Stihl 034AV Super Rebuild

[Vintage Engine Repairs]

OIC
Some saws, like the echo 620, have a bypass hole drilled in the base of the nozzle. It stops full adjustment. Many other carb models do the same, it’s just hidden. All of the H flow doesn’t go through the H adjustment circuit in many saws, it just adjusts a certain % of it.

Ahh yes I’m right with you! Like this one -

 

[Vintage Engine Repairs]

 

[cookies]

your going to enjoy the oil pump output line replacement...i just completed that physical challenge, added a exhaust cooling plate and ported the muffler.
I used boiling water to fit the line on the pump then installed the pump with line into the saw. For the brass fitting I used a screw to stretch the line while holding the line on the back side with forceps to prevent the line from spinning then drove the brass nipple in with a hammer/punch.

 

[Vintage Engine Repairs]

your going to enjoy the oil pump output line replacement...i just completed that physical challenge, added a exhaust cooling plate and ported the muffler.
I used boiling water to fit the line on the pump then installed the pump with line into the saw. For the brass fitting I used a screw to stretch the line while holding the line on the back side with forceps to prevent the line from spinning then drove the brass nipple in with a hammer/punch.

Haha I have done oil lines to 3 different saws so far that use the stiff line. The key is heat from a lighter and a little press fluid. Best advice is not to cut that double length size hose until you have attached one end to the fuel pump barb. Heat the hose for literally 3 seconds and then holding the unheated section with pliers that should be just a little further back than the full length of the barb, push it on. It will slip on no problem. The first time I ever did it was a nightmare! With heat and a little practise, it’s very simple.

if you heat too much hose it will kink trying to push it on, and if you hold the hose where it slips onto the barb it won’t go on. Too cold and it won’t go on and too hot and it just crumples

Don’t forget the spring too! To install the brass ferrule It’s either a 1.5mm or 2mm punch that fits right inside down to the bottom, then just tap it home.

 

[Vintage Engine Repairs]

your going to enjoy the oil pump output line replacement...i just completed that physical challenge, added a exhaust cooling plate and ported the muffler.
I used boiling water to fit the line on the pump then installed the pump with line into the saw. For the brass fitting I used a screw to stretch the line while holding the line on the back side with forceps to prevent the line from spinning then drove the brass nipple in with a hammer/punch.

I’m guessing the pressure and vac test went all well? That’s the stage that I find most tense lol.

 

[SteveSr]

Carb is getting a new nozzel check valve, a welch plug, and all the other standard parts

You need to seal around the new nozzle and especially the welch plug. Thin cyanocarylate (super glue) works well. Leave the carb open in a humid/damp location for a day or two to make sure that it cures completely. You probably should have just resealed the welch plug. Did you find anything under there that needed cleaning? So far, I haven't. I just check for flow with spray carb cleaner.

 

[Vintage Engine Repairs]

You need to seal around the new nozzle and especially the welch plug. Thin cyanocarylate (super glue) works well. Leave the carb open in a humid/damp location for a day or two to make sure that it cures completely. You probably should have just resealed the welch plug. Did you find anything under there that needed cleaning? So far, I haven't. I just check for flow with spray carb cleaner.

I use a very very small amount of clear nail polish on the bottom edge to take up any imperfections on the welch plug mating surface, but I have never coated around the top of the plug on any of them.

 

[SteveSr]

I use a very very small amount of clear nail polish on the bottom edge to take up any imperfections on the welch plug mating surface, but I have never coated around the top of the plug on any of them.

Look up nitrocellulose (nail polish) for resistance to your particular motor fuels or actually perform a test. In the States they used to use nail polish. I think that it is fairly resistant to regular gasoline but not at all to alcohol. YMMV.

Any time that you rebuild a carb and replace the welch plug you should probably do a leak test by pressurizing the venturi with a home made Stihl adapter as shown in the attachment

 

[Bob Hedgecutter]

Look up nitrocellulose (nail polish) for resistance to your particular motor fuels or actually perform a test. In the States they used to use nail polish. I think that it is fairly resistant to regular gasoline but not at all to alcohol. YMMV.

Any time that you rebuild a carb and replace the welch plug you should probably do a leak test by pressurizing the venturi with a home made Stihl adapter as shown in the attachment

But what if we don't get none of your moonshine fuel over here?

 

[Vintage Engine Repairs]

Look up nitrocellulose (nail polish) for resistance to your particular motor fuels or actually perform a test. In the States they used to use nail polish. I think that it is fairly resistant to regular gasoline but not at all to alcohol. YMMV.

Any time that you rebuild a carb and replace the welch plug you should probably do a leak test by pressurizing the venturi with a home made Stihl adapter as shown in the attachment

Excellent attachments thanks!

No worries with Ethanol fuel here. I don’t like the idea of any sealant pasted all over the plug regardless though.

The best of both worlds - I use nail polish and the brush to spread a very thin layer onto grease proof paper, then take the welch plug (you know how it will semi stick to your finger if you press firmly on the top of it) and dab it right onto that nail polish and then transfer it to its seat in the carb.

It’s so little that it’s not visible by eye, but enough to take up any minor imperfections between the plug and carb contact surface.

I have been thinking of ways to test the validity of the welch plug. I’ll run it first, but any issues I’ll pop out the metering lever and needle assembly, block the H and L drilling’s in the metering chamber floor with blutack and then put it back together. Then I’ll fill it with a few psi of air from the fuel barb and check for leaks. You could spray soapy water through the venturi.

 

[vienster]

Loc tite makes three different activators that speed up cure time. I didn't know about this product for years. If it's hot out it speeds up cure time to the point that fasteners will cure before you have a chance to insert them. It also specifically lists magnesium as inactive and that this product is required with it, but i've used it on magnesium without it.

 

[cookies]

I’m guessing the pressure and vac test went all well? That’s the stage that I find most tense lol.

I am still waiting on the tester tools to come in the mail, I had to have some words with the local dealer when they refused to sell the carb block off tool stating its dealer only...they ended up calling stihl and being told to sell it to me.

 

[Vintage Engine Repairs]

Today was the start of the rebuild:

Firstly the bearings, thanks @Mattyo for the tip regarding washers on a bolt to install them.



Once installed I checked that they were fully seated and level with a dial indicator and float glass plate.


Pulling the crank through with @Mattyo ’s tools


Centring the crank


Seals


Disappearing c-clips, bloody fingers from stabbing yourself, swearing profusely and c-clips falling in the engine is a thing of the past, the 10 and 12mm install tools are worth their weight in gold.

New piston rings installed


Torqued the cylinder down

 

[Vintage Engine Repairs]

Ok chaps, back rebuilding today.

Firstly after drilling out the fuel tank for the larger fuel hose:


I tested the new drilling to make sure it didn’t leak, I also tested the cap washer and tank vent

A little #3 on the intake manifold


Pressure and vac testing



New clutch springs, drum, rim and bearing



New HT lead and sleeve
Connecting the throttle rod


Recoil


andddddd...


Done!

 

[BuckthornBonnie]

The term meticulous still doesn’t do your work justice. Nice build, there.
On the pto side bearing... I’ve seen some saws with varying clearances between the bearing and the oil pump. Having that dial would be nice to see the tolerances. I always use the pump to seat bearings (heat method) but appreciate all the ways it can be done.

 

[Whiskers]

What’s the range an 034 super sell for in Australia? I know prices can be pretty high for saws.

 

[Vintage Engine Repairs]

The term meticulous still doesn’t do your work justice. Nice build, there.
On the pto side bearing... I’ve seen some saws with varying clearances between the bearing and the oil pump. Having that dial would be nice to see the tolerances. I always use the pump to seat bearings (heat method) but appreciate all the ways it can be done.

Hey mate and thank you! I tried heat first and even at 150 it didn’t go in, after that I just did the alternative above. I much prefer heat, but this just wasn’t having it. Both bearings were very tight, the tightest I have done before. The older saws I have worked on go in at about 125-130c

As for bearing - firstly I checked with a 0.03mm feeler gauge to see if it would fit in anywhere between the pump housing and the bearing and it didn’t.

As for the measured degree across the outer race there was a max variance of 0.05mm or 0.002”.

The oiler that’s used as the bearing seat is cast so it’s unlikely to be perfect and that could be the reason, but either way it’s less than the thickness of a human hair, even I can live with that... just

 

[Vintage Engine Repairs]

What’s the range an 034 super sell for in Australia? I know prices can be pretty high for saws.

Typically around the 600-700 mark, but the issue is finding them. They are so hard to find and when they pop up they are totally battered.

 

[cookies]

vac/pressure tester came finally, passed both tests with 0 drop/rise..new spark plug and fuel fill cap are the last two parts i am waiting on to consider it finished up. Today I did my own muffler mod on it by cutting the divider out of the lid and opening up the outlet 200% I welded a curved baffle over that inside then cut and welded the old hole filled outlet cover over the new large outlet. Total time of about 2 hours doing it, not nearly as loud as simply cutting a hole with a little cover screwed on and the exhaust is cross directional to protect the users hands and the saws paint.

 

[Dirk-O-Rama]

Thanks for this thread.

I just picked up a well maintained, one-owner (friend, and not a professional) 34S that's in excellent condition; I've always had smaller machines and this thing has just ruined me for chainsaws.