029 woes

[cookies]

There are 0 ring end gap measurements in any oem repair manuals because they assume you will use oem parts. Apparently at some point in the past there was a rash of over sized circumference caber rings. The times I have used aftermarket pistons and cylinders I spent the extra 20 bucks to use oem rings. Aftermarket crank seals require inspection under 10x magnification to look at the lip seals for imperfections...I have thrown a few into the trash saving headaches.
People expect aftermarket parts to be and behave just like oem, this is almost never the case. Every single am piston or p/c I have used performed off the mark for oem max rpm when dialing in the carb. Set aftermarket max rpm by ear not tack

 

[stihltech]

Also, is the arrow on top of the piston facing the exhaust? How long has it ran so far. You could still be seating the rings.
Look around on here for many post showing correct way to diagnose and repair saw motors.
And I'll say it again- without a pressure and vacuum test it is just a guess. And it could end up with another ruined piston and cylinder.

 

[Romper]

Also, is the arrow on top of the piston facing the exhaust? How long has it ran so far. You could still be seating the rings.
Look around on here for many post showing correct way to diagnose and repair saw motors.
And I'll say it again- without a pressure and vacuum test it is just a guess. And it could end up with another ruined piston and cylinder.

Tonight I just completed assembly of my 029 Super with a 49 mm assembly of Chinese origin. Checked compression at 117 before even trying to start it. It fired up with about 5 pulls. It will be interesting to see where the compression goes after a break in. I realize that longevity of the Chinese junk is a fraction of Stihl OEM parts. I have run Chinese stuff in a number of Poulan overhauls but don’t have enough hours on them for abnormal wear yet. Thanks so much far any input. I am only into my first two STihl overhauls.

 

[Romper]

There are 0 ring end gap measurements in any oem repair manuals because they assume you will use oem parts. Apparently at some point in the past there was a rash of over sized circumference caber rings. The times I have used aftermarket pistons and cylinders I spent the extra 20 bucks to use oem rings. Aftermarket crank seals require inspection under 10x magnification to look at the lip seals for imperfections...I have thrown a few into the trash saving headaches.
People expect aftermarket parts to be and behave just like oem, this is almost never the case. Every single am piston or p/c I have used performed off the mark for oem max rpm when dialing in the carb. Set aftermarket max rpm by ear not tack

Thanks so much for your input. I think I now have a comfort level on the 029s to try to work with OEM parts. Typically when compression goes down after use have you experienced ring problems or cylinder out of round conditions? Maybe it would be a combination of the two.

 

[thompsoncustom]

Thanks so much for your input. I think I now have a comfort level on the 029s to try to work with OEM parts. Typically when compression goes down after use have you experienced ring problems or cylinder out of round conditions? Maybe it would be a combination of the two.

no typically after use the compression numbers will go up a little on a fresh rebuild as the rings wear in.

make sure when u are getting your compression numbers your holding the throttle wide open somehow, another person if the easiest but can't be done with tape or a zip tie.

 

[irhunter]

Tonight I just completed assembly of my 029 Super with a 49 mm assembly of Chinese origin. Checked compression at 117 before even trying to start it. It fired up with about 5 pulls. It will be interesting to see where the compression goes after a break in.

This is interesting. I think you should start a new thread...reporting this and future results with this set of parts.

The brand of the parts, and supplier, would be good to know.

Roy

 

[dmb2613]

I have rebuilt many of the 1127 Stihls with the cross pop up piston and china cylinders if I could not get a used 039 cyl they run and cut very well and are lasting good. only down side is the weight. You do need to check out the cylinder good, they have edges that need attention and some are just not usable.
But they run like a scalded dog And some do need a decompression valve. especially if you worked on the timing. You have to work on the muffler to get git power out of them.





i could not get hold of a used 039 cylinder

 

[cookies]

Thanks so much for your input. I think I now have a comfort level on the 029s to try to work with OEM parts. Typically when compression goes down after use have you experienced ring problems or cylinder out of round conditions? Maybe it would be a combination of the two.

Typically what I find on saws with lower compression that do not have scored pistons/cylinders are worn rings, rings with loss of spring tension, piston ring groove wear, piston surfaces worn smooth (no oil retention, decreased seal at low rpm), carbon in piston ring grooves causing stuck rings.
Honestly the ms-290/311/390/029/039 are a pain in the azz requiring lots of time for full disassembly of the saw to change the piston/cylinder, the sealant must be applied not to thick or too thin and the crank seals hand held in place when tightening the bolts down. The cylinder base bolt hole threads have to be cut by the bolts and are best to be done before assembly with a good chance of a reused bolt breaking off. When built with oem parts and treated right they run forever.

 

[Romper]

Typically what I find on saws with lower compression that do not have scored pistons/cylinders are worn rings, rings with loss of spring tension, piston ring groove wear, piston surfaces worn smooth (no oil retention, decreased seal at low rpm), carbon in piston ring grooves causing stuck rings.
Honestly the ms-290/311/390/029/039 are a pain in the azz requiring lots of time for full disassembly of the saw to change the piston/cylinder, the sealant must be applied not to thick or too thin and the crank seals hand held in place when tightening the bolts down. The cylinder base bolt hole threads have to be cut by the bolts and are best to be done before assembly with a good chance of a reused bolt breaking off. When built with oem parts and treated right they run forever.

Yes these 029s are a pain to overhaul. My new overbore kit fired right up. Tried measuring ring gap on the standard bore set that was new Chinese stuff and 75 compression It was .010 between the pin locators and .070 above the locators. Seems high to me. Unfortunately I don’t have a set up for testing pressure.

 

[Romper]

Typically what I find on saws with lower compression that do not have scored pistons/cylinders are worn rings, rings with loss of spring tension, piston ring groove wear, piston surfaces worn smooth (no oil retention, decreased seal at low rpm), carbon in piston ring grooves causing stuck rings.
Honestly the ms-290/311/390/029/039 are a pain in the azz requiring lots of time for full disassembly of the saw to change the piston/cylinder, the sealant must be applied not to thick or too thin and the crank seals hand held in place when tightening the bolts down. The cylinder base bolt hole threads have to be cut by the bolts and are best to be done before assembly with a good chance of a reused bolt breaking off. When built with oem parts and treated right they run forever.

Ok thanks I have another 029 I did an upper end on. It fired up but lost power after not even one tank of gas. I am going to pull it apart again and check ring gap and seals, compression on that one is at 75. It will start and run and idle ok then. I have not put that one in wood yet. unfortunately I don’t have set up for pressure test. Good tip about the cylinder bolts. Might be a while before I get back to that one.

 

[irhunter]

Here is some good info on end gap:

https://www.arboristsite.com/threads/piston-ring-end-gap.82327/

Sooner or later, just about everyone who works on saws, ends up buying, borrowing, or cobbling together a pressure/vac tester. Having one is really central to saw repair.

Just sayin'.

Roy

 

[a. palmer jr.]

Longevity of the Chinese piston/cylinder can be increased by increasing the amount of oil in your fuel mix. You might be able to run an OEM at 60:1 but I would keep the Chinese one nearer to 40:1. I usually put 3.5 ounces of oil to a gallon of non-ethanol gas on these which is around 36:1.

 

[a. palmer jr.]

Here is some good info on end gap:

https://www.arboristsite.com/threads/piston-ring-end-gap.82327/

Sooner or later, just about everyone who works on saws, ends up buying, borrowing, or cobbling together a pressure/vac tester. Having one is really central to saw repair.

Just sayin'.

Roy

I cobbled my pressure gauge together using some hose and fittings, a blood pressure bulb and a gauge. Cost was practically nil.

 

[irhunter]

I cobbled my pressure gauge together using some hose and fittings, a blood pressure bulb and a gauge. Cost was practically nil.

Me, too.

I had a pressure gauge and vac tester from my auto repair activities. Added a BP bulb, hose barbs...

 

[Romper]

Me, too.

I had a pressure gauge and vac tester from my auto repair activities. Added a BP bulb, hose barbs...

I’ve got a couple vac pumps and the fittings should be no problem. Question, what are you using for a block off plate with the carb removed?? Maybe inner tube and an aluminum flat plate?? Thanks ahead of time for the encouragement on this.

The other night I saw on utube a repair tech shoot a spray of some sort on the clutch side of a running saw. The saw stalled right away apparently indicating a leak of the seal on that side. What would the spray be—carb cleaner maybe??? I guess that would make the mixture too rich to run. Looks like a quick way to identify a bad seal.

 

[irhunter]

Here is the test video I like:



Note: the service manual for the saw will tell you how much pressure and how much leaking is OK.

Every saw is different as far as blocking plates. Look at the pressure specs, and you will see you don't have to hold much pressure...and, not for very long.

I have some fairly stiff foam I carve into plugs which work well in carb ports. I will get some pics.

There probably should be a thread: Show your backing plates.

Anything that will cause the motor to speed up/down will work for a spray. Starting fluid, carb cleaner, whatever. But, the nice thing about a pressure/vac tester when building back a saw...you test before the thing is all back together. Test as soon as the sealant has cured and the oil seals are in.

Roy

 

[irhunter]

Some of the plugs, plates, adapters I use.

 

[cookies]

sections of flat rubber cut to fit between the carb intake and also the muffler to seal up the case/cylinder then use the impulse hose to attach to the pump. I find I like the stihl carb block with port for testing stihl chainsaws, think it was 20 bucks. Others make block off plates from flat plate they have laying around. Paying for a good cylinder/piston set once and crying once is better time management due to not having to do the job a second time and the saw will have better power.
Guy up the road who runs a small engine shop bragged about rebuilding his ms290 for 30 bucks last year using a farmer tec kit, saw did not make it through a florida winters worth of firewood before it started getting weaker. Several hours wasted you will never get back and we only get so much time before we are gone.

 

[northmanlogging]

New seals and upper ends on two of these saws. Low compression at 75 psi. Used cheapo Chinese parts. Other than OEM steel stuff is farm tech or Sara Zila parts any better. I am afraid I got what I paid for

 

[Romper]

Broken rings likely

No broken rings on one tear down. End so at .010, so that’s ok I guess. Must have leak or something.