Stihl 028 AV Wood Boss compression

[Bret59]

I'm very new to the site and over the last few days I've been reading quite a few posts to try to figure out an issue we're have with a Stihl 028 AV WoodBoss. I picked this saw up at a yard sale for $5 last fall. The saw looked clean and the owner explained he couldn't get it started one day and so it set for a several years. He eventually gave it to his nephew to take to a high school shop class to see if he could get it running, but no luck. It then set for a few more years until I found it at the yard sale. There was no bar or chain with it but it did have a nice plastic case, easy call for $5.

My Dad is the saw mechanic for the family having started working as a faller in Eastern Oregon back in the early 60's. Any time I run across a vintage 50's to 60's McCulloch I send it his way and he's actually rebuilt several of them to run. I gave him the Stihl and the first thing he found was no spark. I ordered a new ignition coil from ebay and sent it to him; he's in Eastern Oregon and I'm in Eastern Washington. The new coil fixed that issue but it still wouldn't start. He then pulled the top end off and found a very bad piston but the cylinder appears fine. The piston was the 44mm so I ordered a new aftermarket piston kit from ebay. Dad installed the new piston but it still wouldn't start. He checked the compression and found it to be 40. He then called a local saw mechanic and was told that the Stihls have to have a matched cylinder and piston; not any Stihl 028 44mm piston will work.

I can't find the post now but I remember reading that there are letter markings on the cylinder and piston: A, B, A/B, etc. Is this the reference to being a matched set? The saw we have has a C stamped on top of both the original piston and cylinder. So is there any truth to the statement that the P/C have to be matched? If so, how do I get a new piston to match the original cylinder?

Thanks in advance and looking forward to any advice you can offer.

 

[drf255]

Pics would help.

The compression tester needs to have a schrader valve in the tip to get any accurate reading on a chainsaw.

There are ABC cylinders for sure, the difference is very very small, but there has to be a reason the factory did it. This shouldn’t make much difference in what you are describing.

Really need more info to help. I know the older metal handle 028’s came with points and that they could be eliminated by adding a newer Stihl coil, but I’m not sure on the details.

Which piston did you buy? The ONLY aftermarket piston one should use is the METEOR brand. There are some models where there isn’t a meteor available, but the 028 isn’t one of them. It’s possible, with a cheap piston, that the squish is huge on the saw. Was squish checked?

 

[67L36Driver]

Three bore sizes were offered on the 028. 42mm (very early production), 44mm and 46mm (Super).

It’s very possible you have a 44mm piston in a 46mm bore given the extremely low cranking compression.

A dial caliper is very good investment when tinkering any engine.

 

[HarleyT]

Post the link to the piston's e-bay listing.
That could be the problem.

 

[Bret59]

Here is the link to the piston I purchased: https://www.ebay.com/itm/Stihl-028-...254205&hash=item213bcdb530:g:o~8AAOSw0AFcp2~W

I'm pretty sure the bad piston and cylinder are original and both are 44mm. The guy I purchased the saw from was only an occasional weekend woodcutter and not likely to have tried any serious repairs himself; in fact he didn't. I won't have access to the saw for a couple weeks when we go visit my parents for Memorial Weekend. I'll get some photos and the squish measure then. What should the squish be?

In the meantime I'll put a quality dial caliper and compression tester on my shopping list. Angelo C also suggested we check for a stripped key on the flywheel. Thanks for everything, I'll keep you posted.