Changed out the crank seals on 4900 today. the 4200-8500 series has to be the easiest saws to change crank seals on that I've done so far. Plenty of room to work. Flywheel and clutch are easy to get off. Oil pump comes off with two screws. And the biggest + is the nice big metal seal body that's easy to get a screw into to pull 'em out.
Since my OEM 530019075 seals are still back ordered.................I went to my local bearing house and picked up some SKF 6904 seals. These are the equivalent of the National/Timken/FM 471466 seals that others have mentioned are a match for this saw series. They fit the saw, but look different. The metal seal body comes much closer to the shaft bore. The configuration of the sealing lip is quite a bit different too. You can see the old seal sitting on the crankcase to the left of the new seal in my pic. The seals were pretty tight on the crankshaft after installation. There was quite a bit of rotational friction afterwards too (despite the seals being oiled with mix oil before installation). Things freed up after a minute or so of running. Not sure whether these differences will affect the longevity of the seals in this application. Time will tell.
I changed the FW side seal and then ran the saw for a minute or so before tackling the PTO side. It ran richer ('wanted' to be leaned out a bit) after the FW side was done. Saw passed a pres/vac test. Fired it up again and remembered Mark's admonishment to change both seals anyways. As I was pondering this I noticed that the saw was smoking pretty good. Oily, slick feelin' smoke. Saw was pulling bar oil through the PTO side seal methinks. Wasn't doing that before the FW side seal was replaced. That seal didnt' look so good, so maybe it was leaking bad enough to keep the PTO side from sucking oil. Pulled spark plug and saw it was sooty/oily.
Rebuilt the carb and replaced the fuel line before doing the PTO side seal. Could NOT get the governor out of the carb. This is the first governed HS that I've dealt with which
refused to let go of the governor body. Had a thick orange/red sealer (more orange...........and thicker than what I've seen before) on the governor body threads. May give it another shot later. I'll have to remove the choke shaft to get a good straight shot at it with a bigger hollow ground screwdriver tip.
Runs and tunes fine now. Saw acted weird (like my PP330 did with the bum HDA164) for the first minute or so of running after the carb rebuild and PTO side seal replacement. Thought the PTO side seal must've gotten damaged during installation. Suddenly it started running and tuning like normal. Had it idling and running for a good 1/2 hour after that with no changes. Smoke went away right about the time that the saw started running 'right'. Maybe the weird running was due to the residual bar oil fouling the plug.