Decompression plug or valve?

[briscoe]

My saws are MS 261 , MS341 and MS460 

 

I am wondering whether to replace the decompression valves with plugs and wondering if there is advantage to this?

 

The tiny spring inside the valve often looses tension over time and they occasionally fail. Also genuine ones from well known engineers are 25 quid whereas you can buy them for 4 quid on ebay but then concerned about quality. Do people use these after market valves and how many opt for the plugs? I've read the valves are designed partly to decrease wear on pull start mechanism. 

[Doug Tait]

The decomp valve rattled out on a 560 of mine and I asked the dealer for a replacement. They gave me the choice of an "overly expensive" replacement valve or a free bolt which the new saws are delivered to them with. The only criteria in their opinion was would I find it difficult to start without one, no mention of it damaging the saw. Been fine without it so far.

[Macpherson]

Hi, I haven't had any issue with failing decompressors apart from cleaning them if I have an engine in bits, I have them on a few saws and stonecutters. 

 

I'd say for sure that they act as a cord saver and a wrist / finger saver particularly on big saws when a casual attitude to starting can end up with yet another unwelcome strain when the toggle gets ripped out of your hand when you least expect it.

 

 

 

 

[Stubby]

13 minutes ago, Doug Tait said:

The decomp valve rattled out on a 560 of mine and I asked the dealer for a replacement. They gave me the choice of an "overly expensive" replacement valve or a free bolt which the new saws are delivered to them with. The only criteria in their opinion was would I find it difficult to start without one, no mention of it damaging the saw. Been fine without it so far.

Its ok if you can judge pulling it gently just over center then giving it a good tug . If you don't do this you can bend the metal pins that engage with the starter pawls .

[Doug Tait]

21 minutes ago, Stubby said:

Its ok if you can judge pulling it gently just over center then giving it a good tug . If you don't do this you can bend the metal pins that engage with the starter pawls .

 

The guys at the dealer obviously recognise that I'm a sensitive, gentle type of saw user!

[adw]

Deco valves are there to protect the starter and starter components as well as the operators arms, wrists and fingers, that said up to 60cc I would remove them and fit blanks, leaking valves reduces power, using them for hot starts can make effect starting. An oem valve is rated to the compression of the engine, so fitting any old valve will ever pop to soon, or not at all.

[spudulike]

ADW and Stubby have the whole picture nailed. The only thing I have to add is that I used to lap grind the valve in to stop it leaking if the vacuum/pressure engine test showed a leaking valve.

The OEM parts are quality, the aftermarket are poor at best and listen to ADW - they often pop shut too early.