230psi in a Poulan (42cc, wild thing, etc)!

[777funk]

I accidentally free ported my first cylinder with this thing. Bought a new cylinder and this time I went a little too far and reduced squish to almost zero. I can still squish solder, barely (very hard to turn past TDC). I took a little off of the outer edge of the piston top, just incase.

But what I was surprised to see is that I ended up with 230 psi of compression. The ring gap was bigger than I hoped for (about 0.020"), but that didn't seem to matter much. I suppose the pin bridges much of that. Is there such a thing as too high on compression?

 

[David Young]

what saw was this. did you test compression after you ran it? did it run ok what is the exhaust port at?

 

[dangerousatom]

Id be a little worried about the piston thermally expanding vertically ( 2-3 thousandths ) while the combustion chamber ceiling lowers once heated up. If your near zero clearance now somethings going to give once she hot.

Maybe recheck your squish with a full wrap of solider around the piston top ( hold it in place with a light brush of super glue ) and if the wife lets you toss the saw in the oven at like 200 for 15min before rotating w/most plastics removed. Otherwise Id heat up the jug till its good n hot.

If your running no gasket your all good IMO just find w/e is +10k thick and use it as a gasket.

 

[777funk]

what saw was this. did you test compression after you ran it? did it run ok what is the exhaust port at?

Just ran it today for the first time. It ran a little stronger than stock. It's still not a super strong saw. It's plenty for the 14" bar, but I was hoping to make it strong enough for an 18". It's the Wood Shark 1975. Same 42cc engine as the Wild Thing.

I didn't change the exhaust port other than a little wider. If I remember right, the saw ended up at 104 122 78 after bringing the cylinder down. I didn't change intake or exhaust. I did bring the transfers up a hair. I would like to try a bigger carb and see what happens. My MS250's carb has a wider throat than this thing and of course a decent amount more power. Seems like it's linkages are all different than this saw so it wouldn't likely be easy to mount it. I'll look at it when I get some time. All I really need is throttle. Should be able to feed it gas to get it started without the choke (at least for a test run).

 

[dangerousatom]

Id try porting the butterfly screw and bar before trying a larger carb. You create alot more intake room out of a tiny carbs vs a larger 80cc^ carb
.
.

 

[hacskaroly]

It's plenty for the 14" bar, but I was hoping to make it strong enough for an 18". It's the Wood Shark 1975. Same 42cc engine as the Wild Thing.

Well, it can be done, this guy ported his 34cc Poulan and is running a 36" bar on it...

 

[Jake Dykstra]

Lol. Then he cuts a 12 inch log.

 

[greystone mountain man]

Lol. Then he cuts a 12 inch log.

But it will still pull a 36 just not in 36 wood

 

[old guy]

Starters usually don't live long with that much comp.

 

[Barneyrb]

Something isn't adding up here, that's a clamshell engine and almost impossible to change the squish. It can be done but a lot of work involved.

 

[old guy]

Something isn't adding up here, that's a clamshell engine and almost impossible to change the squish. It can be done but a lot of work involved.

I did it with a poulan 2900, but as you say it is a lot of work, I did the bearing pockets with sand paper on a piece of pipe, it took me 9 hours.
I had good measuring tools left from my machining days, I had to keep everything the same from a starting point. It changed comp from 139 to 164. I don't think I would do it again.

 

[777funk]

Something isn't adding up here, that's a clamshell engine and almost impossible to change the squish. It can be done but a lot of work involved.

Link:

I found it easier than my Husqvarna 55, since with the Poulan, the bottom of the clamshell is easier to sand since it's flat (sanded on a stationary belt sander) and the bearing pockets are easily sanded with a 1/2" drum sander in a dremel.

The work made a much bigger difference in the 55. Although the Poulan sounds a lot stronger than it is now at idle. And when pulling, it's quite a pronounced thud, thud, thud.

I'd like to try a carb for a slightly bigger saw (say the 55 or a Stihl 026) to open it up a little more than it is now.

Was it worth it? Probably not (yet). My goal was to make this thing close to a similar sized Stihl or Husqvarna in power. The MS250 is also a clamshell design and I really like that thing.

 

[Mastermind]

Is there such a thing as too high on compression?

Yes. 230 is getting to that point. Too much heat. Too much parasitic loss. Tune is tough to keep stable as the engine gains temperature.

 

[el33t]

According to Husqvarna, the standard compression read on small CC saws that are relatives of the Wild Thing, such as the Husqvarna 236, Jonsered CS2234 or McCulloch CS340, should be 180-210 psi. That is, 230 psi is (only) 10% more than the standard value.

For larger chainsaws, the standard value is 125-165 psi.

 

[Mastermind]

According to Husqvarna, the standard compression read on small CC saws that are relatives of the Wild Thing, such as the Husqvarna 236, Jonsered CS2234 or McCulloch CS340, should be 180-210 psi. That is, 230 psi is (only) 10% more than the standard value.

For larger chainsaws, the standard value is 125-165 psi.

True story....the smaller displacement saws can run more compression without issues.

 

[old guy]

Guess that explains 180lbs comp in my 55.

 

[thompsoncustom]

HD-12 carb will work on a wild thing without to much work and has a much bigger throat.


If I remember right I had to bend the throttle linkage and close the hole in the butterfly and that was about it. believe I also modified the little black plastic air filter holder so I could get the cover on it all.

After you open up the exhaust, port it, and raise compression that tiny carb these things come with just wont flow enough air.