Stihl 028 diagnosis and rebuild

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
jug finished.jpg
It was the exhaust block. Once I had that good it held from 16 inches to 13 for like 11 minutes. Took twenty minutes to leakdown to 8.

I’m moving on. Just figured out my T27 scrench is too fat for the cylinder bolts. Stuck without the right tool for tonight.

You can take a chain file to open up slots in cyl fins if that is problem? If it's a big deal get right tool.
 
The crankcase and oil tank have a common wall sealed by the gasket. As do all of the pro grade saws really.

I did have an 048 that the gasket failed. It wouldn’t run. They are noted for the crankcase screws getting loose per my Stihl guru. [emoji2960]
 
That said, Stihl specs call for less than 3 PSI leak down in 20 seconds. But any leak is cause for some concern and you should seek the source of it. Because like all things they get worse if left unaddressed.

This is the reason I'm so particular about small leaks. If I have even a slow leak, I pressurize the case and spray with soapy water to find out where it's coming from. I had a couple of 038S's recently that had a cylinder gasket leak where the rubberized coating of the gasket had started to break down. Earlier there was an 034 with a leak where the manifold joins the cylinder, even with a good manifold and properly adjusted clamp (a little Dirko solved that). Since Stihl pro saws require splitting the case to change seals, I do the soapy water test on the seals while turning the crankshaft. If they pass that test it is much work saved. I realize that this may be the minority opinion, but I'm retired and don't do this for a living, so I have the time and patience for this stuff.
 
This is the reason I'm so particular about small leaks. If I have even a slow leak, I pressurize the case and spray with soapy water to find out where it's coming from. I had a couple of 038S's recently that had a cylinder gasket leak where the rubberized coating of the gasket had started to break down. Earlier there was an 034 with a leak where the manifold joins the cylinder, even with a good manifold and properly adjusted clamp (a little Dirko solved that). Since Stihl pro saws require splitting the case to change seals, I do the soapy water test on the seals while turning the crankshaft. If they pass that test it is much work saved. I realize that this may be the minority opinion, but I'm retired and don't do this for a living, so I have the time and patience for this stuff.

I do the same, try and find the leak. There's been a time or two I couldn't find a leak - the above mentioned 038 Super, I believe which leaked through the fuel pump screw-hole. Once I found that I just told the customer, I could put some loctite on it and that might work awhile or it might not but the other option really was to replace the case.
 
I do the same, try and find the leak. There's been a time or two I couldn't find a leak - the above mentioned 038 Super, I believe which leaked through the fuel pump screw-hole. Once I found that I just told the customer, I could put some loctite on it and that might work awhile or it might not but the other option really was to replace the case.
Fuel pump screw hole? Or the oil pump screw hole?
 
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?
I bought an 028 to rebuild and flip and I can tell you that the piston doesn't have to look brand new in order to run like new. I buffed out a deep score and it works. The rings were seized and I had to heat up the Piston and dig out little pieces at a time. I restored the piston and ordered new rings. It was nice and clean around the oil seals indicating that they don't leak. Crank case gaskets almost never leak unless someone separated the crank case looking for an easy fixl and left it with a leak when they gave up on the repair.
309ba08a766d37bdb53bee541fba511b.jpg
8a83ca7a98bdc746434ccac3da09b654.jpg


Sent from my Z557BL using Tapatalk
 
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?
Ever since I read about big bores unbalancing the engine, I've had second thoughts about using them. If you have a heavier piston then you need heavier counterweights or it's just going to vibrate to death.

Sent from my Z557BL using Tapatalk
 
Back
Top