Strimmer carburetor insulator

[openBrain]

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 ( ) 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.

insulator.png (32.94 KiB) Viewed 3364 times

[chrisb]

Nice application. What kind of plastic did you use, that is heat and fuel resistant enough?

[mlampert]

That's some serious reverse-engineering - nice!

... it perfectly fitted and worked the first time.

I wish that would happen to me too every now and then

[Kunda1]

I get it machined into a medium-hard plastic, and ... it perfectly fitted and worked the first time.

Can we see the final product ?
BTW, nice job!

[openBrain]

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.

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]

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 (113.53 KiB) Viewed 3184 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 (390.43 KiB) Viewed 3184 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 (468.08 KiB) Viewed 3184 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 (762.1 KiB) Viewed 3184 times

Unfortunately the seal at engine side is sticked thus I can't picture the other side of the part ATM.

[chrisb]

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.

[Kunda1]

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?

[openBrain]

@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]

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/