Porting a Chinese G621 Clone

[Chris-PA]

First off, in spite of the homely color scheme, this is not a copy of any Sthil product nor does it have the name Stihl on it. It is a straightforward clone of a 62cc Zenoah/RedMax G621AV.

I picked it up for a couple of reasons: First, I wanted a project saw that was bigger than the 40cc saws I've been playing with lately. Second, I've like the Zenoah G621 for some time, but they don't come up often and they usually go for more than I think they are worth (and more than I can justify). Third, I have read all the fuss about Chinese clones, and wanted to see for myself – my other data point is the Earthquake. Last, the G621 shares bars and chains with my McCinderblock and I have some spares. So that is the justification. It was $210 to my door.

My initial impressions were not too favorable. I figured the castings would be aluminum, that it would have lots of molding flash on the plastic parts, casting flash on the aluminum and probably indifferent assembly quality. I planned to tear it down before even running it. However, it was obvious that something was misaligned in regard to the air filter housing (I forgot to take a picture of it), as the bolt didn't line up with the hole in the cover, and the whole cover was shifted over to the clutch side when installed by almost 1/4”. I tried messing with the A/V bushings, but that was not the problem. There were cracked and bent fins on the top of the jug – not a functional problem but ugly.

Also, the bar was awful, with rivets that were not flattened and the sprocket tip was not aligned with the bar. The “tools” provided would be better termed “litter” if you saw them lying about.


To top it off they didn't even step up to the good TriLink chain, rather some awful looking “DOKIO” stuff. Still, I expected a project and figured I'd make of it what I could. Cutters are not even close to the same length on each side.



One of the first things I did to it was to spend an evening with an X-acto knife cleaning up the plastic parts. Simple and easy work, kind of like building model cars when I was a kid. It looked better after that. Then I took it to work to weigh it on the digital shipping scale, and got 12.4lb (12lb, 6oz.), which was considerably lighter than I expected. So that was a pleasant surprise.

 

[Chris-PA]

On to the tear down: Standard G621 – inboard clutch with rim drive (firsts for me). Muffler has decent outlet area with the 5 gills, and I can see there is an adequate hole size in the next baffle in, as well as the first baffle – I don't intend to modify this muffler for now.




These are not bar nuts! Must have gotten them out of some supply catalog.


My degree wheel made from a CD fits perfectly!

Stock timing duration:
E 162
I 150
T 124 (Blowdown at 19)

Exhaust port width is 54% of bore, intake is 46%. Unfortunately the squish is a 0.050”.

I'm impressed! All I'm going to do is drop and widen the intake and pull the gasket.

 

[Chris-PA]

Some casting defects in the exhaust port floor (removed them):



The ol' HUAYI carb – doesn't look bad actually. Probably a bit small for a 62cc saw, and I may look for a bigger on eventually. There is a bit of a ridge around the venturi that I cleaned off when I was reassembling it.





Chao Jing cylinder. Looks OK actually – a little rough along the edge of the transfer divider and around the ports.




Here's the opened intake port:

 

[Chris-PA]

Final timing numbers:
E 160
I 159
T 122 (Blowdown at 19)

Exhaust port width is 54% of bore, intake is 52%. The squish is a 0.035”, which is bigger than I'd like but I'm not ready to set up a fixture for turning it – maybe another day.

It turned out the alignment problem with the air filter cover was due to the oversized holes in the cylinder (or rather the location accuracy – the oversized holes let me fix it). Once I cleaned out the antisieze from the holes I was able to rotate it so that it was centered properly. Now the carb and filter stud are properly centered, and everything fits nicely:


The bar got the rivets peened and the tip straightened on the hydraulic press. It's still crap but might be serviceable:


And here's the finished product:


I did pry open the gills a bit:


It's an under 12-½lb 62cc saw with decent timing numbers. I barely even “ported” it, as the numbers were about where I would start anyway. The 24” bar makes it fall right on it's nose.

It started and ran, but while I was tuning it it stopped running on the H. So I pulled the carb apart and sprayed it out – then it ran great. It was too late to cut with it – maybe tomorrow I can get it in some wood before we get another foot of snow. It will be humorous to see how long the bar and chain last.

 

[zogger]

Nice write up! Looking forward to the in the wood report.

 

[Thommo]

The starter assembly on the Chinese saws seem to fail quite often and the air cleaners don't seal very well, but apart from that they seem ok. It will be interesting to see how the chain performs. The Chinese copy Carlton chains wear in the rivets so they have to be adjusted twice per tank of fuel.

 

[Terry Syd]

Neat project, too bad about the small carb. From the picture it looks to be a Walbro WA/WT clone. I think the maximum venturi size in that series of carbs is around 13.5mm. If a Walbro HD or Zama C3M could be shoe-horned into it you could get a 17mm venturi, which would be about right for that displacement.

The ports and timing look very good and with a bigger carb could likely be turned into a lightweight little weapon. I note the 19mm bar studs, do you think a Husky small mount bar could be worked onto the powerhead? I mention that because I put a lightweight 20" narrow kerf bar on a Stihl 029 (64cc) and the lighter weight and faster cutting changed the whole persona of the saw.

What's with the coils? It looks like there are two separate coils, one for the ignition and the other for what?

 

[Chris-PA]

The starter assembly on the Chinese saws seem to fail quite often and the air cleaners don't seal very well, but apart from that they seem ok. It will be interesting to see how the chain performs. The Chinese copy Carlton chains wear in the rivets so they have to be adjusted twice per tank of fuel.

I forgot to mention the air filter - the two halves don't seal worth a darn, so I will have to glue it together. I'll be getting a real one for it. And the chain is a joke - I will sharpen it properly just to see, but I don't expect anything from it. I have an older loop of TriLink that is a copy of Carlton, and it has been perfectly fine.

 

[Chris-PA]

Neat project, too bad about the small carb. From the picture it looks to be a Walbro WA/WT clone. I think the maximum venturi size in that series of carbs is around 13.5mm. If a Walbro HD or Zama C3M could be shoe-horned into it you could get a 17mm venturi, which would be about right for that displacement.

The ports and timing look very good and with a bigger carb could likely be turned into a lightweight little weapon. I note the 19mm bar studs, do you think a Husky small mount bar could be worked onto the powerhead? I mention that because I put a lightweight 20" narrow kerf bar on a Stihl 029 (64cc) and the lighter weight and faster cutting changed the whole persona of the saw.

What's with the coils? It looks like there are two separate coils, one for the ignition and the other for what?

Ahh, but that's the thing - it's an HDA clone. I looked at the clones of the Zenoah mid-sized saws (based on the the G5000), but decided against them because they used WT carbs originally. One of the guys on the Earthquake thread measured the carb on a 58cc and it was still 13.5mm. So I decided to go with this one even though I thought they were a lot heavier. So anyway, it should be no big deal to fit a bigger HDA eventually.

As for the ignition, I wondered about that too and did a little research. About 2/3 down this page is a good explanation: http://www.outdoorking.com/forum/ubbthreads.php?ubb=showflat&Number=37014&page=all. Basically, it is a CD ignition and the other coil is just to provide a high voltage power supply:

I'm not sure why they used it.

The bar is a D176 mount, and I have a couple of those. I guess with a rim drive I could switch to 0.325"? I'm a rim drive noob.

EDIT - the carb that is in it is a 15mm venturi

 

[Terry Syd]

Chris, that looks like no CDI system I've ever worked on. I don't see a set of points on the saw, according to the schematic, you would need a set of points with that system. Usually a modern CDI system has a solid state SCR to trigger the capacitor and the SCR is controlled by the voltage from another trigger coil. (Although I did convert a VW engine to a CDI system that used the old points as the trigger for the capacitor.)

Is there a manual for the engine? Perhaps that would have some more information.

 

[Chris-PA]

Chris, that looks like no CDI system I've ever worked on. I don't see a set of points on the saw, according to the schematic, you would need a set of points with that system. Usually a modern CDI system has a solid state SCR to trigger the capacitor and the SCR is controlled by the voltage from another trigger coil. (Although I did convert a VW engine to a CDI system that used the old points as the trigger for the capacitor.)

Is there a manual for the engine? Perhaps that would have some more information.

Sorry, I posted the schematic to show what the second coil is used for in general - I realize it is for a points ignition, but the actual "switch" (points, transistor, etc.) is a detail that isn't all that important. The IPL lists it as a "source coil", which I believe is consistant with the type of system shown in the diagram. Again, I don't know why they used it or what advantages it may have.

 

[Terry Syd]

If you get a chance, take a picture of where those wires go. Maybe they go to a capacitor, or maybe to a lighting system for night time work LOL!

A CDI system puts out a strong voltage spike and is a more reliable system for starting. Maybe they wanted to make sure that it never had a fouled plug/hard starting.

 

[CR888]

lnteresting thread Chris, nice pics and all. You love playing with cheaper saws and l hope it turns out well for you. AS member MCW has a bit of experience with chinese saws and he say its a bit hit and miss as far as getting a good one or not but he did specify that ALL the carbs were crap and failure to change one could lead to premature death of saw. He said changing the carb for a quality one was a must. l think that chain will cut better than you think. Good luck!

 

[w8ye]

I have a Japanese Zenoa 621 model airplane engine whereas the cylinder says Husqvarna all over it, the open port layout is like the one in these pictures and the cylinder wall finish is far superior to this clone.

The carb on my engine is a Walbro HDA-48

 

[diggers_dad]

Neat project, too bad about the small carb. From the picture it looks to be a Walbro WA/WT clone. I think the maximum venturi size in that series of carbs is around 13.5mm. If a Walbro HD or Zama C3M could be shoe-horned into it you could get a 17mm venturi, which would be about right for that displacement.

The ports and timing look very good and with a bigger carb could likely be turned into a lightweight little weapon. I note the 19mm bar studs, do you think a Husky small mount bar could be worked onto the powerhead? I mention that because I put a lightweight 20" narrow kerf bar on a Stihl 029 (64cc) and the lighter weight and faster cutting changed the whole persona of the saw.

What's with the coils? It looks like there are two separate coils, one for the ignition and the other for what?

Shindaiwa used a similar setup on their 488 series saws. What I refer to as the coil they call an "exciter coil" and the second part (the one the spark plug wire attaches to) is called the "ignition coil".

From what I've seen the coils didn't do too well on the Shinny's . There was enough of a failure rate that the Chinese are making replacements for them.

 

[Chris-PA]

I have a Japanese Zenoa 621 model airplane engine whereas the cylinder says Husqvarna all over it, the open port layout is like the one in these pictures and the cylinder wall finish is far superior to this clone.

The carb on my engine is a Walbro HDA-48

Yeah, the finish isn't that pretty, but it looks to be functional- we'll see!

The HDA-48 is the same size as this one. It looks like an HDB-8 will be the ticket. It has a 16.66mm venturi and a choke built in, with similar linkages. The needle screw heads are much longer, but that should not be a big deal.

 

[diggers_dad]

Wow what a piece of junk.

Depends on perspective. It's a new saw and the build quality isn't so great, but it is serviceable. 62cc's for a touch over $200? Not too bad.

I have enjoyed Chris's builds on the Quakes and he's a little over critical on some of the fit and finish; he seems to be kind of picky. I don't personally know him, but I'd say he's a little OCD and probably likes things neat and tidy. All that attention to detail results in some good write ups and VERY detailed information. I'll be using a lot of his information when I pick one of these up to experiment with. I'm glad he's sharing what he does as he does it.

Thanks Chris!

dd

 

[Chris-PA]

I don't personally know him, but I'd say he's a little OCD and probably likes things neat and tidy.

Someday I must pan back a bit so you can see the absolute crap hole that I work in! There is probably a pile of junk from every project I've ever worked on, with half a dozen more on top of it. When I need to get to the table saw it's like an archaeological dig. My desk at work is just the same - they gave up trying to get me to clean it up years ago.

BUT...

I am a little picky about how things fit together. This one is not too bad now. If it holds up I may order some small bits - A/V covers and air filter cover screw, etc. - from RedMax just so it looks a little nicer. But the air filter is like $37 ( ) so I'll be making this one work!

 

[diggers_dad]

If I find a junk RedMax with a bad p/c I'll send it your way so you can make your project look nice.

The guys like us with the messiest desks are usually the ones who get the most work done.

dd

 

[Jeff Lary]

Yes Chris nice job I am not for or against any tool or saw, but if you get enjoyment form what you are doing it's all good. I have said this before but it bears repeating, your stove will not burn any better with wood cut from a $50 dollar saw than it will with a $700 dollar one.
As far as Chris goes, I don't know him either. I will tell you this My son had a pp 255 given to him for me cause it was not running. Chris was a wealth of information for me to get parts for that saw. He told me that not only would 255 parts work but so would parts for about 4 other saws. Who the hell knows this stuff? Well he did and he saved me hours of frustration finding parts for the old girl.
Is it a 4 cubic inch Husky ? no it is a 42 cc carry on the Polaris Ranger trail trimming saw, and fun to run too. Thanks Chris for sharing all the information you have learned,... it helped me and many others I bet ! I hope he always reads my posts because people like him save my bacon quite often, and if you saw me you would understand how much bacon that is ! Jeff