Ryobi post mortem!

Not oil lack.

Something was inside the engine I reckon, bolt or a bit of metal or stone.,

Reply to
The Natural Philosopher
Loading thread data ...

swarf in the crack case, but something gouged the side, and that something must have been about the size of the clearance between the crank counter weight and crank case. That something has likely been lost by the original opening up, or smashed into the smaller pieces. Maybe you'll identify a missing something when you disassemble further?

Reply to
Andrew Gabriel

Yes it doesn't look typical of an overheating seizure

AJH

Reply to
andrew

Any idea how the clutch is likely to come of?

Parts 46, 47, 51 on the diagram here:

formatting link
persuasion does not pull it off, and the end bit rotates freely - So I can't at the moment see how it would unscrew.

Reply to
John Rumm

More to the point, having thought about this, what is actually stopping it from working?

My limited understanding of two strokes:

on the induction / compression stroke, the upward motion of the piston sucks the fuel/air/lube mixture into the lower part of the crank case while also compressing the charge in the upper part of the cylinder. On the power stroke, the piston is forced down, and close to the bottom of its travel it exposes the exhaust and induction ports. Exhaust goes out one side, and fresh fuel etc spills round a channel in the cylinder wall from the underside of the piston to the combustion side.

So if the piston and rings are intact (at least the top half anyway), and there are no scores etc in the top bit of the cylinder, the induction should still work. There is a spark, and yet it does not start. This suggests to me that either there is damage to the cylinder at the sides where I can't see it through the ports, or the timing of the spark is out.

The ignition module seems to be a sealed unit on the part diagram. How does it sync with the crank rotation?

Reply to
John Rumm

Scoring is caused by hard grit - easily done with careless use of petrol containers. In particular, for cheap strimmers, a rust particle is hard enough to cause scoring. OTOH, scoring doesn't loose enough compression to really matter, unless it's really excessive (strimming in a volcanic ash cloud perhaps).

Pickup looks like scoring but isn't. This is inter-metallic sticking (galling) between ring and cylinder, leading to a broad, shallow score. This will write off a cylinder quite easily. It usually starts from poor storage out of use. Ryobi claim themselves that they're at risk of this, hence their recommendation to only use synthetic two stroke oils which don't break down so easily to an acidic residue. Dry storing over Winter is a big help, as is pulling the plug and giving a squirt of WD40 before storing. OTOH, giving a drop of 3-in-1 instead will encourage it, as that stuff is dreadful for its breakdown products.

Running without lubrication won't score but will give a general pattern of wear instead. You won't see this so easily, but you'll measure it and it certainly ruins compression. OTOH, it takes quite a while to develop, in terms of domestic strimmer usage.

My money is on corrosion leading to some form of inter-component pickup without any foreign solids being needed at all. A tale familiar to Jag owners.

Reply to
Andy Dingley

Is that the remains of a tiny washer in the middle of this photo?

formatting link
could be a curled up bit of swarf but it looks like a broken washer. What sort of diameter is it?

It looks to me like the engine has ingested something through the inlet tract.

Tim

Reply to
Tim Downie

You could be right....

hang on, I will go have a look;

Hmm, its not there now, so must have been loose enough to drop out while I was photographing.

I would guess about 1 to 2mm tops - that's a fairly close up shot. The gouge in the case is I suppose a third of the thickness of the big end.

A bit of its own carb perhaps? I am not sure how else something of sufficient size would get through the air or fuel paths.

Reply to
John Rumm

Yes the descending piston pressurises the crankcase and forces mixture via the transfer ports into the cylinder.

Yes but not if the crankcase seals are blown. One of the first signs of crank bearing wear is when it won't sustain a slow tickover, at higher tickover the leakage is less significant.

Is any of the spark plug interior missing? If you bring the piston up on its forward stroke just after the exhaust port is closed and then feed some coils of starter cord into cylinder via the plug hole and then rotate the flywheel to jam the piston against the rope does the flywheel slip? Clutches tend to have a normal thread that needs impact to remove and flywheels the same but opposite thread IIRC but I haven't stripped a chainsaw that far for 20 years as it's generally a gonner by then.

Two strokes tend to be predictable from cold and then difficult when warm if they don't restart straight away. I think some of this is due to the fact that petrol only ignites in a limited mixture range, when cold if the mixture is too rich the petrol wets the walls (and sometimes spark plug and drowns it) but the remaining mix is ignitable, as long as it fires quickly enough to blow the excess out.

It is known for misfires to shear the woodruff key to the flywheel which hoses the magnets.

By its position relative to the magnet in the flywheel that induces the primary current. There's probably some clever solid state stuff inside that tells a capacitor when to discharge through a coil, including some advance/retard function

AJH

Reply to
andrew

ok understood. The rear access to the crankcase is easy enough to assess. The front of it is obscured by the housing at the moment until I can work out how to take the final output and clutch off.

Not sure if I can get to a bit that is not freely rotating at the moment - I might be able to turn the rotor pawl assembly through the vent holes in the case...

Thanks for that...

Reply to
John Rumm

the monkey that was 'fixing' it left it in.

Reply to
The Natural Philosopher

Fill the crankcase with parafin and see if the level drops over night.

Typical FOD is from leaving the air filter off but I have seen screws holding the throttle butterfly come off, the middle electrode or ceramic from the plug being lost and bits off the ring ends.

AJH

Reply to
andrew

I was aware of the metal debris in the crank before I took it in though

- I don't think their "fix" was more than take apart enough to look for any scoring then give up.

Reply to
John Rumm

Yup, good plan. Not sure I have any parafin, but must be able to find something suitable.

Oddly enough I did take a careful look at the carb today to see if there was anything obviously missing. The butterfly and its retaining screw was still there! Plug is all in one piece as well.

Reply to
John Rumm

This is a Ryobi. They have a habit of the screw fasteneres working loose and so rather than a "seal" having failed, there's just a gap opening up between cylinder and crankcase.

Strip and re-assemble with Loctite. Needs an odd-sized Torx #27, but easy.

Reply to
Andy Dingley

The main crank to cylinder bolts were actually very tight... (and had threadlock on them)

Reply to
John Rumm

"Friday engine" and some worker itching to get home for the weekend dropped something into the engine where it sat (possibly in the muffler/ silencer assembly) until it dislodged one day. I suspect you've have a heck of a job proving that, though...

cheers

Jules

Reply to
Jules Richardson

Yes, BTDT... my lawn edger was a non-working cast off from a friend, and upon dismantling I found the key had sheared (the flywheels are pretty soft metal). I ended up cutting a deeper groove in the flywheel and making a new (slightly taller) key. That did the job until my homebrew key disintegrated :-)

I tempered and quench-hardened the next version, and that's been holding since, although the engine's still a bit temperamental (I suspect worn- out carb)

cheers

Jules

Reply to
Jules Richardson

barrel assembly for £38.

if that is true it would be a very cheap diy repair.

Reply to
Mike

Not just crankcase & barrel, that's crankcase, barrel, piston and crankshaft too - pretty much a short engine

Indeed!

Reply to
Andy Dingley

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.