Dahlke micro 4b initial thoughts.

[Mgumby16]

Finally got the dahlke out again. The Honda gx160 ran much better then the crappy motor that I originally put on it. A few other things I did that improved suction, was to increase the high pressure line size to 2 inch so that the little pump doesNt have any constricted areas to fight before the power jet. Another thing that could be improved upon is the inlet to the power jet. It comes as a simple 1.25 inch OD inlet No threading no nothing The problem is that 1.25 od inlet is like 1 inch ID which is just killing the pressure from the pump which is 1.25 outlet pump.

So I cut the inlet and widened it take a 1.5” threaded pipe fitting that I welded to it. In my eyes if your building a small dredge that is running an underpowered pump to help with weight savings then you should do everything possible to make the rest of the set up as efficient as possible. I shouldn’t be the one doing that.

I some ways I wish I could own dahlke cause there are many changes I would Make that would make the 4B a kick ass dredge.

Another QC issue I noticed is that the riffle tray bows upwards which only makes the issue with the bottom bowing down worse. Also the riffle tray is super heavy for what is supposed to be a super portable dredge, an aluminum riffle tray with a top and bottom section so that top mat cleanout can be done would be sooo sooo sooo much better.

Sorry for the ranting. Overall I like the dredge a lot but there are many more changes that I’m going to make to it.

It is very small and light and perfect for those one day trips or for taking to remote areas to do a bunch of prospecting with.

 

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[Reed Lukens]

"Another QC issue I noticed is that the riffle tray bows upwards which only makes the issue with the bottom bowing down worse."

Don't forget to inflate it. That keeps the bottom up against the riffles.

 

[Vance in AK]

OK guys, I'll join the discussion here with my own questions & quest for direction.
Back in April I mentioned I was looking at a 4b with no jet or hoses. Ended up picking it up this last week on a trade that I cant really get hurt on.
Heres my first question. This one has a GX120 with a DP-125. Looking at an old classifted ad for a use maching I see an old 4" (non b & tapered box) setup the same way. Anyone have any experience with this pump/motor on a 4B? Will it work?
Mgumby16, I see yours has a different riffle tray than mine. Mine has angle for the first portion & then all dovetails. Those with experience is the setup I have useable in areas of primarily fine gold?
My machine doesn't have air & I am ok with that. My initial plan is to use it for more of a prospecting dredge & longarm. Suggestions for a powerjet since mine is missing? My thought is simply to find a used Keene. Problems with this idea? Finally what do you guys use to inflate them? Mine has what looks like a radiator drain petcock on it.
I'm sure I will come up with more questions as I stare at this thing this winter.

 

[Reed Lukens]

You just blow it up with your mouth like a pool toy.

 

[russau]

OR you could use a battery powered flotation device air pump .

 

[Reed Lukens]

It's like 2 breaths... not a big deal

 

[Vance in AK]

It's like 2 breaths... not a big deal

Uhhu
Especially on a balmy 37* day like this morning!

 

[Mgumby16]

OK guys, I'll join the discussion here with my own questions & quest for direction.
Back in April I mentioned I was looking at a 4b with no jet or hoses. Ended up picking it up this last week on a trade that I cant really get hurt on.
Heres my first question. This one has a GX120 with a DP-125. Looking at an old classifted ad for a use maching I see an old 4" (non b & tapered box) setup the same way. Anyone have any experience with this pump/motor on a 4B? Will it work?
Mgumby16, I see yours has a different riffle tray than mine. Mine has angle for the first portion & then all dovetails. Those with experience is the setup I have useable in areas of primarily fine gold?
My machine doesn't have air & I am ok with that. My initial plan is to use it for more of a prospecting dredge & longarm. Suggestions for a powerjet since mine is missing? My thought is simply to find a used Keene. Problems with this idea? Finally what do you guys use to inflate them? Mine has what looks like a radiator drain petcock on it.
I'm sure I will come up with more questions as I stare at this thing this winter.

From what I can tell the dahlke hasn’t ever really had a standardized riffle design. Most seem to have slight variations but all include the dovetail riffles. It should be pretty good on fine gold but probably not equal to a full size 4 inch dredge.

That motor and pump is undersized in my opinion at least for any standard 4 inch jet. I generally think the pump that is sold with dahlke micro 4B is too small especially since most come with a 5 hp engine. If it’s comes with. 5 hp you might as well put a normal 250-300 gpm pump on it.

When weight comes into play the 4hp engine is ideal and if you can build a tri-jet or an infinity jet then I think that motor and pump combo will work great. But it won’t work well with a normal Keene powerjet.

I plan to try using a 4.5 hp Subaru engine on mine that has a gold divers 1556 pump which I think is a better pump the dahlke dp150 since the gold divers uses an inclosed impeller and the dahlke does not. I plan on doing some testing with a vacuum gauge set up to determine which pump/engine combo works the best.

Fee free to ask any other questions.

 

[Vance in AK]

This is my box.

 

[Reed Lukens]

Those are the same riffles that mine had... They aren't any good for fine Colorado gold...

 

[Reed Lukens]

Just set it up with expanded like Bob did back in the day -
That looks like the 125 pump in the pic below, which might work fine with expanded riffles. The dove tails require more water to run properly.

 

[Vance in AK]

Just set it up with expanded like Bob did back in the day -
That looks like the 125 pump in the pic below, which might work fine with expanded riffles. The dove tails require more water to run properly.

Had actually thought about that Reed. I have the straight box. would you vary the size like in the pic? Angle & expanded? What size expanded would you use?

Anyone point me to plans for a tri-jet or infiniti jet?

 

[Reed Lukens]

Look for some nice light weight 1.25" to 1.5" expanded. I'd hit a scrap yard first and see what you can come up with.

Infinity jet schematic -

Dawn of the stealth dredge

It might sound stupid at first, using well pumps in this application. But I did do a little bit of research first. I started here, where Keene engineering put together a paper on dredging basics/troubleshooting/making your own. Its one of the few places that I was able to find actual number on...

www.treasurenet.com

A trijet would be more than enough.

 

[Vance in AK]

Look for some nice light weight 1.25" to 1.5" expanded. I'd hit a scrap yard first and see what you can come up with.

Infinity jet schematic -

Dawn of the stealth dredge

It might sound stupid at first, using well pumps in this application. But I did do a little bit of research first. I started here, where Keene engineering put together a paper on dredging basics/troubleshooting/making your own. Its one of the few places that I was able to find actual number on...

www.treasurenet.com

A trijet would be more than enough.

Thanks Reed.

The post you linked also has this tidbit of info
"
-3”and 4” suction nozzle works at 106 GPM at 45 psi
-3” and 4” power jet runs at 180 GPM at 35 psi
".

Sounds like a suction nozzle might pair better with the DP-125? Don't know it's actual output...
Would that make sense since my current intention is longarming in shallower streams?

 

[Reed Lukens]

A suction nozzle uses more water because it's pushing everything up the hose. The powerjet is way more efficient and you can really feel the difference, but I use both, they both work and both have their places.

This quote is wrong... just way off base...
-3”and 4” suction nozzle works at 106 GPM at 45 psi
-3” and 4” power jet runs at 180 GPM at 35 psi
NOT!
You have to consider hose length and venturi sizes into this.

Dawn of the stealth dredge

It might sound stupid at first, using well pumps in this application. But I did do a little bit of research first. I started here, where Keene engineering put together a paper on dredging basics/troubleshooting/making your own. Its one of the few places that I was able to find actual number on...

www.treasurenet.com

 

[Mgumby16]

Had actually thought about that Reed. I have the straight box. would you vary the size like in the pic? Angle & expanded? What size expanded would you use?

Anyone point me to plans for a tri-jet or infiniti jet?

here are some of my numbers that I used when building my 4 inch tri jet. It worked well. It allowed me to run the 4 inch Keene ultra mini with a Honda gx120 and a Keene p160 pump.

 

[exosis]

I also have a Dahlke Micro 4B, the newer black version. As far as I know the black poly body has significantly more floatation (and is much heavier), than the original gray one. People advertised this dredge (with air) weighing 100lbs-- when I got mine in late 2017, I weighed it with the air tank, air hose, suction hose, GX160, snorkel, and it weighed 189lbs (!!) I never bought it expecting it to work out of the box. In fact I knew it would need dramatic mods. I have only recently gotten around to the mods, but my version will have basically nothing in common with the original 4b except the poly body:
- New motor mount made of aluminum & titanium, that drops the engine 3" for increased stability and adds a mount for a tiny 4L ultralight (2.6lb) air reserve tank, bolted directly to the engine mount
- Replaced the dampener with a heavy polyurethane one that is amber transparent so you can see through it
- Replaced the engine from GX160/DP150 to heavily modded 11HP GX200 with Proline HP350 pump (GX200 horsepower can easily be doubled with aluminum flywheel, stiffer valve springs, modded air intake, different carb, adjusted timings, removed governor)
- I need to work in ultra-remote areas with massive hikes on steep trails with fixed ropes, so I use certain mods others would never consider, like I use a different ultra light suction hose that weighs only 6lbs instead of 30lbs, yes it is less durable and doesn't last, but the weight saving is worth it to me
- The GX200 high pressure output is split into 2 via a low angle WYE connector and feeds a Keene 4" dual log powerjet (the dahlke jet isn't too bad but is too short), in fact I think I might still use the dahlke jet in some shallow places as it allows the dredge to be dragged easier vs. the longer keene jet
- I scrapped the heavy Dahlke swivel nozzle and made a nozzle out of ultra thin walled titanium with a reducer, my nozzle weighs around 1 pound
- I switched to slightly lighter hose clamps
- I'm currently changing the entire sluice setup to deep ribbed V-mat with aluminum expanded metal under punchplate for the entire length of the box as I am working fine gold areas
- I also removed the steel cross bars that are fixed to the poly body as part of my motor mount modification
- I am also building a 6ft x 14ft test pool (3ft deep) to run gold recovery tests on the new sluice setup. I trick I found to speed up recovery testing is to mix 100 mesh gold into +50 and bigger gravels (all the way up to 3.5" rocks). This way, after sucking it up, you can separate the gold out with just a 100 mesh classifier which rejects all the gravels. It may not be 100% accurate but probably very close to that with drastically faster clean ups. Once the recovery system is tuned in, one final pass with truly random gravel & black sand can be done.

The only thing not included in the above is the hot water system, which will use a thin walled titanium tube instead of the usual heavy fire extinguisher.

I weighed out all the parts and the new design weighs 130lbs vs. 189lbs even with the heavier GX200/HP350 engine/pump. It still takes three trips to carry though, the polybody+riffles, the engine block, and all the hoses & dive equipment.

 

[Vance in AK]

I also have a Dahlke Micro 4B, the newer black version. As far as I know the black poly body has significantly more floatation (and is much heavier), than the original gray one. People advertised this dredge (with air) weighing 100lbs-- when I got mine in late 2017, I weighed it with the air tank, air hose, suction hose, GX160, snorkel, and it weighed 189lbs (!!) I never bought it expecting it to work out of the box. In fact I knew it would need dramatic mods. I have only recently gotten around to the mods, but my version will have basically nothing in common with the original 4b except the poly body:
- New motor mount made of aluminum & titanium, that drops the engine 3" for increased stability and adds a mount for a tiny 4L ultralight (2.6lb) air reserve tank, bolted directly to the engine mount
- Replaced the dampener with a heavy polyurethane one that is amber transparent so you can see through it
- Replaced the engine from GX160/DP150 to heavily modded 11HP GX200 with Proline HP350 pump (GX200 horsepower can easily be doubled with aluminum flywheel, stiffer valve springs, modded air intake, different carb, adjusted timings, removed governor)
- I need to work in ultra-remote areas with massive hikes on steep trails with fixed ropes, so I use certain mods others would never consider, like I use a different ultra light suction hose that weighs only 6lbs instead of 30lbs, yes it is less durable and doesn't last, but the weight saving is worth it to me
- The GX200 high pressure output is split into 2 via a low angle WYE connector and feeds a Keene 4" dual log powerjet (the dahlke jet isn't too bad but is too short), in fact I think I might still use the dahlke jet in some shallow places as it allows the dredge to be dragged easier vs. the longer keene jet
- I scrapped the heavy Dahlke swivel nozzle and made a nozzle out of ultra thin walled titanium with a reducer, my nozzle weighs around 1 pound
- I switched to slightly lighter hose clamps
- I'm currently changing the entire sluice setup to deep ribbed V-mat with aluminum expanded metal under punchplate for the entire length of the box as I am working fine gold areas
- I also removed the steel cross bars that are fixed to the poly body as part of my motor mount modification
- I am also building a 6ft x 14ft test pool (3ft deep) to run gold recovery tests on the new sluice setup. I trick I found to speed up recovery testing is to mix 100 mesh gold into +50 and bigger gravels (all the way up to 3.5" rocks). This way, after sucking it up, you can separate the gold out with just a 100 mesh classifier which rejects all the gravels. It may not be 100% accurate but probably very close to that with drastically faster clean ups. Once the recovery system is tuned in, one final pass with truly random gravel & black sand can be done.

The only thing not included in the above is the hot water system, which will use a thin walled titanium tube instead of the usual heavy fire extinguisher.

I weighed out all the parts and the new design weighs 130lbs vs. 189lbs even with the heavier GX200/HP350 engine/pump. It still takes three trips to carry though, the polybody+riffles, the engine block, and all the hoses & dive equipment.

A 60# weight loss is pretty amazing! I would love to see pics. Especially of the recoverysystem!

 

[Reed Lukens]

I also have a Dahlke Micro 4B, the newer black version...
1) - Replaced the engine from GX160/DP150 to heavily modded 11HP GX200 with Proline HP350 pump (GX200 horsepower can easily be doubled with aluminum flywheel, stiffer valve springs, modded air intake, different carb, adjusted timings, removed governor)

The Proline HP350 runs great with room to spare on a 5hp G160 motor, so why go with a G200?

- I need to work in ultra-remote areas with massive hikes on steep trails with fixed ropes, so I use certain mods others would never consider, like I use a different ultra light suction hose that weighs only 6lbs instead of 30lbs, yes it is less durable and doesn't last, but the weight saving is worth it to me

I've used the light weight hose, it does work fine for a month... there is a mid grade "Clear Flow" brand that is just a bit heavier but lasts for a few seasons and is predictable.

I scrapped the heavy Dahlke swivel nozzle and made a nozzle out of ultra thin walled titanium with a reducer, my nozzle weighs around 1 pound

The problem with lighter nozzles coupled with the lighter hose is that they get caught and dragged downstream with any current, ripping the hose off of the dredge in even moderate currents, so keep a rope on it... They really float very easily. It's nice sometimes, to have a nozzle that's heavy enough to be able to set down on the bottom and have it stay in place. Usually, for me, because I have larger hands, I just use a regular keene suction tip coupled to the mid grade hose. I stopped using the light weight hose because once it splits, it unravels from there. Then when needed, I tie a rope around the hose behind the work area and up to my small anchor that I use for exact dredge placement. A little whale tail anchor makes for quick and easy dredge placement underwater. Mine is about 10lbs but that holds my 6" as well. You could probably use a 5lb anchor with the Dahlke... it really makes a difference with mobility.

I weighed out all the parts and the new design weighs 130lbs vs. 189lbs even with the heavier GX200/HP350 engine/pump. It still takes three trips to carry though, the polybody+riffles, the engine block, and all the hoses & dive equipment.

You could probably get away with running the HP350 with a 4hp Honda using 10/30 MobileOne or another synthetic along with 92 octane gas. Using a good synthetic oil increases the hp quite a bit. It should work fine with a single piston air compressor, but not enough for a Gast twin cylinder. The G200 would run the Gast as well, but the dredge won't float it well with the large compresser.

It sounds like you have a well thought out system, the 3" drop on the motor mount should make a huge floatation difference

 

[exosis]

The Proline HP350 runs great with room to spare on a 5hp G160 motor, so why go with a G200?


I've used the light weight hose, it does work fine for a month... there is a mid grade "Clear Flow" brand that is just a bit heavier but lasts for a few seasons and is predictable.


The problem with lighter nozzles coupled with the lighter hose is that they get caught and dragged downstream with any current

Indeed the 11HP GX200 + HP350 is overkill for the Dahlke 4", but I was hoping to use the same (single engine) to run a Proline 5" (with the dual log jet and split hose). The proline guys told me the HP350 should run at 5000-6000 RPM without dangers, which would theoretically turn it into a 500 GPM pump assuming the engine is producing enough torque (except of course the GX200+HP350 in insane mode would weigh 22-25lbs less than the GX270+HP500).
I have only used standard suction hose (heavy) and the ultralight one. Do you have a source for the 'medium' weight hose, I would very much like to try it.
Indeed the light weight nozzle + hose gets blown around in current, this is annoying. I was thinking of a ghetto solution to put some sort of cloth pouch around the hose near the nozzle that I could fill with a few rocks to make it heavier when the current calls for it. I know some snipers would take empty blue jeans and fill them with rocks to make a weight belt without the hassle of carrying weights, so a similar idea. I like your idea of the dredge anchor, I had considered it but never knew anyone who actually used that method, I think I will try it, thanks.

In 2017 I did a remote prospecting trip and found what I believe is a lost placer mine. I had been searching the area based on some old legends which possibly turned out to be true. To reach it you need to kayak 30km along a remote lake, then the river mouth is guarded by a maze of dead heads that cannot be navigated by any boat (seadoo, canoe or kayak is the only option). After which you must make it 8km up river through the densest underbrush of devil's club and alder (no possibility to walk in the river itself). I never actually reached the target location-- I cut a trail 5km up river (which took 9 days) then I flew the DJI Mavic Pro (drone) for 3km and at the absolute limit of the range of the drone I found what appears to be a 1900-era prospector's cabin near the river. I did pan the river gravels and found good color but you can never tell what is on bedrock or false bedrock just from shallow panning. [There is no possibility to land a helicopter in the area, you would have to climb down a live rope, and then if you did that, you would give away the location].

I was hoping eventually to tow the Dahlke (behind a kayak) through the maze of dead heads and then hike it to the lost placer. I need to add extra pontoons for the lake journey because it would capsize even with the engine 3" lower. Then probably remove the pontoons for the journey through the dead heads.