Almost finished with the MS 361 build - I have a few last questions for you guys

[2-StrokeDude]

Well I’ve got the MS 361 all back together now, but I’ve got a few questions about things to do from here. First on the clutch side, the groove in the crankshaft that is just above where the seal goes, somebody was saying there’s supposed to be a clip there? Is this the clip that’s supposed to be there? It’s been a few weeks since I’ve taken the saw apart, so I couldn’t really remember where everything went, but I managed to get the whole saw put back together with lot of frustration and a lot time.

Since this is the first saw I’ve completely rebuilt (top and bottom ends), I’ve never installed crankshaft seals before. I don’t want to run the saw and have an air leak cause it to blow up or something and have wasted $300 in parts, so I know there’s some ways to pressure/vacuum test the cases.

I’ve never done any pressure testing, so what would be the best way to do that? Preferably a cheap way…

I’ve thought about just bringing the saw into a shop and having them put some OEM seals in there and then just having them pressure test everything for me, then I will know that the saw is good to go.

I haven’t ran the saw at all other than putting a little bit of gas down the carbs throat and it fired for a second or two, but I haven’t started it up at all, or broke it in yet since I’m trying to figure out some of the questions I have above.

Now please let me hear all that advice from you wise ones out there who know more than me!

Any help would be appreciated, thanks!

 

[Coralillo Lo Pro]

Yeah, the circlip is just outside the oil seal. Mityvac vacuum pump is what you want for pressure testing. MV8000 for about $43 on Amazon gives you vacuum, the MV8500 kit I got gives you vacuum and pressure but is $75-85. You really have to make sure you seal the exhaust and intake well, I couldn't get any readings on one saw to my frustration til I finally found the muffler face was too warped to seal the sheet of gasket material I'd closed the exhaust off with.

I sort of had the experience you did on my first two saws I rebuilt from the ground up, ruined a couple of seals installing, bearings wouldn't drop into place after heating, had super hard installs banging them in and had some tiny leaks between outer race and casing I had to fill with the type of Loctite recommended. I was using a powerful torch so thought I must have heated the case enough, but I think baking the case is better. I never put the bearings in the freezer either. I tried baking to 400 today with my truck's transfer case to pull an otherwise impossible needle bearing from the case, and it came out pretty easy with the slide hammer after going nowhere before.

 

[2-StrokeDude]

Yeah, the circlip is just outside the oil seal. Mityvac vacuum pump is what you want for pressure testing. MV8000 for about $43 on Amazon gives you vacuum, the MV8500 kit I got gives you vacuum and pressure but is $75-85. You really have to make sure you seal the exhaust and intake well, I couldn't get any readings on one saw to my frustration til I finally found the muffler face was too warped to seal the sheet of gasket material I'd closed the exhaust off with.

I sort of had the experience you did on my first two saws I rebuilt from the ground up, ruined a couple of seals installing, bearings wouldn't drop into place after heating, had super hard installs banging them in and had some tiny leaks between outer race and casing I had to fill with the type of Loctite recommended. I was using a powerful torch so thought I must have heated the case enough, but I think baking the case is better. I never put the bearings in the freezer either. I tried baking to 400 today with my truck's transfer case to pull an otherwise impossible needle bearing from the case, and it came out pretty easy with the slide hammer after going nowhere before.

Thanks for the help, do you think it would be a bad idea to run the saw without vacuum/ pressure testing? It's not even broken in yet. I've heard that if you start the saw up and it idles that is another way to see if there are leaks since it will idle if there aren't any, however I don't really want to trust that method. I just really don't want to seize up the motor or cause anything to break since I've spent around $300 on this saw.

Also what exactly does the circlip on the crank do? does it just help make sure the crank doesn't move from side to side?

 

[2-StrokeDude]

Yeah, the circlip is just outside the oil seal. Mityvac vacuum pump is what you want for pressure testing. MV8000 for about $43 on Amazon gives you vacuum, the MV8500 kit I got gives you vacuum and pressure but is $75-85. You really have to make sure you seal the exhaust and intake well, I couldn't get any readings on one saw to my frustration til I finally found the muffler face was too warped to seal the sheet of gasket material I'd closed the exhaust off with.

I sort of had the experience you did on my first two saws I rebuilt from the ground up, ruined a couple of seals installing, bearings wouldn't drop into place after heating, had super hard installs banging them in and had some tiny leaks between outer race and casing I had to fill with the type of Loctite recommended. I was using a powerful torch so thought I must have heated the case enough, but I think baking the case is better. I never put the bearings in the freezer either. I tried baking to 400 today with my truck's transfer case to pull an otherwise impossible needle bearing from the case, and it came out pretty easy with the slide hammer after going nowhere before.

Also one other thing does the Mityvac 8500 that you have come with all the adaptors that you need to test the seals? do you just connect the Mityvac up to the pulse hose and pressure-rise the case or pull a vacuum on it?

 

[Coralillo Lo Pro]

Thanks for the help, do you think it would be a bad idea to run the saw without vacuum/ pressure testing? It's not even broken in yet. I've heard that if you start the saw up and it idles that is another way to see if there are leaks since it will idle if there aren't any, however I don't really want to trust that method. I just really don't want to seize up the motor or cause anything to break since I've spent around $300 on this saw.

Also what exactly does the circlip on the crank do? does it just help make sure the crank doesn't move from side to side?

Not sure but I'd guess the circlip is to keep the sprocket from contacting the seal. You'd be in trouble if it was the only thing keeping the crankshaft from moving side to side lol. That movement (or lack of it) should be locked into place by the bearings.

I see no harm in starting it up whether there's a leak or not, won't damage it from briefly running it. You can spray starter fluid around anywhere you suspect leaks on an engine and if it changes the idle, you know you have a leak because it's getting sucked in there. That's the cheap non-scientific test. The MV8500 has every adapter needed, yes, I just plugged a suitable size one into the pulse line and pumped it up to 8psi to draw a vacuum or pressure test it. I bought a sheet of gasket material at the auto parts store and cut out little pieces to block the intake and exhaust and clamped the carb and muffler down over them. Cutting up pieces of old bike tire innertube works fine, I started with that but thought maybe some tiny ridges in the material were making a bad seal when the problem that whole time was my warped muffler face. A bit of soapy water around the seals when pressure testing will show any tiny leaks - just don't vac test when doing that, you don't want to draw it in. If you do have tiny leaks between the casing/outer race you want to seal with Loctite, then drawing a vac helps pull it in to seal them.

 

[2-StrokeDude]

Not sure but I'd guess the circlip is to keep the sprocket from contacting the seal. You'd be in trouble if it was the only thing keeping the crankshaft from moving side to side lol. That movement (or lack of it) should be locked into place by the bearings.

I see no harm in starting it up whether there's a leak or not, won't damage it from briefly running it. You can spray starter fluid around anywhere you suspect leaks on an engine and if it changes the idle, you know you have a leak because it's getting sucked in there. That's the cheap non-scientific test. The MV8500 has every adapter needed, yes, I just plugged a suitable size one into the pulse line and pumped it up to 8psi to draw a vacuum or pressure test it. I bought a sheet of gasket material at the auto parts store and cut out little pieces to block the intake and exhaust and clamped the carb and muffler down over them. Cutting up pieces of old bike tire innertube works fine, I started with that but thought maybe some tiny ridges in the material were making a bad seal when the problem that whole time was my warped muffler face. A bit of soapy water around the seals when pressure testing will show any tiny leaks - just don't vac test when doing that, you don't want to draw it in. If you do have tiny leaks between the casing/outer race you want to seal with Loctite, then drawing a vac helps pull it in to seal them.

Awesome, guess i'll buy one of those mityvacs and a few extra seals in case they are bad. Thanks for the help!

Also when I installed the two case halves as well as when I put the cylinder on, some 2 stroke oil got on the gasket paper, think this will be an issue with the gaskets sealing? I hope it won't be since they probably soak up oil over time?

 

[Coralillo Lo Pro]

Also when I installed the two case halves as well as when I put the cylinder on, some 2 stroke oil got on the gasket paper, think this will be an issue with the gaskets sealing? I hope it won't be since they probably soak up oil over time?

I can't see that being an issue at all w the gaskets. Good luck w it! I haven't used my 361 at all since the new piston and rings and coil, ran it some to confirm it was all working, but don't have any Stihl mount bars for it aside from one 20" lo pro bar I use w a mount adapter on my Makita 6421 for milling. The 361 would be a fine small log lo pro milling saw, but would rather use it as a bucking saw for trimming, firewood, etc.

 

[Lightning Performance]

Thanks for the help, do you think it would be a bad idea to run the saw without vacuum/ pressure testing? It's not even broken in yet. I've heard that if you start the saw up and it idles that is another way to see if there are leaks since it will idle if there aren't any, however I don't really want to trust that method. I just really don't want to seize up the motor or cause anything to break since I've spent around $300 on this saw.

Also what exactly does the circlip on the crank do? does it just help make sure the crank doesn't move from side to side?

It's called a snap ring and outside snap ring to be exact not a circlip.

The oil pump gear is indexed by the clip on the crank.

 

[Lightning Performance]

Awesome, guess i'll buy one of those mityvacs and a few extra seals in case they are bad. Thanks for the help!

Also when I installed the two case halves as well as when I put the cylinder on, some 2 stroke oil got on the gasket paper, think this will be an issue with the gaskets sealing? I hope it won't be since they probably soak up oil over time?

Oil is what swells the gaskets

 

[2StrokeFondler]

Awesome, guess i'll buy one of those mityvacs and a few extra seals in case they are bad. Thanks for the help!

Also when I installed the two case halves as well as when I put the cylinder on, some 2 stroke oil got on the gasket paper, think this will be an issue with the gaskets sealing? I hope it won't be since they probably soak up oil over time?

My 20€ china pressure/vac tester does the same as the 80$ mighty. The gauge is not calibrated, but I don't care.
Not gonna shame anybody for buying nice tools. Just wanted to throw a cheaper option in the ring.

 

[2-StrokeDude]

Oil is what swells the gaskets

So you would want oil in there to swell it up so it seals better?

 

[SteveSr]

So you would want oil in there to swell it up so it seals better?

Looking at the photos it looks like the PTO (clutch side seal could go in a but further to get it away from the snap ring. You also have to account for side-side crank play.

 

[Lightning Performance]

So you would want oil in there to swell it up so it seals better?

Oil is how the gaskets work. Sealer is only a face seal. Oil makes the gaskets swell. That is how they work without sealer. Oldest game in town. The oil will squeeze out when you compress a "wet" gasket. Dry gaskets have more installed pressure they say but it matters little as long as they swell to seal the gasket in place.
Some people install them dripping wet some bone dry. In the end they all get wet if oil is involved. Seals resist oil but not gaskets 99.9% of the time. Dry air furnace gaskets would be an exception on a wet fuel burning device like air to air heat exchangers.

 

[Lightning Performance]

Not sure but I'd guess the circlip is to keep the sprocket from contacting the seal. You'd be in trouble if it was the only thing keeping the crankshaft from moving side to side lol. That movement (or lack of it) should be locked into place by the bearings.

I see no harm in starting it up whether there's a leak or not, won't damage it from briefly running it. You can spray starter fluid around anywhere you suspect leaks on an engine and if it changes the idle, you know you have a leak because it's getting sucked in there. That's the cheap non-scientific test. The MV8500 has every adapter needed, yes, I just plugged a suitable size one into the pulse line and pumped it up to 8psi to draw a vacuum or pressure test it. I bought a sheet of gasket material at the auto parts store and cut out little pieces to block the intake and exhaust and clamped the carb and muffler down over them. Cutting up pieces of old bike tire innertube works fine, I started with that but thought maybe some tiny ridges in the material were making a bad seal when the problem that whole time was my warped muffler face. A bit of soapy water around the seals when pressure testing will show any tiny leaks - just don't vac test when doing that, you don't want to draw it in. If you do have tiny leaks between the casing/outer race you want to seal with Loctite, then drawing a vac helps pull it in to seal them.

Pressure tests with a simple air regulator set at 8 to 10 psi, like the one on an air compressor, works just the same.

 

[PV Hiker]

I was taught early on by a Stihl mechanic for the case gasket put bearing grease between your fingers and pull the paper gasket through leaving a thin coat. Then install.

So you would want oil in there to swell it up so it seals better?