My Solo 681 soiled the sheets

[guysmiley]

So after a couple years of firewood I am kicking myself in the butt for not redoing the bearings at the same time as the crank.

Last month I was helping out fell and buck some big madrone and the saw went lean at idle but I finished out the tank assuming a clogged jet. (Saw was not running too lean when the hi jet kicked in)

Turns out the chain side bearing got sloppy and wiped the crank seal and started sucking air.

I had installed the aftermarket 54mm big bore top end in addition to the crank but was not versed in cross-referencing bearings so I ran what was there as they seemed OK and felt fine after pulling... Well, here we are.

Now on teardown I noticed some more unhappy parts. Even though it ran great it looks like some of the nikasil under the exhaust port popped out and I will be getting a new top end to avoid further flakage into the new bearings.

Since it is cheap China/ebay parts and I can not afford a new OEM top end I am kind of locked in on options but I am wondering if it failed due to cheap parts or the occasional leaning out of the saw?


Beyond that even though all the posts here called for C3 bearings, the two I removed which I am sure were OEM were NSK C4. I got an skf and fag Italy c3 set that I was intending on installing. Should I abort and look for some c4 bearings? Pics on the next post

 

[guysmiley]

Also I noticed some wear and flaking paint in the crankcase area. Should I be concerned about the remaining paint and strip it so it does not get eaten by the bottom end or through the ring? Wear I would assume from the bearing failures before (drive side and the before lower needle bearing)

Thanks for any insight!

 

[rupedoggy]

I bet you switched back to 40:1

 

[guysmiley]

I bet you switched back to 40:1

Nope

 

[davidwyby]

@huskihl is the man to talk to. Used OEM is better than new chinese. There might be another (dolmar?) top end that will fit.

 

[davidwyby]

https://www.arboristsite.com/threads/after-market-piston-for-solo-681-dolmar-7900.204083/

 

[guysmiley]

@huskihl is the man to talk to. Used OEM is better than new chinese. There might be another (dolmar?) top end that will fit.

I would love to find a nice used OEM but they seem to be hen's teeth. It would be nice if there was a way to set alerts for keywords in the trading post. I replaced it last time with the big bore NWP kit. I will give hyway a try this time. at the price delta I can do it 3 times for the price of oem, 2 years for one wasnt a bad run

also as far as the mix rupedoggy, maybe it was leaning out with heavy use as a first sign of this bearing wear (stretching out the seal). It would make sense. I did stick with 32:1 and just upped the fuel until it stayed happy with heavy use. I always do appreciate your input.

I guess the main questions are the c3 vs c4 (going to run c3 unless advised against) and the flaking paint in the bottom end, going to strip all that before reassembly.

 

[davidwyby]

Strip, C3

 

[guysmiley]

Ok, now that I had time to stare at the mess, under closer examination, while the bearings weren't brand new, they were not horrible. What actually happened to my best guess is that I did not dress the surface at all where the oil seal goes and judging by the old seal, it started to spin at times and pop out in as much as it could but the oil pump activator prevents it from completely falling out. The spinning plastic driver overheated the metal on the seal and a hot sliver of metal came out and jammed in the teeth on the pump. That jammed the pump and stripped the activator. All of this happened in one tank of fuel.

The wear on the p/c is probably from running lean and cheap parts. Normally I have never needed to use any loctite or similar on seals, they seem to have a nice roughness and some coating already but I am not book learned in this stuff. Here are some fun pics. Note the burn spot on the oil pump tooth that was likely holding the sliver which was probably still attached to the seal so it was able to transfer heat long enough to discolor it!

Well, new bearings are always good, and I will use appropriate loctite and now that the seal has spun will probably try and do some staking or whatever they call it to punch some small dimples in the sealing area to give me a better bite. The new seal presses through with much less pressure than needed. Worst case find a seal with a bigger od and ream it out?

 

[rupedoggy]

Darn