550xp Rebuild

[GuyMo]

Evening.

 

Picked up a non running 550xp for £100 last week with a view to it being my next saw project of this lockdown.

Decent condition, no play in crank etc, however when I pulled the muffler off the piston was scored (the ring still moves, but it’s too bad to salvage). Ordered a Meteor piston to replace it.

The exhaust is totally coked up, so I’m wondering what may have caused this. The spark arrestor is completely clean.

I suppose my question is, when reassembling it, what are the pitfalls with Husky’s?

As there’s no play in the crank I’ve not thought about replacing seals/bearings etc, and I wasn’t planning on splitting the crankcase. Is this a mistake.

Anything else you’d replace as a matter of course as I’ve got it this far?

 

Ive only had/used Stihl up till now.

Any advice is greatly appreciated

 

[billpierce]

Hone the cylinder, Whack the piston in, do a vac check and give it a go!is what i would do if also else seems good

[Heavy Oil Saw]

The exhaust cokes up if they aren’t wide open a lot and for long periods of time. Lots of throttle blipping and idling. Heat and flow helps keep the carbon down. Or the carb has been badly adjusted and been run over rich. If both of these things have been occurring, then more carbon built up.
As above for the rebuild, piston, prez/vac test, ensure all rubber is in good nick and run it.
Hope that helps.

[MattyF]

Done a couple of 550’s and they where easy and still going a year on ,just take ref pics to see what goes where and had no problems... I usually bin the spark arrestor as soon as get my hands on one though.

[Stubby]

9 hours ago, Heavy Oil Saw said:

 Or the carb has been badly adjusted and been run over rich.

Surely on a 550 the A/T adjusts the carb ?

[Heavy Oil Saw]

It was purely a generic comment, to try and help. If it is Auto Tune, then disregard and maybe my other suggestions would/could be helpful. Conditions of the saw, air filter clogged, may have caused the AT to perform in such a way.
No one else has suggested poor running conditions/handling. It may of been used for snedding or other such low rev work. Maybe that isn’t true either, but heavy carbon build up on strimmers occur as they are blipped/not run wide open/idled a lot.
Older diesels coke up bad when not treated like dirt, they need to be hot and run hard, idling and lack of power use kills them. Maybe true of newer diesels, but I’ve never had the pleasure of stripping them.

[Wonky]

I wonder if it was used on the wrong grade/spec of oil....

[adw]

Yes oil quality, or quantity, running at 14000 rpm it's hard to see why it has carboned up the muffler yet shows nothing in the spark arrestor, if the piston is very bad I would certainly pull the seals out and check the condition of the bearing cages, also check the crankcase screws are still tight, depending on the age of this saw, there are a few mods you should do.

[Stubby]

4 minutes ago, adw said:

Yes oil quality, or quantity, running at 14000 rpm it's hard to see why it has carboned up the muffler yet shows nothing in the spark arrestor, if the piston is very bad I would certainly pull the seals out and check the condition of the bearing cages, also check the crankcase screws are still tight, depending on the age of this saw, there are a few mods you should do.

My guess is they have run it without the spark screen in and put it back in to sell to you .  I take them out my self and leave them out . 

[GuyMo]

Thanks all! Very helpful. I’ll let you know how it goes!!!

 

Ive not honed a cylinder before, but the scoring doesn’t look too bad. 
move attached a couple of pics if anyone has any other pearls!