Makita 7900

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Bought new, but hardly used, 5 tanks of fuel. Shut it off after cutting a log, now chain won't spin. Clutch expands, cover and sprocket spin but won't spin chain which tension is good. Can hear a "ping rattle" when I turn it off. Any idea's?
 

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
So, if I understand this correctly- saw still restarts and runs fine- but no chain movement.
With the chain removed, the clutch engages the clutch bell and rotates this and the drive sprocket, but if the chain and bar are refitted- chain does not rotate?

Then best guess is a locked up bar nose sprocket.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Nope, new TsuMara bar, bar fine, spin by hand easily, baffled. Mailed saw to Makita in NJ, none locally will look at it. Literally only 5 tanks of fuel. Idles & Revs fine just won't spin chain weird. I'm 66 have cut a lot of firewood.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
I do hear a "ping rattle" noise when I turn it off, sprocket bearing was good, lubed it. Not sure just how far the clutch should expand but it does and it's almost new. I'll find out soon.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
No, checked brake, pulled brake band out, blew dirt out with compressor, etc...
 

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
I do hear a "ping rattle" noise when I turn it off, sprocket bearing was good, lubed it. Not sure just how far the clutch should expand but it does and it's almost new. I'll find out soon.

No idea what your "ping" might be- but it possibly is not a good sign.
Clutch shoes should expand far enough for the friction areas of the shoes to contact the inner wall of the drum.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
The TsuMara 20" bar is 3/8 pitch and has both 050 + 058 markings on it. It is well oiled, nothing's pinched, nose sprocket turns easily. Mind you I have run about five tanks of fuel with no problems. Makita service center has it, I will post what this baffling problem is when I find out.
After cutting one 15' log, I restarted it throttle won't spin chain, put the chain on a log & pushed it along the bark thinking debris had clogged underneath the cover, nope nada. The clutch drum seemed a bit floppy, like not seated right. Spacer, needle bearing are all there. Took it off & on a couple times to watch the clutch expand, which it does.
There are two "ears / tabs" on the clutch drum, and also two more similar "ears" behind the clutch, not sure of there purpose.
 

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
Sounds a bit like you may have exploded an oil pump or pump drive- thus locking the clutch drum under sprocket driving speed.

Never seen a Tsu Mura bar marked for two gauges- need to see a photo of that.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Although I have never heard of an exploded oil pump, that makes sense as I did increase the oil screw that day. It used to leave a puddle of oil so I backed it off, then I increased it the day it broke, and got plenty of oil on the bar.
Thanks Bob!!!!
Wouldn't have guessed a a little mechanical pump would inhibit a 5.7HP motor LOL.
 

Attachments

  • .050 chain.JPG
    .050 chain.JPG
    3.7 MB · Views: 2
  • TsuMara.JPG
    TsuMara.JPG
    2.8 MB · Views: 2
  • TsuMarabar.JPG
    TsuMarabar.JPG
    4 MB · Views: 2

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
By all accounts your problem is not inhibiting the engine- but the transfer of the HP to the chain.

And yes the replacement tip with be both gauges so you can replace it to either an 050 or 058 bar- but your bar is marked near the tail mount and as per he back of the box it came in as 0.050/1.3mm- so that is the gauge chain you must run.
Nose sprockets and clutch drive sprockets are multi gauge but do not control the travel of the chain other than around the bar- the bar rails keep the drive links in a square to cut orientation.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Yep, saw the 050 new the tail, harder to see it. But yes I have a few boxes of 3/8 050 chain left. Same as my Beloved Husky 55 Rancher I cut with forever.

Bought a brand new / old stock POS 350 Husky, the owner had died, never put gas in it. I used it a little on saplings, now broken, air leak I think. Revs full throttle then dies, tried a new carb, same thing. In my shed if I get bored.
 

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
If an older style 350 it could be the plastic clip holding manifold to cylinder has snapped, but with any 350 it is more likely to be the 4 bolts that go up through the bottom of the plastic case- through the riser and into the cylinder that have come loose.
You can get to 3 of those without removing the tank- but difficult to see/get to the fourth without removing the tank/rear handle.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Although I have never heard of an exploded oil pump, that makes sense as I did increase the oil screw that day. It used to leave a puddle of oil so I backed it off, then I increased it the day it broke, and got plenty of oil on the bar.
Thanks Bob!!!!
Wouldn't have guessed a a little mechanical pump would inhibit a 5.7HP motor LOL.
Bought new, but hardly used, 5 tanks of fuel. Shut it off after cutting a log, now chain won't spin. Clutch expands, cover and sprocket spin but won't spin chain which tension is good. Can hear a "ping rattle" when I turn it off. Any idea's?
Update, mailed 7900 to Makita service center in NJ two weeks ago.. Got there in two days. A week later I called to check on the status and was told there is a TWELVE WEEK wait or longer if they need to order a part!
Today I called to request my 7900 being returned, that TOO may take up to eight business days plus shipping time! Not happy.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Bought new, but hardly used, 5 tanks of fuel. Shut it off after cutting a log, now chain won't spin. Clutch expands, cover and sprocket spin but won't spin chain which tension is good. Can hear a "ping rattle" when I turn it off. Any idea's?
Update, mailed 7900 to Makita service center in NJ two weeks ago.. Got there in two days. A week later I called to check on the status and was told there is a TWELVE WEEK wait or longer if they need to order a part!
Today I called to request my 7900 being returned, that TOO may take up to eight business days plus shipping time! Not happy.
 

Pru

New member
Local time
3:41 AM
Joined
Apr 8, 2024
Reaction score
0
Location
CT
Update, called Makita today asking if they have shipped my EA7900 back to me yet. The person I spoke to said his boss escalated the repair and it needs a new clutch, drum cover, plug, and flywheel! OK the plug was dark in color but not fouled, clutch expanded, I did not look at the flywheel but would explain the "pinging" I heard when shut off. How the heck does a "PRO" grade saw break that much within five tanks of gas? My old Husky 55 Rancher cut over 100 cords with no problems.
 

Bob Hedgecutter

Moderator
Staff member
Local time
7:41 PM
Joined
Sep 12, 2021
Reaction score
521
Location
Way Down South New Zealand
Ask for photographic evidence and or the damaged parts to be returned.
If a bolt rattled loose or some other metallic foreign body made its way in to the arc the flywheel travels- then yes steel will destroy aluminium and break flywheel fins.
Clutch expanded? I am guessing you are meaning weak springs and the friction shoes were contacting the drum- can be caused by many things, like full noise RPM chain brake engagement often.
7900 is a pretty big step up from a 55 and can do bigger and better things- but at more cost to the workings of the saw if everything is not done smoothly and with a razor sharp chain.
 
Top