Strimmer carburetor insulator

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openBrain
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Strimmer carburetor insulator

Postby openBrain » Tue Apr 16, 2019 9:35 pm

Hi all,

The part below (shown from front & rear) is a so-called "carburetor insulator" (actually acting as an intake manifold) for a petrol strimmer.
The original part cracked due to plastic "drying" when ageing along with repetitive disassembly/reassembly.
I thus reverse-engineered it with a caliper ( :D ) and created a more robust version of the part.
I get it machined into a medium-hard plastic, and ... it perfectly fitted and worked the first time. 8-)
insulator.png
insulator.png (32.94 KiB) Viewed 1374 times
chrisb
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Re: Strimmer carburetor insulator

Postby chrisb » Tue Apr 16, 2019 11:00 pm

Nice application. What kind of plastic did you use, that is heat and fuel resistant enough?
mlampert
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Re: Strimmer carburetor insulator

Postby mlampert » Wed Apr 17, 2019 12:31 am

That's some serious reverse-engineering - nice!
openBrain wrote:
Tue Apr 16, 2019 9:35 pm
... it perfectly fitted and worked the first time. 8-)
I wish that would happen to me too every now and then :mrgreen:
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Kunda1
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Re: Strimmer carburetor insulator

Postby Kunda1 » Wed Apr 17, 2019 2:01 am

openBrain wrote:
Tue Apr 16, 2019 9:35 pm
I get it machined into a medium-hard plastic, and ... it perfectly fitted and worked the first time. 8-)
Can we see the final product ?
BTW, nice job!
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openBrain
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Re: Strimmer carburetor insulator

Postby openBrain » Wed Apr 17, 2019 8:10 am

chrisb wrote:
Tue Apr 16, 2019 11:00 pm
Nice application. What kind of plastic did you use, that is heat and fuel resistant enough?
Thx. I wondered the same to myself when I was writing the OP. I have to ask the guy that machined the part for me as it was done in a scrap of material and I can't remember. I'll be back to tell. :)
Kunda1 wrote:
Wed Apr 17, 2019 2:01 am
Can we see the final product ?
Yep. It is actually mounted. I'll try to disassemble to take pictures, but if the seals are sticked I won't take the risk to crack them. ;) I'll give it a try. I will also try to have some pictures of the original part. ;)

I forgot to tell in the OP that, despite I like to play with FreeCAD and petrol engines, I had to design my own part mainly because the spare part wasn't sold anymore and it can only be found as used part in poor conditions. :)
openBrain
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Re: Strimmer carburetor insulator

Postby openBrain » Wed Apr 17, 2019 7:03 pm

Here we are. :)

First about the material, it was machined into a block of PEHD 500 (which is AFAIK similar to what is used for plastic cutting boards).

About the real part. First a picture that shows what the original part look likes (from front and rear) and how it is assembled (took from the user manual).
isolateur_orig.jpg
isolateur_orig.jpg (113.53 KiB) Viewed 1194 times
Now some real world pictures. :)
One with the complete assembly in the strimmer. The part is the natural color (or dirty) one between the carb and the engine.
isol1.jpg
isol1.jpg (390.43 KiB) Viewed 1194 times
Another with the carb disassembled. You can see the front of the part and the mating face of the carb (and the paper seal that goes in between).
isol2.jpg
isol2.jpg (468.08 KiB) Viewed 1194 times
The last one from the true front of the part where you can see the piston through the intake hole (2-stroke engine).
isol3.jpg
isol3.jpg (762.1 KiB) Viewed 1194 times
Unfortunately the seal at engine side is sticked thus I can't picture the other side of the part ATM.
chrisb
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Re: Strimmer carburetor insulator

Postby chrisb » Wed Apr 17, 2019 9:26 pm

Thanks for the material and thanks for showing. I can imagine how the other side looks like, so let it stuck , it won't get better by removing.
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Kunda1
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Re: Strimmer carburetor insulator

Postby Kunda1 » Fri Apr 19, 2019 1:53 pm

openBrain wrote:
Wed Apr 17, 2019 7:03 pm
First about the material, it was machined into a block of PEHD 500 (which is AFAIK similar to what is used for plastic cutting boards).
A comment made on reddit
I would double check the material's gasoline resistance.
@openBrain have you thought about that?
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openBrain
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Re: Strimmer carburetor insulator

Postby openBrain » Fri Apr 19, 2019 2:22 pm

Kunda1 wrote:
Fri Apr 19, 2019 1:53 pm
@openBrain have you thought about that?
Sure. :) And the guy that machined it for me knew the application so proposed a convenient material.
Advantages of PEHD 500 for this usage are :
  • Good chemical resistance
  • Usage temperature
  • Null water absorption
chrisb
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Re: Strimmer carburetor insulator

Postby chrisb » Fri Apr 19, 2019 4:20 pm

Chemical resistance is indeed high, I have already used PE - though not with the HD extension - with fuel and had no issues. The temperature is something to think about, the data sheets talk about +80° (Celsius I guess!).
https://www.otvplast.eu/semi-finished/t ... lyethylen/