Stihl 028 diagnosis and rebuild

[JW51]

I’ve got a hand-me-down 028 AV woodboss that was my only saw for a while, quit on me, but I’d like to get going again as a backup. I’ve worked on a few small and large engines, but this will be first chainsaw I’ve been into this deeply.

Long story, short - it has compression around 105 lbs so I’m thinking at least rings and maybe piston/cylinder are in my future. Piston looks fine from the exhaust port so I’m not sure what’s up yet.

I’ve got tons of questions, but in the interest of brevity, I’ll just take them one or two at a time.

Currently have the the air box/ handle removed and been trying to conduct a crude vacuum test with a cheap brake bleeder. I’ve struggled to get the intake boot plugged fully but will figure something out. Really want to get this done before I pull the cylinder.

1). What sort of reading (my gauge reads inches) am I looking for and how long should it hold?

 

[TheTone]

7 to 10 psi pressure and same in inches of vacuum. It should hold for a few minutes without moving. The vacuum measurement is probably the most important and probably the only one you can do with your present equipment.

 

[67L36Driver]

Holding vacuum for a few minutes is not in the cards, really.

Gauge drops quickly or slowly is more indicative.

I have my fourth 028 project in the past two months.

It runs but, a little loud. [emoji2960]

 

[HarleyT]

7 to 10 psi pressure and same in inches of vacuum. It should hold for a few minutes without moving. The vacuum measurement is probably the most important and probably the only one you can do with your present equipment.

My wife says that 7-10 inches is barely acceptable.....

 

[JW51]

Finally found one of of my kids’ glue sticks was about the diameter needed to plug the intake boot.

Takes about 20 seconds to bleed down from 10 inches of vacuum. And I’m pretty sure what I’m losing is still at the boot.

Sound good enough to proceed and assume crank and case seals are good?

 

[67L36Driver]

I’d call that golden. [emoji106]

 

[JW51]

Sweet.

Off with the jug!

 

[Mad Professor]

Might want to do seals anyway.

028 gasket set w/seals is NLA

But seals are same as BR400 blower, and BR400 gasket set is < $$$ than individual seals (4203 007 1050).

Iv'e got to order 1 or 2 BR400 gasket sets, as I've an old 028S and a BR400........ And seals are original.

 

[Yukon Stihl]

I have had saws hold 7-10 psi vacuum for 10 min and longer

 

[JW51]

Thanks for all the input. I do have a crude way I can use a bicycle pump and apply some pressure to the tank and spray to look for bubbles. Probably do that one more time, to test my theory that whatever small loss is through the intake boot.

But for now, I’m gonna go ahead and ask some questions to help me think about cost and options for the top end.

Overall goal for this project is to make it a good cutting and reliable saw again, maybe a couple simple performance mods....and do so on the (relative) cheap. But without taking silly shortcuts.

I didn’t get the jug pulled last night for further analysis, hopefully tonight. In the meantime.....

1) I’m assuming the lowest cost scenario is rings only. How can I tell if the piston is good enough to re-use?

2) If the piston needs replaced but cylinder is OK, what should I go buy? Sounds like the meteor pistons are pretty highly regarded?

3) Buying a piston and rings for $30-$40 doesn’t put me too far from the cost of one of the cheaper aftermarket top ends, perhaps even one of the “028 Super” big bore ones? Anyone have experience with those parts and have some guidance on re-using the OEM (presumably small bore) cylinder with a new piston vs a whole new AM top end?

 

[Mad Professor]

Thanks for all the input. I do have a crude way I can use a bicycle pump and apply some pressure to the tank and spray to look for bubbles. Probably do that one more time, to test my theory that whatever small loss is through the intake boot.

But for now, I’m gonna go ahead and ask some questions to help me think about cost and options for the top end.

Overall goal for this project is to make it a good cutting and reliable saw again, maybe a couple simple performance mods....and do so on the (relative) cheap. But without taking silly shortcuts.

I didn’t get the jug pulled last night for further analysis, hopefully tonight. In the meantime.....

1) I’m assuming the lowest cost scenario is rings only. How can I tell if the piston is good enough to re-use?

2) If the piston needs replaced but cylinder is OK, what should I go buy? Sounds like the meteor pistons are pretty highly regarded?

3) Buying a piston and rings for $30-$40 doesn’t put me too far from the cost of one of the cheaper aftermarket top ends, perhaps even one of the “028 Super” big bore ones? Anyone have experience with those parts and have some guidance on re-using the OEM (presumably small bore) cylinder with a new piston vs a whole new AM top end?

After inspecting piston/cylinder, you can check wear using feeler gauges at piston skirt to cylinder. Crude but it works, don't mar the piston with the steel feelers, put a bit of oil on things. Post pictures.

OEM parts are best but most expen$ive. After market Caber rings Meteor piston.

If you need cylinder a 028S has biggest bore and is a bolt on. OEM new/used or Meteor.

 

[JW51]

After inspecting piston/cylinder, you can check wear using feeler gauges at piston skirt to cylinder. Crude but it works, don't mar the piston with the steel feelers, put a bit of oil on things. Post pictures.

OEM parts are best but most expen$ive. After market Caber rings Meteor piston.

If you need cylinder a 028S has biggest bore and is a bolt on. OEM new/used or Meteor.

Have you used an aftermarket 028 cylinder?

 

[Mad Professor]

Have you used an aftermarket 028 cylinder?

I used OEM on my 028S/036/064/026

I have used aftermarket on my 038 saws, back when Tecomec was still made in Italy

 

[TheTone]

Takes about 20 seconds to bleed down from 10 inches of vacuum. And I’m pretty sure what I’m losing is still at the boot.

Probably but don't assume that. Twenty seconds to bleed down from 10 inches vac is IMO a significant leak. I like to have the manifold on when I vac check, if possible (tests manifold along with the rest). I got a graduated set of rubber stoppers from the Widget Co. (very reasonable price) and I smear a little Dow-Corning high vacuum grease (from when I worked as a chemist) on the stopper where it meets the manifold. Forms an air tight vacuum seal.

I have had saws hold 7-10 psi vacuum for 10 min and longer

Ditto. Most of mine hold that long.

I do have a crude way I can use a bicycle pump and apply some pressure to the tank and spray to look for bubbles.

By tank I assume you mean crankcase, and yes, that's the way to be sure.

 

[Mad Professor]

and I smear a little Dow-Corning high vacuum grease (from when I worked as a chemist) on the stopper where it meets the manifold. Forms an air tight vacuum seal.

I've used that grease a lot. Great for high-vac applications, but a PITA to get off totally clean. Hydrocarbon solvents/paint thinner works pretty good.

 

[JW51]

I bought a rubber stopper for the intake and shored up my exhaust block a little bit.

Pumping the vac up (down?) to 20 inches...it now takes 2 minutes 24 seconds come to zero.

 

[Yukon Stihl]

When i find one that loses Vac...
I switch to pressure and find the leak.
Vac/pressure test the first things to do when you get an unknown saw.
I just bought a group of Stihls,028 great condition and ran good,didn't really want it but it came with 2 not running saws that the PO gave up on,026 and 034,both in decent condition all with bars and chains.
026 had a china carb on it that was no good,but the vac/pressure test told me the saw was sound and should run.Took a old carb off a red lever donor and the runs great
034 had a china carb on it.Failed vac test and pressure showed that it needs bearings and seals.Took me all of 10 minutes to shelve the 034.PO spent hours on both and gave up.

 

[Sam R]

Stihl specs are no more than 3 psi leak down in 20 seconds. Some of you guys go pretty nuts making sure your CCs are not leaking one atom of air.
Of course if you're tearing it down anyway and get more than 1 in 20 seconds you might do seals as a good measure, but come on.

 

[JW51]

Stihl specs are no more than 3 psi leak down in 20 seconds. Some of you guys go pretty nuts making sure your CCs are not leaking one atom of air.
Of course if you're tearing it down anyway and get more than 1 in 20 seconds you might do seals as a good measure, but come on.

Thanks, that’s helpful. I have a redneck way setup to apply some pressure, but not measure the leakdown. Is there a similar spec for vacuum? As in, so much loss in so many seconds.

I’ve not been able to locate a leak thus far. My muffler block is a doubled over piece of gorilla tape...definitely a suspect. I don’t have things torn down to the point to spray soapy water on the crank seals. Would like to rule out some other possibilities first. For all I know, my crappy vac pump might leak on it’s own. That’s probably something I need to verify as well.

 

[HarleyT]

Yeah, getting too anal over a very slow leak, can drive you crazy.

Especially if it is just a leak at the block off devices.




I remember when I was young, I was working on a Homelite 330, and it had a real slow air leak. I ended up tearing the saw down to the bare block/engine. There was a tiny hole in the bottom!!!!


Tearing down that pig of a saw was no easy task, let alone putting the damn thing back together!!!

That tiny hole, looked like it was made that way!!!!

I re-read all of my Homelite manuals, trying to find out anything about this damn hole!!!

Finally, I called the phone number on one of the manuals, and finally talked to an actual tech at Homelite.{This was in the 1990's}.

He said, "oh, it was made that way"........