Summary
I’ve been testing the Baumr SX45 as a chainsaw to use for light felling and limbing, mostly while thinning forest. So far I like this saw: light enough, powerful enough, reliable, easy to repair. It’s a generic Chinese product with cheap and easy access to generic spare parts.
The main problem with this model (sold with the Baumr brand) is that the chain is really way thinner gauge than the bar so it won’t work very well for long. I also think the bar is way too long. The chain and bar problem is, however, easy and pretty cheap to repair. You can expect to have other quality control problems to fix when you buy these saws.
I've been testing a few of these saws, some with friends, over the last 5 years. They're all still working and I'm liking them more.
Bush repair
The last few months of drought and terrible bushfires should be teaching white Australians that we’ve had the wrong relationship with the Australian bush. For 2 centuries we’ve turned our back on the sophisticated Aboriginal culture of forest management with cool fires, and now most of the country is a real mess. Many forests are now so thick and flammable that they can’t be simply burnt back into good condition: they need a lot of work, cutting and dealing with the fuel, before they can be safely treated with a cool fire.
Currently, the Australian way to manage the bush depends on big machinery: pushing up piles, smashing soil and plants, burning waste in huge, hot windrow fires. I don’t think this is the way to fix the forest - but wait and see how much pressure comes, after these bushfires, to send the bulldozers around every house, town or road that has a risk of fire.
In forests around human settlement, we can step down fuel loads with selective cutting of undergrowth and thinning of trees. This produces lots of fuel that needs careful disposal, so as not to damage living trees or soil with hot fire - hopefully some fuel can be burnt productively, like heating houses, cooking food, making charcoal. Then the forest might be ready to re-start cool burns and re-establish the more open, less flammable forests of Aboriginal times.
 |
| Here's a patch of badly overgrown native forest near Stanthorpe, Qld. The old stringybark is crowded by 60 year old black cypress trees. In a fire, the understorey would burn so hot it would incinerate the older stringybarks. |
 |
| Here's a nearby forest area that has been thinned by chainsaw and then given a cool burn. A new ground cover is starting to grow. |
Small saws for forest thinning
Doing this sort of thinning work over the last few years, has introduced me to small chainsaws. Previously I used bigger saws, when I was focussed on milling larger trees for timber. Now, spending many hours thinning, I have a new interest in small saws, light for lifting up and down all day, just powerful enough for the small wood I’m cutting.
The economic thinning saw
My favourite thinning saws have been the Stihl 024: 42cc engine, running .325” chain. These are light, reliable and repairable, with easy access to non-genuine parts (here's my blog post about them). However, small professional saws are very expensive new (the Stihl MS261, the smallest professional Stihl sold in Australia, costs about AU$1500). Farmertec sell a Stihl 026 / MS260 copy, but it's around AU$500. Even a suitably sized Stihl consumer saw like the MS231 costs $750 - a good quality unit that will work well straight out of the shop, but not cheap or easy to repair (few non-genuine parts). For an explanation of the difference between professional and consumer chainsaws see my post about the Huztl MS360 kit.
Minimising what we spend to do what we need to do is important: minimum spend is minimum carbon emissions, minimum need to earn money and maximum time to do what needs to be done.
So I’ve been looking at what are available as cheap but good enough thinning saws - good enough means reasonable to use, reliable and cheaply and easily repairable. The Baumr SX45, from ebay, cost AU$91 delivered. I wanted to find out what they’re like, and if they could make a good thinning saw, so I bought one (and then another!).
The generic Chinese chainsaw
 |
| Here's the SX45 with a 13" GB bar. Note the metal bar oil tank below the muffler, with a slightly corrugated surface - this is one of the characteristic marks of the Chinese 45cc chainsaw |
The Baumr SX45 is a 45cc petrol chainsaw, based on a standard Chinese model that is marketed under many brands. In Australia brands include Baumr, Giantz, Rockwell, etc., and there are a range of other brand names used overseas for the same basic saw. The well-known Chinese chainsaw parts online shop Huztl.com sells this saw as a Joncutter G4500. There are various minor variations in the cladding of the saw under different brands, but the essential parts appear to remain the same.
Is the SX45 a copy?
I expected, when I bought the SX45, that it would be a copy of a big brand saw - probably a Husqvarna (the Baumr SX82 appears to be a close copy of the Husqvarna 372). It does have some Husqvarna design characteristics (like having the carby on the same chassis as the motor), but as far as I can see it isn’t a close copy and doesn’t have interchangeable parts with any particular big brand saw. For example, the piston diameter of 43mm is not shared with any major brand saw I can find. The clutch drum doesn’t match any old-brand saw I can find either (internal drum diameter of 68mm, bore 15mm) but is shared by many Chinese saws and are easily bought online.
The professional saw
Roughly speaking, chainsaw designs are divided between professional and consumer. Professional saws have a metal (I hear it’s a magnesium alloy) crankcase coming in 2 halves with a vertical joint in the middle. This allows easy and quick servicing or replacement of piston and cylinder. The metal crankcase casting also forms a chassis for the saw and includes the bar oil tank. The chain bar studs are threaded into the metal chassis, and the cylinder is bolted down onto the crankcase. This design is strong and easy to repair and is used by many manufacturers for their professional saws. Big brand manufacturers like Stihl and Husqvarna sell professional saws for 50% to 100% higher prices than their consumer saws, which is worth it to professional users.
Consumer saws are quite different: they have a plastic frame with a metal engine inside, using only just enough cast metal to form a cylinder and crankcase. The chain bar studs are screwed into a plastic moulding. These saws work well but as they age they’re less durable and more difficult to repair.
Despite its low price, the SX45 has a professional type of design, with a metal chassis and easily unbolted cylinder. I’m not saying it’s a “professional saw”, but the design gave me some hope it’s a unit that could be maintained and repaired for a long and productive life.
Spare parts
Machines wear and break. Any tool I depend on needs to be repairable, which includes having access to parts at reasonable cost.
Parts for this saw are easily available from several sources including Aliexpress, Ebay and Huztl. They are often listed with titles including “4500 chainsaw” or “Chinese 45cc chainsaw”. All the usual parts are cheaply available, including clutch drums, clutches, ignition modules, cylinder and piston kits, carburettors, etc..
Huztl stocks some parts, including outer panels, clutch cover, etc., for their Joncutter 4500 which I expect would fit the SX45, but strangely not the clutch drum - a frequently changed part.
This easy availability of spare parts indicates that there are a lot of people - somewhere - repairing these saws. That’s a good sign for its essential quality as a machine.
First impressions
I was pleased with the saw, on arrival. It seems strongly built and I like the metal chassis. The saw started easily after fuelling and oiling, and was tuned slightly rich as a new saw should be - this increases lubrication of the piston and cylinder and reduces the top speed while running the saw in. After a few tanks of fuel the carby can be leaned out slightly, to get a little more power and make a bit less smoke.
With full tanks and a 13” bar with chain, the SX45 weighs 6.5kg. This is 5% heavier than a Stihl 024 at 6.2kg, but the SX45 also has an engine with just over 5% more cc’s.
The rewind starter is a bit strange: it seems to have 2 springs. The action of pulling the starter cord does not directly turn the crankshaft: a second spring seems to take up the tension, then crank over the motor with a delayed effect. This is a bit annoying to me - you can’t really feel what the compression is like. Some new Stihl consumer saws have a similar mechanism, maybe it compensates for the ongoing decline in consumer arm strength. I’m sure I can modify it if it breaks or annoys me too much.
Problems
If you’re going to buy cheap saws like this, you can expect to have some problems to solve - a bit like if you buy a 2nd hand saw, but better because you have a warranty if the problem is bad enough. I accept that if I buy a cheap saw or a kit saw, I’ll need to give them some attention.
There are 2 types of quality problems with these saws. Firstly there are the predictable and consistent ones from bad planning or design: the main one is the bar gauge (a problem I expected and which I expect all these saws to have). Secondly are the random problems of poor quality control, for example I had an off-centre clutch drum (a real surprise, but I expect it is rare).
All the problems I’ve had so far were easily remedied.
Chain bar gauge problem
The few Baumr chainsaws I’ve seen share a problem common with many Chinese chainsaw bars: the bar groove is way too wide for the chain. This is a design/planning problem, that I think all these saws can be expected to have, even though it could be solved without being more expensive.
The SX45 is sold with a chain that is 1.5mm (.058”) gauge (the thickness of the drive links that slide along in the bar groove). However the groove in the bar is way too wide for this, making the supplied chain very sloppy in the supplied bar. This would probably work okay for a while, but would soon enough give trouble as the chain leans to one side and the bar has trouble following in the cut.
There are two effective solutions to this bar guage problem. The best solution for most people would be to get another good quality bar with matching chain - I give more detail at the bottom of this post.
The cheap and more troublesome solution is to install a chain with a bigger gauge into the supplied bar: a 1.6mm (.063”) gauge chain fits easily. After the paint was worn out of the groove by the chain (in the first session of cutting) the 1.6mm chain was loose and the bar groove needed closing. This isn’t hard to do: have a look at my video on hammering and dressing chainsaw bars:
https://www.youtube.com/watch?v=O1gyOhSIu-c
Periodic hammering and dressing is part of using cheap Chinese bars - get used to doing it if you don’t want to buy expensive bars (which will eventually need the same treatment if you want them to have a long life).
Bar length
 |
| Here's the SX45 with supplied bar (soon to be cut short) |
For my thinning saws I like a 13” bar which carries a 56 drive link (DL) chain (.325” pitch). A short bar gives the saw more power (less bar friction), makes it lighter and safer and the shorter chain gets better lubrication.
 |
| One of my usual 13" bars above, the SX45 supplied bar below |
Little quality problems
There have been a few little problems with the SX45 that I’ve fixed, but not everyone might have them. Here they are.
Off-centre clutch drum
I was pleased to see that the clutch drum supplied had a rim sprocket. This is the “professional” type of clutch drum, where the part that drives the chain - the rim sprocket - can easily be replaced without wasting the whole drum.
 |
| See the rim sprocket in there behind the clutch? |
 |
| Here is the rim sprocket on top of the matching clutch drum |
To change sprockets on the SX45, you need to remove the centrifugal clutch - this saw has an “outboard” clutch, with the sprocket behind the clutch and clutch drum (modern Stihls and many Huskies have an inboard clutch so you can change sprockets without removing the clutch). Removing the clutch is done by spinning it clockwise off the crankshaft (it is threaded on with a left hand thread). To do this you need some sort of tool to engage with the clutch and turn it. Suitable tools are easily available on Ebay, Aliexpress or Huztl (here's a link to the Huztl clutch tool). I usually drive off clutches using an impact driver.
Here's a video on how to remove the clutch
 |
| This is a clutch removal tool sold by Huztl for some Husqvarna models. It works fine for the SX45, driven by an impact driver and a 3/8" socket adapter that fits straight into the back of it. |
 |
| Here's a tool sold on Aliexpress specially for removing Chinese chainsaw clutches. It's made for manual clutch removal where you screw the plug on the right into the sparkplug hole to lock the motor, and turn the 3-pronged tool with a spanner. I haven't tried it yet but I expect the 3-prong tool would be easily driven by an impact driver and a socket, thus avoiding the need to lock the piston with the plug. |
 | ||||
| Here's a clutch removing tool I made from an M12 connector nut with some pieces of spring steel welded on. It was easy to drive with an impact driver and 19mm socket |
 |
| These are sold on ebay as "socket adapters" and are great for removing chainsaw clutches along with a suitable socket or clutch tool |
How to re-assemble the clutch (when the spring and weights come apart)
Air filter joint problem
 |
| Here's the air filter as supplied, with O-ring in place. This doesn't seal well enough to keep out sawdust |
The air filter has an O ring that tries to seal it to the carby, but I found this let in a lot of sawdust, which you could find stuck to the rear inside face of the carby throat. That’s not good: in time, especially if working in dry, dusty conditions, this would risk causing wear to the engine.
I tried adding an extra O ring, but that didn’t help. What did help was to cast a gasket in the filter: I carefully cleaned the filter in the sealing area with isopropyl alcohol and degreaser, dried it, then squeezed in a layer of polyurethane sealant (I would have used silicone if I had some). I then sprayed a light layer of oil on the carby (to stop the polyurethane from bonding to the carby), pressed the filter into place and tightened down the filter cover. Since then I’ve had no more dust getting in.
 |
| Here's the top of the carby where the filter attaches. I spray light oil over this area before fitting the filter with a made-in-place gasket |
 |
| To form a gasket, I take out the O-ring and put polyurethane sealant into the space around the spigot. This is black Sikaflex 11FC. This picture shows the gasket after it has set and I've prised the air filter off the carby. |
 |
| Here's the freshy formed gasket after trimming off the surplus polyurethane |
Oiler vent problem
On the second SX45 I bought, I had trouble with the bar oil flow. It didn’t oil well at first - it seemed to have trouble priming the pump. I tested it the usual way by revving the motor while pointing the bar at a suitable surface and watching for oil to spray onto it. Loosening and retightening the oil tank cap seemed to provide a momentary flow of oil, that soon dried up. This suggested a blocked oil tank vent: if air can’t get into the tank, the oil has trouble getting out. Same happens with chainsaw fuel tanks.
 |
| This is the oil pump chamber of the SX45 - note the bar studs on the right. The red arrow points at the little rubber duck bill oil tank air vent - it lets air in when the oil is pumped out. There is usually a foam plug covering the duck bill. |
It took me a while to find the vent, hidden in behind the oil pump cover, behind the clutch.
The vent was behind a little foam plastic plug (and a random piston pin clip apparently stuck in the hole on the assembly line). It was a little rubber “duck bill”, that wasn’t able to quack - the end was blocked. I cut a sliver off the end of the duck bill and pushed it back into place. After that, the saw oiled fine.
Ignition switch
We've had several ignition switches fail and require replacement. These are easily and cheaply found on Aliexpress. It's easy to put a new switch in upside down: remember that the saw stops when the switch is closed, so you want the switch to be off /open in the up position.
Front handle
Some friends of mine who use these saws frequently bend and sometimes even break the front handle. This handle is rather too lightly made of a soft aluminium material. This bending tends to happen when the saw is pinched in a cut and wrenched backwards. Replacement handles are easily and cheaply bought on Aliexpress. I haven't had this problem myself.
Bar pattern
The chain bar on this saw uses the Husqvarna small chainsaw bar mount pattern: the slot for the bar studs, the holes for the chain tensioner, and the oil feed holes match the pattern in smaller Husqvarna saws. This is important to know if you want to buy a good quality bar for this saw (like the GB bar).Here’s a link to a catalogue of chainsaw bar mount patterns: http://www.acresinternet.com/cscc.nsf/673d78ec01557aea88256b00005457e6/e39f46cf37dbe4a088256e0d0051dd49?OpenDocument
Opening the engine
 |
| Here's the cylinder and carby of the SX45 |
The SX45 chainsaw engine is really very easy to repair. It took a few minutes to remove the top cowling, unscrew the carby, unbolt the cylinder, and get down to the piston.
I measured the bore and stroke:
Cylinder dia: 43mm
Stroke: 31mm
Piston pin diameter: 11mm
This works out at 45 cubic centimetres (some of these cheap saws don’t have the cc’s they are sold as, so it was interesting to check).
The piston pin clips are a very common source of failure on cheap chainsaws. These are the spring wire clips that hold the piston pin in the middle of the piston. Sometimes they aren’t well installed, and fall out when the saw is nearly new - this happened to a neighbour’s Baumr SX82.
 |
| This is what the piston pin clips look like in the SX45 |
 |
| This is what the clips look like after the centre tail is cut off |
I now use the technique of other people building Chinese chainsaw kits, and cut the tails off my piston pin clips (I use a cutting disc in an angle grinder). Any time I’m opening up a chainsaw cylinder, I also check that the clips are tight in their grooves. The SX45 had “e” shaped clips so I took them out and cut off their tails.
Re-assembling the SX45 was quick and easy. A generous taper on the bottom of the cylinder skirt makes it easy to insert piston and rings (make sure the rings are aligned with their pins).
What to do to an SX45
These are my recommendations for upgrading an SX45 into a long-lasting, hard working chainsaw:
- Put a reasonable bar and chain on the saw - the setup supplied will be too sloppy to work for long (the bar groove is way too wide for the chain). I recommend a 13” bar. See below for more details.
- Cast a silicone or polyurethane gasket to seal the air filter to the carby
- Check the carby tuning. The second SX45 I bought was tuned a bit lean on the high speed jet (adjusted with the H screw). Lean tuning like this risks burning the engine. See carby tuning instructions at the end of this post.
- Buy a 4mm T-handle allen key for servicing the saw - a small L-shaped allen key is supplied but is clumsy to use.
- Buy or make a clutch removal tool so you can remove the clutch to change sprockets or service the oil pump.
- If you’re game: open the engine, cut off the tails on the piston pin clips and check they’re well seated.
- be prepared to replace the fuel hoses when they perish.
Using a 13" GB bar
I bought a couple GB bars for these 45cc saws. This was a 13” bar to fit Husqvarna, .325” pitch, 1.5mm (.058") gauge, GB product code UHL13-58LH, costing just over $50 with a chain. I was a bit surprised to find that this bar was a little wide gauged (the slot for the chain was a little wide) from new, and fit a 1.6mm (.063") gauge chain from new. I am now running only 1.6mm gauge chains in it. Both bars had the nose sprockets fail with brittle breaks, but I never got around to making a warranty claim.I don't know if all their bars are like this, but I recommend you try a 1.6mm gauge chain in the bar, perhaps after running with a 1.5mm chain for a while, and perhaps plan on using 1.6mm gauge chains in the longer term.
FYI as a rule, Stihl chainsaws with .325", 3/8" and .404" pitch use bars and chains with a 1.6mm gauge (.063" in American language), and Husqvarna uses 1.5mm (.058"). If a 1.5mm gauge bar is worn, it can be good to use 1.6mm gauge chains, but most bars will eventually need hammering and dressing.
With all chainsaws, it's best to start with 3 chains, and rotate them as they wear out. When all the chains' teeth are sharpened away, get 3 new chains and change the drive sprocket on the chainsaw.
13" bars for this saw take a chain with 56 drive links (56 DL). If you do a bit of chainsawing, I recommend learning how to punch and rivet chains yourself, so you can shorten or lengthen chains, as well as being able to buy a roll and make up loops cheaply from new.
Tuning the carburettor
Here's what the manual has to say about tuning the carby. Pretty good instructions really:
The adjustment screws are generally located on the starter cord side of the unit. The high speed and low speed mixture screws are generall marked "L" and "H", respectively. In the adjacent image, idle speed is (A), low speed mixture is (B) and high speed mixture is (C).
Factory Settings
Each adjustment screw has a general "factory setting", which is measured from the adjustment screw being rotated "IN" (right / clockwise) until fully seated (but not tight). From this point, the setting is made by counting the number of full rotations of the screw "OUT" (rotate left / anti-clockwise). Factory settings are:• Idle Speed – Approximately 5 turns out.
• Low Speed Mixture – Approximately 2.5 turn out.
• High Speed Mixture – Approximately 2 turns out. Use the factory settings as the basis for tuning. Set all adjustment screws to factory settings, then test the engine before further tuning. Use a suitable flat-blade screwdriver and ensure that the screwdriver is properly engaged with the adjustment screw before rotating.
Tuning
1. Start and allow the engine to idle uintil it is warmed up – tuning a cold engine will result in rich running when the engine is warm. If the engine does not idle, use the throttle to keep the engine running ("blip" the throttle; do not run the engine continuously at high speed).2. Adjust Idle Speed – Rotate the adjustment screw one quarter (1⁄4) turn at a time – rotate "IN" (right / clockwise) to increase idle speed; rotate "OUT" (left / anti-clockwise) to reduce idle speed. Set the speed so the engine idles as fast as possible without engaging the clutch. Never set the idle so the saw chain rotates when the throttle is released. If the engine will not idle, adjust the low speed mixture (step 3).
3. Adjust Low Speed Mixture – Rotate the adjustment screw one quarter (1⁄4) turn at a time – rotate "IN" (right / clockwise) to lean the low speed mixture; rotate "OUT" (left / anti-clockwise) to richen low speed mixture. Rotate the screw IN until the engine begins surging or wants to stop – this is the lean adjustment position. Make a note of the number of rotations of the screw to reach the lean adjustment position. Then, rotate the adjustment screw OUT – the engine should start running better. Keep rotating the screw OUT until the engine starts to load up – this is the rich adjustment position. Make a note of the number of rotations of the screw to reach the rich adjustment position and compare it to the lean adjustment position. Then, rotate the screw IN to a position where the engine idles best – it should be about midway between the rich and lean position settings. At this point, you may have to re-adjust idle speed (step 2).
4. Adjust High Speed Mixture – Rotate the adjustment screw one quarter (1⁄4) turn at a time – rotate "IN" (right / clockwise) to lean the high speed mixture; rotate "OUT" (left / anti-clockwise) to richen high speed mixture. Rotate the screw OUT until the engine begins slowing and running roughly at full throttle. Then, rotate the adjustment screw IN – the engine should start running better. Keep rotating the screw IN until the engine reaches maximum speed. Then, rotate the screw OUT one eigth (1/8) to one quarter (1⁄4) of a turn to richen the air/fuel mixture for engine cooling purposes.
Breakdowns
So far my only breakdown of an SX45 motor has been very simple to repair: mud wasp nests in the muffler. The 2 round pipe exits for the muffler suit mud wasps very well. |
| Cooked mud wasp nests in both muffler exits - easily remedied with a screwdriver |
Links
Here's a video of a bloke fixing a Chinese saw of the same breed, that wouldn't run because of a missing flywheel key (messes with the timing):
