MS660 Decompression Valve

[arto_wa]

I assembled MS660 Farmertec clone kit last month and was glad all parts were there 100% and quality was good.
The saw runs very well and has lots of power.

As recommended by some members on this forum, I used Stihl OEM decompression valve and wrist pin needle bearing, as well as Hyway crankcase seal kit.

Everything else is what came in the kit.

I have one concern & question to see if others have had this issue:

Initially it was reasonably easy to start the saw since the decompression valve worked as I was expecting; I.E. It would pop up after the saw started and everything was fine.

Now in the last few starts, the decompression valve pops up immediately or prematurely after the saw even tries to fire and it becomes really tough to pull the rope. Resetting the valve and the same thing happens.

The decomp valve was new takeoff from Stihl MS660 bought from eBay vendor.


Have others had this issue, and how did you solve it?
Did I get defective decomp valve?
Is there another brand decomp valve that would work better (I.E. not pop up so quick)?

Cheers

 

[Wood Doctor]

I usually check the decomp valve after any pull that I make with my MS660. It will pop up even without a fire, likely because it has so much compression. My logger buddies don't even use the decomp valve. They just drop start with it up. Pretty tough guys.

 

[arto_wa]

I usually check the decomp valve after any pull that I make with my MS660. It will pop up even without a fire, likely because it has so much compression. My logger buddies don't even use the decomp valve. They just drop start with it up. Pretty tough guys.

Thanks, I have my doubts about a drop starting this since I am not a logger but will give it a try.
I have done it with my small saw many times in the past, but prefer not to.

I was just looking at another new decompression valve with this description:

"Husqvarna part No. 503 71 53-01 fits all the standard model Husqvarna chainsaws, also useful on modified modern Stihl chainsaws with high compression because they have a higher release pressure than the standard Stihl valve."


The outlet hole is clearly larger in this valve.
Anyone here with experience with this or similar decomp valve?

 

[Ryan'smilling]

Thanks, I have my doubts about a drop starting this since I am not a logger but will give it a try.
I have done it with my small saw many times in the past, but prefer not to.

I was just looking at another new decompression valve with this description:

"Husqvarna part No. 503 71 53-01 fits all the standard model Husqvarna chainsaws, also useful on modified modern Stihl chainsaws with high compression because they have a higher release pressure than the standard Stihl valve."


The outlet hole is clearly larger in this valve.
Anyone here with experience with this or similar decomp valve?


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This looks like the one from a 395xp. If so, it actually has 2 holes that size. I have a mean and nasty ms261 that would do the same thing, push out the decomp even without a pop. Swapped it with the decomp from my 395xp and it's much much friendlier now. So, yes, that's the one I'd use in your 660.

 

[Ozhoo]

You could just drill the hole in your existing decomp a bit larger...

 

[arto_wa]

You could just drill the hole in your existing decomp a bit larger...

I had considered that, but has anyone here done it and did it help?

One should probably remove the stem out of the way in order to do it properly and how to reattach the "button" so it will stay in place?

 

[arto_wa]

This looks like the one from a 395xp. If so, it actually has 2 holes that size. I have a mean and nasty ms261 that would do the same thing, push out the decomp even without a pop. Swapped it with the decomp from my 395xp and it's much much friendlier now. So, yes, that's the one I'd use in your 660.

That sounds encouraging, thank you!

 

[motorhead99999]

Mine pops up every time you pull the rope wether or not it fires. I just stopped using it and just make sure it’s top dead center before I pull it over.

 

[noodlewalker]

I had considered that, but has anyone here done it and did it help?

One should probably remove the stem out of the way in order to do it properly and how to reattach the "button" so it will stay in place?

A suggestion for if you remove the cap... A 5/32 X 1/2" roll pin. I modify the Farmertec ones this way with good results. I would suggest drilling the hole before you remove the cap though, just for the fact that it will want to move on you if you remove it, then replace it, then try to drill it.

 

[Ryan'smilling]

I had considered that, but has anyone here done it and did it help?

Tried that first. I'm not good at small drill bits. Broke two bits and threw in the towel.

 

[JeffreyZirkle]

You know, I have ran a lot of saws, even the big Stihl ms880 mag and never use the decomp. Nor do I drop start the saws. I must be one of those tough guys.
But I will say this, I have a Stihl Ms250 that is only a few weeks old and that thing is tough sometime to pull start. I am guessing that it is the weight ratio. I tend to pull the saw out of my grip hand when I start it. I am used to my big saws and their weight, you do not have to grip them hard.

Sent from my SM-N960U using Tapatalk

 

[TheDarkLordChinChin]

You know, I have ran a lot of saws, even the big Stihl ms880 mag and never use the decomp. Nor do I drop start the saws. I must be one of those tough guys.
But I will say this, I have a Stihl Ms250 that is only a few weeks old and that thing is tough sometime to pull start. I am guessing that it is the weight ratio. I tend to pull the saw out of my grip hand when I start it. I am used to my big saws and their weight, you do not have to grip them hard.

Sent from my SM-N960U using Tapatalk

Yeah lol small saws can really jump when you hit a compression stroke.
A big saw with a long bar might be hard to pull but if you start it logger style gripping the trigger grip with your right hand and pulling the starter rope with your left hand and with the bar resting on a log or something the saw wont go anywhere if you hit a compression stroke. Might hurt your arm/wrist though so be ready.
TBH it doesnt take all that long to get used to starting your saws this way, it can be a bit daunting at first knowing you might hurt your arm but you will learn how to time your pulls.

 

[motorhead99999]

You know, I have ran a lot of saws, even the big Stihl ms880 mag and never use the decomp. Nor do I drop start the saws. I must be one of those tough guys.
But I will say this, I have a Stihl Ms250 that is only a few weeks old and that thing is tough sometime to pull start. I am guessing that it is the weight ratio. I tend to pull the saw out of my grip hand when I start it. I am used to my big saws and their weight, you do not have to grip them hard.

Sent from my SM-N960U using Tapatalk

I red somewhere the ms250 has a small recoil pulley on it which makes them hard to pull over

 

[arto_wa]

Thank you all for the replies and some pretty good suggestions!

I went ahead and ordered one of those "Husqvarna part No. 503 71 53-01" decompression valves I mentioned in the post #3 above since they are supposedly rated for higher compression release pressure.

I will try it out and report back later.

 

[drf255]

I had considered that, but has anyone here done it and did it help?

One should probably remove the stem out of the way in order to do it properly and how to reattach the "button" so it will stay in place?

The Husky 395 blue button decomp 100% helps. I drill both holes slightly larger and it won’t pop until the saws fire.

I keep like 5-10 in stock. The Stihl decomp valve seems to be ok in sub 70cc saws for me. At 70cc I swap it out. All my saws are modded though.

 

[Wood Doctor]

As long as we are talking about these decomps, how long do they usually last? If they do start leaking, won't that cost you some compression and power? I've had several customers ask me to get rid if then and plug the decomp hole in the cylinder with a threaded insert instead.

 

[CR888]

I opened up my 660 decomp which helped, but I'll position the piston just past TDC before giving it the beans.

 

[TheTone]

The decomp on my MS440 Mag closes on about the 2nd or third compression, so it's not very helpful.

 

[arto_wa]

The"Husqvarna part No. 503 71 53-01" decompression valve arrived today and now after having done one cold engine start and 5 - 6 warm starts with it installed I am pleased to report that it has made a huge improvement when starting the saw!

The starter rope is now lot easier to pull when the decomp valve is open and the valve is so far staying open until the engine fires up.

Stirrup start, drop start or "nutcracker start" no problem!

So far so good!