Inboard or Outboard clutch benefits

[bmp01]

36 minutes ago, Piston Skirt said:

Also, because the chain is substantially closer to the crank bearing there is less levering force from it on the crank PTO part which permits using smaller shaft diameter.

That.

It doesnt matter the route the forces take, clutch or cltuch bearing  route.

[doobin]

I fear I may be a bit special, I find changing a chain considerably more annoying on an outboard than an inboard clutch!

 

It's that annoying bit when you have the chain and bar o, and then you need to stick the cover back on and align it with the tention hole in the bar, without the chain coming out of the rails. That's what gets me. So much simpler with an inboard clutch.

[openspaceman]

3 hours ago, bmp01 said:

That.

It doesnt matter the route the forces take, clutch or cltuch bearing  route.

That's my take, it's the distance from the bearing  that defines the force the bending moment exerts on the crank and bearing and this is less significant in use than someone trying to yank the chain out of a jammed cut. I can see a hot, tight chain contracting having a bad effect too but how would it get that tight and hot if the oiler is working.

[Piston Skirt]

3 hours ago, openspaceman said:

That's my take, it's the distance from the bearing  that defines the force the bending moment exerts on the crank and bearing and this is less significant in use than someone trying to yank the chain out of a jammed cut. I can see a hot, tight chain contracting having a bad effect too but how would it get that tight and hot if the oiler is working.

It gets pretty hot.
The crankshaft gets heat from the engine and the clutch (which does slip all the time).

One of the outboard clutch benefits is also keeping that heat away from the crankcase (including oil tank).

 As for chain - it is quite a lot of force just to tension it right - try it with the bar & chain in vice and pull it to realistic tension.

A hot chain sags, if you tension it and let it cool, the forces grow very seriously. That’s why chainsaw manufacturers recommend loosening the chain for storage.

[openspaceman]

37 minutes ago, Piston Skirt said:

It gets pretty hot.
The crankshaft gets heat from the engine and the clutch (which does slip all the time).

One of the outboard clutch benefits is also keeping that heat away from the crankcase (including oil tank).

 As for chain - it is quite a lot of force just to tension it right - try it with the bar & chain in vice and pull it to realistic tension.

A hot chain sags, if you tension it and let it cool, the forces grow very seriously. That’s why chainsaw manufacturers recommend loosening the chain for storage.

I realise that contraction causes massive forces but I don't think I ever re tensioned a chain that was loose because it was hot. I also never loosened off a chain for storage but then I never ran chains super tight that I couldn't pull them round with thumb and forefinger.

[Piston Skirt]

Just now, openspaceman said:

I realise that contraction causes massive forces but I don't think I ever re tensioned a chain that was loose because it was hot. I also never loosened off a chain for storage but then I never ran chains super tight that I couldn't pull them round with thumb and forefinger.

Probably because You are doing things pretty correctly and not abusing the machinery, sir

I’ve seen the tension / sagging problems mostly in the forestry industry where some guys simply can’t tell if the new chain is breaking in and then think the bar nuts have to get tightened. They do all those things from overtightening the chains (especially in winter), overtighten the bars up to the level where pins get ripped out through magnesium... and the list goes on.

[Decro]

When I posed the question originally I never expected this depth of knowledge and opinion in the answers. I was tending to favour the inboard clutch for convenience in changing chains and cleaning but the remarks concerning the load from an overtightened chain or snagged bar have got me thinking. There seems very little clearance between the clutch bell and brake band so could the outboard clutch provide some support against the crankshaft flexing/bending under load.

Regarding the balance of machines with the different clutch arrangements, would this be more noticeable on top handle saws which tend, I believe, to generally have outboard clutches. 

Sorry if I'm starting another round of debate.

[bmp01]

3 hours ago, Decro said:

When I posed the question originally I never expected this depth of knowledge and opinion in the answers. I was tending to favour the inboard clutch for convenience in changing chains and cleaning but the remarks concerning the load from an overtightened chain or snagged bar have got me thinking. There seems very little clearance between the clutch bell and brake band so could the outboard clutch provide some support against the crankshaft flexing/bending under load.

Regarding the balance of machines with the different clutch arrangements, would this be more noticeable on top handle saws which tend, I believe, to generally have outboard clutches. 

Sorry if I'm starting another round of debate.

First part: No, brake band is a wibbly wobbly thing. And gets hot if rubbed too much....oo-er-misses.

 

Second part: Lets exagerate things a bit and imagine a top handle saw with the bar and chain half a meter away from the engine;  top handle above the engine. Apart from being horribly cumbersome, I think you can see it would be almost imposible to react the chain pulling force in a cut, single handed. So again, its an advantage to have chain as close as possible to engine centreline. As you say, the manufacturers seem to agree.

[Paddy1000111]

I guess it comes down to husky Vs Stihl. If you want an outboard go with husky, if you want an I/b go with Stihl. It's not like they spec a Stihl 261 with an I/b or o/b clutch. 

 

I prefer I/b clutch mainly because of ease of maintenance. If I wear through a drive sprocket I don't need an impact gun to get the clutch off or take the spark plug out to put a piston stopper in. If I'm out in the field and I'm clearing brash out the way to fell something and get a load of bailer twine (F'n farmers) wrapped around the drive sprocket I can use my scrench to take off the sprocket/clutch/bearing if needed (or send the e-clip into a low earth orbit never to be seen again, whatever I fancy).

I regularly take my clutch drum off, clean the bearing and regrease it (once every 2 weeks-one month depending) as I have before taken it off to find that bailer twine got wrapped around the shaft and melted the plastic bearing carrier. The only time I need to remove the clutch is to change shoes/springs but I have yet to have the need! 

On the chain brake front I haven't noticed much of a difference between the I/b and o/b version in the repair sense. One plastic cover and it's all exposed. On the other hand inspecting the chain brake is easier on an o/b clutch but it's not impossible on an I/b.

When changing chains though, having to hoop the chain over the clutch then hook it into the bar is a pain in the ass. I can change a chain on my 261 whilst holding the saw with one hand and fitting the bar with the other, something I can't do on a o/b clutch. Having to disengage the chain brake and then having to get the other side of the handle into the hole in the frame, whilst lining up the bar studs whilst simultaneously balancing the bar is also annoying. 

 

When I think about the practicalities of an I/b clutch, the worry about a slight bit more force on the crank kind of goes out the window. We're talking a few mm here not miles. For me, the I/b outweighs the o/b as the only advantage of an o/b is carrying an extra chain brake with you but I've never broken one, all the rest seems down to theoretical physics 

 

[bmp01]

15 hours ago, Paddy1000111 said:

We're talking a few mm here not miles. 

In terms of overhang from crank bearings its a few mm in a handful of mm - big percentage for the engineer's sums.

With you on the rest of it.