Stihl 034 Special Scored Piston

[tnam]

Hi Everyone,

Yesterday I travelled 2.5 hours to buy an 034 Special. Paid $500 Aud for it. I'm pretty broke and it was a stretch but needed a saw of this size. I got it home and had a look through the exhaust port before starting and she looks pretty shot? I don't have a heap of experience so just reaching out for what you all reckon. Typical of a saw this age?

It started, idled and ran well when I tested. The fella wasn't comfortable with me taking a peek inside yesterday so I took a punt.

Is it going to damage the saw further running it like this? Costly fix? I'm comfortable replacing the piston and cylinder but not sure about other air leak tests and their cost. In saying that I don't really have a lot of time to stuff around with it and need it asap

 

[president]

the piston looks newish with the witness marks
visible , perhaps light marks on the cyl?
they sometimes clean up well . a presure test and new seals
might do it if the bearings are good!

 

[a. palmer jr.]

I think I see why the seller didn't want you to take a peek inside. I don't know anything about the currency in your country but I wouldn't give much in American dollars for a saw with a damaged top end.

 

[irhunter]

Is it going to damage the saw further running it like this?

Probably. It depends on how bad the jug is right now. Don't run it without pulling the piston and taking a look.

Costly fix?

Maybe, just a piston kit...and, a pressure/vac test.

I'm comfortable replacing the piston and cylinder but not sure about other air leak tests and their cost. In saying that I don't really have a lot of time to stuff around with it and need it asap

I suspect this will either take more time than you want it to...or, more money.

It needs the pressure/vac done before pulling the piston. And, don't buy parts until you have tried to clean up the cylinder.

That's my 2 cents. Sorry about the not-so-great news. They are nice saws!

Roy

 

[John Lyngdal]

the piston looks newish with the witness marks
visible , perhaps light marks on the cyl?
they sometimes clean up well . a presure test and new seals
might do it if the bearings are good!

Agreed. The cylinder might(will) need an acid treatment to remove some aluminum deposits.
Chances are you only need a new piston after the cylinder bore is cleaned.
No need to spend extra $$ for an OEM piston, I'd suggest a Meteor piston for a final solution.
I'd recommend purchasing a cheap AM piston to determine if your cylinder bore cleaning process was successful before installing a quality unit.

 

[Vintage Engine Repairs]

Where are you in Aus? Happy to help out where needed if you’re in the same state.

Don’t run it like that, take the cylinder off, clean it up and replace the piston and rings. Meteor is great and budget friendly.

We can do the seals together if you’re close.

Edit: just saw your location as QLD - cheaper to buy one than come here for a PV test haha.

Also, 500 AUD is a great price for a 034s. With a bit of extra money in the piston you’re still less than I paid for mine which was $700 I believe?

Either way, in future, my advice is walk away from any deal when you can’t inspect the piston no matter how good it seems.

 

[Dennisthemenace]

As others have said, try to work out what caused the scoring. It's not normal wear so something is wrong, no use bunging a piston in and hoping for the best.
I think the seller was lucky you came along but a 034 Super is a desirable saw. Especially if the jug can be saved

 

[Ironhorsedoctor]

Agreed. The cylinder might(will) need an acid treatment to remove some aluminum deposits.
Chances are you only need a new piston after the cylinder bore is cleaned.
No need to spend extra $$ for an OEM piston, I'd suggest a Meteor piston for a final solution.
I'd recommend purchasing a cheap AM piston to determine if your cylinder bore cleaning process was successful before installing a quality unit.

I wouldn’t do an acid treatment unless you know exactly what you’re doing! Misplaced acid or acid migrating under the cylinder plating will destroy a potential serviceable OEM cylinder. Scotch bright and a little elbow grease works well! Miner scratches as long as your nail doesn’t catch on it is acceptable. Your finger tip will let you know if the aluminum transfer is gone! I agree on not spending extra $$ on a OEM piston but I disagree on using the cheapest AM piston. If you’re satisfied with the condition of the cylinder use a Meteor piston and caber rings. Why would you want to do it twice for as little as $15 USD. If you don’t have the means for pressure testing just replace the crank seals while you have the saw nearly half disassembled. The Stihl 034 is a saw worth saving and short cutting on repairs is sometimes unfortunately a waste of $$ and time. Tune the carburetor for a 40:1 mix. That was manufacturer’s specs back in the 80’s and the bottom end will thank you too! Lastly if you don’t determine the cause of the failure it will most likely fail again. Good luck with your project!

 

[tnam]

Thanks everyone for your replies, I really appreciate it. You're a bunch of bloody legends!

It has been a **** experience and I was pretty devastated but now that I'm over it I'm actually excited to rebuild her and do some learning. I'll just have to take my time with it and use my 300mm Makita battery saw for felling small stuff in the meantime

Just to confirm, if I do the crank seals while I'm there I won't need to do a pressure test before pulling the cylinder? Just do one once she's all assembled.

I've seen a lot of cheap cylinder honing tools available. Any of y'all have experience with how are they compared to scotch brite + wet/dry paper? Using muriatic sketches me out a bit.

https://www.supercheapauto.com.au/p...obgiR_wSUmj1UQ6giXUaAjbCEALw_wcB&gclsrc=aw.ds
Things to check as potential causes of the scoring: Air filter, Impulse line, crank seals, cylinder bsse gasket, carb intake boot.. am I missing anything?

 

[Vintage Engine Repairs]

Thanks everyone for your replies, I really appreciate it. You're a bunch of bloody legends!

It has been a **** experience and I was pretty devastated but now that I'm over it I'm actually excited to rebuild her and do some learning. I'll just have to take my time with it and use my 300mm Makita battery saw for felling small stuff in the meantime

Just to confirm, if I do the crank seals while I'm there I won't need to do a pressure test before pulling the cylinder? Just do one once she's all assembled.

I've seen a lot of cheap cylinder honing tools available. Any of y'all have experience with how are they compared to scotch brite + wet/dry paper? Using muriatic sketches me out a bit.

https://www.supercheapauto.com.au/p...obgiR_wSUmj1UQ6giXUaAjbCEALw_wcB&gclsrc=aw.ds
Things to check as potential causes of the scoring: Air filter, Impulse line, crank seals, cylinder bsse gasket, carb intake boot.. am I missing anything?

Don’t worry, you have a bunch of great people on here who will happily journey with you on the rebuild, myself and many others love this particular saw and consider it one of stihls best. Rest assured know that time spent now will result in a saw that will outlast you!

I don’t recommend using that hone to try and remove the transfer. It will just gum up right away and won’t remove it. Also avoid ball hones which are diamond or silicone carbide coated. it will destroy the Nikasil leaving a far too aggressive crosshatch and premature wear can result.

Just swapping out the seals isn’t going to be a sure conclusion that the engine is air tight and won’t run lean. Though if you replace the seals you can test everything else with pressure using a bike pump and some block-off’s. You mentioned you’re in a budget, buy nitrile seals from a bearing supplier they’re about $5 per seal rather than $25 per seal.

Also, the 034 is delightfully simple to work on, but note, if you need to change the main bearings (you shouldn’t but I’ll mention it anyway) you need the case pocket to be at least 180c and a frozen bearing to get them in, even then you may need to tap them home. Some cases are looser than others, the 034 is a tight case lol.

Also the oil pump hose is a pain, if you change it, leave the whole hose it’s full length and attach it to the barb then cut it - use a lighter or hot water and some lubricant. Don’t cut it to length and then try attaching it, you’ll fail a few times before you have success with it which is what leaving it full length will give you.

Just a couple of tips to keep in mind.

Here is a thread I made of rebuilding mine

https://www.arboristsite.com/threads/stihl-034av-super-rebuild.348873/
Edited to correct spelling

 

[irhunter]

OK...you really don't want to pressure test it...lot's of people are that way until they score their first brand new piston.

There is really no replacement for pre- and post-tear-down vac and pressure tests. But, like I said, many folks start out skipping the tests.

There are a number of low-cost approaches to cobbling together a vac/pressure tester.

But...it's you saw.

As far as cleaning the cylinder...this is a great way and only requires homemade arbors and an electric drill:



Roy

 

[president]

I wouldn’t do an acid treatment unless you know exactly what you’re doing! Misplaced acid or acid migrating under the cylinder plating will destroy a potential serviceable OEM cylinder. Scotch bright and a little elbow grease works well! Miner scratches as long as your nail doesn’t catch on it is acceptable. Your finger tip will let you know if the aluminum transfer is gone! I agree on not spending extra $$ on a OEM piston but I disagree on using the cheapest AM piston. If you’re satisfied with the condition of the cylinder use a Meteor piston and caber rings. Why would you want to do it twice for as little as $15 USD. If you don’t have the means for pressure testing just replace the crank seals while you have the saw nearly half disassembled. The Stihl 034 is a saw worth saving and short cutting on repairs is sometimes unfortunately a waste of $$ and time. Tune the carburetor for a 40:1 mix. That was manufacturer’s specs back in the 80’s and the bottom end will thank you too! Lastly if you don’t determine the cause of the failure it will most likely fail again. Good luck with your project!

T1

 

[OM617YOTA]

My one saw plan for over a decade was an 034S I got used. For a bit I was keeping three houses in firewood with that saw.

Sucks that you got skunked, the saw is well worth rebuilding.

Hope you contacted the guy and told him about the jackwagon move he pulled. Doubtful, but hopefully he'll send you back the funds to rebuild it. If not, may he get a lifetime free pass to the finest brothel in the land, and a pecker that's never able to peck again.