Starter Rope Compression

[JasonRKBA]

Easy to pull is why I love my 025.

 

[Michael Rupley]

Al you are a wise man I always had a great deal of respect for your opinions but they sometimes differ with mine. I know that is what makes a horse race right? You seem to use common sense to determine things. That is good but does not always follow.
I built 20 or so 2100 saws through the years. Some were racers and some not. I even built one with a 3120 crankshaft (see post heart of a lion AS). The thin ring was always used for my fastest saws. I don't think it had anything to do with ignition forcing the rings out to seal. I just don't know how it could be unless there was a dykes type ring, or holes behind the ring to do that. The 2100 did not have these things. However it did have a LOW FRICTION thin ring. Loggers used to change the ring at the end of the season and have hardly any wear on the cylinder, but the ring was worn. This was the beauty of the thin ring 2100.
Al it is probably hard to believe but a two stroke can run, and run good without a ring, if the clearance is tight.
How much compression does the saw have at 13,000 RPM? We measure at cranking speed but it has to be high at running speed.
Seems you have said a few times that saw racing is not what interests you. I get that but I think saw racers must first learn what makes a stock saw run well, before modification to increase performance. I am mainly interested in resale so now my focus is on stock again because there are 1,000 people wanting a stock saw for every one wanting a modified saw that costs a few hundred more. The internet has made everyone think he can make a better modified saw.

 

[Terry Syd]

Old trick, squirt some motor oil into the spark plug hole and crank it over a few time. Then pop in the compression tester and see if the compression jumps up a fair bit. If it does, it means the rings are worn.

The thicker oil will help seal the rings and give a truer reading that you would get with new rings.

If it doesn't bump up the compression a fair bit, forget the rings. You can just remove the gasket from under the sparkplug and pick up that bit more compression that you think you need.

 

[drf256]

I used to work on 025’s often. I’m at 230’ ASL and the most compression I’ve ever seen in one was 155# with a good tester on a cool dry day. Generally they ran 140-150.

All of the 42mm variants I ran through were dual port open transfers. The 42.5mm were quad port open. You might be able to see inside through the ex port and tell what you have.

Between the ambient temp and humidity and the extra 500’ of elevation, coupled with the fact that testers are generally not so accurate, I’m in the don’t fix what’s not broken camp. I’d bet on a cool dry day at a lower elevation, his # will come up.

People put too much emphasis on compression numbers. I’ve seen scored jugs make more compression than good jugs. Also, as stated above, dynamic compression is what matters more. At 13,000 rpm, there isn’t a lot of swept volume and there really isn’t time for much ring blow by. If the piston is smooth and the saw starts, run it.

Seems like the OP is enjoying cutting wood. Before needlessly spending money, I’d step up to a pro-style saw like an 026 and see if you like it better than your 025. You’ll need a different bar mount and chain though.

To the OP, if you want a spiced up 026/260 I know a guy. Would just take a few months to get to it.

 

[drf256]

Here’s a welded popup I went a bit too big on.

 

[Al Smith]

That comment I made on the rings sealing under power most likely came from Jennings or MacDizzey .At any rate it's too early in the morning to spend 3 hours on the internet to find it .
Having said that when I resleeved the Mac 125 and fit the piston it would blow the piston out with no rings .That was a time consuming job using a Lisle precision hone .Well the whole job took some time to be honest about it . Since I haven't put enough time on it to even seat the rings .Runs okay though just not often, shelf queen .
If the OP wants to change the rings ,sounds like the easiest thing to do .Just keep in mind because the cylinder will not be truly round the static compression usually will not jump up to it's full potential until the rings seat .It took me the best part of one summer cutting down a 10 cord pile of oak to size at 15-20 minutes at a time before the rings fully seated on a Stihl 038 Mag .That saw now wears a D-handle if that says anything .

 

[Terry Syd]

Here’s a welded popup I went a bit too big on.

Fork me! How did it run

 

[Bigmac]

So damn true. I know the leak down on the 300 in my truck but have no idea about my saws. I guess cause they run fine.

I’m weird but I test the comp on almost everything, I do it for baseline, if I have a problem I can rule out that, If I see a big drop I know something is up!

 

[Bigmac]

So, I am sitting here trying to decide if I want to rering a good running 025.Has 130+psi compression.However it feels like it has much less.It seems to turn over especially easy when pulling the rope, but starts and runs great.So I had the recoil off and noticed the rope is just over the top of the spool. Hmm. So if this is the case could this further increase the leverage factor giving me the impression of low compression?

I have had a few 025 one was 135psi the other 140, and I am at about 30-50 feet above see level, the 135 psi was an excellent runner and started really reliably! 2 pulls max! Personally I would sell it and get an 026, and then put some time and money into it. On the clamshell 025, re ringing is a bit more work, and the return minimal, and you should replace the seals at the minimum while you are at it. It will cost you a few buck to do it all and imho is better spent on a better saw, or run it as is!! I have sold the 025’s for more than than what I have bought all my 026-ms260’s, and the 026 is way more mod able. I have had some decent gains on big, 90cc pro saws with rings, but I prefer new piston and rings, the piston skirt is usually worn too, an on piston port saws I can make a difference in starting, an is really noticeable on smaller saws!

 

[drf256]

Fork me! How did it run

I removed a lot of the dome and got it down to 215.

Ran ok for me back then, now I’d round file the damn thing.

The saw saw 20k on a way too lean piss rev and didn’t grenade.

 

[Stump Shot]

So, I am sitting here trying to decide if I want to rering a good running 025.Has 130+psi compression.However it feels like it has much less.It seems to turn over especially easy when pulling the rope, but starts and runs great.So I had the recoil off and noticed the rope is just over the top of the spool. Hmm. So if this is the case could this further increase the leverage factor giving me the impression of low compression?

I would recommend popping the muffler and taking a peak inside just to confirm nothing else is the reason for the compression drop.(carbon scoring etc etc)
Also can see if there is any springiness left to the rings by pushing on it with something dull like a popsicle stick.
This should give you a better idea of what is going on and whether or not to continue to run the saw or pull it down for service.

HB, That is on the agenda.However what size piston do I have?Stihl dealer looked at the numbers and was unable to make a decision.It's an older 025 so I suspect that it is a 42MM.Piston view through the muffler and is near perfect.Anyway I will toss a set of Stihl rings at it.

You can measure the bore diameter by using a plastic straw, place it in the cylinder thru the exhaust port and roll the piston up so it leaves a crease in the straw and back up, remove and measure it to confirm your suspicions.

 

[Kenskip1]

Well for the time being I am going to just run it. I put in a new oil pump tonight and now it oiles the way that I like it. Someone mentioned about going to a pro saw. Well sir, I have a 51 Husky that blows 170 PSI. Also a Echo CS 550P, a Stihl 041 ad a couple of others.What I want from the 025 is a saw that I can mount onto my Polaris and head off into the sunset. The Stihl saw is light and simple to use.BTW, all my saws are metacliculusly maintained.Thanks for all the information.

Here is where the 025 is going to wind up. I have the 51 saved for a rainy day.It's a runner for sure.
https://weldingweb.com/showthread.php?702739-ATV-Project&highlight=mount+atv+chainsaw

 

[Bigmac]

That’s great, I was just saying run it and and enjoy it as is, I wouldn’t recommend putting a bunch of money into it and except huge gains, you better getting a different saw for that. They are great saws for what your doing, I have had several, it’s not meant to be an offense.