.404 chain options

[mjeselskis]

We're running Oregon an 18HX093E chain on a processor we built. When the chain is sharp, on bigger wood we end up stalling the chain and hitting the relief in the pump. I'd like to avoid reworking the hydraulics, if possible. For those running .404 chain, is there a less aggressive chain option?

[mike_belben]

How low are your rakers set and whats the relief pressure in the saw circuit?

[mjeselskis]

How low are your rakers set and whats the relief pressure in the saw circuit?

The rakers haven't been filed so they are factory height.

The relief is kicking out around 1200. The problem is that it's a cartridge relief in the pump. It's stamped 3000psi, but I'm only getting 1200 at most when it stalls. I haven't been able to find a replacement cartridge, so I'm trying to address it with the chain. It's an Eaton 70142 or 70145 pump,I can't remember the exact displacement.

I did swap the fwd/rev relief valves from side to side and it didn't change anything.

[sawguy21]

You likely won't be happy with a less agressive chain, time is money. Is the machine so old that the cartridge is difficult to source?

[mjeselskis]

You likely won't be happy with a less agressive chain, time is money. Is the machine so old that the cartridge is difficult to source?

The pump is probably 20 years old. I found a few places that may sell a new relief cartridge, but the price is pretty high considering I'm not sure it's the problem. If I had a bad relief valve, I would have thought swapping the fwd/rev valves would have made a difference in the kickout pressure. We don't cut that much wood, so a little slower sawing wouldn't kill us.

[snowstorm]

Stihl has two harvester chains. The heavy one the takers are at .050 just like the 18x. Slow your feed rate some chartige relives can be taken apart and shimed.

[mike_belben]

A 3000psi relief that stalls at 1200 is the issue needing changed, not your chain. 

Its either bypassing at the relief, inside the pump housing around worn out guts or inside the valve or saw motor.  

Fluid that does no work generates excess heat.  Use an temp gun to find the hottest location in the system.  Good chance your issue is inside.  

Take apart every relieve cartridge in the system.  A little rust, plastic or rubber seal chunk, teflon tape or one itty bitty metal chip is all it takes to hang a relief open and cause issues such as youre having.  

[Corley5]

I run Oregon 18HX on my processor. On occasion a batch of new chains are "grabby" right out of the box.  A couple grindings smoothes them out.

[mjeselskis]

A 3000psi relief that stalls at 1200 is the issue needing changed, not your chain.

Its either bypassing at the relief, inside the pump housing around worn out guts or inside the valve or saw motor.  

Fluid that does no work generates excess heat.  Use an temp gun to find the hottest location in the system.  Good chance your issue is inside.  

Take apart every relieve cartridge in the system.  A little rust, plastic or rubber seal chunk, teflon tape or one itty bitty metal chip is all it takes to hang a relief open and cause issues such as youre having.  

Mike, you're not wrong. I'm just looking for an option to avoid an expensive rebuild/replacement on the piston pump.
It would make sense that it may be bypassing within the casing somehow since swapping relief valves side to side didn't change it. 

[mike_belben]

I fail to make the connection to what i suggested vs what youre afraid of.  Most valve sets have a relief cartridge in them.  It may be bypassing there if you have one.   

My life has proven that avoidance isnt a very good maintenance strategy, but its your time and money in this case. 

[Corley5]

The relief on the valve for my Block Buster's saw motor is set at 1,500.  Grind your chains.  You set that relief too high you'll pop chains.

[Skeans1]

When you tested pressure explain how you did. Are you blocking off the ports at the motor to test the feed pressure? How many RPM's is the shaft at the motor turning unloaded? 

[mjeselskis]

I fail to make the connection to what i suggested vs what youre afraid of.  Most valve sets have a relief cartridge in them.  It may be bypassing there if you have one.  

My life has proven that avoidance isnt a very good maintenance strategy, but its your time and money in this case.

I'm thinking the pump may be worn out. I will check the relief valves for debris like you mentioned and check for hot spots. It's a simple hydraulic circuit so limited options for what could be wrong, which is a good thing, I suppose. It's a variable displacement pump controlled by a external lever arm moving the swash plate. As the bar leaves it's parked position, it brings the pump to full speed before it starts sawing. Since the originally drove hydraulic motors on a commercial mower, it has forward and reverse, but I'm just using one direction. Each of the 2 lines coming from the pump have a relief built into the pump. the pump goes straight to the saw motor, no valves. 
I have a gauge tee'd into the line feeding the hydraulic motor and the gauge is mounted on the control panel so I can watch it while sawing. Once the relief opens and the saw stops, the pressure is 1000-1200.
I don't have a tach to check rpm, but if I remember from when I was sizing the saw motor, I'm on the low end but in the recommended range for the .404 chain

[mjeselskis]

The relief on the valve for my Block Buster's saw motor is set at 1,500.  Grind your chains.  You set that relief too high you'll pop chains.

Thanks, good to know that it can cut ok at 1500. What chain do you run, and do you grind different than the factory angle?

[Corley5]

.404 18HX 74 drivers.  Grind it the same as the factory.  They can be rough out of the box.  Sometimes the cutters are high.  Takes a couple grindings to smooth them out.  The old Woodland Pro from Bailey's used to be really bad when new.  If you hang a chain with 3,000 PSI behind them they could very well break.

[mike_belben]

Alright, now i have a pretty good picture of what youre working with, im familiar with the standalone zero turn pumps.   

I expected there to be a more conventional control valve in the system. 

You can save a piston pump pretty often if you catch it soon enough and lap all the surfaces with wet sandpaper on glass.  Pretty common with old obsolete skid steers. 

[mjeselskis]

Alright, now i have a pretty good picture of what youre working with, im familiar with the standalone zero turn pumps.  

I expected there to be a more conventional control valve in the system.

You can save a piston pump pretty often if you catch it soon enough and lap all the surfaces with wet sandpaper on glass.  Pretty common with old obsolete skid steers.

Mike, I'm familiar with the sandpaper and glass technique. I just did the heads on my Subaru that way. What surfaces do you do inside the pump using that method?

[mike_belben]

When you open it up you'll see the wear. the piston feet are definitely gonna ride against the swash plate and you may have scoring on the end plates or ends of the cylinder, etc.  Anything you can buff flatter will help.  Any failure of a charge pump to lube the high pressure side will result in a quick death so look that section over good.


Fwiw, surplus center has a bunch of new variable displacement pumps with a piggyback tandem pump for $60 right now.  They have a funky metric spline which is why theyre almost free. Im tempted to buy a few.  Doesnt hurt my feelings to turn and mill a keyway or weld a coupler over the metric bits.  Drill and tap to SAE Oring for ports etc. 

[mjeselskis]

Thanks, appreciate the help. I haven't opened up a variable displacement pump before. Anything to watch out for?

[mike_belben]

I have some commercial aluminum cookie sheets with big edges thatre handy for pumps or valve bodies where bits and bobs go rolling off when you crack the case.  

1. Clean the exterior first

2. Scribe alignment lines across seams so youll know how to clock it on reassembly.

3. Setup a camera to dictate your notes into while you pull it apart.  Be sure to mention which way and order each valve, spring etc comes out.  Calipers are handy so you can call out checkballs by diameter and location.  Punching little dimples near a check hole on non critical surfaces works good.  "The .325" checkball goes in hole 2 here." [Dink dink]