Chinese brush cutter (GTL BC520), should I try to port this?

[Homeowner]

I bought such thing, not sure what was going on in my mind, but hey I got it cheap! It seems that Mitsubishi TL52 has very similar looking parts at least when you search cylinder kits at ebay, maybe this is some kind of clone of that.

Manufacturer's page, mine has some minor differences, blade shield is different and mine does not have plastic on shaft near the clutch housing:
http://www.gtl-tools.com/products-show.asp?id=1675

Today I finally realized that it actually has a mixture screw so thing actually seems somewhat usable now, I'm not sure what this idiot was thinking again when confusing mixture screw to idle speed and wondering why it has no effect, I guess engaging brain would be good every now and then, but it seems to be more offline as I get older...

Anyway I did mod it bit already, I have owned it now 3 days, so surely it was the time, took base gasket off and filed a bit on edges of ports and transfers as there was not much rounding on transfers or bottom side of ports.

One reason why I pulled cylinder off was because I saw some scratches in piston after 2 hours of use, despite it running pig rich.

There were some scratches in cylinder too, also some of plating had flaked a bit at edge of transfers, I believe, but I have no experience of such things, it is learning process.
I took some pics for you to laugh at

Idea was to put some rounding to edges so that piston rings does not catch so much to those edges, which might help this motor to last tad longer, I'm just not too sure if it will help at all, especially with my poor hand skills and eyes, I'm probably not making it right at all.

Would be interesting to get bit more power out from it, bit over 2HP from nearly 52cc is not much, but I'm not sure what should be done to cylinder and is it even possible to get much more out of it?
Milling is bit impossible for me, I have Chinese clone of Dremel with hose attachment though, I just need to learn how to use it properly, but rising compression further might not be possible.

It seem to cut fine just about anything I have tried within limitations of chosen blade, but for some reason I like to try improving everything I get hold of.

Another mod I had to do was to file throttle trigger, it had quite sharp edges, but they generously had lot of plastic used to make that trigger, so I used file to reshape the trigger, now it is much improved.

 

[ANewSawyer]

I would start with a good flowing intake and exhaust. I don't know anything about porting.

 

[LegDeLimber]

I see that the HP rating is at 6000 rpm. Just remember that we are more accustomed to seeing HP numbers at 9000 ~~ 14000 rpm.
So that rating maybe isn't too bad.

How is the wear pattern on the piston and cylinder?
Are there any high spots or wear marks showing on the piston or cylinder walls?
I am always curious how well these Chinese units are made.


The (factory) top edges of the transfers looked like they'd cut ya.
If you don't have a set of diamond bits, I'd say to grab a set of something like these.
Harbor freight or Ebay.
I suspect that ebay is more practical from Finland!
http://www.harborfreight.com/50-pc-diamond-rotary-point-set-69665.html
I just picked up mine from HF, since there was a store in my city.

The question of porting?
Well the general opinion is that the power handling capabilities of the drive line, IS, the major limiting factor.
I.E. shaft and gear head.
I like to grease mine a couple of times each season.
I think a fresh dose of grease makes for a smoother running tool
with less vibrations in the hands.

Clutch construction and how the bearing(s) are arranged etc, would be my next area of concern for power handling.

Other than that? Well we are kind of a group of enablers here!
I've muffler modded all of my weedbeaters.

Stuck a larger carb on one....
For a brief moment, the tachometer was showing mid 1100 thousand and still had some throttle left.
But I was already getting a lil butt-puckered from spinning the edger blade that fast, So I let off.
Haven't done a "piss rev" of it since.

I've often wanted a backpack style trimmer and IF my budget ever allows for one, it would probably be an Asian unit like yours.
So that makes me a little more curious about your luck with this unit.

Do keep us updated on your results
and how the unit holds up to usage over time.

 

[LegDeLimber]

Oh and did you check the compression before you pulled the cylinder?
Did the engine have enough run time for the rings to be seated?

 

[Homeowner]

Oh and did you check the compression before you pulled the cylinder?
Did the engine have enough run time for the rings to be seated?

I lack of some very much needed tools, like compression tester and air leak tester, so I could not test compression before, but what I could see, at TDC there is a lot of room above piston, I guess compression might be increased a lot if one would have access to milling tools.

I guess they put lower compression because of emission like car makers at 70's.

Not sure if rings did get seated in that 2 hours of use before I pulled cylinder off, but I think they have seated now, it starts to run much better already, surely it is not a screamer, has kind of 4 stroke feel to it as I can use it just fine at rpm where some chainsaws idle.

One tank of fuel lasts now over 2.5 hours of constant use, but I'm having stuff getting stuck between shield and blade every half hour so haven't been able to run full tank of fuel without stopping.

Triangle blade that came with it got bent from small branch so that it cut itself into shield, way too thin material that blade, imo.


I'm not sure about wear pattern, I did not clean anything for the pics, using Aspen fuel so it stays nice and clean. just those few scratches that can be seen in pics, but not much other wear, might be much more visible wear now as I have run it more and some heavier use.

New cylinder and piston costs around 30 dollars delivered on ebay and cylinder is really easy swap, so might be interesting to do some testing with this.

Really good point with driveline being limiting factor, it might be that I'm better off with tiny improvements on bad points like those knife edge transfers, now that it has been run a little, thing is picking up rpm much better and to be honest, I don't need more power to it.

Full tank of fuel is roughly 2 pounds (900 grams) and as that lasts 2.5 hours, it is 360g/hour, I guess typical rating is around 450g/kw/hour with these kind of engines, so it is likely that I'm using less than 1kW of power, it might not scream to 9000rpm, but even that 1.6kW would be enough for my usage, at least so far.

Thanks from the tip about those diamond bits, must got a set as I might get new cylinder and piston, those probably need some improvements also so that engine would last bit longer.

Carburetor is bit different from what I'm used to see, it has rotating cylinder with hole (carb is 15mm) that turns by throttle cable, which connects to top of the carb, while at least in chainsaws throttle linkage connects to side of carb and there is usually throttle butterfly.

Air filter is ridiculous tiny ring of foam, I saw better air filter box at ebay, that should fit this model too, it would have much better panel filter, that is one improvement I'm going to do, it might help with breathing a bit too.

Muffler mod might be possible too, there is internal baffle with two holes, it would be easy to drill new hole to that baffle, but not sure if I'm going to do that as I kind of like how quiet this thing is, then again new muffler was not that much on ebay

I need to get grease nipple to this thing, corner gear had red grease in it and some purple grease is coming out from bearing that is on other side of corner gear, so there is some grease for sure, but I feel like putting new grease in soon, it is Chinese made tool and quite often there is bit of extra metal floating around, so that is one thing to do.

After putting cylinder back, I have used it for perhaps 6 hours, so I'm somewhere around 8 hours of use so far. Manual did state that re-lubing should be done every 60 hours, but might do it bit more often, I'm hearing little gear whine so might be good time to put some grease in.


Another mod would be new handlebar, many better models have right handle closer to shaft and left handle further away from shaft, so that would be one thing to do, also that trigger is still not quite what it should be, my index finger finds some pain as it is quite stiff to push and despite filing it is not yet quite perfect shape.

Surely it is not a Stihl or even Husky, but for the money it might do the job around the house.

 

[LegDeLimber]

Yes, I'd highly agree with cleaning out the drive line lubes.
Better to feel like you just lost a little bit of grease and cleaning supplies
vs the machine parts.
and The fresh dose of grease really does help damp the vibrations that sting your fingers.

oh yeah. Don't forget to clean and lube the flex shaft of your porting tool, while you have the supplies out.

About the compression. Are you familiar/comfortable with using solder for checking the clearance between piston and cyl head?
If not, then you'll need to read up on it in the chainsaw section,
before trying it.

The carburetor should have some threads on the needle that runs through the center of that rotating cylinder.
You will probably find some type of cover in the middle of the arm or cam where the throttle cable connects to the carb.
The needle should have some sort of slot or tip for a tool to adjust it.
(I couldn't get any photos to upload this morning.)
But it is also possible that it uses some type of clip and some manor of height adjustment shims or washers to affect how deeply into the barrel that it sits.

You probably have seen how the starting method uses a cam or something to lift the barrel out of the carb body,
But without rotating it while in the cold start setting.
This lifts the needle from the metering orifice, in the carb body
and allows a richer mixture for starting.
Thus you see how raising/retracting the needle affects the mixture.

Usually if the carb has a high speed circuit adjustment screw,
it is on the side, somewhere near where the fuel inlet is at.

Muffler mods and noise.
Yeah, the tradeoff kinda sucks. I'm quite comfortable with using the better rated grade of foam earplugs.
But it's just not convenient to get them handed out for all of your neighbors! phooey huh.
Thus my interest in the concept of, home made, fiberglass packed, muffler additions.
but that's another days dream I suppose.

 

[Homeowner]

Yes, I'd highly agree with cleaning out the drive line lubes.
Better to feel like you just lost a little bit of grease and cleaning supplies
vs the machine parts.
and The fresh dose of grease really does help damp the vibrations that sting your fingers.

oh yeah. Don't forget to clean and lube the flex shaft of your porting tool, while you have the supplies out.

About the compression. Are you familiar/comfortable with using solder for checking the clearance between piston and cyl head?
If not, then you'll need to read up on it in the chainsaw section,
before trying it.

The carburetor should have some threads on the needle that runs through the center of that rotating cylinder.
You will probably find some type of cover in the middle of the arm or cam where the throttle cable connects to the carb.
The needle should have some sort of slot or tip for a tool to adjust it.
(I couldn't get any photos to upload this morning.)
But it is also possible that it uses some type of clip and some manor of height adjustment shims or washers to affect how deeply into the barrel that it sits.

You probably have seen how the starting method uses a cam or something to lift the barrel out of the carb body,
But without rotating it while in the cold start setting.
This lifts the needle from the metering orifice, in the carb body
and allows a richer mixture for starting.
Thus you see how raising/retracting the needle affects the mixture.

Usually if the carb has a high speed circuit adjustment screw,
it is on the side, somewhere near where the fuel inlet is at.

Muffler mods and noise.
Yeah, the tradeoff kinda sucks. I'm quite comfortable with using the better rated grade of foam earplugs.
But it's just not convenient to get them handed out for all of your neighbors! phooey huh.
Thus my interest in the concept of, home made, fiberglass packed, muffler additions.
but that's another days dream I suppose.

There is actually mixture adjustment screw on side, which I fist thought of being idle adjustment, but idle is adjusted near where throttle cable is. With mixture adjustment screw I got it work as well as it can work with current setup.

This one has plastic flap in air filter box which makes mixture richer when starting.

I think that I need to add more oil to fuel, there were so many blood sucking insects biting me that I could use some smoke screen...

 

[TBS]

These are copies of the komatsu zenoah trimmers which are pretty damn tough trimmers. Muffler mod it and modify the air filter housing, I did that to my 128ld and richened the mixtur , that woke it up big time.