What did I buy? (China saw content warning)

[Leafy]

So in the quest to follow ChrisPA's advice on a cheap project I was trying to put a G621 clone so I bought this https://www.ebay.com/itm/X-BULL-20-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 thinking it was one with slightly different plastics the clutch cover looked way too small to be hiding an external clutch of a G5000 clone. I figured I could buy a 30 pack of top ends kits for $6 each on alibaba and I could try crazy *s-word porting for laughs.

Then when it arrived, sadness, I didnt realize the G5000 clones came as a 62cc.

But the case does kind of look like a G621?

And the transfers dont look like the other G5000 clones. I didnt feel like I needed to do anything to them, except they didnt deburr the transfers before chroming it so I did have to hit the transfer with the stone after tapering the ports. You can see the exhaust port was dead flat on the top and all I did was make it as wide as I could to clear the exhaust bolts. The bore is 45mm, which means the stroke must be 38mm if the stated displacement is correct.

Then I just took the flash off the intake elbow and tried to match the carb as well as I could. Throttle plate is like 14mm, venturi looks to m 13mm based off that. This is a WT carb? Theres no casting marks on the carb anywhere besides the junon lable, and really on any part of the saw.

And then I pillaged the ports with my makita die grinder. I tried to turn the rpm all the way down to not take too much out but instead I just bounced around the port and made a mess, learning I guess. All I did to the exhaust was widen it from 25mm to 30mm, the pockets for the exhaust bolts are 35mm apart so thats as wide as I wanted to go. For the intake all I did was widen it the same amount, make the bottom of the port flatter and match the rubber intake boot.

Muffler was already really open,I wouldnt have ground off the crimp if I could do it again. All I needed to do was make the inlet larger than the exhaust port on the head, and add those holes under the cover. And since I opened the thing up I just drilled out the "baffle" for the sake of it. I kept the bottom bit of crimp and then just tig'ed it back together with no filler and like 20 amps. I also had the belt sand the *f-word out of the flange side so it had a prayer to seal without the gasket, wasnt even in the ballpark of flat.

So basically I was disappointed as soon as I saw the external clutch, so I didnt time it. I did pull the base gasket and didnt check squish either way, just said *f-word it. Anyways I bought it because a 30" spruce fell across the path in my woods over the winter and it would have taken a month of sundays with my mac3200 to cut that up to move, so I figured I'd use this anyways. I knew the chain would be crap but I didnt want to buy a new chain until I knew exactly what was going to be on it, being a chinese crap saw. Its a 76 link .325 chain by the way. Holy hell, how do you suck so bad at making a chain? It came in a bag that had Oregon graphics on it, looked like the guy didnt give a *f-word grinding it, some of the teeth were burnt, some were not sharpened far enough, and some it looked like he just forgot to hit at all. I got at it with the roller guide and it just got worse. Some of the teeth are so hard the file just skates over them unless you really bear down and work for it, some were so soft that they clogged up the file like they were aluminum, heights were all over the place. After the first tank of 40:1 the damn thing needed to be sharpened on the soft teeth, like yeah they're that bad.

Anyways it actually runs pretty great after leaning it way way out. Oils a reasonable amount out of the box. I actually can't lean on it hard enough to stall it in the wood without using the dogs, which is pretty impressive to me. It seems like it cuts best at a slower speed, I should take a video and use the spectrograph app to figure out the rpm, but it sounds like it drops ~2k rpm from free rev to where it seems happiest when cutting, I bet it would move some serious wood with a non *s-wordty chain.

But here's where the question is, should I change to a 3/8" chain and just deal with having a torque monster saw and lay on it, or is there a carb that uses similar links and has an external impulse line I could fit fairly easily. Linkage and impulse/fuel lines are the big concern since I can 3d print a different intake runner out of nylon or urethane, then I would consider actually timing it, doing math, and changing port timing.

 

[Leafy]

Update. I tached it out at 10300 free rev and 9k in its happy place in the cut. The chain still blows and starts to suck like after 2 tanks. I do have a whole gallon through it now though. It has a d176 mount and uses a 325 x 058 x 76dl chain. I broke down and made a bailey's order for a 3/8 d0009 mount 20" bar and a 72dl still semi chisel chain, I also threw an Oregon 78dl 325 chain in there to see if that would be close enough. It seems to take small spline sprockets so I bought a 3/8 7t and a 325 8t to try.

I also bought a he18a carb to try and cram that in.

 

[Leafy]

Good news bad news post. Good news I found you can get an air filter that doesnt leak and a 3 port muffler on aliexpress. If the 3 port is empty like this one I dont see any reason to cut open a muffler for this style saw. More good news, the HE18A basically bolts in, you need to cut the husky throttle lever part off, bend the inpules nipple, and drill a hole for the throttle linkage. It is like 3/16th longer than the standard one so the air filter cover doesnt quite line back up, but I can trim the nut hole to make it line back up. The idle screw also doesnt line up well, could trim the plastic here too.

Cut here after you take the plastic cam out. If any of the husky 365 guys see this picture they're going to beg me to take the metering cover off to see if its a 2 jet zama c3m for $12.

I drilled this hole by taking the plate off this carb and the stock carb, lining up the shaft flats and drilling it. Cant just swap the plates because they're different diameters.

Correct routing

Starts way easier than with the stock carb, revs up lots faster really snaps up. I'll put it in wood tomorrow and tune the H.

Actual bad news. I checked the stroke only 32mm, so its only a 52cc saw. We'll have to see what the ebay seller does for me.

 

[Leafy]

Since there's few people watching this now I thought I'd update. With the new carb it free revs to 11600 and still 4 strokes so the stock carb was still choking it but the 17mm venturi is probably too big. It seemed to gain torque in cut anyways but it would probably be better with a 15mm carb. Next thing to do would be an intake that matches the throttle plate since this intake is smaller than that. But I went be doing that.

Seller realized the their saws aren't even close to their advertised size and they're refunding me I'll put to back to basically stock and send it back. Maybe I'll buy another if I want a 50cc saw by the fact they use a weird size chain 76dl makes it not really worth it compared to a huztl ms260.

 

[Leafy]

Screw it, this is a build thread, someone just move it to the general section. The ebay seller realized he probably pays the factory in china less for this saw than the return label to him so he refunded me and told me to just keep the saw. So I figured I'll do more work on it. Port timing is hilarious.

Exhaust 111 ATDC total area 360mm^2 mean 180
Transfer 129 ATDC total area 160mm^2 mean 108
Blowdown 19deg Exhaust bd area 110mm^2
Intake 105 BTDC (closes 75 ATDC) total 300mm^2 mean 125

Lol rough calculations says thats optimal for like 4-6k rpm.
It looks like I need to raise the exhaust to 100 degrees and widen the transfers from 20mm wide to 30mm wide and widen the intake to as wide as the exhaust. I'm also going to have to take a little off the squish band of the piston, guess its a bit of a head slapper, probably should have checked squish.

Oh and the answer to the silly chain length. Looks like the 20" bar isnt really 20" but its a bit bigger than an 18". The other bar pictured is a d009 mount 20".

I have the improved husky HD style intake coming hopefully tomorrow along with the 3 port muffler. I need the splined clutch drum to show up to use the 3/8 bar on it.

 

[Wonkydonkey]

Where and How did you work out the timings and best rpm.

Cheers.

 

[Leafy]

I found a copy of Macdizzy's spreadsheet, and I can't find my source online for it any more. It's designed for motos but has everything required for piston port motors except for describing optimal mean intake port area which I just figured should be around 80% of the exhaust give or take 40%. I figure with the too big carb I'll be less sensitive to the intake port of it is too small.

 

[Wonkydonkey]

I’ve seen macdizzys, but not read through the whole lot


http://www.macdizzy.com/cylinder_map5.htm

Cheers

 

[Leafy]

I actually found an even nicer spreadsheet that calculates the blair and jennings methods at the same time. Its kind of nice, and funny how difficult it is to get an actual engine to make both happy at the same time. This one you can download here.

I think I've settled on timings now.
E 100deg cut to 32mm wide for the top half of the port, leave the bottom the same.
T 118deg Just cut another 1mm on the opening and also try to get more of this from filing the corner off the piston
I Keep at 105deg abdc, but widen as much as the piston skirt will allow.

This gives 43deg of primary compression and 18 deg of blow down. Heres the screens of the inputs and results.

 

[Leafy]

So I ended up close to the timings I was looking for, I ended up with the below.
E 98*
T 120*
I 105*

But the intake kind of starts to open on the side at 95*, I think I need to put some JB in that corner to get the primary compression back up maybe, because its easier to bog now. I'm also not sure the carb is quite tuned right or maybe its still seating the rings I kept noticing it 4 stroking in cut after I cut, then I'd lean it out a /16th of a turn and it would be good for a while. Now its free reving at 11900 rpm and 10500 in cut, so I gained 1500 rpm in cut. I did change the chain to an oregon LPX chain.

Here's my setup for the popup, I just took the bumps off + a bit more eyeball of about 20 thou from the top fo the bumps.

Exhaust port with dykem to see how flat I was.

Finished port from outside.

Looks a lot bigger from this angle eh?

Here's the piston, there was such a huge amount of space between the top of the piston and the top ring land that I got all 9 degs of transfer change on the piston.

Noodled up some fire pit wood. Went good. You can see the paper airfilter upgrade. I think it needs the latch on air filter cover style, I asked the aliexpress seller if they could get the covers that matched the air filter that might be pushing it.

 

[Leafy]

I realized that the holes under the nut plate were worthless and basically covered whenever I was actually cutting. So I put a different cover on to really block the holes and added a 3/4" od tube to this one, it was what I had. It got me to like 110% port area from like 50%. Hopefully it helps. I have a single port muffler on the way, 2 tubes this size would be correct for this saw I think.

Then I did a silly thing. Printed a new intake manifold. This was a first one, I measured wrong or something so I had to make a new revision that let the "firewall" get closer to the cylinder.

After moving the carb further forward I had to extend the throttle rod. You want to unbend the bend I'm pointing to, about 5mmish.

Also had to trim the divider out of the port to be able to get to the L.

The cover almost fits now, but not quite. I found the high rise version of the covers from the same seller as the air filter so we'll see how those work.

 

[Leafy]

So now it still 4 strokes at 14500 rpm, lol. Guess it liked the bigger intake. Though at that rpm the 4 stroking sounds weird, like a miss fire, maybe the Chinese coil can't keep up I turned to back down to like 14200 and cut a tank worth of fuel with it. Way more fuel efficient than when I had that mess up in the intake porting and no fuel in the air filter.

 

[cus_deluxe]

Your intake opens how many degrees before tdc?? Dont quite understand what you mean by

E 98*
T 120*
I 105*

But the intake kind of starts to open on the side at 95*

.
What were you hoping to accomplish by grinding on the intake roof? Sorry, theres just a lot of puzzling things going on here it seems like.

 

[Leafy]

That's closes degrees after TDC. And I didn't grind on the intake roof besides where I slipped with the die grinder.

 

[cus_deluxe]

Just never heard it described that way,

Intake 105 BTDC (closes 75 ATDC)

this is toward the beginning and had me cornfused. And the pic of the intake just looked like the roof had been ground. I can relate to the grinder slipping and chattering haha.

 

[Leafy]

Just never heard it described that way,

this is toward the beginning and had me cornfused. And the pic of the intake just looked like the roof had been ground. I can relate to the grinder slipping and chattering haha.

Oh yeah that's when it opens btdc (abdc). I switched to closing atdc when I realized that was most important to how it relates to the transfers opening and creating primary compression and that's probably more important than actual duration.

 

[cus_deluxe]

So your still saying that the intake opens 105 before top dead center?

 

[Leafy]

Yes 105 atdc, 75 btdc, 105 atbc, and 75 bbdc are all the same point .

 

[Wonkydonkey]

 

[Wonkydonkey]

So, working this out backwards ....BBDC is before bottom dead centre,or 180* so 105 +75 =180

So your working from the bottom ? or just too mucho leaf in your pipe

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