Stihl 026 rebuild

[drf255]

You can generally go no gasket on a 260, unlike the 026. You need to check either way.

The 260, just like the 026, came with a standard and adjustable oil pump (PRO version). The PRO is clutch driven.

All 026 are 44mm. 260 are 44 or 44.7mm. The ones that are listed as 49cc on the sticker are usually 44's, the 50cc are 44.7.

 

[Brewz]

I already have done a nice muff mod, advanced the timing and replaced the fixed jet carb with a wt194.

Would love to see some pics of your muffler mod and also am very interested in what you do to advance the timing.

 

[Macman125]

I will take some pics next time I go out to the shed. As far as the timing goes, I filed the flyheel key almost half way across. This obviously compromises its integrity. To solve any sheering issues, I used some lapping compound between the flywheel and crankshaft, spun it a few times and cleaned it off. This makes it less likely to slip on the crank once tightened down.

 

[Brewz]

Would love some pics....... its all learning and I am finding when I search on similar threads from the past, the pictures that have been posted are missing.

As for advancing the timing, does it make much difference?
Are we talking advancing it on the piston upstroke?

I will go do some searching while all you Americans are just waking up.
makes it a slow conversation when we are 12 hrs out of sink

 

[Canadian farm boy]

For advancing your ignition timing all you have to do is file .020"-.030" from the key. (Make the top half of the key narrower. Leave the bottom half of the key as is) This will advance your timing approx 4*-6*. When you reinstall the key into the crank make sure that the side of the key that you filed is on the RH side. this way when you reinstall your flywheel it can be positioned in a slightly further counter clock ways position on the crank.

When I file a key I hold the bottom half (round side) of the key in a pair of vise grips and clamp the vise grips in a bench vise. I then use a flat file on the key and check my filing progress with a pair of calipers. I'd post pictures of how I do this but I currently don't have any. I hope my discription of how I file a key makes sense

 

[redfin]

Was working outside around the house today and it decided to rain.
So I wandered into the garage to tinker with stuff.
I dug out my dremmel and decided to do a bit of work on the 026 cylinder.

First of all I measured the exhaust port width with a piece of paper by trimming it to the width of the port when following the curve of the cylinder.
I got 23.4mm (53.18%) of the bore width.
From what I have read on here, 70% is an upper limit depending on the motor being ported so I decided to stay conservative on my first attempt.
I measured the side skirt of the piston that covers the ports and it was 31.3mm. I wanted to keep some meat in there to stop gasses bypassing the piston skirt to the exhaust port so I aimed for a width of 28mm (63.63%)
I ended up with 27.4mm (62.2%) and was happy with that.
I left the intake and exhaust ports top height standard and lowered them both by about 1mm.
I removed about 1 to 2mm of material from all around the exhaust port to bell it and tidied up the intake, smoothing it out and rounding curves to help aid air momentum. I didnt't take too much out as it is thin walled and I figure the flow will be restricted by the carb and intake boot no mater how much metal I remove.
Then I moved to the transfers and ground down the square edges, trying to build a smooth transitional surface to get the air flowing into the transfer faster and smoother. I extended the leading edge facing the intake port and rounded out all the curves.
I didn't touch the top of the transfers. Firstly I dont have a bit I would be comfortable using on them without risking damage and also, I figure getting the fuel/air mix flowing in smoothly is the main aim and leaving the top standard will keep velocity high.

I would love to hear some critique from more experienced porters on my job thus far, good or bad!
The lines in the exhaust port below are me feeling the surface out with a screw driver, not cracks

View attachment 473296

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Your grinding looks good. I would square up your corners on the intake floor without lowering it.

 

[Brewz]

It's raining today so plan to file the flywheel key, square the intake lower corners and polish out the exhaust port

I will post some pickies when done

Really appreciate all the help folks!!!!!

 

[Brewz]

Exhaust port polished and muffler matched:





Intake port bottom corners taken out a bit more:



muffler mod extended and new spark screen made to suit:







Timing advanced by filing the key.
I measured it and calculate I ended up with just under 6*........ hope I didn't go to far but its an easy fix with just a new key if I did.



So now its just sitting under a rag on the bench waiting on piston, rings, carb kit, fuel and oil lines etc.

I cant wait to see how it goes. Fingers crossed I haven't killed it.

Cheers

 

[Macman125]

I am having a difficult time trying to download pics of the muff mod. Anyways, My muffler has been gutted, I took a dremel and cut a slit vertically on the flywheel side about 1.25 inches long. I then took a torch and heated the cylinder side of the muffler and used a flat screw driver to pry and shape an exit that projects the gasses forward, away from the saw.

 

[Brewz]

All good mac, I get the jist of what you have done.
I thought about cutting the muffler side but wanted all my port covered with a spark screen as I often cut in dry dusty highly flammable conditions.
The stainless spark screen mesh I have used is as fine as the stock stuff but with a better open area or about 48%.
I went fairly big as I figure about 50% is blocked by the spark screen and focused the additional opening at the top of the muffler where the exhaust port faces.

 

[Macman125]

I cut usually in winter only, so usually things are pretty wet. It is a little screamer though. I am hoping to kind of duplicate you work here. I am looking forward to seeing the finished project so I can weigh whether or not I want to go ahead with it.

 

[drf255]

Great job Brewz.

Smart muff mod, I like the sleeper look. If you have the ability to weld, add a strip of metal to the clutch side of the muffler. It will keep all the carbon off the saw case. I'll try to dig up a pic.

Your exhaust port is amazing. The sign of a true artisan is when a jug looks like it came from the factory when you're done with it. You're there already. Without a caliper, I'd say it would be difficult to for anyone to know you opened that exhaust port. The lines are perfect.

Great work!

 

[drf255]

Sent from my iPad using Tapatalk

 

[Brewz]

Thanks for the compliments drf.
I did my apprenticeship as an electrician at a massive steel works, and as apprentices, we spent the first year locked in a training center learning to file to the thousandth of an inch, hacksaw straight lines, tap holes, and all the fine arts of most hand tools you can lay your hands on. I was taught from the start to measure twice, cut once and to take your time, checking and checking again. Precision and neatness was beaten into us by a 4 foot tall 65 year old Scotsman who carried a length of electrical conduit and would whack you with it if he saw you do something wrong........ true story!

I now cherish these skills i was taught and use them in my work and every day life.
I tell my kids....... "A job worth doing is worth doing right!"

Anyway...... back to the saw......
I made a degree wheel







Youtube taught me how to set TDC and I used the long extension from my compression tester as a piston stop. Cost me $0.00

I am not sure how to measure or present the numbers properly so I will list what i measured below:

With factory gasket and .028 squish, from TDC with piston going down:
Piston top at exhaust port top: 96*
Piston top at exhaust port bottom: 150*
Piston skirt base at intake port top: 30*
Piston skirt base at intake port bottom: 71*

With factory gasket and .028 squish, from BDC with piston going up:
Piston top at exhaust port top: 84*
Piston top at exhaust port bottom: 30*
Piston skirt base at intake port top: 150*
Piston skirt base at intake port bottom: 71*

Removing the gasket added 2* to these figures.

Pooping myself now....... is this good or bad?

 

[drf255]

Put your stop back in and double check TDC again. Your numbers all add to 180*, but they should be the same in both directions. Your wheel likely not at TDC.

Removing the gasket should change the numbers differently. The exhaust floor should move more than the roof.

For the exhaust roof, shine a flashlight through the plug hole and shut the lights off. When you see the light coming out, you found the true exhaust opening.

98* about right on exhaust opening, even with the better older jug. That's the real reason I sand my chamber flat. The most I've gotten one down to is 104*. Makes a difference in lower end grunt. The compression bump is a side effect of the exhaust drop.

 

[Brewz]

Will go double check

I dont really know what all these numbers mean. I am currently doing some reading trying to make sense of it all.

Exactly what points do I need to measure to?
Do I start at TDC or BDC?

 

[drf255]

I got confused at first as well, still am at times.

2 stroke, so numbers mean same thing up and down. It gets a bit confusing.

Exhaust opening, transfer opening and intake closing are the critical numbers.

 

[drf255]

Every engine design different, so what works for one may be worse for others.

Everyone has different opinions on what works best. There really no "right way".

Peer through the exhaust and see where your transfers open.

Oh, and don't use your degree wheel to rotate the motor. Once it's right, don't touch it. It's so easy to grab and natural to do so, but you will throw your readings off. Use the flywheel only. While you have the jug attached, use a rope in the chamber and snug the flywheel nut down.

 

[Stihlofadeal64]

 

[Brewz]

Ok
The TDC is spot on and I still get the same numbers.
I measured exhaust open duration to be 170*
I measured intake open duration to be 140*
I measured transfer open duration to be 120*

Blowdown is 27* from when exhaust opens to when upper transfers open.