Thumpstar 110cc wierd oil leak

b44 · 06-11-2019, 08:32 AM

Hi all, thought my sons thumpstar 110cc had a bad gear shaft seal, so i replaced it, however was leaking from stator cover, but found strange looking oil tracks, can anyone shed any light on the pics, I'm thinking just silicon it up, but the tracks look like they have a purpose
Cheers

b44 · 06-11-2019, 09:03 AM

It's exactly like this, a few people say it's a over flow, but I've filled it to exactly what manual says 950ml

Mudflap · 06-11-2019, 10:00 AM

It's a vent/drain. Are you sure you're not seeing chain lube instead of a leak?

There is a seal on the crankshaft and a big O ring behind the stator plate that should keep oil out of the flywheel area.

b44 · 06-11-2019, 10:51 AM

Definitely a leak, there is oil in the stator area, I'll have to pull cover off again and check the seals, thanks for the help

dingerjunkie · 06-11-2019, 12:28 PM

I'm thinking that the only thing that could be leaking into there is a failed crank seal.

The vents are to allow ventilation/drainage of water or other humidity. On my old Honda CR250 didn't have such venting. I had to take the stator cover off to let things dry after every wet race or face corrosion on the electrical components.

dirtbkr188 · 06-11-2019, 02:03 PM

A very common occurence - someone installed the wrong length bolt to hold the left side engine cover and punctured through or cracked the case, resulting in engine oil seeping out from that bolt hole.
As stated above, the cover is machined to act as a drain for water should any get into the flywheel area, as there is usually no gasket used.

b44 · 06-11-2019, 06:53 PM

I'm thinking it's crankcase seal, it's done it since new, stator cover has never been touched,

dirtbkr188 · 06-11-2019, 09:31 PM

Can you see oil leaking down from behind the flywheel anywhere?

How long is the bolt you took out of that hole?

b44 · 06-13-2019, 07:49 AM

Yes oil coming from behind fly wheel, not sure if bolts caused it, never pulled cover off till now

dirtbkr188 · 06-13-2019, 08:32 AM

As Mudflap mentioned above, there is a center crankshaft seal, a big outer o-ring, and there are two small o-rings behind the stator plate for the mounting screws. You'll need a flywheel puller to access the stator plate, I believe it is the one shown below - M27mm x 1.0 with LH left hand thread.

b44 · 06-13-2019, 11:06 AM

Thanks alot, would the 2 small orings need to be replaced aswell?? I've got oil seal kit, but no 2x small orings

dirtbkr188 · 06-13-2019, 01:55 PM

Usually, no, they don't need to be replaced, but they will "oil stick" to either the engine case or the back of the stator plate, just so you're aware. Also, the two countersunk philips screws that hold the stator in place usually need to be loosened with an impact driver

b44 · 07-31-2019, 11:10 PM

Thanks for the info guys, replaced stator orings seals, allgood now

06-11-2019, 09:03 AM	#2
b44 Join Date: Apr 2016 Location: Australia Posts: 89	It's exactly like this, a few people say it's a over flow, but I've filled it to exactly what manual says 950ml
	0

06-11-2019, 10:00 AM	#3
Mudflap Join Date: Sep 2014 Posts: 1,894	It's a vent/drain. Are you sure you're not seeing chain lube instead of a leak? There is a seal on the crankshaft and a big O ring behind the stator plate that should keep oil out of the flywheel area.
	0

06-11-2019, 10:51 AM	#4
b44 Join Date: Apr 2016 Location: Australia Posts: 89	Definitely a leak, there is oil in the stator area, I'll have to pull cover off again and check the seals, thanks for the help
	0

06-11-2019, 12:28 PM	#5
dingerjunkie Join Date: Aug 2007 Posts: 60	I'm thinking that the only thing that could be leaking into there is a failed crank seal. The vents are to allow ventilation/drainage of water or other humidity. On my old Honda CR250 didn't have such venting. I had to take the stator cover off to let things dry after every wet race or face corrosion on the electrical components.
	0

06-11-2019, 02:03 PM	#6
dirtbkr188 Join Date: Aug 2009 Posts: 521	A very common occurence - someone installed the wrong length bolt to hold the left side engine cover and punctured through or cracked the case, resulting in engine oil seeping out from that bolt hole. As stated above, the cover is machined to act as a drain for water should any get into the flywheel area, as there is usually no gasket used.
	1

06-11-2019, 06:53 PM	#7
b44 Join Date: Apr 2016 Location: Australia Posts: 89	I'm thinking it's crankcase seal, it's done it since new, stator cover has never been touched,
	0

06-11-2019, 09:31 PM	#8
dirtbkr188 Join Date: Aug 2009 Posts: 521	Can you see oil leaking down from behind the flywheel anywhere? How long is the bolt you took out of that hole?
	0

06-13-2019, 07:49 AM	#9
b44 Join Date: Apr 2016 Location: Australia Posts: 89	Yes oil coming from behind fly wheel, not sure if bolts caused it, never pulled cover off till now
	0

06-13-2019, 08:32 AM	#10
dirtbkr188 Join Date: Aug 2009 Posts: 521	As Mudflap mentioned above, there is a center crankshaft seal, a big outer o-ring, and there are two small o-rings behind the stator plate for the mounting screws. You'll need a flywheel puller to access the stator plate, I believe it is the one shown below - M27mm x 1.0 with LH left hand thread.
	0

06-13-2019, 11:06 AM	#11
b44 Join Date: Apr 2016 Location: Australia Posts: 89	Thanks alot, would the 2 small orings need to be replaced aswell?? I've got oil seal kit, but no 2x small orings
	0

06-13-2019, 01:55 PM	#12
dirtbkr188 Join Date: Aug 2009 Posts: 521	Usually, no, they don't need to be replaced, but they will "oil stick" to either the engine case or the back of the stator plate, just so you're aware. Also, the two countersunk philips screws that hold the stator in place usually need to be loosened with an impact driver
	1