, hose date codes.

If two say one thing and one another, then the other one is a lie and you can say this. When all three disagree: Walk—not because some guy is a lying, ole Detroit weasel—but because you can’t resale a machine you can’t explain, and you can’t explain it if you can’t price it.