OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Ryobi Trimmers & Brushcutters Ryobi/Homelite trimmer flywheel taper

My second question here today regarding re-assembly of a Ryobi/Homelite RY70113 (aka PLT-3043) trimmer.

The flywheel in these machines is a zinc casting. Where it sits down on the engine shaft, there is a steep taper and a cast-in shaft-key spline that sits in a keyway on the shaft. When I removed mine, the flywheel was seated into the shaft taper nice and firmly - it required a tap with a hammer on the end of the shaft to pop the flywheel off the taper.

Now that I come to reassembly, I can't seem to get that strong grip of the flywheel onto the shaft, as in, no matter I tighten the flywheel down onto the taper by screwing down the clutch plates, if I take off the clutch plates to check if the flywheel taper has grabbed onto the shaft taper, it actually hasn't grabbed - you can easily lift the flywheel back off. I'll confess that I'm paranoid now, because the first time I built up the machine, I tried pulling the starter rope a few times, great until all went slack - I had chewed off the little zinc spline on the flywheel, not because I didn't get it sitting right in the shaft keyway, but because the flywheel must have been able to lift slightly off the taper. Maybe the real cause is not getting the clutch plates yanked right down ultra-tight. But, since I'm on my second flywheel, I don't want this new one getting chewed up too. You know, I can't just keep buying dead RY70113 trimmers from the tip shop (landfill recycling business) - they want $10 for each one - too many and I should have just bought a new trimmer!

So, any good tips on getting the flywheel back on nice and tight?

Hi Ian333, welcome to Outdoorking. One of the problems with zinc parts intended to fit together tightly, is that the material is neither hard nor strong, and it can easily develop burrs when you try to reassemble the machine. My first guess is that you have a burr there somewhere, perhaps too small to see even, but possibly detectable with a sensitive fingertip or a magnifying glass.

Essentially though, if that is a half crank machine (the 26 cc is, don't know about the 30 cc) I don't know why you would bother.

Grumpy, thanks for the welcome.

Yes I'm not thrilled at the engineering of a taper and the tiny spline all made from zinc. I'm used to machine tool tapers (on lathes and mills). They grip as soon as you fit them. Anyhow, I have checked carefully, the surfaces here are clean and undamaged. However there is a slight rock when the tapers are engaged, so there is no true taper fit. How it was originally made to fit in the factory is a mystery to me.

Perhaps I'll try just yanking down on the clutch plates as hard as I can. If it still spoils, I'll have to get another tip-shop trimmer of the same make, use its crankcase, but this time not take off the flywheel - leave the mysterious factory fit of the taper well alone.

The 30cc is also a half-crank machine. However, at the tip-shop it is the best of the commonly found trimmers. One could say that if there's piles of them at the tip shop, that might be giving some kind of message as to quality.

So why bother? Well, its a big leap from spending $15 at the tip shop to buying a secondhand Stihl. If my rebuild works, it will be kudos. And, at least I'm cutting my teeth on a $15 outlay, rather than making beginner's mistakes on a high-end machine. I've learnt a lot so far.

I understand the reason you've given Ian, but why not just buy an off-brand full-crank trimmer? I've got a classic Echo and a modern generic full-crank 25.4cc thing sold under half a dozen brands, and I only use the generic, not the Echo, because it is so much nicer to use and gives so much less trouble. The generic cost me $1 on ebay, and took 90 minutes to fix, using no new parts at all. It didn't even need a tune, because it had only ever run for a few minutes before it went wrong.

I doubt you care, but what went wrong was the previous tenant left it out in the sun, and the plastic axle the pull-starter reel rotates on, grew a bit. That meant he couldn't pull the starter, so the guy gave it away to another guy who put it on ebay with a warning that it looked as if it had been run without oil in the fuel, because the engine was seized. Oddly enough, no-one but me wanted to pay even $1 for it. All it needed was dismantling the pull start and sandpapering the shaft with a finger-tip until the reel rotated easily. Hopefully I'll have the sense not to leave it out in the sun, but meanwhile it is the nicest trimmer I've ever used, by far.

Excellent story - which shows yet again that many machines got for a song can be fixed quite simply - people balk at servicing fees so the item gets tossed. Another example is computer monitors - the most likely fault is bad capacitors (Google badcaps) - just needs a screwdriver, soldering iron and new caps - a real cinch.

So anyhow, what is the model nr and 'brand' of your generic full-crank trimmer, so I can Google it and see what to look out for?

Meantime, I'll try get this one running. I already spent $6 on new fuel lines, so it had better work.

I haven't found all the aliases it has, Ian, but here are a few:
Parklander CG260EF, Pope Gardenline 101PLT25, Sanli GTB26. I don't recall its GMC or Aldi Gardenline model number. As it happens the one I am using is a Pope Renegade, model 101PLTFCB, which is an earlier model than the others I've listed, with a one-piece end cover that incorporates the pull-start. I have a 101PLT25 as well, with a detachable pull start, except that it's missing the pull start, so I don't use that one until I find a starter at the right price. The engine is identical though, on all of them. Note that it is 25.4 cc, and is advertised both as 25 cc and 26 cc by different brands.

Well here's my new tool to tighten up the clutch plates on that particular model of Ryobi trimmer.

Basically I grabbed an offcut of 25 x 6 mild steel bar of a handy lever length, and put screws in to create pins that can engage the clutch plates. See photos below.

The tool had to be double ended, because to get the clutch plates off, the pins have to be spaced 47mm apart, while to tighten them on, the pins have to be 50.5mm apart. I just used some 3/16" BSW dome-head screws that were in one of my screw jars, they were a nice fit, but a bit long, hence the washers on the back-side of the tool, just packing the screws up so the projecting pins are the right length (3.4mm). I drilled my screw holes 4mm and tapped 3/16 BSW - handy I got those BSW taps on eBay a while ago. To let the engine shaft through, I drilled a 10mm centre hole. That the steel bar has mitred ends is just because it's an offcut from another job.

Now to see if it works, as in, to get the clutch plates down really tight so that the flywheel can't lift and strip its spline off when running. Stay tuned.

I assembled the trimmer, tightening the clutch plates as hard as I could using the shop-made tool shown in my previous post. I was afraid to go too tight, because all I was working against was the piston pressing up on the wad of nylon cord I had pushed down into the cylinder. I didn't want to spoil the piston rod or bearings in some way by yanking down too hard with the tool. Still, the clutch plates must be pretty tight.

So I ran the trimmer for about 20 minutes cutting grass. So far so good, the flywheel is obviously still engaged on its taper. I guess my failure with the first flywheel was from not tightening it down properly by fully tightening the clutch plate over it to jam the flywheel onto the taper. Fingers crossed.

To minimise the risk of breaking the piston or rod when you do the rope-in-the-cylinder trick, make sure you put in just the right amount of rope so that the piston is halfway up the stroke after the rope has compressed as much as it is going to. If you do the rope trick and end up with the piston near the top or bottom of the stroke, you are greatly magnifying the forces on the piston and rod, due to the crank and rod acting as an over-center mechanism.

Thanks Grumpy, that is indeed very useful info to know.

But in thinking about what you say, I don't really understand why the stresses would be greater at the end-stroke as compared to the mid-stroke position of the piston. Sometimes I feel a bit thick, but I want to get it. Where would you say the greatest magnification of force would be if the piston is stopped near the end stroke? The gudgeon? Big-end bearing? Elsewhere? Sorry to ask, and hope you don't mind explaining further. I did Google over-centre mechanism but didn't find anything helpful.

Just think of the crank, connecting rod, and piston as an over-center linkage, like a clamp used in an industrial jig. As it moves across top dead center, the crank pin can move an inch, while only moving the piston a few thousandths of an inch. Of course all but a few thousandths of that crankpin movement is horizontal, while the piston can only move vertically, so the piston only moves by the "vertical component" of the crankpin's movement, and ignores the horizontal component. That is, the crankshaft has a "mechanical advantage", or force multiplication, of around 100 to 1 as it moves across top dead center.

However when the crankpin is at exactly half-stroke, the crankpin and the piston move equal amounts. The crankshaft then has a mechanical advantage of only 1 to 1.