3120xp "safe" squish

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it looks nearly balanced with the 36".. and yes, the 20" looks weenie on it... perhaps with a 15 pin sprocket or something it would be impressive.

I have a couple 3120's coming my way by the sounds of it.. an experienced logger around here told my buddy "it's the biggest husky saw he's ever seen"... and another buddy has 2 3120 powerheads... I plan on making a mill, and well, it looks like I might have the powerplants for it.

How does it run? can you get it to turn over?
 
As far as squish bigger jugs need more clearance. Bigger machined squish bands need more clearance. Dome top pistons call for more,and dometop and with foreged need more yet. With all those plusses to add up to stack up. The ruel is around .020 with 50-60 maybe up a hot 80 cc partial work saw. Hot rods with small dome volume, cooling ability and length of run times also what piston material i am using i come with my own rules i play by without any recent deto or failures. You can scorch a
stock.saw with may deto on 87-89
octaine. That list all plays in
aswell as rpm ran at. Ie rod rotating mass flexe. I have ran as tight as .008 on a 7.2cc dome poulan 3400, turned bout 15,000 10000 in cut with a aggressively made chain. It was ran on 70% 110 blue and 30% 90 ethanol free. At 32:1 with good old fashioned yamalube aircooled from the 70s-80s era i love there oil even more the old stuff, id say take all those numbers make sence of em and if you are still comfortable run it. Remember cranking comp is soooooo much lower tben running cyl comp. I hope that makes sence. Btw pqc cyls run huge squish like .060 min on a hotty with 200+ psi.
 
Dave27483 said:
Ok so it's all built, squish set at 0.022" (yes I did) and muffler opened up a bit more. Brand new 36" bar and full chisel skip chain.
I will be putting it through this huge pine tomorrow and post a video. View attachment 441917View attachment 441918
And here it is with a 20" bar, looks like a joke on this saw.!
Click to expand...

Correct me but why does a 120cc saw need a skip chain on a 36" bar. With pine lined up to cut.
Did you all ready have it?? Or get it super cheap
Take a shop file to the rakers on the 20". Guessing you can take it down at least .40-.80 below stock based where I put mine on the 660@20" not in pine either
 
Does not seem like people pay 2 cents to combustion chamber size or shape along with the other variables. Fingers crossed good luck guys. I know there a ton out like this. Just gotbit in my ming there hqs to be q more controlable way to do it then just take off this nimber on band and this off base. Maybe for a toy but a working saw i wonder.
 
Jimbo209 said:
Correct me but why does a 120cc saw need a skip chain on a 36" bar. With pine lined up to cut.
Did you all ready have it?? Or get it super cheap
Take a shop file to the rakers on the 20". Guessing you can take it down at least .40-.80 below stock based where I put mine on the 660@20" not in pine either
Click to expand...
I don't think it needs it but I thought I would try a skip chain. Less teeth to sharpen. And yes for the 20" bar I lowers the depth gauges down heaps. It is now throwing very healthy chips :D
 
smokey7 said:
As far as squish bigger jugs need more clearance. Bigger machined squish bands need more clearance. Dome top pistons call for more,and dometop and with foreged need more yet. With all those plusses to add up to stack up. The ruel is around .020 with 50-60 maybe up a hot 80 cc partial work saw. Hot rods with small dome volume, cooling ability and length of run times also what piston material i am using i come with my own rules i play by without any recent deto or failures. You can scorch a
stock.saw with may deto on 87-89
octaine. That list all plays in
aswell as rpm ran at. Ie rod rotating mass flexe. I have ran as tight as .008 on a 7.2cc dome poulan 3400, turned bout 15,000 10000 in cut with a aggressively made chain. It was ran on 70% 110 blue and 30% 90 ethanol free. At 32:1 with good old fashioned yamalube aircooled from the 70s-80s era i love there oil even more the old stuff, id say take all those numbers make sence of em and if you are still comfortable run it. Remember cranking comp is soooooo much lower tben running cyl comp. I hope that makes sence. Btw pqc cyls run huge squish like .060 min on a hotty with 200+ psi.
Click to expand...
I have taken the advice of brad Snelling, I trust his advice.
 
Remind me of his post of this advise. I have never seen squish numbers on big saws just as low as .015-.018 on a ripper and normal.020 on A worker. Please take no offense to what I say or what i Talk about I'm just trying to learn like the rest of us unfortunately I have learned with a few catastrophic failure as myself Just sometimes questions can pose
interesting answers. .060 is tight on a 75 mm bore on a cast lined pwc motor for squish especially with small domes and wide squish bands. Im building a old it 400 dirt bike. Would love to makebit hotter going to be wondering on what squish i could do i dont touch with .093 solider fing huge squisg. If i camd down to say .030 it be a huge jump in compression and all
 
No offence taken smokey, believe me I did a fair bit of reading before I just went in and did this. I really did not want another engine failure on this big beast.
I'm also running 25:1 oil mix just to make sure it will stay properly lubricated. And possibly keep combustion temps down a little.
I ran it today with the 20" bar for just a short period and it went really well, idled nice revved clean and no flat spots!
I will run it tomorrow with the new 36" bar. Looking forward to it as it was hard to gauge how good the tourqe was cutting a 12" log. It just sat on the rev limiter the whole time :laugh:
 
I bet it did with the 20 inch bar and mean for Christ sakes the Wreckers could have been gone and you would have never got it to stop four stroking. I'm jealous of this week seems like its a quite nice unit I discussed in the cylinders make me nervous but I've used worse I think you'll be fine Just be cautious like you are being and will be just fine
 
You will have no trouble at all with a squish of .022". I've seen an 066 come from the factory with a squish of .017". It's been a while, but my 084 worksaw has a squish of .020"-.025" and turns 14,000 RPMs at WOT. It's been used for stumping and pulling a 72" bar nearly buried in oak.
 
Dave27483 said:
No offence taken smokey, believe me I did a fair bit of reading before I just went in and did this. I really did not want another engine failure on this big beast.
I'm also running 25:1 oil mix just to make sure it will stay properly lubricated. And possibly keep combustion temps down a little.
I ran it today with the 20" bar for just a short period and it went really well, idled nice revved clean and no flat spots!
I will run it tomorrow with the new 36" bar. Looking forward to it as it was hard to gauge how good the tourqe was cutting a 12" log. It just sat on the rev limiter the whole time :laugh:
Click to expand...

24:1 sounds like a little much, perhaps if you're milling with it it would stay hot enough to be tolerable... I think you'll end up running it around 32:1 if you spend any amount of time at low loads.
 
25:1 is what they recommend down under for the 3120 and 088.
 

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