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Dumas scarab 55" build

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Dumas scarab 55" build

Old 03-02-2019, 05:47 PM
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sleeper607
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Default Dumas scarab 55" build

I am finally building this thing, the key to this will be I am doing it on a budget. Not HGTV or any of the how to car shows budget but more like a sub 100 bucks or maybe sub 50 bucks. So I bought the hull 2 years ago and still don't have any funding available for this, so I figured if I built it on a budget that would be the only way it would ever get completed. It needs a motor and exhaust, servos, prop shaft and tube along with some misc. stuff that would have to fit within my budget. So my criteria for a motor is it must fit my budget, be water cooled and be able to sit low in the hull so I can run the lid, also I don't want to change the rails currently set up for a big nitro. I will say that I have a plan and I am making progress. I will say I am cheating on the budget a little since the motor was given to me but anyone could have the same motor for free also. Another cheat is that I bought used servos a while back and don't remember what I paid but it was only a couple of bucks so technically I could account for that.
Old 03-03-2019, 05:50 PM
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sleeper607
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The motor is a featherlite 21cc weedeater motor, the cooling fins have been cut back and a 1-1/2 copper pipe cap fits as a cooling jacket. I am waiting on more parts (should be here next month) and need to make a hardware store run at some point. But I also have to make motor brackets to mount the motor to the rubber mounts.
Old 03-06-2019, 11:25 AM
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If the hull has 5" space between the rails you could have left the front part of the green shroud on that has the recoil starter in it..The 21 cc won't get much speed and I've found out that Poulan made these in 18cc,20 and 21cc and and later went to a 25cc. Some of them were labeled as 20 and 21 cc and were actually 18cc motors. Don't have much power ,even as a weedeater.Did you tap the exhaust to accept the plumbing fitting ? What is that on top of the cooling jacket ? You could put a larger venturi carb on the engine to get more rpm out of it. I did that with a 21cc and 25cc trimmer I used in the yard. A carb with a little larger venturi but only up to 11.11 mm or it's too much for the little engine, You don't really need the choke on the carb as you can choke it with your finger.
Old 03-06-2019, 06:14 PM
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The problem with trying to run the recoil is that it runs off the flywheel which will not let it sit low in the boat. So I have the copper cap on top of the motor with 2 o-rings at the plug and I will probably just rtv the bottom I have to tap or solder on some nipples for water. I may need to run a bigger carb but we will see how this one goes. So I picked this motor instead of a homelite or other weedeater I have laying around since this is a undesirable motor to me so I won't care if it spits its guts. The exhaust I ground drown the fitting and it fit perfect but could have tapped it then I will sweat on some tabs or make a bracket and put some springs to hold it on, and maybe a nipple for water. So my plan is now that the motor is stripped of flywheel and ignition is to run an adapter and glow plug and run it on nitro which will keep it light and pickup some power.
Old 03-06-2019, 06:55 PM
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Here's a thread that deals with gas /glow conversions. http://www.rcuniverse.com/forum/engi...-glow-how.html
Old 03-09-2019, 06:23 AM
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I have read that thread, that was one of the inspiration behind doing this.

The story of my life to end up buying 200 bucks worth of stuff for a 100 dollar budget because you buy or get the wrong thing.

Murphy's law of the further away from a parts store you are will be directly related to the number of times needed to visit said parts store to finish the project.
Old 03-09-2019, 08:16 PM
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Originally Posted by sleeper607 View Post
I have read that thread, that was one of the inspiration behind doing this.

The story of my life to end up buying 200 bucks worth of stuff for a 100 dollar budget because you buy or get the wrong thing.

Murphy's law of the further away from a parts store you are will be directly related to the number of times needed to visit said parts store to finish the project.
I know what you're talking about. I buy most of the items I need for a boat or an airplane online,but do use things from hardwares that are for other uses and reinvent them to whatever project I'm doing.I'd often go into Lowes and look for stuff and when I'd tell the associate what I was going to use it for I got funny looks or they'd say that can't be used for that. I even have one guy in the hardware dept that if he sees me coming he goes the opposite direction.Latest thing I bought at Lowes was sliding door finger pulls,which I cut the back off and will use them as front and rear vent hole trim on my Expresscraft VX Rocket Probably will put some screen on the inside of the vents also.The white patch on the transom was where a wrap to center tuned pipe exited. I patched and filled it in and will cut a hole on the left transom to be the exit.

Old 03-11-2019, 04:40 PM
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Well I made a hardware store run today and I think I have pretty much everything I need to put this together. Aside from making the wrong size glow plug adapter work and a nipple for the cooling head, or end up buying them. Then there is a list of everything that needs to be completed.
Old 03-11-2019, 05:01 PM
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Originally Posted by sleeper607 View Post
Well I made a hardware store run today and I think I have pretty much everything I need to put this together. Aside from making the wrong size glow plug adapter work and a nipple for the cooling head, or end up buying them. Then there is a list of everything that needs to be completed.
Also don't forget to glue an ample supply of pool noodles in the bow and on the sides of the hull.Also some pieces under the hatch cover in case it gets knocked off in a roll or flip.Most stores have them out already.
Old 03-11-2019, 05:13 PM
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If I even find an untouched Scarab KV 38 I think I'll paint it like the first one I had.The radar arch broke so I never replaced it. I'd also put a bow rail on it like on the first.It was built back in the early 80s and the original owner put an OS 77 VRM in it.I sold the engine to a collector and later sold the hull and hardware to someone else.

Last edited by Tidnab; 03-12-2019 at 04:04 AM.
Old 03-15-2019, 03:50 PM
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This is what I have in mind for decals on mine.
Old 03-24-2019, 05:59 PM
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I worked on the boat today, more the engine than boat. I gutted the spark plug to tap for a glow plug only to realize the ID was too big to tap for the glow plug. After coming up with several bad ideas I decided to buy a cheap 10mm to glow plug adapter from eBay and as soon as it arrived I realized I have a 14mm spark plug. So now today I modified and tapped the 14mm spark plug for the 10mm to glow plug adapter. I figured I would do it this way first before spending more (3 times) on the correct adapter. I also pulled the old drive shaft and tube out of the boat, the old one was kinked and sloppy, it also used a liner which I am doing with out. Another thing I did with the engine was cut some of the casting back and tried to tap some holes for motor mounting bolts, which when I went to tap it it wouldn't go and was a mess and I ran out of time. I started to lay out the exhaust out of 1/2 and 3/8 copper piping and figured I should route it a little different to get away from the radio box a little more, so I need a coupling for that. I want to cover up the hole for the old tunned pipe, I am going to try some white epoxy to see if that works.
With that said I still need to make a bracket for the exhaust springs to the engine for the exhaust manifold and maybe a stabilizer for the exhaust. Drill the transom for the exhaust and solder the exhaust together and add a nipple for water. Bend up some engine mounts. A set screw or something for the starter pulley. Install the stuffing tube, cut and install drive shaft. Install nipples into cooling head on engine. Plumb water cooling. Mount servo box and servos, route control cables for servos. Reglue mounts for hatch and add some screws or some thing. I guess I need a gas tank of some sort. Once that short list is complete I need to run the engine and tune it for nitro. And finally hit the water... after a much longer list.
Old 05-15-2019, 01:02 PM
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Default Dumas scarab unbuilt 55"

Hey Tidnab,

I have one unbuilt. Interested?


Originally Posted by Tidnab View Post

If I even find an untouched Scarab KV 38 I think I'll paint it like the first one I had.The radar arch broke so I never replaced it. I'd also put a bow rail on it like on the first.It was built back in the early 80s and the original owner put an OS 77 VRM in it.I sold the engine to a collector and later sold the hull and hardware to someone else.
Old 05-15-2019, 03:18 PM
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Originally Posted by Amartins42 View Post
Hey Tidnab,

I have one unbuilt. Interested?
Sent you a PM.
Old 05-23-2019, 03:21 AM
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Here's a couple of threads by FlogginHarvey on building this hull to get the most out of it.
http://www.rcuniverse.com/forum/speed-rc-gas-boats-236/8756371-old-school-dumas-scarab-resto-2.html
http://www.rcuniverse.com/forum/speed-rc-gas-boats-236/9316571-nib-dumas-scarab-38kv-kaama-build.html
Old 05-23-2019, 04:04 AM
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Originally Posted by sleeper607 View Post
I worked on the boat today, more the engine than boat. I gutted the spark plug to tap for a glow plug only to realize the ID was too big to tap for the glow plug. After coming up with several bad ideas I decided to buy a cheap 10mm to glow plug adapter from eBay and as soon as it arrived I realized I have a 14mm spark plug. So now today I modified and tapped the 14mm spark plug for the 10mm to glow plug adapter. I figured I would do it this way first before spending more (3 times) on the correct adapter. I also pulled the old drive shaft and tube out of the boat, the old one was kinked and sloppy, it also used a liner which I am doing with out. Another thing I did with the engine was cut some of the casting back and tried to tap some holes for motor mounting bolts, which when I went to tap it it wouldn't go and was a mess and I ran out of time. I started to lay out the exhaust out of 1/2 and 3/8 copper piping and figured I should route it a little different to get away from the radio box a little more, so I need a coupling for that. I want to cover up the hole for the old tunned pipe, I am going to try some white epoxy to see if that works.
With that said I still need to make a bracket for the exhaust springs to the engine for the exhaust manifold and maybe a stabilizer for the exhaust. Drill the transom for the exhaust and solder the exhaust together and add a nipple for water. Bend up some engine mounts. A set screw or something for the starter pulley. Install the stuffing tube, cut and install drive shaft. Install nipples into cooling head on engine. Plumb water cooling. Mount servo box and servos, route control cables for servos. Reglue mounts for hatch and add some screws or some thing. I guess I need a gas tank of some sort. Once that short list is complete I need to run the engine and tune it for nitro. And finally hit the water... after a much longer list.
Any updates on the Scarab ?
Old 05-23-2019, 03:55 PM
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Well, I filled the hole from the old tunned pipe and that turned out pretty good, pulled out the old stuffing tube out, bent some motor mounts, made a exhaust spring holder from a washer, and maybe something else I'm forgetting. The exhaust springs won't fit like I thought they would, so it is a matter of deciding on what to do with that. Then I painted a bathroom, and bought another project (70 Buick Skylark). Since its getting nice outside I'm trying to do stuff outside. So the scarab is still on the bench but not much progress has been made.
Old 05-29-2019, 08:11 AM
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Great project!
Old 11-10-2019, 04:24 PM
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Ok, now that winter is setting in I am back inside staying warm working on the boat again. So the last time I worked on it I couldn't for the life of me tap the motor for the 5/16 motor mount bolt. Today I realized my tap sucked so I reshaped it and it threaded nicely, with the exception of minor cracking on the bottom of the case. Now I need to straighten my crude motor mount brackets and drill them and notch the one for shape of the bottom of the motor. Once the motor is mounted I can do the stuffing tube and exhaust. Then water cooling lines to the exhaust and head. I still have to mount the servo box then servos in the box. I need to decide on gas tank and location, I may just use the weedeater tank. And the list grows.
Old 06-11-2020, 12:36 AM
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Nice boat
Old 06-11-2020, 04:54 PM
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Thanks, not much more progress but still working on it.

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