540 Oil Pump Internals

[lesorubcheek]

I never disassembled a 540 oil pump before, but this one was very gummed up and needed cleaning. The mechanism for the adjustment looked kinda neat, so thought I'd share. Here's how it looks:


Fundamentally, it works like the other gear driven Homelite pumps. The shaft is rotated by a worm gear that's turns with the crankshaft. The shaft has a cam groove that rides against the cam rider bolt, so as the shaft rotates, it is pushes forward. Where most pumps have a cam that rides on both sides of the rider bolt that forces a forward/backward motion, this one uses a spring to push it back. Just like other pumps, there's a notch on the end of the shaft that acts as a valve so based on it's orientation is either open to the inlet on the backstroke pulling oil in, then closed on the inlet and open on the outlet as it pushes forward forcing the oil out. So the spring keeps the shaft pressed back so the cam is in contact with the cam rider bolt, or, and this is the magic, until the rear tip is in contact with the lower bolt. The lower bolt has 2 indents. One is larger and deeper than the other. So the 3 positions are the deepest indent, allowing the most travel of the shaft, the smaller indent allowing medium travel and no indent which allows the least travel of the shaft and therefore the least oil flow. So, based on the lower adjusting screw position, the cam rider bolt comes in contact with the cam at a different spot as the shaft is allowed to go back only until it bottoms on the lower bolt. Hope I got this right and it makes sense.

Dan

[stillsawing]

Does saw have to be running to make an adjustment or must it be shut down and remove the detent screw for a travel change? Thanks for info, am I correct in thinking the 540 has a European influence? 

[lesorubcheek]

Feb 22, 2022 18:02:28 GMT -5 stillsawing said:

Does saw have to be running to make an adjustment or must it be shut down and remove the detent screw for a travel change? Thanks for info, am I correct in thinking the 540 has a European influence? 

Good question. So the detent screw is rotated with 3 positions to change the stroke length. Here's the section from the manual that hopefully will help.


Not sure I completely agree with it though. The 540 and 8800s have it's worm gear actually turned by the sprocket. The worm gear can free spin on the crank if it's at idle, and there's a chain brake too that ensures no movement of the sprocket. If the clutch isn't engaged, the oil pump worm isn't turning (unless something is jammed), so you'd think it'd be fine to adjust the oiler in this case. Maybe Homelite just wanted to make it idiot proof, who knows.

The European influence point has stirred up many cans of worms in the past. There are those who swear up and down the 540/8800 are Solo designed and some say Solo built. Part of this is because of the 290/340 which really are rebranded Solo saws and the 540 was in the same time frame with similar layout. It's been said that the big reason for the move to vertical cylinders was due to fires that had been started due to heat of the horizontal cylinder. Sit a saw down on dry leaves and the heat from the cylinder and muffler down low could ignite the leaves. So it may have even been government mandates that forced a design change, but not sure, it just kinda adds up.

There are some parts on the 540/8800 that are made in Germany, like the cylinders, and maybe the pistons, but the magnesium body castings are Lunt which was pretty much making all the Homelite Magnesium parts since the early 70s. All I can say is that anything is possible. I haven't seen any documented evidence to show what if any involvement Solo had with the 540/8800 design or construction. It's very possible that Homelite contracted with Solo or other German engineers to design at least parts of the saws, but that's purely speculative. The only real facts are that some parts are marked being made from Germany, others from the US. Since Husqvarna and stihl were starting to gobble up the market, it makes sense that Homelite would try come up with a competitive saw of their own, so yes, even if Homelite designed it 100% and just had some parts made by German companies, you still would have to agree it was influenced by European models.

Dan

[blythkd]

I always thought the design was influenced by the 410. Design wise, it's almost a carbon copy of the 410, just bigger with some small changes in lines.

I never realized the 540 had an adjustable oiler, but then again, I never was around very many. I had an 8800 and I thought it had a plastic pump? Maybe it was a cheaper non-adjustable version then the 540 had? That one actually looks like a pretty good oiler to me.

[lesorubcheek]

Feb 22, 2022 21:12:38 GMT -5 blythkd said:

I always thought the design was influenced by the 410. Design wise, it's almost a carbon copy of the 410, just bigger with some small changes in lines.

I never realized the 540 had an adjustable oiler, but then again, I never was around very many. I had an 8800 and I thought it had a plastic pump? Maybe it was a cheaper non-adjustable version then the 540 had? That one actually looks like a pretty good oiler to me.

You're right, the 410 needs to be included in the mix. They share some parts, like the starter, and designed similar. The whole side mount carb deal is strange, but hey, it does work. You're right about the 8800 having a plastic housing. You're probably right that they cheapened it to save some money. Still seems odd they went with the plastic rear handle first on the 540 and then went magnesium on the 8800. Had to be because of complaints in durability. Tons of saws were turning to plastic by then, you'd think they'd try to strengthen the existing plastic version. Hey, I'm not complaining, I like magnesium, but it just seems strange.

Dan