An incident on a harvesting site left a particularly beloved saw squashed. But could it – or at least part of it – be salvaged?

DON’T you get ticked off with petty politics? Forestry feels like a blame game at the moment, with our leader passing the buck about tree planting. They aren’t even maintaining the forests we have, just transforming them into unmanaged scrubland.

I’ve been doing my bit this past summer on several woodland restoration schemes, transforming old, unmanaged woods into little patches of well-looked-after, diverse woods that will be there for generations to come. It’ll take a couple more visits before the woods are pristine, but they’ll get there eventually and the happy landowners can now enjoy something they previously saw as an annoying problem.

I’m in no mood to expand on my thoughts on planting, but I am in the mood to get back to basics – and what better subject than a flat saw, and how to unflatten it?

Forestry Journal: Crankshaft with bearings and stuffers.Crankshaft with bearings and stuffers. (Image: FJ/SB)

For many years I’ve been a big believer in a summer shutdown – park everything for a week or so and everyone goes off on their summer hols. Having the whole operation on stop makes for a more relaxed break, with no phone calls about hauliers going AWOL or machines playing up and I don’t have to take executive decisions while half cut in a hot tub.

This year we got the dates wrong, although I did leave strict instructions that only matters of life or death should be allowed to interrupt my holiday.

For this reason I didn’t discover the one minor issue until the day after we returned home. One of our small saws had found itself under a rather large beech stem.

“It’s not too bad,” I was told. “It needs a top cover and a handle. Or two...”

The chainsaw is not new, but is one of the most popular in the inventory – a Husqvarna 550 XPG Mk2. It’s the only saw we have with heated handles, which I like when cutting firewood in the winter.

Weeks passed and the broken saw sat in the van until the guy we’re currently training to get his forwarder ticket decided he was ready to have a day on his own (still with a qualified driver on site, of course), so I found myself with a free afternoon.

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I cleared my workbench of old harvester chains and bits of worn-out proportional valves and laid into the now mouldy wreckage with some gusto, which quickly turned to a growing sense of despair.

The top cover was only slightly damaged where a stick had pierced its lower edge below the primer bulb. When I unclipped it, the carnage was quickly revealed. The stick had left a trail similar to a bullet. There was a clear path of destruction and I was about to find out just how extensive it was.

The 550 is just about Husqvarna’s most popular professional saw. It is remarkably powerful for such a small machine and the Mark 2 handles better than the Mark 1, which I found awkward and unforgiving to use. We run them for brashing and dressing out edge trees and rough trees in the crop. I don’t employ a hand cutter unless we have a lot of edge trees to do in a hurry, or we’re doing a lot of hardwood.

Having a 550 equipped with a 15” bar on site lets anyone with a few minutes knock the odd oversize tree down. I often do a half-hour at the end of the day when there isn’t really time to scoot off for another load. If you do a bit of felling when you can, it avoids doing it when you have to. Especially bearing in mind it might be raining when you have to.

At first glance it didn’t look too bad. The top cover appeared salvageable, the starter cover was okay, as were the clutch cover and chain brake handle, and the exhaust wasn’t crushed. I could see lots of broken plastic though, and once I removed the starter housing I realised I wasn’t going to rebuild this little gem. The top edge of the crankcase casting that the starter housing screws to was broken into several pieces.

That means the crankcase on the ignition side was scrap. These come in pairs, so the saw required a complete crankcase set, plus gaskets, bearings and a complete strip and rebuild. I happen to know the time allocated for this job at the dealer is six hours and the cases cost £220 plus VAT. Bearings are £18 plus VAT each, gaskets another £20 and they need to be carefully pressed into cases that have been heated to around 180C, with the correct tool, which I don’t have. You can’t knock them in with a brass drift and hammer like we used to do with the saws we rebuilt 20 years ago.

I’d gone this far, so thought I might as well strip the saw, box up all the parts I could re-use in one box and all the parts I needed to replace in another. In the keep box was the piston and cylinder (but not the piston ring), the crankshaft, exhaust, both outer covers, flywheel, oil pump and clutch. That was pretty much it.

In the broken box was everything else. The carburettor had the choke shaft snapped off, all the ECU wiring had been ripped out, all the plastics that carry the air cleaner and the primer bubble were smashed, both handles were broken and the heated handle wiring was wrecked. The stick that had been pushed through the top cover had broken everything in its path. If you’d spent hours researching how to do the most damage with a single blow you could not have done more.

I haven’t disassembled many of the newer breed of chainsaws – by that I mean scavenging-engine-equipped ones. Low-emission engines have been around for many years now, but I haven’t needed to rebuild a saw since we moved entirely into mechanical harvesting on reasonably flat sites.

Forestry Journal: The path of destruction. The path of destruction. (Image: FJ/SB)

The first thing I noticed when taking the 550 apart was how compact everything is. It’s mainly the same parts I recognise, but they’re all very petite, and crammed in together.

There are some real head-scratchers. To get the last screw out of the plastic section under the carburettor you have to lift the cylinder off. The hardest screws to undo are the ones that secure the exhaust. At first I thought they must be secured with thread-locking compound, but no, they’re just incredibly tight and long. I’d hazard a guess this is how Husqvarna solved any issues with exhausts coming loose.

The clutch isn’t easy to get off. There are a couple of indents with a helpful ‘off’ and an arrow, but I know from experience that using a punch and hammer here can result in a broken centre casting. Servicing dealers have a special tool that locates in the indents and is spun by an impact gun to remove them without damage. I don’t have the tool, so I carefully use persistence and patience rather than force and try to use each indent in rotation so it shares out the stress. The oil pump is behind the clutch, familiar to anyone who has had the common chain oil leak which I have had on a couple of bigger Husqvarnas. I repaired a 572 recently (although I have to admit this 550 has never leaked chain oil). The rubber pipe that pushes into the oil tank at one end and into the oil pump at the other becomes a loose fit and allows oil to weep past, particularly once the oil is warm. The answer is to clean the pipe and the recess it fits into and refit it with a smear of good-quality sealant. I don’t use silicone, but a black RTV-type instant gasket. Apply to clean, dry surfaces on the pipe and casting, assemble it loosely, leave it to cure for a few minutes, then tighten everything down and leave it for 24 hours before putting oil in the tank. I leave the saw on its side with the pump upwards and the oil tank cap removed while it’s curing.

Splitting the crankcases is also a much more involved process than with the older piston port, case-charged models. There are no separate crankcase oil seals on the 550. The crank bearings are a composite type with the seal built in. To get them out is – you guessed it – a special puller. The cases need to be heated to around 180C so they will let go of the bearings. Then the puller can be used to remove the bearings from the crankshaft. At this point I knew this saw wasn’t going back together, so I used the tried-and-tested method. I put the flywheel nut back on and, holding the crankcases with one hand, I beat on the nut with a copper hammer. I did the other side with the clutch centre and the cases came apart, leaving the bearings in situ. I heated the cases with a heat gun and the bearings popped out with a gentle tap.

If I were to rebuild a 550 I think I might pay our local Husqvarna dealer to assemble the bottom end for me. It might prove a good investment as I don’t see how you would get the bearings centralised and all the clearances correct when using the hammer and brass drift techniques I employed for many years.

Forestry Journal: There's no fixing that There's no fixing that (Image: FJ/SB)

The final piece of this jigsaw is the crankshaft itself. The one in my 550 seems just about perfect, no play and smooth rotation with no discolouration anywhere, but this saw has always been run on good-quality oil, so I’d expect that. The crankshaft comes in three pieces – the main assembly, rod, big end, webs and shaft is one and two metal and plastic ‘stuffers’ that fit over the webs. These are to ‘stuff’ the void in the crankcase and their function is to reduce the swept volume in the bottom end of the engine. In traditional two strokes this void was where the fuel and air charge was held before it was pumped into the cylinder through the transfer ports.

I’ve never seen this set-up before and it is the major difference I noticed and the one thing that clearly demonstrates how much the technology has advanced.

Could this saw be rebuilt? Well yes, it could, but not by replacing parts with new items. It wouldn’t be financially viable. The cost of the crankcases, both handles, the carburettor and just a few of the small parts soon get you close to the cost of a new saw. There are lots of second-hand parts available on the net, but the time and effort needed to get everything together would be unreasonable, unless you have lots of time on your hands, which I don’t.

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The obvious choice would be to buy a saw with a blown top end, a seized piston and cylinder. There are two problems with this approach. I would really want to replace the crank from a saw that has had a catastrophic failure, even if it’s just a seized piston. The tolerances in all high-quality small saw engines are so fine I wouldn’t be able to trust the bottom end of such a saw. This would mean a total strip and around six hours of work, plus bearings and gaskets. The second is that the 550 I’ve just pulled apart is, of course, a G model, so any parts donor would need to be the same.

So what’s the answer? How did I get from the bent and buckled wreckage at the start to a shiny, new-looking model? Simple. I walked into my local dealer and bought the only 550 XPG they had on the shelf, for a very good price.