Stihl MS 390 carnage - disassembly.

[MacAttack]

Did you check P/C clearance on the new used piston? Ring end gaps?

Piston / cylinder feels very nice. I'm waiting for the rings to be delivered so I can check end gaps and file them if I need to. Thanks!

 

[MacAttack]

These bearings are a light press-fit on the crankshaft, so require a bearing splitter/ puller to remove. Freezing the crank and heating the new bearings makes installation easy. Remove the seals on both sides of the new bearings. I wash out the grease with mineral spirits or brake clean, dry them and re-oil with whatever 2-stroke oil you plan on running in this engine. That insures proper lubrication on startup.

Great input, thanks!

I had read about the old bearings coming off with just a little heat, mine were on much tighter than that!

 

[Mad Professor]

Piston / cylinder feels very nice. I'm waiting for the rings to be delivered so I can check end gaps and file them if I need to. Thanks!

Check the P/C with feeler gauges at the skirt so you know it's tight or loose. Mics are better.

 

[MacAttack]

Check the P/C with feeler gauges at the skirt so you know it's tight or loose. Mics are better.

How many thousandths of clearance should I be looking for at the skirt? I have feeler gauges and a digital caliper, I don't have micrometer though.

 

[Mad Professor]

How many thousandths of clearance should I be looking for at the skirt? I have feeler gauges and a digital caliper, I don't have micrometer though.

New P/C ~0.002-0.0025". Double that and it's getting sloppy, much less and it may seize.

 

[MacAttack]

New P/C ~0.002-0.0025". Double that and it's getting sloppy, much less and it may seize.

Many thanks! I will check later.

 

[Mad Professor]

Many thanks! I will check later.

Reason I mentioned is Stihl sized P/Cs. Should be stamped on top of Cyl and crown of piston. A, B, or C.

Later replacement pistons were stamped A/B and were a compromise to fit A or B.

I can't remember if A or B is a bit larger?

Meteor stamps their sets too.

 

[MacAttack]

Reason I mentioned is Stihl sized P/Cs. Should be stamped on top of Cyl and crown of piston. A, B, or C.

Later replacement pistons were stamped A/B and were a compromise to fit A or B.

I can't remember if A or B is a bit larger?

Meteor stamps their sets too.

My good used piston is a Mahle, I'll look and see what's casted into it.