Author Topic: Finally Have My Ported Earthquake G3800 Clone Running Right!  (Read 473 times)

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Online Chris-PA

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Finally Have My Ported Earthquake G3800 Clone Running Right!
« on: December 12, 2015, 06:37:07 pm »
I have a 38cc Earthquake, which is a Chinese clone of a RedMax G3800 - only they modified it to meet emissions.  It's kind of an interesting contrast given that this is the saw Zenoah started with to make the strato GZ4000, and this is the alternate non-strato approach to meeting emissions.  It had modified port timing, lower volume transfers runners and a cat (think Echo and others).  So of course I ported it and got rid of the cat muffler for a modded normal one, but I could never get the thing to rev like I wanted.  I went through maybe 4 different tear downs, cut the jug, swapped the ignition to a Ryobi system and back again, swapped the carb and back again.  That whole adventure was documented here: http://www.arboristsite.com/community/threads/what-i-learned-porting-an-earthquake.270735/

I hadn't used it in a while, but was out cutting since it was in the 60's today and decided to run the Earthquake.  And.....it was a slug.  Well maybe that's extreme, but it still just didn't want to rev and the spool up was lazy.  That's been the persistent issue with this build, and while you can convince yourself it's pretty good, if you let it sit for a while and run other better saws it's pretty apparent when you pick it up again.  So I took it down to the bench and yanked the jug.

The first obvious thing was that it's been a head slapper.  There were two spots in the casting of the combustion chamber under the spark plug boss that looked like they slumped a little, and I had tried to grind them out when I decreased the squish, but they looked to have been just kissing the piston dome - maybe just enough to polish the carbon.   So that had to be dealt with, which I did by grinding some more on those spots in the the combustion chamber, and by a little filing on the top of the piston.  I also filed off the orientation arrow which they had cast on the piston crown, as it had left a neat little dent in the edge of the squish band!  Which shows that using solder to measure squish in a couple of spots isn't necessarily good enough, especially with a domed piston.

But the main thing was the transfers.  If you look at the pictures of the transfers I showed earlier ( http://www.arboristsite.com/community/threads/what-i-learned-porting-an-earthquake.270735/#post-5157085 ), I had only ever raised the intake side outlets (and the intake side transfers are quite small on this jug).  From what I have read they should be even, or the exhaust side ones should open first.  I was pretty convinced this has been the problem.  So I took some measurements and cut some card stock, and just hacked away with a small ball end cutter until I evened them all up.  It wasn't that pretty, but not that bad either.  I left the total transfer duration at 106 (21deg blowdown).

So I slapped it back together and took it back up just before dark - and finally it has the snap I wanted!  I even took some of the extra spark advance out I had put in to try to get the rpms up.  So all the stuff I tried - compression increase, squaring up the intake, spark advance, opening the lower transfers, opening the muffler more - none of it really addressed the sluggishness problem.  Those mods may have helped it to run like it does now, but but without fixing the transfers it wasn't good enough.  Which of course I had been told. 

I'll try to get a video of it now - it's finally what I expected it should be. 

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Online 3000 FPS

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Good deal Chris.   It was a good read.   I am not a big fan of the earthquakes but I know you love to tinker with these saws and figure things out so good for you.
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Online Chris-PA

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Thanks!  Really I'm a fan of Zenoah designs, and the clones are a way to get older models cheap.  Actually this saw was purchased as a parts mule for my GZ4000's for $35 delivered - but I've been playing with it ever since! 

Offline Cut4fun .

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Never ran the copies. But the ported 3800 redmax was super light and nimble for 38cc.  http://chainsawrepair.createaforum.com/redmax/redmax-3800/msg444/#msg444

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Online Chris-PA

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Ran it a bit clearing brush and bucking a bit of ash.  Throttle response was nice while cutting brush.  Took this video:

https://www.youtube.com/watch?v=B-12jcD7DYc

Once it got loaded in the cut it was running around 10,500rpm.  Seemed to run pretty clean - at least I didn't stink too bad like exhaust after running it today. 

Offline weimedog

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A great read, thanks for posting. :)

Offline Cut4fun .

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@Chris-PA   have you figured out why the copies weigh so much more then the redmax 3800 originals?

Sounds and looks good in the cut. Wonder if you could make the chain hungrier.  :P
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Online Chris-PA

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A great read, thanks for posting. :)
Thanks!

@Chris-PA   have you figured out why the copies weigh so much more then the redmax 3800 originals?

Sounds and looks good in the cut. Wonder if you could make the chain hungrier.  :P
I don't think do weigh much if any more than the originals.  My G621 clone weighs under 12.5lb, or withing 0.1lb of the original if what I've seen is true.  I never weighed the Earthquake, but it's lighter than my GZ4000's by a little, which is about right.  The difference between how much mag is in the alloy might make a small difference, but the alloy part of the G3800 chassis is so small it would barely be noticeable. 

The chain was Tri-Link lo pro semi chisel.  I had touched a rock with it cutting brush earlier, so it had just been filed and the depth gauges set.  That was a 16" bar on a 38cc saw cutting a pretty hard piece of ash - I feel like that was all it's got and a more aggressive chain would just bog it. 

Offline Cut4fun

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A great read, thanks for posting. :)
Thanks!

@Chris-PA   have you figured out why the copies weigh so much more then the redmax 3800 originals?

Sounds and looks good in the cut. Wonder if you could make the chain hungrier.  :P
I don't think do weigh much if any more than the originals.  My G621 clone weighs under 12.5lb, or withing 0.1lb of the original if what I've seen is true.  I never weighed the Earthquake, but it's lighter than my GZ4000's by a little, which is about right.  The difference between how much mag is in the alloy might make a small difference, but the alloy part of the G3800 chassis is so small it would barely be noticeable. 

The chain was Tri-Link lo pro semi chisel.  I had touched a rock with it cutting brush earlier, so it had just been filed and the depth gauges set.  That was a 16" bar on a 38cc saw cutting a pretty hard piece of ash - I feel like that was all it's got and a more aggressive chain would just bog it. 

Thats what I was wondering how it would do with a PS PS3 chain on it.  You got any to try?
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Offline Cut4fun

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Just trying to save some paper weights listed.  Paper weight listed for 5000 is  accurate as I owned one.

G3800AVS 9.1lbs

GZ400 9.7

GZ4500 9.6

GZ4000 9.5

G5000AVS 11.2
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