Replace this Stihl 045 AVSE Piston?

[Entisol]

I recently acquired an old Stihl 045 AVSE. It runs well, but the SEM type GE ignition is starting to go. It runs great unless it gets very hot. It will die when hot but run again when it's cool. It's another issue figuring out how to fix the ignition, as most fixes I've seen pertain to the Bosch. That's another story.

I had tested the compression, and it was making about 130psi on my tester. I think my tester reads low, my newer Stihl saws also read about 130psi.

I pulled the cylinder to see how things look. I'm planning a mild port job and base gasket delete (that would bring my squish down to ~.030). The rings were free, but it looks like the piston skirt has worn. Looking inside the cylinder, I'm guessing the vertical lines are aluminum transfer from the piston skirt.

Assuming the vertical lines on the cylinder are aluminum transfer, I know I'll have to remove that. Would you replace this piston? Is there a decent new piston available? I see 54mm pistons listed on Dukes and Lil Red Barn, but I'm worried about the quality. Any suggestions?
View attachment IMG_6092.jpgView attachment IMG_6091.jpg

 

[Entisol]

There is about .005” gap between the skirt and the cylinder wall
View attachment IMG_6097.jpeg

 

[Entisol]

I’m not sure if these pistons came with any sort of coating. If they did, it’s mostly worn off on the sides.
View attachment IMG_6098.jpeg

 

[Coralillo Lo Pro]

I got a Proline one from Sawzilla for my 045 Super, he makes a point of saying they're not Chinese, so I assume Taiwan. I ended up switching the rings out with Caber's. Meteor never made a piston for the 045/056 Supers, which is my usual go-to. I would say get an old Bosch flywheel and buy the Sagenspezi ignition, last one I got was about $75 ordering thru their website instead of Ebay. Do a pressure/vac test too because if the seals are no good, you'll just burn everything out in short order after repairing it. The 045 had a proprietary clutch side bearing with built in seal that is next to impossible to find. The 056 went to the traditional two part bearing and seal setup and there are AM ones now available, so it's a much easier rebuild than the 045's are.

 

[Entisol]

I got a Proline one from Sawzilla for my 045 Super, he makes a point of saying they're not Chinese, so I assume Taiwan. I ended up switching the rings out with Caber's. Meteor never made a piston for the 045/056 Supers, which is my usual go-to. I would say get an old Bosch flywheel and buy the Sagenspezi ignition, last one I got was about $75 ordering thru their website instead of Ebay. Do a pressure/vac test too because if the seals are no good, you'll just burn everything out in short order after repairing it. The 045 had a proprietary clutch side bearing with built in seal that is next to impossible to find. The 056 went to the traditional two part bearing and seal setup and there are AM ones now available, so it's a much easier rebuild than the 045's are.

Good to know. Last night I tried one of the Proline SEM modules from Sawzilla, but I wasn't getting spark. The Proline SEM module is rebated about 1/8" in from the edge of the plate, so I think the gap is excessive between the coil and the magnets on the flywheel. The Proline module might work for another SEM coil, but I don't think it will for my application. In the picture below, the factory SEM type GE is on top, Proline on bottom. I spoke to Sawzilla before I ordered, they said I could try it and return if it didn't work. I'll try returning it next week.

I pressure/vac tested last night, luckily all's good. Good info on the bearing/seals, I did not catch the difference between the 045 and 056.

 

[Coralillo Lo Pro]

Interesting. There was a bit of difference between the Bosch and Sagenspezi, the coil seemed recessed a little from the edge in comparison, but the plate size may have been different so it was still in the same place in relation to the flywheel magnets. Ah, that's right, there was the SEM GE ignition in some of the 045's, and the TS360cutoff saw/056 SEM ignition was the GA. So yeah, if yours is a SEM GE that Proline's not gonna work unless you get a GA flywheel. Or you can just get a Sagenspezi and a Bosch flywheel. The SEM GE is apparently the worst of the ignitions to have.
Great news about the pressure/vac being good. I have the 045 service manual if you need it and I have the tech notes for all the changes they made to the second gen 056 to learn all the 056 things that will not work in an 045. The first gen 056 was basically the 045, but then Stihl erased all trace of that version and just listed parts for the second gen 056 saw.

 

[Entisol]

Interesting. There was a bit of difference between the Bosch and Sagenspezi, the coil seemed recessed a little from the edge in comparison, but the plate size may have been different so it was still in the same place in relation to the flywheel magnets. Ah, that's right, there was the SEM GE ignition in some of the 045's, and the TS360cutoff saw/056 SEM ignition was the GA. So yeah, if yours is a SEM GE that Proline's not gonna work unless you get a GA flywheel. Or you can just get a Sagenspezi and a Bosch flywheel. The SEM GE is apparently the worst of the ignitions to have.
Great news about the pressure/vac being good. I have the 045 service manual if you need it and I have the tech notes for all the changes they made to the second gen 056 to learn all the 056 things that will not work in an 045. The first gen 056 was basically the 045, but then Stihl erased all trace of that version and just listed parts for the second gen 056 saw.

If you can share the manuals and tech notes, I’d appreciate it. Looks like you’ve been through this, it can be hard to tell exactly what you have with these saws. I pulled the flywheel expecting to find a Bosch, and found one I hadn’t even heard of. I have an Oregon Universal Ignition Module, I might try to make that work with the SEM coil before I hunt down a new flywheel. The Bosch seems easy to fix with the Oregon Universal Module, but I'm not sure if the SEM GE will work the same way.

Can you tell if this is the rare clutch-side seal?
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[Coralillo Lo Pro]

Can you tell if this is the rare clutch-side seal?

Not sure on the bearing/seal, that's not the number I think was on the 9523 003 0440 bearings, I thought it started with 527 and was seven numbers but not sure of anything. Cross referencing actual bearing numbers to part numbers is next to impossible. Yeah, been through the wringer with the 045 and 056 learning more about them than I possibly ever wanted to know. SEM ignitions are one thing I never did get into though. Sent the manual and other info to your Inbox.

 

[hotshot]

Seal is a 9639 003 2690, and the 045 PTO side bearing & seal were always two piece, but pre-assembled when you bought the bearing from Stihl.

https://www.ebay.com/itm/234780027623
Measure your 54mm piston skirt with dial calipers across the thrust surfaces down low, it should be larger than 2.123” to be reusable. That 0.005” clearance you measured with a feeler is excessive.

If you do decide to reuse it, I’d ditch those outdated wrist pin circlips with hooks & replace them with the revised 9463 650 1300. You’ll need to burr cut a small removal notch in the pin bore edges with a Foredom or Dremel to help get them back out in the future, as you’ve got an old revision piston there.

Good luck on finding a new SEM GE module, they failed so often that the replacements were gobbled up fast.

 

[Entisol]

Measure your 54mm piston skirt with dial calipers across the thrust surfaces down low, it should be larger than 2.123” to be reusable. That 0.005” clearance you measured with a feeler is excessive.

Thanks hotshot. I measured the piston skirt, it is too small. I'll try a Proline piston with Caber rings and circlips without hooks. Good info on the seals/bearings. Luckily the saw is holding pressure and vacuum for now, but I'll keep an eye out for spares. I'll let everyone know if I figure out a fix for the SEM GE module.

 

[Coralillo Lo Pro]

That's interesting - I saw the 2690 seal listed in the 045 parts list and wondered why because I always thought it was an all-in-one package deal w the bearing because that's how Stihl provided it. No one mentioned in all the time I spent on these saws that you could replace the seal on the 0440 bearing. Good information to know.