Texas rose

Howdy folks, I borrowed a 029 Rollamatic Stihl chainsaw to cut down a couple of trees. This had been standing for a couple of years, so I checked the saw oil and filled up with new fuel mix of 25 to 1.

It cut down the trees OK but now it will only run for a few seconds, and wont rev up.

I took the plug out and it had a greyish coloured paste around the end of the electrode.
I could see a piece of metallic substance on top of the piston. I managed to get the substance out of the plug hole, it appears to be a sort of flattish 8mmx4mm piece of aluminium/white metal particles stuck together.

What I can see of the piston top is showing a fairly deep pitting right below where the plug electrode would be in the combustion chamber.

The piston skirt looks OK from what I can see of it...where did the particles come from?

It did make a rattling/grating sound when coming to a stop when trying to get the engine to run past the tick-over stage, but still started and run about 4 times before I decided to look down the 'plug hole'.

Can anyone throw some light on the matter?

Anyone have a workshop manual, Or, how do you get the engine out from the saw casing - I've got as far as taking the carb and ancillaries off, there's only the flywheel to remove - so I could check the innards...as you are probably aware the engine does not have a bolt-on cylinder head per say, but I have to investigate further, so, I need to get the engine bottom end off, and this cannot be done in situ!

Any help/tips you are able to give will be grately appreciated.

Thank you,

Texas rose.

Tumbleweed36

Hi,

I own and use that same model chain saw. My guess is what you got out of there was a little carbon which does happen from time to time in those.

Your problem is that you have put too much oil in the gas. That chain saw (all Stihl Products) uses a a 50-1 oil/gas ratio. Therefore, you have plugged it up with oil (double what it requires).

What I would suggest so you don't have to tear into it too much. Use a kitchen type baster and with straight gas, try to flush out the top of the cylinder through the spark plug. Empty the gas tank and flush it out with straight gas (no oil) until it is fairly cleansed. Then empty the flush gas out and put a small amount of fresh gas (no oil yet) in the tank, slowly (not enough to start) pull it through with the choke on, so as to infuse some gas in the intake line.

Then, empty out all the flush stuff and put some 50-1 gas/oil mixture in there (use HIGH TEST gas with a Stihl) and give it a go. If you can keep it running for a few seconds, it might just take off and be fine. I would bet that will take care of the issue unless it is just too gummed up to go. I would also guess it might run a little rough until all the oil is out of the carb and line to the cylinder.

Do let us know how you come out with this.

Texas rose

Thank you Tumbleweed36,
the stuff I got out of the cylinder was definately of mettalic origin...I would love it to be a simple fix/remedy as you are suggesting

There seems to be a wettish grey coloured deposit on the piston wall and barrel, which can be wiped off with a rag. The piston rings seem to be OK as far as I can see.

I would feel happier if I could get the piston out to investigate where the metallic foreign matter came from.

At the rear of the flywheel, the casing is showing marks of having been rubbed by the edge of the flywheel, which suggests that the flywheel may be 'flopping about'.

The problem seems to be in getting the flywheel off. There doesn't appear to any pre-drilled holes to attach a puller to.

Once the flywheel is off, is it a simple matter to remove the engine from the saw casing?

Thank you for your input thus far.

Anybody got a book??

What's the chances that the engine is OK...after all it was starting, albeit packing in quite quickly each time?

Texas rose.

Tumbleweed36

I think it is quite likely fine if you will do what I mentioned. However, you have to make that choice.

I think the thing you can wipe off with a rag is simply from the overabundance of oil you have used and being in the cylinder area has changed properties some so it does not appear to be oil. I also believe the small metalic pieces you speak of are from carbon deposits (they can appear as metal).

This is my third Stihl, so have worked with them quite a bit. This is my second model like you have. BTW, used to live in the middle of a woods, so used the heck out of the ones I have owned. Many days of cutting down maybe three or four large trees and cutting them up. Good luck on your task.

Texas rose

Thank you once again Tumbleweed36, I think I just needed assurance...a pat on the head, from someone with experience (you) to guide me on my way.

It's nearly bedtime here in the UK, so I'll have a further investigation in the morning.

I'll try your tactics ... but I'll have to refit all the bits I took off first.

Bye the way, there was no blue smoke emitting from the exhaust to indicate excessive oilmix being burnt

I'll let you know how I get on, bye for now.

Texas rose

Tumbleweed36

BTW, if you need a manual, just google using this phrase: "Stihl 029 chainsaw manual" and it will return several places to download a manual. Hope that helps.

Texas rose

Hello Tumbleweed36, have tried your suggestion, but no joy.

Investigated further and found, as supected, that the top ring is seized owing to the piston scraping the bore wall and becoming damaged.

I managed to get the flywheel off and further discovered that both crank support bearing ball cages have broken up allowing the crank to 'flop about'.

I don't know which came first the damaged bearings or the scraped piston?

My next problem is getting the saw brake off the end of the crank so that I can withdraw the crank from the casing to enable me to ascertain how much more damage has been caused.

I haven't told the owner of the saw...but I'll bet he'll say it was in perfect order when I borrowed it even 'tho I have used it very little.

Thank you for the tip about the maual, I'll have a search and see what I can find.

Thank you for your continual help.

Tr.

SABL

Hi Tr and TW

This is all I found:

http://www.stihlusa.com/stihl_owners...ety_manual.pdf

Hard to say why the saw suffered major failure. Only thoughts I have are:

Wrong oil in the gas.... must be 2cycle oil.

A very low grade of gas causing pre-detination (causing the pitting of the top of the piston and putting extreme stress on the "bottom end" of the engine.... failed bearings)

I don't know if spark plug will be a factor, but make sure he had the correct one installed.

Best of luck,
SABL

MrChooks

Whilst not much help to your problem now - I am just wondering if this damage isn't a further example of why 50:1 mix just doesn't seem to cut it as long term 2 stroke fuel.

The oldies were run on 30+:1 standard gasoline to standard 20w-30 engine oil. Now, these "little devils" are being run on a 50: 1 mix, albeit with a purpose designed 2 stroke oil.

Nonetheless, the oldies tended to just plain ware out over time - catastrophic failures were pretty rare and generally attributable to a failure to add oil to the fuel - now, on a "50:1 diet", total engine failures seem to be much more common.

Texas Rose's damage certainly has all the symptoms of a major failure in the lube system - particularly as the damage is to both piston and bore and main bearings.

Maybe the answer is to "top up" the oil ration in the fuel . I run my only 2 stroke on 40+:1, as plugs are cheaper than engine bores - but it's long out of warranty - so there is no risk of voiding anything

Texas rose

Hello SABL, yes I used a top quality 2 stroke oil, but I mixed it at 25:1 as I used the same mix in a strimmer.

It turns out that the piston head is not pitted after all, just got carbon deposit on it, but it has suffered a little from scoring, due to contact with the cylinder wall. I was going to clean the piston up and deglaze the cylinder and I think I would have got away with it, but, the crankshaft bearings ball cages have collapsed (some kind of plastic) allowing the balls to move around/congregate in their track....this may have been the cause of the piston damage?
The last work this saw did was to trim a few side twigs off a bough I was going to cut up for logs. I'm wondering what the history of this saw is, but I am reluctant to contact the owner as I'm sure he will say it was like new before I borrowed it

Thank you for your input SABL.

Texas rose

MrChooks

Texas - if the bore, pistons & rings are OK-ish - then you might be able to get this "lill devil" going by simply replacing the ball bearings.

Air cooled 2 strokes are pretty tolerant of "not too serious" bore damage, as their piston / rings and bore tolerances are quite loose.

The bearings are generally not very expensive and if you can get them out - any 1/2 decent bearing supplier will be able to read the spec off the side and provide you with a replacement. (Bearings are easy and generally don't have to be sourced from the OEM (Stihl) and are often much cheaper when bought from a bearing supplier)

If the cages have collapsed - the existing bearings are completely shot - so don't attempt to run the engine whilst they are still in place.

Texas rose

Howdy Mr Chooks, as I said at the top I was running the saw on a 25:1 mix, so I would assume if anything, it ought to have been a bit blue smoky if the mix was too oily?

If I had used the proper 50:1 mix I think the saw may have failed earlier?

There was never any blue smoke when using the saw. Perhaps if the crank bearings had a metal cage instead of their plastic ones they may have lasted longer...incidently it appears - not having stripped them out 'cos I can't get the saw brake off yet - that the only damage is to the plastic bearing cages and not the balls/tracks/or races.

Perhaps the owner (my neighbour who is not living at home just now) was having trouble before I borrowed it? He certainly didn't mention anything untoward at the time of borrowing.

Thank you for your input ...now if you know how to get the saw brake off the end of the crank???

Texas rose

SABL

Any time you borrow something, it is ALWAYS in pristine condition.... YSR

The 25:1 is not an issue (I believe) and will only foul the plug... I don't think it would have any affect on the octane rating and cause pre-detonation (I think I spell it right this time).

I checked the Stihl site and the tech/parts manuals are 4sale only and not online.

Maybe the owner will forget you borrowed it??

You never know if the owner forgot to mix the gas in the first place.... some peeps never read the owner's manuals.

Texas rose

Stihl 029 chainsaw.

Howdy once again Mr Chooks, there's no way I can run the engine in the state it is in, I've only to get the saw brake housing off the crank and then I'll be able to get at the bearings/seals.

I will clean up and use the original piston. I put a vernier gauge on the piston and it measured 48.82 mm diameter, and not 46mm.

It has been suggested by a Stihl dealer that this piston (and Cylinder) could be a replacement from a 39 model Stihl as the original 29 model piston was 46mm as standard fitting.

Texas rose

MrChooks

Texas - I am no expert on chain saw brakes - but if its locking mechanism on to the crank is not immediately obvious (like visible bolts / screws etc) - then it is likely to be a "pressed fit" and you will likely need a "gear puller" to remove it from the shaft.

Are there any bolt holes in the brake face that might be locating hole for a "gear puller" ??

SABL

Hi Tr

Maybe Tw will take a peek at his Stihl and offer some advice. I don't own a chainsaw, or would look at it.

Hard to say what holds the brake housing in place...got a pic??

I will ask the kid and see if he or friends own a Stihl.

Texas rose

Mr Chooks, It appears to be a machined, 19mm tube type nut that holds it onto the crank. There is a tool that you screw into the plug hole which locks the piston which in turn allows you to loosen the brake assembly, but I don't know if it is a left or a right hand thread?

I can block the crank from turning as it is fully exposed. But I do not want to put enormous pressure on until I find out how it is mounted on the crank and whether it is R or L hand thread?

Texas rose

MrChooks

Texas - if it's a screw on fitting - you can work out the thread direction by looking at the engine rotation direction. The brake WILL cause the screw on brake plate to tighten when the brake is applied.

So have a look at the shaft / brake and imagine that the brake plate is a nut and the shaft is a bolt that screws into it. - Then you should be able to see which way is tighten / loosen.

The problem you are likely to face is that use of the brake will have made the brake plate very tight on its thread - so you might need some (gentle) impact to free the locking threads and get it to turn. But be careful - too much impact can do damage

Texas rose

Yes, I could get a pic, but I wouldn't know how to put it on here?

Tr

Texas rose

Mr Chooks, Yes, I will have a look in the morning, by your deduction it's likely to be a LEFT HAND thread, it's far too windy and cold out there tonight, and there is no heating in my workshop...BRRRRRR!

I've taken a couple of pics, but don't know how to put them on here.

I did read on the web somewhere that an air driven impact wrench was required to loosen off a similar brake, but it was not referring to a Stihl, but I do have such a tool.

Tr