What I Learned Porting an Earthquake

[drf255]

Nice work Chris.

Thanks for sharing.

 

[Chris-PA]

Little booger was tossing some wood strings and yet never looked it even started to foul the clutch cover.
In that 2nd vid, the light is on the stream of noodles and a bit before mid-vid, You'll notice how quick that easter-bunny nest is growing.

As for the transfers? Somewhere else (RC plane?) I saw a fellows cylinder that he had
done by clamping it on the drill press and doing a bit touch-off in the ports
Because of not having a rt angle head.
While you're trying this, You might want to use a notched stick or something
to reach into the bore and support to cutter shank
and help prevent it from kicking out of the port IF it happens to grab a little.
if it swung out, it beat the jug to death before you could even think "aw #@%*"
heck, a hunk of wood fitted just like an arbor for turning the base flange,
Would be nice to have in there.
who knows, might even be able to drill the diagonaly and use something to poke down to and influence the cutter a wee bit
or even run the cutter itself, down the angled hole.

Yeah, they clear noodles quite well. That's why I made that bumper on the front, as I end up noodling with it quite a bit - I use it to block up the crotches and knots for the small stove, which takes wood up to 14". The front of the case has sorta-dogs cast in and they get in the way noodling.

I considered lot of schemes like that for doing the transfers - some sort of long reach small diameter end mill might work.

Wasn't there a 50cc~ish engined one somewhere?
[[ I may have to duck a few scored pistons being thrown at me for asking this ]]
But where's the contender to try knocking the Husky 346 off of the throne?

The 45cc units are based off of the Zenoah/RedMax G5000, and I have seen them made up to 62cc. There are so many variations of that design being made in China. I have no way of knowing but if you totaled all of them I would not be surprised if it is the highest single model of chainsaw sold anywhere. The limitation with them is that the original used a Walbro WT carb, and the clones seem to stick with that design - pretty small for over 50cc.

Zenoah designed some good saws but was never able to get the volume or market share. A lot of those designs live on and probably sell higher volumes as Chinese clones than they did for Zenoah.

 

[Chris-PA]

I like the exhaust height......but would like to think that an opening point of 120 - 118 on the transfers would be great.

That's interesting - that would be a blowdown of 14deg?

I was thinking about that and realized that because I have trouble with transfers (unless they have covers), and I'm working on newer homeowner saws, I often have larger blowdown angles than are discussed here as those larger angles are part of how they reduce scavenging losses. In my playing around I have been able to make a couple of saws run pretty well with longer blowdown and longer intake duration - it may not be as much as I might get, but I like the idea of reduced scavenging losses.

The small BD angles do work nicely on stratos so I don't doubt your approach may make more power.

 

[rattler362]

Very good read Chris Thanks'!

 

[Chris-PA]

Before I started posting here again (for some stupid reason I have not figured out) I did some more work on this saw and had documented it on another site. I figure I would update this thread though since the "Big One" (Earthquake thread) is rumbling again:

I hadn't used it in a while, but was out cutting since it was in the 60's in early December 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, 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. 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 was on a roll and didn't take and pictures of the result. 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.

 

[smokey7]

Good work on the toy saws!!! Determined is how I would describe you. I love a good challenge. I wonder how well you would do with that other jug you showed the pics of the much larger transfers? I'd like to see that saw ran in a limb bumbing environment. It's strong in the buck I just wonder how well it would do in its other uses. A1 job on the build except the pics you have shorted us of the finished ball nosed work on transfers. Good job man.

 

[Chris-PA]

I wonder how well you would do with that other jug you showed the pics of the much larger transfers?

Yeah, I've wondered that too. There's a lot more volume in those transfers, especially the exhaust side runners. In general I like the idea of lower volume higher velocity transfers, but I have no data as to which works better.



This is the jug of my 62cc G621 clone (made by the same company that makes the Earthquakes). It's got more volume too, but it's different in that the exhaust and intake side runners are more evenly matched. It runs very well.

 

[bikemike]

Put a pipe on it and it may draw more through the transfers