Stihl MS 460 - any known problems or parts that break?

[Muddy42]

So I have just got hold of and fixed up a 2011 Stihl MS460 with a badly scored piston.  I disassembled the saw and pressure/vac checked the crankcase.  I gave it a pass eventually, after a few dramas with a serious leak in the decompression value (hissing air so I replaced it) and then realizing my pressure tester had a leak.

 

So I removed the cylinder and piston and cleaned everything up.  This saw has been well used.  The cylinder might have been salvageable, but it was already not genuine so I opted for a replacement Meteor cylinder and piston. The fuel and impulse lines are a bit hard but hold pressure fine, the intake boot doesn't have any signs of holes or cracks. The spark seems OK, I only did a basic carb clean (metering side). The carb holds pressure through the fuel line

 

I got the saw reassembled and it started up fine last night, idles and revs OK, although I was pretty gentle on it and it needs tuning. So for £140 and my time, I'll hopefully have a working saw.

 

But I still have this niggling feeling that I might have missed the cause of the piston scoring? Why is the saw now on its third cylinder?  Could it simply be the decomp value? Before I go spending more money on sprocket, bar and chain and using the saw properly, is there anywhere else I should check?

 

Its the first time I have replaced a cylinder, hence the question.  Thanks in advance.

 

 

[Dan Maynard]

It's pretty long in the tooth, could either be wear or someone mis-fuelled it. Assuming it's similar inside to the 461 it should be a good saw.

[Muddy42]

Just now, Dan Maynard said:

It's pretty long in the tooth, could either be wear or someone mis-fuelled it. Assuming it's similar inside to the 461 it should be a good saw.

 

Thanks, that's reassuring.  Yes it has seen a lot of use, but everything seems sound enough.

[Stubby]

Hopefully you don't have an air leak from somewhere . Crank seals or wherever . You say it passed this test so thumbs up . Good job .

[Muddy42]

9 minutes ago, Stubby said:

Hopefully you don't have an air leak from somewhere . Crank seals or wherever . You say it passed this test so thumbs up . Good job .

Thanks, yes it definitely held a vacuum with the Mityvac. For pressure, I epoxy-ed up the holes in my cr@ppy ebay pressure tester (lesson learned, refund requested, negative feedback pending) well enough for it to hold 7psi for a few minutes. Fingers crossed.

Edited February 7, 2023 by Muddy42

[Stubby]

1 minute ago, Muddy42 said:

Thanks, yes it definitely held a vacuum with the mityvac. For pressure, I epoxy-ed up the holes in my cr@ppy ebay pressure tester (lesson learned, refund requested, negative feedback pending) well enough for it to hold 7psi for a few minutes.

Spud would know whats acceptable in that respect . @spudulike

[spudulike]

My pressure and vac check is pump to....15 InHg, wobble the crank to and fro and check for leakage - if the reading stays solid and doesn't stop dropping, release the vacuum, pump up to 10 psi, wobble the crank to and fro and see if it drops. 

If you get a leak, you then investigate. I personally don't create a vacuum or pressure and then hold it for 5 minutes and mostly found if there was an issue, it would show up pretty quickly.

On what you should check to stop it going pop again...most saws that passed through my workshop for rebuild/port/ full service etc were checked in regards to stopping it seizing : -

1) Compression

2) Vaccum and Pessure leaks. If the decomp leaks, I reground the seating and sealed with a little grease. Make sure you are also testing the inlet manifold and impulse line when doing the test!

3) Fuel filter....almost definitely worth replacing

4) Carb - strip, check diaphragms and metering arm height, check gauze strainer, clean and rebuild. MS460s tend to build up wood chip behind the metering diaphragm.

5) Tach tune to around 12,500-13,000rpm - make sure the engine is stable when flat out and not fluctuating.

 

If you do this, it is pretty certain that your saw will last. The pressure/vac check is the solid foundation and the tach tune sets the saws maximum revs so the machine shouldn't fail again.

 

The 460 is a pretty solid machine - I did find that I often had to pull the limit cap off the H carb screw as this model often over revs once they are loosened up.

 

Others may have their opinion but this is what I did and it was a pretty reliable method for me.

 

[spudulike]

54 minutes ago, Muddy42 said:

For pressure, I epoxy-ed up the holes in my cr@ppy ebay pressure tester (lesson learned, refund requested, negative feedback pending) well enough for it to hold 7psi for a few minutes. Fingers crossed.

Why didn't you use the Mityvac for both pressure and vacuum? That is the reason most use them

[Muddy42]

1 hour ago, spudulike said:

Why didn't you use the Mityvac for both pressure and vacuum? That is the reason most use them

How was I to know the cheap ones only pumped vacuum?!

[Muddy42]

13 hours ago, spudulike said:

My pressure and vac check is pump to....15 InHg, wobble the crank to and fro and check for leakage - if the reading stays solid and doesn't stop dropping, release the vacuum, pump up to 10 psi, wobble the crank to and fro and see if it drops. 

If you get a leak, you then investigate. I personally don't create a vacuum or pressure and then hold it for 5 minutes and mostly found if there was an issue, it would show up pretty quickly.

On what you should check to stop it going pop again...most saws that passed through my workshop for rebuild/port/ full service etc were checked in regards to stopping it seizing : -

1) Compression

2) Vaccum and Pessure leaks. If the decomp leaks, I reground the seating and sealed with a little grease. Make sure you are also testing the inlet manifold and impulse line when doing the test!

3) Fuel filter....almost definitely worth replacing

4) Carb - strip, check diaphragms and metering arm height, check gauze strainer, clean and rebuild. MS460s tend to build up wood chip behind the metering diaphragm.

5) Tach tune to around 12,500-13,000rpm - make sure the engine is stable when flat out and not fluctuating.

 

If you do this, it is pretty certain that your saw will last. The pressure/vac check is the solid foundation and the tach tune sets the saws maximum revs so the machine shouldn't fail again.

 

The 460 is a pretty solid machine - I did find that I often had to pull the limit cap off the H carb screw as this model often over revs once they are loosened up.

 

Others may have their opinion but this is what I did and it was a pretty reliable method for me.

 

 

Thank you, this is very useful.  I need to go in there again (and best to do it when everything is clean) so I might as well test for leaks again more thoroughly. 

 

Edited February 8, 2023 by Muddy42