Highest Compression Engine

[Cantdog]

You know....if you only replace one ring at a time, think of the cost savings! 50% of the full job!!

LOLOL! Right, and if you just replaced one main bearing you could save even more!!-----

but these saws do carry pretty high comp numbers. Fortunately Jonsereds allowed for this by giving the 621 a pretty large diameter starter pulley to give you the leverage to easily start it. However the 80 has about the same size pulley and you have to be committed to starting that one!! Any half azzed attempt will not get it started and probably net the puller a couple very sore fingers when saw decides it wants the cord back...... suddenly!!

 

[spudulike]

Sir, not to rain on your charcoal but I suspect that their is oil in the cylinder. Oil as we all know will not compress.I would start it and I think that it may smoke to burn all the excess oil out of the cylinder.Get it good and warm and re-test it. It will go down, Ken

Here is me running it a couple of days ago - the bore is clean of oil!


http://www.youtube.com/watch?v=HYGe0WL24Y4

Spud

 

[spudulike]

Could be excess carbon build up in the combustion chamber. I had a Husky 266 with almost 200 psi comp. I pulled the cylinder and scraped all the carbon out of the chamber (and the exhaust port as well) and the compression dropped to the 170's.

Looks reasonably clean for an older saw!

Spud

 

[DougMN]

I tested the 621 I bought the other day and it read 150. Maybe it needs a ring?

Sorry for the incorrect post,I should have looked up how many rings it had before I replied.

 

[Coloradobum]

I find it easy to believe you're running 200+. I had a 250R racing ATV with race piston and headwork that ran at 280psi. Race gas only. If that motor could handle it a smaller chainsaw engine should be able to.

 

[MacLaren]

Ya know, this has got me really curious as to how much compression my 2094 has. It has no decomp button and will just about rip your arm off starting it!

 

[pioneerguy600]

Ya know, this has got me really curious as to how much compression my 2094 has. It has no decomp button and will just about rip your arm off starting it!

The 2094 does have a high comp engine but it also has a flat top piston, most likely you will find it in the 185 range stock.

Pioneerguy600

 

[thomas72]

I had an echo 610 that had around 225psi on one cylinder. I also have a McCulloch 92 kart engine that pushes a little over 210psi.

 

[jonsereds 621]

How about 230psi - I didn't believe it either, engine looks pretty standard on this Jonsered 621! It pulls over ok and the gauge is one I use all the time so I know it reads ok.

Spud

Yup, 220 often on a 621 here, got an older harder to start awkward one at 160 however. new rings maybe ? It has more drag too, once it starts (6-7 pulls against 3-4) it seems to have more power however, so it gets more use !....Think I,ll leave it be, It'll most likely outlast me. Finest piece of portable equipment I've handled so far, leaving aside the weight. Can't help myself now, always looking for more. UK.

 

[Cantdog]

That's the onset of CAD.....fortunately it's not terminal.....but does take up a bunch of time....and funds...

 

[jltrent]

I have checked a lot of saws and the most I ever got out of one was a Poulan Pro at 180psi. Anything over 140 is good and even down to 120-125 is okay with little to none piston damage.

 

[bulletpruf]

Is there not always oil in the cyl when starting??? Not arguing about if oil will increase compression values, but what is the condition to get accurate compression figures. Absolutely dry just assembled or the way the saw is when used?? I also have a 621 that repeatedly will hit those figures after being pulled until the guage does not go any higher. I also have an 80 that I've pulled to 238. These old Jonsereds are high compression motors. They a have a substantial piston crown (not just a few 1000ths but like 1/8th"-3/16") and two rings. Both of which will increase comp values at rope pulling speeds. (especially compared to modern flat top pistons with just 1 ring). If the rings are new and have close end gaps (0.005-0.006") these numbers are not uncommon with these old motors. Remember these saws were designed to run on real gasoline with extra lead added!! Not pitiful the unleaded, oxygenated, ethanol fuels of today. Comp figures will go down when a saw is warmed up from cold this is known. So what is the standard for getting these figures?? I know how I do it. How do you all?? Hot, cold, just assembled dry or checked with mix in the cyl, throttle wide open, high idle, closed??? Just askin???

My 80 did 235 psi; I have two gauges and they both read within a pound or two of each other. Since I'm only 3 psi short of your 238 psi, I might have to head into the garage after dinner and see if I can beat it!

FYI - I tested about 7 Jonsered XF's (60's vintage, 111 cc) a few weeks ago and none came close to 200 psi. I also have 4 complete 621's in the garage, but haven't checked compression on any of them. Now I'm curious.

 

[Stihl 041S]

LOLOL! Right, and if you just replaced one main bearing you could save even more!!-----

but these saws do carry pretty high comp numbers. Fortunately Jonsereds allowed for this by giving the 621 a pretty large diameter starter pulley to give you the leverage to easily start it. However the 80 has about the same size pulley and you have to be committed to starting that one!! Any half azzed attempt will not get it started and probably net the puller a couple very sore fingers when saw decides it wants the cord back...... suddenly!!

With .......conviction........

 

[bulletpruf]

My 80 did 235 psi; I have two gauges and they both read within a pound or two of each other. Since I'm only 3 psi short of your 238 psi, I might have to head into the garage after dinner and see if I can beat it!

FYI - I tested about 7 Jonsered XF's (60's vintage, 111 cc) a few weeks ago and none came close to 200 psi. I also have 4 complete 621's in the garage, but haven't checked compression on any of them. Now I'm curious.

Finally got the 80 torn down and freshened up. I really didn't want to monkey much with the jug and piston, so I just cleaned everything up and reassembled with the same rings and base gasket. I was rewarded with 242 psi on the compression test! Same gauge that I used the last time, so really does look like the cleanup did actually give me a slight boost!

 

[KASH]

Back in the early seventies my brother was using an 80 for cut skid I think he spent more time changing recoil ropes than he did cutting.
kash