BUNN LPG bulk grinder rebuild

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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cannonfodder
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#1: Post by cannonfodder »

A few weeks ago I picked up a BUNN LPG grinder on ebay for an agreeable price. I have been bidding on bulk grinders for months but was unwilling to pay the prices they commonly sold for. Given the LPG's new purchase price or $500 I could not see spending the common $250 price for a used grinder. While that sounds like a bargain on the surface, add in a set of new burrs which tip the scales at $200 you now have a $450 used grinder that could be purchased for $500 new. Did not make a lot of sense to me.

As I mentioned I eventually won one for under $100. Having purchased used grinders before, I know what kind of a disrepair they tend to be in. Most of these come from failed businesses, they failed for a reason. Probably because their coffee was honorable because their equipment has not been cleaned for 4 years. This grinder lived up to my expectations arriving caked with old coffee on the inside.

The reseller apparently tried to clean it up with some quick orange cleaner because the machine stunk of citrus and rancid coffee, yum. So a complete tairdown was in order. Thankfully, BUNN makes a well built but easy to work on grinder. Unlike many espresso machine grinders that take hours to disassemble to the frame, the LPG stripped down to the frame in moments.

Four screws and the hopper comes off. Four more screws and the upper sheet-metal lift off the frame exposing the innards of the grinder. Inside is a simple circuit board which controls the timer. All the parts are connected with wire harnesses so simply disconnecting 3 harnesses disconnects all the electronics. The motor and burr carrier are mounted in one cast aluminum piece. Removing 3 screws allows you to lift the entire motor and burr housing off the frame for further work.

The motor on the grinder is mounted above the burrs. The coffee falls vertically into the burrs and the motor drives the lower burr. The upper burr is stationary. Grind adjustments are also made from under the grinder which is a pain and requires a stubby screwdriver. Remember this is a bulk grinder. You would normally set the grind and never change it again so ease of adjustment was not a high priority.

To get to the burrs, you remove that bottom adjustment plate. Two screws and it comes off. You can then remove the old, rusty, coffee caked and molded burrs. Yum, blue cheese coffee. The burrs are mounted to their carriers with two screws. Easy to remove and replace.









The motor is attached to the carrier assembly with two long hex bolts. Once removed the motor cap can be removed and the guts of the motor pulled right out. The grinder uses a DC motor so it is difficult to pull out of the housing. The magnets in the housing are quite strong. The motor uses bronze bushing, no ball bearings. Once I had the motor core, carriers and other parts dissembled it all got a soaking in JoGlo to clean up the abuse the grinder has seen. A few hours later and it is spic and span and ready to reassemble.






Old burrs, new burrs





My new burrs arrived and I put the grinder back together. It looked nearly new. I ran a pound of old coffee through the grinder to break it in, adjust the grind and make sure it was all working. It mulls through a pound of coffee in a flash. The vertical path of the beans is nice but the grinder does suffer from some extreme popcorning when you get to the end of the beans. I have yet to brew a cup with it, been to busy working on some espresso. Hopefully it will produce a decent cup of coffee and this little post will provide some insight into the grinders workings.

Dave Stephens

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Bluecold
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#2: Post by Bluecold »

The burrs should be the same as the G1/2/3 since the Bunn site has the same spareparts code for both(05861.1002). However, your burrs look totally different from the spareburrs espressoparts.com shows on their site.
What gives?

Also, the lower plate has a built in 'dechaffer'. How does that work?
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another_jim
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#3: Post by another_jim »

The Espressoparts page has a picture of the Ditting burrs. Bunn has different motors (I think) for their various grinders, but always the same burrs.

The bottom plate has two holes where the coffee exits. These are covered by two flaps. If the flaps are removed, the grind is staticky and the chaff flies around. With the flaps on, the grind is well behaved, but about 1 to 1.5 grams are retained by them.
Jim Schulman

AidanC
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#4: Post by AidanC »

Dude I can believe how dirty that was. When I opened my grinder after 5 years it was freakishly clean. All mine needed was a quick dusting.

I don't think I could be game enough buying a second hand grinder. Thought the price you paid for yours is a good buy. Shame the burrs are so expensive.

wookie
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#5: Post by wookie »

Bluecold wrote:Also, the lower plate has a built in 'dechaffer'. How does that work?
According to the Bunn patent, the rotor by design does not immediately sweep the ground coffee out of the grinder. Rather the rotor has to make multiple rotations to force the ground coffee through the flexible exit (blades/doors/flaps) & this delay is sufficient to break up most of the chaff. Apparently (the description is ambiguous) this primarily happens as the chaff is forced past the flexible blades as it leaves the grinding chamber.

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Sherman
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#6: Post by Sherman »

cannonfodder - thanks for the pictorial. It gave me a lot of confidence to tackle my own teardown/rebuild. Not entirely sure, but it appears that the previous owner was running molasses and honey through this thing - yuck. Fortunately, a scrub and soak in Joe-Glo has done wonders. New burrs are in, the grinder is ready to rock. I'm curious to see what, if any, difference I notice between this and my old Maestro+. Don't want to get my hopes up, but already I notice a significant difference in grind evenness just by visual inspection.

I'll be running some tests this week to see "what condition my condition is in".
Your dog wants espresso.
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danetrainer
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#7: Post by danetrainer »

I bought two of the Bunn LPG/2's, that a 20 some location drive up coffee chain had owned for half a year, because they thought people would wait for french press to brew. They sold off 25 or so of these grinders and they are pretty cool as they have two separate hoppers on top with 3 programmable timer buttons on each side to supply your desired bean and dose amount.

Bunn states these burr sets are rated at a Rockwell hardness of 66C, and 30,000 lbs coffee, esentially "lifetime" of the grinder ...not withstanding abuse, of course.

Dave, I was surprised how damaged your burrs were (very unlikely they ground anything near 30,000 lbs). Luckily for me the LPG/2's sold here were esentially new...Bunn has a hefty price for those burrs.

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cannonfodder (original poster)
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#8: Post by cannonfodder (original poster) »

My grinder has rust on the burrs. The shop I got it from used orange cleaner on it. A lot from the stench. Took me a while to get it all washed out. A new set of burrs is 200 or more. My grinder is still going strong. Use it every day for a press pot or two.
Dave Stephens

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Sherman
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#9: Post by Sherman »

another_jim mentioned in another thread that grinder sharpness wasn't as important as ridge definition. Wonder if this applies to brew grinders as well?

Upon inspection, I was taken aback both by the low height of the burrs (not sure of proper terminology - I'm trying to define the distance between cutting edge AKA the "crest" and lowest point at the same radius, AKA the "trough", near the outer edge of the burr) and how dull the ridges felt; when installing the new burrs, the ridges were significantly more well defined even though the burr height remained unchanged.

I'm with danetrainer on this one - given the rated lifetime of these burrs, I wonder what the previous owner must've gone through with the old set.
Your dog wants espresso.
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another_jim
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#10: Post by another_jim »

I'm more an ideal type, good at math, but not engineering. So I can say for sure the ridges' action is to push the bean fragments through the burr by scissoring together, but I do not know which sort of wear, losing height or sharpness, will compromise that action most.
Jim Schulman

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