Would anyone who has used a petrol powered tool like a big garden chipper believe the automatic (centrifugal/(petal?)) clutch to only engage once you were a (fair?) bit above tickover?
I've taken the clutch off and everything is free and there are no broken (but could be weak) springs but even on tickover it feels like the clutch is fully engaged?
I will email the manufacturers and it could well be that the clutch is only there to aid sub tickover revs, eg, *just* whilst being started (so you don't have to pull start the entire mech), a bit like a de-compressor?
The only similar clutch I have experience of is the one fitted to Suffolk Punch lawn mowers and this certainly had to be significantly above tickover to drive the machine.
I wonder though if the difference there is that the clutch affects it's drive (assuming you mean cutters and / or being self propelled) whereas this clutch just drives the hammermill / flales / disk cutter etc.
eg, This chipper isn't going to move if the clutch is engaged and you wouldn't want your fingers anywhere near it if it was running (internally).
So, the $100 question is is this particular clutch simply to leave the engine output disconnected from the workings just while you start it or should it also stay disengaged when it's ticking over.
I've since emailed the makers and am awaiting their reply.
Can you check the spring pull needed for the clutch to engage and from the weight of the shoes etc determine when the spring tension would be overcome and so engage?
Are you sure the clutch doesn't bind in some other way? I don't know what you mean by "even on tickover it feels like the clutch is fully engaged".
Is it possible that the clutch is only to ensure that when the blades are jammed you don't have the full weight of the engine on them in self-destruct mode?
I've not measured anything technically yet but using two screwdrivers I prized one shoe up and the springs felt pretty tough. There are three clutch 'shoes' that slide in guides and three springs that go between the ends of each. So, when levering one shoe you are only stretching the springs on both ends by half what they would normally do.
It feels pretty free in all other aspects and the outer (with the V belt pulley) turns freely with the engine at rest.
We started the chipper and after letting it warm for a bit, ran the engine at it's slowest speed (on the tortoise) and if you put say a block of wood on the output pulley you couldn't stop it (eg, it wasn't just 'drag' that was making it spin).
Yes, I guess that is also possible. The sales blurb only mentions the clutch re 'easy starting'. It would make sense however that if any of the cutting / flail stuff seized (or was jammed), especially instantly the clutch would ensure the engine wasn't also brought to a dead halt. However, from what I have seen so far I think it would still stall the engine, not allow it to tickover as I imagined and as I am familiar with similar equipment.
The more I think about this (dangerous I know!) I can't see why the cutter mechanism should be allowed to run at tick over speed although no load starting feature is a must have. Once the cutter is rotating there must be the temptation to lob something in, forgetting to increase the revs. This would almost certainly jam the machine and stall the engine due to insufficient stored energy in the cutter at low rpm and insufficient engine power (esp. if petrol) at tickover to recover from the load. To my mind a well designed machine should not start rotating until the revs were close to nominal engine power.
I'd expect the engine to have a governor anyway so the user control would be much closer to a binary switch between tickover and "ready for work" I can't really see why it would want an analogue control of speed.
We tested this yesterday (on tickover) with some light brush in though the 'shredder' bit and it just shredded it! ;-)
You can see one in action here (albeit on full power etc):
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Understood. The side cutter (up to 3.5" diameter wood) is basically a
400 x 12mm steel disk with a small cutout and blade on one side and on the same shaft, 24 steel flales on a 3 panel steel frame. A picture speaks 1000 words: ;-)
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And yes, it confirms what you say above in that pdf:
"Another outstanding feature of our hammermill machines is the centrifugal clutch. It is designed for easy no-load starting while of offering operator and engine protection not available with a direct drive machine. The clutch will also disengage if the machine is overloaded. This allows the engine, flywheel, and rotor RPM?s to quickly recover to full speed and complete the task at hand."
So, whilst that confirms the 'easy starting', 'safety shock load fuse' and 'anti-stall' roles, it doesn't actually state the clutch would be disengaged at std tickover. ;-(
Or at least a good bit above tickover. ;-)
It has (like most mowers etc) that increase the throttle (often via an 'air flap' as the revs drop.
The only other thing we haven't really investigated is the slow running on the B&S engine and if the slow running revs are stable and slow enough. We have the manual for the engine so should be able to check any setup steps offered in that.
To answer your first question I think it's 5+ years old but we have no idea how much use it got prior ownership but I feel 'not a huge lot'. I think it was more neglected than worn out (like, the bearings that should be (according to the handbook, 'greased every 8 hours use' had never been greased at all (inside the grease nipple / entry was completely devoid of any signs of grease)).
So, I think the clutch pads are steel and the inside of the clutch bell was slightly 'galled' but I think I'd expect that with a steel on steel solution.
Well, I cleaned it up with some WD40 and although it says the clutch hub is self lubricating (large oil-lite bush) and so shouldn't be 'lubricated', I did wipe a very fine smear of bearing grease inside the bearing pre re-assembly just to see if it made any difference. It didn't seem to.
I think we need to know what it is *supposed* to do before we can determine if it is doing it or not (which was sort of my question). ;-)
I must admit, like you I would expect the clutch to disengage at idle but that's not the same as knowing how it's meant to work. I imagine you've not got a lot of variables to play with. Idle speed, clutch spring strength and friction. You've already said that the idle is very slow and it would be odd for the springs to have lost their strength in 5 years of occasional use. Might the "galling" be significant?
Well, it seems to be but I think I'd like to re-visit that in general to see what adjustments are available on that particular engine (re throttle position / fuel - air mix etc). Unlike say an outboard or motorbike where the tickover is simply set conventionally, these things use the air pressure flap governor thing so it seems awkward to set tickover. That said, once I read the engine handbook there may be a procedure for disconnection that governor and then setting the tickover without interference. ;-)
If the carb has been as poorly maintained as the rest of the machine I wouldn't be surprised if it isn't way out of adjustment.
Agreed, not but not impossible? Batch fault or something? It may be that it is a Briggs and Stratton supplied clutch and / or I might be able to get some more information on it, as we did with the Taper-Lock bush that holds the main cutter / flywheel on the main shaft. [1]
Depending on how the metallurgy works at that level it could well cause the clutch to 'hang on' later than it might before low rev / pre stall disconnection but I can't see how it could impact how soon it engages initially?
Cheers, T i m
[1]
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(you can just see the main cutter blade and the pass-through slot on the left)
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Not sure if it's actually this make but it gives a good idea about how it works and how you are supposed to deal with it.
I had to learn similar with the self centring bearings and the (cotton covered Kevlar reinforced) drive belt. ;-)
Yup, it looked and felt (hardness and weight) like it.
I think the 'shoe(s)' was(were) far too thick and solid for it(them) to have ever had a lining.
And if that were the case, you might have thought the issue would be the clutch slipping not gripping. ;-)
However, I think the role of this 'clutch' is more like a 'dog (clutch)' than what we might traditionally consider to be a clutch, with it's gentle slipping / gripping action.
I'm still waiting for a reply from the American manufacturers so that might explain things better.
So, I got a reply from their engineer yesterday and it confirmed that the 'clutch' is really only there for two things ... to allow easier starting (not having to spin over all the chipper gear) and to protect the engine in the even of a seizure within the chipper mech.
So that's good then as it means it's working as designed. ;-)
You are welcome Bob, in fact, the answer came by email but in the form of a .pdf and 'in response to several queries on this matter' document. ;-)
The chipper has been since used and the reports are that it's working very well. ;-)
I did thank the tech guy for his reply and asked for further clarification on greasing and the bearings.
According to the user handbook the bearings should be greased every 8 hours. However, upon stripping the machine / bearings it was obvious the grease nipples had never been used (as the internal pathways between nipple and bearing were devoid of any signs of grease).
The bearing and housing looks like this:
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And the (self centring) bearing out of the housing looks like this:
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You should be able to see that the grease would enter through the nipple, go down into the groove in the inside of the spherical part of the casting, go round the groove till it finds the holes in the bearing outer and then pass though into the bearing itself. Except, when you apply grease it just comes out between the bearing and casting? Now, that either suggests the grease isn't getting to the holes in the bearing (alignment issue), or that there isn't anywhere for the grease to get out of the bearing so it finds the lest path of resistance and comes out the sides. Maybe when the bearing seal lip wears slightly, that will allow us to 'purge' the bearing with grease?
Or maybe the instructions are wrong and these (particular) bearings are sealed for life?
I have read of people who regularly grease such (chipper / arb machinery) bearings till they see grease coming out and others say that if the bearing is sealed for life, that you can blow the seals out by doing so (and maybe that's happening but they don't realise if it's an inner bearing)?
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