MS261 M-Tronic Build

[Heavy Oil Saw]

@spudulike Spot on, glad you understood my terminology. All seems fine then, no rotational movement in the crank at the bearing ends, no movement up or down in the piston (all new parts), or the the crank big end. There is movement as you suggest in the crank.

Thank you for replying so fast.

I’ve lathered the internals with 2 smoke oil, to preserve it while it’s open, and give maximum lubrication on dry pulling and eventually start up.

Found the fuel tank breather blocked/failed, so that’s on order as well. Trying to cut down potential on problems when fault finding a non starter. Pretty much only the carb is left unopened, but passed a pressure test.

Gotta pressure test the cylinder as well.

Has anyone deleted the base/cylinder gasket to any detrimental affect. I’ve read early 261s had too little squish for this, but later ones are looser in tolerance, and can accept it better. Any opinions?

[spudulike]

I don't know on the squish, the breathers only let air in but do flow one way only.

[Heavy Oil Saw]

Started again, after checking the play in crank and piston. Ensured the arrow on the piston was pointing towards the exhaust. Moved from island to table as the kids are doing their art lesson today.



Now just waiting on parts. Hoses mainly, and an air filter, lets see when they’ll arrive.
Gotta build something to pressure test the crank seals, I have rubber sheet to seal things up, need some plate to screw it all down. Can you pressure test through the spark plug opening? As I could cobble an old spark plug in to an adapter and block cylinder inlet and outlet. Keep the cylinder at BDC(?) and let the pressure build, 7psi I believe

[spudulike]

Yes on pressure and vac testing through the plug hole, I made an adaptor as you are suggesting.

 

[Heavy Oil Saw]

Thought I’d knock up a couple of plates and “gaskets”, while I wait for a seal kit for my Mityvac (put it to bed full of fuel and it’s perished the seals/age as well).
As you can see, they certainly aren’t aerospace quality, but nothing I do is, but hasn’t ever failed me. This could be a first [emoji33].
Used in-hex bolts on the exhaust side as I cut them down to allow clearance off the cylinder. The large washers are for comedic affect. Had the chipped cylinder/inlet manifold/old exhaust gasket as templates, and cut the best I could using a dremel, old Ikea kids table and vise-grips (I don’t have a vice at home).
All mounted, it looks feasible, and I’ll indeed spray them with leak detector as well to ensure my leak isn’t self induced. They’ll all get cleaned before installing on the saw, so no nasty pixie dust is ingested.
Here’s some pics.

[Heavy Oil Saw]

Here it is installed. Those washers cover up the butchery behind them. Talking of butchery, where’s that old spark plug?
That’s my 1 year old daughter in the background plodding about, hoping she takes a liking to “mechanics”.

[Heavy Oil Saw]

Got it pressure tested. Held a 7psi pressure for over 10 minutes, and vacuum of 10inHg vac.

Here’s some pics

[spudulike]

I usually just give the saw vac or pressure, waggle the flywheel around and if there is no immediate drop, all is good. You pretty much always get a leak straight away on a faulty machine and is obvious from the start of the test. I know many will say you should.......but I will be damned if I sit around for 10 minutes watching a little gauge do its thing....sounds like watching paint dry.

Glad it is looking good though, always an important test as if you get any weird running, you know the main engine is 100% sound and the issue must be somewhere else.

[Heavy Oil Saw]

I usually just give the saw vac or pressure, waggle the flywheel around and if there is no immediate drop, all is good. You pretty much always get a leak straight away on a faulty machine and is obvious from the start of the test. I know many will say you should.......but I will be damned if I sit around for 10 minutes watching a little gauge do its thing....sounds like watching paint dry.
Glad it is looking good though, always an important test as if you get any weird running, you know the main engine is 100% sound and the issue must be somewhere else.

We’ve got three kids in the house, so I got distracted, and came back later and found no drop in pressure, I wouldn’t choose to stand there and watch the gauge, unless it was a decreed law by the manufacturer. Not doing it for a living, and having never built a 2 stroke, with the inherent dangers of lean running from air leaks, I’m glad I’m taking my time, and proving my work as I go.

[ChrisNewport]

Ideally needs to be tested again once the inlet manifold is in place. Few times I've seen leaks on the inlet to cylinder.