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Electronics

CB38 petrol trimmer

In this article, I will describe the repair I performed on my edger following a major oil leak.
I bought this device from Bricomarché in April 1995 for I believe 800Frs ( a little over 120 € ... ), and the address on the back of the user manual states the USA. I first looked for any information on the net and, after spending some time behind my keyboard, it is clear that they are simply non-existent! At the same time, I wasn't expecting anything else, considering that my machine's brand hardly exists.
So if no supplier, no spare parts either.
Anxious to keep it in perfect working order because it is very practical to use, I set to work once again.

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Before reading the following, please know that I can in no way be held responsible for any damage that your equipment may suffer during or / and after this type of intervention.
top view of the machine front view of the machine rear view of the machine

This machine has a particularity: it does not have the 2 traditional handles that can be found on a brush cutter. For its handling, there is only an axial handle located just behind the launcher's cage, the throttle located below that can be manipulated with the index finger, and a handle in the form of an arch located a little more far on the driveshaft.

If you take a good look at the rear of the engine, you will be able to distinguish the traces of oils. On the right, is the exhaust, at the top center, the cylinder with the location of the spark plug (original type Champion RDJ7Y ), on the left the Walbro diaphragm carburetor ( this one being fitted with a manual fuel priming pump ... ), and at the bottom just above the fuel tank, the hatch which gives access after removing the 4 torx screw to the crankshaft.

Model identification :
Charlotte ... charlotte ... is this not the name of a potato? rolleyesLet's continue ... We can read one thing, The very important thing on this plate is its origin from the USA.
At a time when almost everything comes from China, it is rather reassuring !!!
It is therefore this plate that will have to be removed, in order to check the condition of the fiber gasket.
rear seal CB38 side [200x150] view of the nameplateFirst of all, I wanted to replace this seal with one of my own making, but the technical constraints of the material, its thickness and its shape soon made my good will! I ended up going with blue joint compoundview of a tube of joint paste, more practical to implement, and just as effective, since it is widely used in the automotive world! I still give you the dimensional drawing of the original seal, which was distorted in its thickness in places, deformations not visible on the photo.
I carried out this repair in November 2007, and today in April 2009, no more traces of oil, a clear sign that my new seal is holding up.



 
 
Engine oil :
But where can this oil come from, you will tell me? Well, if we consider that this engine is of the 2-stroke type, and that it uses a mixture of SP95 gasolinedosed at 4% of synthetic oil " Special Motoculture engine 2T", also taking into account that the tank has a capacity of 600ml, that gives us a quantity of oil of 24ml. A part of course is burned with gasoline, but there is enough left for the lubrication of the crankshaft.

Motor shaft
:
photo of the drive shaftWith the wire head removed from the machine, the drive axis then looks like the following photo:
On the other hand, the head is fixed using a plastic wheel ( no. 9 on this documentation) from which the bolt comes out very often, with the risk of losing it in the grass ... This is an American 5/16 "(7.94mm) diameter steel bolt( no screw on the right ... ) whose thread length measures 12 mm, with 8½ threads for an approximate diameter of 8 mm. The hexagonal head of the bolt corresponds to a Ø 13 mm wrench / socket. Note that this bolt has no marking, which makes it more difficult to examine.

If I refer to this conversion table and after having carefully measured it using my caliper, this bolt would therefore have the following characteristics:


Nominal diameter UNC Un ified Screw Thread - C oarse Series 
thumb mm TPI Pitch (mm)
5/16 " 7.94 18 1.41
 
tpi diagram
Hoping that this information will be useful to you in case you lose yours ... wink
 
Note :
This engine has never disappointed me, it still starts as well and as easily as when it started.
The disadvantage of this small machine: it does not have a clutch between the engine output and the transmission shaft. It therefore sometimes happens that the engine stalls during use, especially during the automatic unwinding of the line head (original equipment! )

Note :

 

I offer you for free download the multilingual user manual of this machine, as well as several links leading to an exploded view of the equivalent machine although more recent (a Homelite F2015, the cutting parts and various accessories are almost identical to those mounted on the CB38)
:

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You can order at this address:

LOMAPRO SARL 
This email address is being protected from spambots. You need JavaScript enabled to view it. 116 ROUTE DE THIONVILLE ZONE TILLY 57140 WOIPPY Tel: 03 87 30 16 17

 

 
[Edit of May 3, 2016] :

The link to the HOMELITE website ...

So I carried out new ( long ... ) research on the Internet, and I was still able to find a match ( perhaps partial, I did not check everything ... ) with a Homelite F2020 or UT-20788.

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It is understood that I could not be held responsible in any way for any error in the reference of a spare part.
This new link provides access to a PDF document concerning the F2020 model (UT-20788), and this is for informational purposes only.

Philippe
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