I can't get the cover back on after I fixed the tension on the chain. There is a metal ring and it no longer seems to fit.

its probably like the gas model. so you remove the 2 nuts holding on the side cover of the blade side, remove the cover and the blade and chain. To fit back, slacken the adjuster screw a little bit, or if fitting a new chain then a fair amount, as you have to be careful that the pin on the adjuster fits into the proper hole on the saw bar, as you fit back on the bar, of which you have already cleaned out the grooves. supporting the bar in the slackest position, fit on the chain, making sure that the cutting edge at the bottom is coming towards the motor. Then slide the bar and chain away from the motor to take up the slack, then fit back the metal guide in the original position, fit cover with the adjuster pin in its hole on the bar, and replace the 2 nuts almost tight but slack enough to use the adjuster to set the chain to cutting position..slightly sagging on the sprocket nose type, or snug on the solid nose type..then tighten the cover 2 nuts firmly but not excessively as that will damage the machine..NB the bar & chain depends on the adjuster, not on the nuts tightness to maintain tension

Check that the chain brake is in disengaged position by
moving the front hand guard towards the front handle.
Remove the bar nuts and remove the clutch cover (chain
brake). Take off the transportation ring.
Fit the bar over the bar bolts. Place the bar in its rearmost
position. Place the chain over the drive sprocket locate it in
the groove on the bar. Begin on the top edge of the bar.

Make sure that the edges of the cutting links are facing
forward on the top edge of the bar.
Fit the clutch cover (chain brake) and locate the chain
adjuster pin in the cut-out in the bar. Check that the drive
links of the chain fit correctly on the drive sprocket and that
the chain is in the groove on the bar. Tighten the bar nuts
finger-tight.
Tension the chain by turning the chain tensioning screw
clockwise using the combination spanner. The chain
should be tensioned until it does not sag from the
underside of the bar.
The chain is correctly tensioned when it does not sag from
the underside of the bar, but can still be turned easily by
hand. Hold up the bar tip and tighten the bar nuts with the
combination spanner.
When fitting a new chain, the chain tension has to be
checked frequently until the chain is run-in. Check the
chain tension regularly. A correctly tensioned chain
ensures good cutting performance and long life.

The cover looks easy, but it is a special fit problem. There is a screw device with a very small pip which fits into the chain bar on the side. When you put the chain and bar on together, you have to adjust this BACK toward the sprocket with a flat screw driver. Now you can fit the bar and chain in with the chain around the sprocket and very loose. Place the cover on after visually seeing a passage for the chain oil from the angled plate - through some slots in the side, though the side hole in the bar, and up through that invisible inside drilled hole between the chain groove and the bar side hole. Move the cover back and forth before tightening. Ensure that the screw pip device is snapped into the bar so that you can move the bar forwards and back using the flat screw driver. Now tighten to less than hand tight. Adjust the bar forward so you can just see three bottom guide teeth in the chain when you pull on the middle of the chain from the bottom of the bar. Now you have the right tension on all those sharp links and you can give the cover bolts a good tightening, not to crack the plastic or metal though. Be sure to clean all the dust out of the band area with a tooth brush as this can lock up the band and not let the chain revolve at all - making it act as if the chain brake is on. Also be aware of the tiny roll/spring pin in there which wants to fly out when cleaning. It controls how the band works when you trip the chain brake.

It sounds like you just purchased this saw. If so, try to contact MFR, there must be a tel # in the instructions. I have had similar problems the were caused by translation.

This may not be the answer you are looking for but I would get a small file and file the ring just enough to make it fit. I really don't understand why it got too tight in the first place but you stated that it only needs a fraction wider to work. Use a small file or drill to open the hole to the size you need and start cutting wood again. The Rancher is a great chain saw.

I just posted an answer a minute ago for basically the same question....here is the link...should be the same deal for you.
http://www.fixya.com/support/t7191865-am_trying_replace_chain_saw_when
Take care.

There's two 1/2 inch nuts on the side of the cover from which the bar protrudes.
Remove these nuts and the cover -- leave the bar loosely in place.
Look for a slot-head chain-tensioning screw (may be on front under the bar, or perhaps on the side).
Turn this tensioning screw counter clockwise -- you will notice a pin moving back towards the drive clutch -- this pin fits into a hole on the bar and is used to set the chain tension by pushing the bar away from the drive clutch.
Once it is loosened, the bar can be pulled closer to the drive clutch, allowing you to fit the chain back onto the bar -- be careful to align the drive teeth on the chain into the slots on the drive clutch.
When the chain is back in place, turn the tensioning screw clockwise to tighten the chain onto the bar.
Replace the cover and put the nuts back on only finger-tight.
Tighten the chain some more using the tensioning screw.
Tighten the 1/2 inch nuts fully.
Note: The chain needs to be quite tight -- lift it by a link and be sure it does not come out all the way from the bar.

The humming is the motor trying to turn. Remove the drive end cover from the bar and chain--back off the chain adjustment CCW several turns. If the saw has a chain brake, release it. When the cover is loose, remove the bar and chain, inspect the entire mechanism for any damage--particularly the chain itself. Run the motor without the bar and chain, and check for oil oozing out of the side port in the motor case where the bar fits. To reassemble, fit the bar in place after cleaning the small oil passages in the drive end, then fit chain over the sprocket. Pull the bar outwards to tighten the chain, then fit the cover and fasteners finger tight. Adjust the lower run of chain up to the bar (the lower run of teeth cut toward you), but not so tight that you can turn the chain by hand. Tighten the fasteners and recheck chain tension. Chain saws don't seem to like cutting hedges and other small branch, but tough bushes and the like. Make sure the chain teeth are properly sharpened. Hope this helps!

The unsafe solution is to remove the brake entirely and as long as you cut with only the lower side of the chain, kick-back is a minor problem. The safer option is to replace the band purchased from a servicing dealer. Good luck!

Ensure it isn't tripped before removal is the best advise I can give. It is difficult to reset with the cover removed, Dolfoff explains it well. GL
Lou
Reset Chain Brake
Please follow this link, cursor down to “Best Solution”, while there click the “Was this helpful? [Yes}” button.
http://www.fixya.com/support/t3102817-re_install_side_cover_after_chain HTH
Lou
If no vice a "C" - clamp to a work surface might work.