Basic Rebuild: 034 rebuild and mods

A friend brought me this saw and the story went something like this: “It has been sitting in the shed for a couple of years, and was hard to start and keep running, but if I kept playing with the choke and revving it up it would run enough so I could get the cuts done. But now it won’t start at all.”
So I pulled the rope through and no compression, so I told him he probably burned it up. “No, no, don’t say that! It just needs a spark plug,” he says. So I pull the muffler and show him this:



And I tell him the piston and jug are goners. The chain is an old Oregon that has been filed back to nothing, no two cutters alike, and the saw is covered with fine dust. The filter has the flocking worn away in spots. So I tell him it will cost a lot to fix and he says never mind it is yours, so on the project pile it goes.
So I have accumulated a bunch of 1125 series parts, and I don’t have an example of an 1125 saw in the collection. (034, 036, MS 360)
So apart it comes. I am fairly sure this is a lean failure, and so as it comes apart, I will be testing for faults that would confirm this. The first thing off is the carb so I can do a pressure / vac test. And here is what I notice on the little Tilley carb inlet fitting:



So I have my first major lean fault. The engine is sucking air at the fuel inlet fitting at WOT. Anytime there is damage to a piston the fault needs to be identified as the saw is torn down so that any and all faults can be repaired during the rebuild. I did not find any air leaks or other major faults, but the intake side of the piston was dull grey and all the machine marks were worn off, indicating long term dirt ingestion, which is confirmed by the air filter being shot. This also causes lean running, so I have confirmed that it is a lean failure. The intake side shows no scoring damage, which pretty much rules out straight gas, and there is no melt damage to the underside of the shroud, so the saw was not overheated.
The only other major problem is that the case is busted at the front left side:



No problem as I have a new one! Along with a MS 360 piston and cylinder.



And with a little trimming of the shroud, it will fit nicely over the bigger cylinder. So I will have an 034 sleeper, since it will have the 036 piston and cylinder, and the muffler will also breathe a little better than the original.



As the saw comes apart, I notice that the 034 has a non-adjustable oil pump, so that will get upgraded to an adjustable one.



I also will put in the new style bar studs, and the new cover as well.

Now it is time to split the case. I will be using the Stihl tools. They are pricey but work brilliantly, and while I have done this before with a hammer and a brass drift, using the right tool for the job is not only faster and smarter, but eliminates the chance to damage any critical parts. It might not pay to buy these unless you do this a lot, but if you ruin a crankshaft without them, then it sure would have been worth buying them then. I know Andy did a post of how he made a splitter that worked well, but I don’t recall if he made a tool for pulling it all back together, and that is the other half of the trick to swapping out a crank, case halves, and bearings.
First drive out the two dowels and remove the five T 27 screws.







Then install the splitter over the bar studs:





Once in place tighten the bolt and the case will start to split with a pop – pop – pop as the crankshaft and bearing slide out of the case.

Now the crankshaft has to be pushed out of the flywheel side of the case. A different tool is used for this. On the tool is a chart that says use hole number 7 for the 1125 series saw.





So the number 7 on the plate goes at the six o’clock position, and the three holes labeled with 7 line up with the three holes in the crankcase, so a long bolt is threaded in and the plate is clamped to the case. There is a machined surface on the crankcase to let the tool seat against. Then tighten the bolt, which is left hand thread ( I will show you why during assembly) and the crank and bearing slide out of the case.





So now the old bearings need to come off of the crank, since I will use it in the new case, which comes with the bearings already installed.



If I was changing bearings, I would heat the case with a hot air gun and use a laser thermometer to get it up to temp, and the bearings would just about fall in. Since they are already in the case, all I have to do is get the old bearings off, clean and lube the crank, and use the same two tools to pull it all back together, WITHOUT A HAMMER!!!

So to remove the bearings I use a bearing splitter, and tighten it up until I hear the bearing pop once. Then mount the two bolt puller to the splitter and pull the bearing off, with no prying or levering. These crankshafts can easily be damaged by prying or pressing or hammering, so again, the right tool is needed to do the job right.






Now the crank is ready for cleaning and install.



Here is a close up of the damaged case and the new one.



As I was looking through a pile of mufflers I noticed that one has a vent slot as well as the outlet hole, so I will use that shell, open up the hole a bit, and reinstall the screen and put on my hearing protectors!



So I will clean everything up, get the bench organized, and then next will be reassembly. I will show you how the Stihl tools are used to pull the crank into the bearing on one side, then pull the crank through the other bearing and pull both halves together.

Nicely done!!! I love the 034.

This thread really shows why the right tools make things so much easier. Now only if those tools were cheaper...I have the stihl vac/pressure tester and it works great. Makes things a lot simplier. I was lucky enough to get it for less than list from a ex-stihl mechanic.

Great post here Stihl #1..the pictures rock and helps show why stihl designed parts the way they did. Keep them coming.opcorn:

The 034, 036, ms360 family is a nice lineup. Balanced well and the build quality is great.

EXCELLENT step by step !
I had an 034 and now have an 034 super (I like the super) and use it more often than not .:greenchainsaw:

How about some pictures ? Nothing shows on my computer but little x's. Thanks in advance

These are the adapters that come with the 2 crankcase tools.



One end is threaded to screw onto the spindle of the tool, and the other end is threaded to fit either the clutch or flywheel side of the crank, so it can be pulled through the bearing. A ball bearing should have a tight fit between the race that spins and whatever it is spinning on, and it can have a looser fit for the race that does not turn. So the bearing will go into the mag case easily by heating the case, but the crankshaft stub must be carefully pulled through the inner race, the one that spins, not hammered in or pressed in, as either could fold the crankshaft up through the big end.
The mag side tool comes with 2 plates, and as I showed earlier, it has numbers that match the series number of the engine so you know which set of holes to use to push the crank out.



I also keep an assortment of bolts, nuts and washers in the same box with the crankshaft tools.



The next must have item is the shop manual, as it tells you which adapter to use for pulling the crank through, and details on how to use the tool. The tool itself doesn’t have any instructions with it.



So the next step, following the details in the book, is to put the correct adapter on the spindle, then lightly oil the stub of the crank, slip it through the bearing, and then thread it into the adapter.



Next rotate the tool until all the slack is out and it is tight against the case, then rotate the spindle, which will also rotate the crank, and while you do this keep the rod pointing up so it doesn’t get bent against the case, and pull the crank in until the spindle on the tool is tight and will not rotate any more. I use a scrench since the spindle is the same size as a bar nut, and that way I don’t get it too tight. Then take the tool off and check that the crank spins free.





It now spins easily, and the whole process to pull it through takes maybe 20 seconds. WITHOUT A HAMMER! Did I say you don’t need a hammer to do this? These tools work so well that I get mad when I think about how many saws I struggled with and wasted time on trying to do this with a hammer and not messing anything up along the way.

So now I make sure the dowel pins are sticking up just a little bit to help keep the gasket in place, and then follow the book to use the other tool to pull the crank through the clutch bearing, and at the same time pull the case together.

For the next step I put the new bar studs in, with a drop of red LockTite to keep them in place. I use the double nut method to tighten them up.





Then select the right adapter and put it on the tool. So I oil up the crank, thread it into the adapter and tighten the spindle, again being sure the rod doesn’t get pinched and making sure the gasket stays in place. I put 2 screws through the clutch side into the magneto side to help keep the gasket lined up as well.







Once the case halves are seated install the 5 crankcase screws and start them, but then hammer in the 2 dowel pins before torqueing the screws to spec.



Now check the crank to see how it spins.
OH NO! It is jammed up and won’t turn at all!!!
Not to worry. Take a small dead blow hammer and hit both ends of the crank sharply.



Now it spins freely. This releases the bearings and centers the crank so there is no left over bind from the pressing and torqueing to get the case halves together. The crank won’t always be tight after doing this, but I always give each side a tap to be sure.

Next I install the seals. I put some good grease in between the double lips, and on a seal with a hard metal body just drive it in with the press tool and the dead blow. This tool works for both sides by flipping it over, so I never use a metal faced hammer on it. On engines with the soft rubber sides on the seal I put on some sealant on the outside of the seal, but it is not needed here.







And now the clutch side. On this model the seal actually fits down into the bearing, not the case.



Now we are ready to start putting everything else back on. I like to get the handle housing on, and then the piston and cylinder. Then I can do a pressure and vac test before going any further, to make sure the crankcase has no leaks. If there are any it is easy to find and fix them while the saw is still apart. The annular buffers are OK so I will reuse them. I always use the STIHL Press Fluid lube to put these in as well as any other rubber parts such as o-rings or fuel lines or grommets. It really makes it easier.



I will upgrade the DG buffer screws from slot heads to T27.



Here is the 034 piston on top of the 036 piston. The 036 is 2mm larger in diameter, and the cylinder has more cooling fins on it. There was a 034 Super that had the 48mm diameter piston.



As a wise man once said, “There is no replacement for displacement.”

Next cut off the protruding gasket material and lube all the crank bearings. I got tired of squirt bottles that either leaked or didn’t work, so I just dip a screwdriver in the oil and let it run down to where I want it to be.





Next is a new little end rod bearing, lubed of course, and then put the piston on.



Slide the new wrist pin in and then be sure the arrow is pointing towards the exhaust.




I put a couple of spacer blocks under the piston to keep it steady and then put in the circlip. I start the circlip like this with the opening at 12:00.



Then I use a small screwdriver to carefully push it in.



Then be sure it is seated all the way around. STIHL has a high dollar tool for this that actually works very well, but you need about 10 different ones for the entire product line, and the little orange screwdrivers are free, so that is what I use at home.

On most STIHL pro saws, put the intake manifold on before mounting the cylinder. Line up the tab with the seam on the cylinder and tighten the clamp for about a 4mm gap.





This is the best ring compressor set out there for small two-strokes and I think Bailey’s has them, and they are less then $10 when I bought these.



Oil up the rings and piston, and the cylinder walls.
Be sure the ring end gaps are lined up with the locator pins, and put the cylinder on top of the little bit of piston that is sticking up above the edge of the compressor.





Then just slide it down in place over the rings with a little downward pressure.



Then remove the spacer blocks and ring compressor. Notice that I didn’t forget the gasket. If I did then the cylinder would have to come back off.

Now put the back two cylinder screws in place before working the cylinder the rest of the way down. Then fold the manifold back and wrap a piece of small starter rope twice around the manifold, and get the cylinder down in place.





Now pull the rope and the manifold will pop through the opening. This way you don’t tear a hole in it like will happen if you use needle nose pliers. Ask me how I know!





Put the front screws in and be sure the gasket is lined up, and start the screws in and gently snug them up, then use a cross pattern and torque to spec.





Now I am ready to do a pressure and vac test. These are the tools I will use. I will plug the deco valve hole, which you should always do when doing the test. I will leave the plug in as I don’t really need a deco valve for this saw, and since I am using the 034 shroud there isn’t an opening for it anyway.



I use an old 066 muffler spacer to hold the rubber in place over the exhaust. This is easier than trying to use the muffler. This spacer fits most STIHL pro saws.

Put the spark plug in tight, and the adapter on in place of the carb. Be sure to put the little brass ring in the manifold first, as it helps it seal.



Now I pump up to about .5 bar, or 7 PSI, and it should hold steady, and it does.



Then pull the same negative pressure and it should hold as well. While the vac is present, always rotate the crank to verify that the seals are good, especially on a saw that has been running and you are troubleshooting.



This one holds well under vac. I guess it dang sure better since it is mostly new parts!!!

So all that is left is to reassemble the saw and check it out. I will add some more pics when I do the carb eval, since it seems that there are always lots of questions on carbs.

An absolutely awesome tutorial. Well done!

An absolutely awesome tutorial. Well done!

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I was thinking the same thing.

Awesome job man! You must have a very nice camera, pics look just beeeooootifull! I want to do do the same project on an 038 Super, I will probably be looking through this thread a lot.

Well done sir!!

Very impressive. Have you considered publishing a book?

Great job. Well done.