Author Topic: Stihl 460  (Read 705 times)

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Offline mdavlee .

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Re: Options for a MS460
« Reply #30 on: April 23, 2016, 07:41:44 pm »
Corrected for altitude that's about 158 for compression.

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Re: Options for a MS460
« Reply #31 on: April 23, 2016, 07:44:07 pm »
Corrected for altitude that's about 158 for compression.

That is true with the bigger cc saws you lose a lot of compression up high where I am. 
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Offline 660magnum

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Re: Options for a MS460
« Reply #32 on: April 23, 2016, 10:36:21 pm »
Raising the exhaust port will reduce the compression a little. But altitude has a big effect.
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Re: Options for a MS460
« Reply #33 on: April 23, 2016, 11:48:45 pm »
Raising the exhaust port will reduce the compression a little. But altitude has a big effect.

Hey Jim how are you.   
Yea I did raise it a little but I don't think I raised it that much.    It could be the Hyway cylinder already had a high exhaust port.    Since I did not check it with a degree wheel I really do not know.  But I have to be honest the saw still feels pretty strong to me.   
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Offline 660magnum

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Re: Options for a MS460
« Reply #34 on: April 24, 2016, 06:43:41 am »
Yes, the Hyway cylinder exhaust ports are already about as high as you dare go.  AFAIK the higher ports are like a long duration cam in  four stroke and reduce your over all volumetric change. Therefore the compression is reduced.

To minimize the squish, and also to widen the squish band, and/or even pop-up the piston overcomes any compression loss due to increased timing.

Naturally you already knew all this and I'm just running off at the jaw being a troll.

The typical big problem I've seen on aftermarket cylinders is the shape of the top of the exhaust port (The Arc) and the lack of beveling on the top of both the intake and exhaust ports tends to score the top corner of the piston crown and the wear the edge from the top of the ring.

Hyway has been better at this than the other brands.

A ring with a rounded top edge at any of the ports will still give decent static compression but the power will be diminished.

Kevin had a 272 with a AM cylinder come in with 150 pounds of compression but ran like it was four stroking until it was too lean to run. The ring top was round at the transfers. A new ring and all was forgiven. 
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Re: Options for a MS460
« Reply #35 on: April 24, 2016, 10:17:35 am »
Well I guess that explains the lack of compression.   
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Offline mdavlee .

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Re: Options for a MS460
« Reply #36 on: April 25, 2016, 05:48:10 pm »
Usually a few degrees isn't that much difference.

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Re: Options for a MS460
« Reply #37 on: April 30, 2016, 06:09:11 pm »
Well I ordered a plug for the decompression valve and blocked it off.    I took another compression reading and it is up to 150 psi now.
Could be the ring has started to seat in some and with a plug in the decompression valve.    Could be one or the other or a combination of both.
What I am seeing now is more like what I would expect from it.  I still think it should be even higher and could get better as the ring seats more.
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Offline mdavlee .

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Re: Options for a MS460
« Reply #38 on: April 30, 2016, 08:26:46 pm »
150 is almost 180. That's pretty close to what it should be.
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Re: Options for a MS460
« Reply #39 on: April 30, 2016, 08:43:26 pm »
150 is almost 180. That's pretty close to what it should be.

Great thanks Mike.
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