Rebuild?

[doc47]

I have a rebuild kit for my Stihl O28WB. Is there a video or other tutorial on the procedure? Or is there someone out there willing to chat with me about the procedure? I have decent mechanical skills and good tools. I'd like some guidance before I dive in.
Thanks in advance.

 

[Bob Hedgecutter]

Rebuild for what?
Are you putting a new top end cylinder and piston on the old crankcase?
Do you know what caused it to need rebuilt?
Do you have a 100% complete saw to start rebuilding?

Have done a few of the 028 and 038 rebuilds from scratch- have examples of 028's here for reference- happy to help, but have never been a video maker.

 

[doc47]

Thanks for the reply. Yes, it's a complete saw I've had since about 1975. It completely lost compression.
The kit I have is for a top-end rebuild: cylinder, piston, piston ring, surclips, and it looks like a carb rebuild kit is included.
I can take some better photos, if needed.

 

[doc47]

Bob, I noticed you're a Kiwi. That made me smile. I've been doing a lot of work on a BMW motorcycle and two guys have been advising me. One's from Oz. The other is from Dunedin, NZ.

 

[Bob Hedgecutter]

Thanks for the reply. Yes, it's a complete saw I've had since about 1975. It completely lost compression.
The kit I have is for a top-end rebuild: cylinder, piston, piston ring, surclips, and it looks like a carb rebuild kit is included.
I can take some better photos, if needed.

Ah the good old Chinese kits- never liked them- never as good as original nor do they last as long. You have to be pretty particular with those Chinese retaining clips for the piston wrist pin- or they fall out.......
Photos of the inside of the original cylinder? Original piston?
Do you know what caused the old top end to loose compression?

 

[doc47]

Good eye, Bob. I haven't taken anything apart yet.

 

[Bob Hedgecutter]

If you have the tooling- BEFORE you tear it all apart- be a great time to do a pressure and vacuum test on it to determine why it lost compression.
Could be as simple as just needing new rings.
Picture of the piston through the exhaust port (with the muffler first removed) is always a good place to start.

 

[doc47]

Good idea. My resources are quite limited, though. I live and run an NGO in West Africa (Senegal & The Gambia). I could do a compression test but vacuum (leak-down?) is not possible without a 3-day journey.
I'll check and try to photograph the piston.
I have to pull the cylinder anyway, no? Even if it's just rings.
What size are those Allen bolts?

 

[doc47]

Compression 30 psi
What I can see of the piston looks fine. I can't see the cylinder wall at all.
Is there an exploded view diagram of the saw anywhere that you know of?
And yes, that is a busted muffler stud! Perhaps another reason to replace the cylinder. I doubt I can get that thing out with an easy-out. I'd probably have to drill and tap it, but that would be difficult. The stud is most certainly harder than the cylinder.

 

[Bob Hedgecutter]

What type of compression tester are you using?
If its a cheap automotive type- odds are it is giving you a false reading- as they are not designed for small engine testing- they need high volume of high pressure gasses to measure. Small engine testers have a weak Schrader valve in the very bottom of the hose where it fits into the sparkplug hole.
Do you have another known good running saw you can test with the same tester- what does that read?

Piston looks a little like it might be suffering from carbon scuffing- that will wear the piston and rings- see how it is built up as a hard crust in the exhaust port?

Use google and type in Stihl 028 ipl (illustrated parts list)- should be many to choose from.

Muffler stud could be extracted by bush methods- hacksaw a slot across the broken stud- yes you will partially cut the cylinder as well, but nothing ventured, nothing gained- soak in a good penetrating oil, heat with a propane torch- hit it with the penetrating oil while still hot- try turning the stud out with a slot screwdriver no wider than the 5mm of the broken stud.
Heat and oil are certainly your friend in trying to break the bond.
Decent penetrating oil can be made by mixing 50% acetone with 50% auto trans fluid.

The Allen bolts are NOT hex, they are TORX size T27. The cylinder bolts themselves are 5 X 18mm from memory.

Vacuum and pressure testing can also be done in a Bush method- cobble together something out of a large volume syringe- cattle drench gun- boat tote tank primer bulb- some tubing and some bits of tyre tube to block the intake and outlet of the cylinder.
In this instance though- with the broken stud- you are never going to get a good seal of the exhaust with just one viable stud.

 

[doc47]

Bob, I appreciate your advice. I'm learning, and that's fun, as well as practical!
I'm using a nice automotive comp tester. I'll check my 031AV with it for comparison.
If there is carbon scuffing, what should be done? Replace piston? Rings? Both?
What is the advantage of keeping the old cylinder when I have a replacement?
I have a Dremel(oid) tool for cutting a slot in the stud, but the transformer that runs it crapped out on me and now I can't even find it. I can't think of any other way to cut a slot without major damage to the exhaust port.
ATF is no problem. Acetone? No way! Would some other ionic solvent work? Paint thinner, perhaps?
I do have a diminishing can of WD40. When that's gone, there are Chinese knock-offs that are sold here in spray cans identical to WD with similar but different names. RS52, etc. I have no idea whether they are any good.

 

[doc47]

You are spot-on. Compression on the 031 was also 30 psi.

 

[Bob Hedgecutter]

You are spot-on. Compression on the 031 was also 30 psi.

And the 031 runs?
So therefore compression is not your issue and something else is?

If it were mine, I would cut the slot with a good old hand held hand powered hacksaw- like I said, bush fix.

Never tried a paint thinners brew- might work, but I have no experience in doing so.
No experience with the knock off WD40 either- Kroil is my go to for instances like these.

 

[Bob Hedgecutter]

Doc- where did we get to? have you decided to put it in the too hard basket- starting looking at why the saw is not performing as it should by means other than compression?
No reason just for fun you cant swap out the original piston and cylinder for the Chinese one and then work on fixing that muffler stud problem at your leisure.

 

[doc47]

Hi Bob! Sorry I haven't been in touch. I was sidetracked by trying to get two BMW F650GS motorcycles back in running order. And that is still a work in progress...sadly! Hence, the chainsaw has taken back-bench.
Since the cylinder is in parlous condition with regard to being able to mount the muffler again, wouldn't it be reasonable to replace the cylinder, rings, etc. and rebuild the carb with the kit provided? (That is, once I get at least one motorcycle running! That has to be the priority, since they are my only transportation.)
Then, if the saw still won't run, I can explore further. The biggest problem is that the only T27 bits I have won't fit through the holes in the cylinder. I will have to have something welded together to accomplish that job.

 

[Bob Hedgecutter]

As I said- you can pit the cheap one on to get it running then work on the original one.
In my experience the cheap top ends are very "variable" in the port timing and never seem to make as good as original power- so you might get it to run, but never as well as it could run or did run.

Online order the Stihl T handle T27 tool- will last for many saw repairs and at 200mm is long enough for any cylinder. The cheap knock off ones usually snap or round off the splines on cylinder bolts.