MS 460 port timing numbers

[Lignator]

OK...before I grind, here's the plan:

using an OEM cylinder and piston on a Stihl MS460-

the numbers are ATDC,

stock:
intake: 73 deg (146 duration)
exh: 103 deg (154 duration)
trans:123 deg (114 duration)
blow down: 20 deg

proposed:
intake: 83 deg, I need to grind .118" off the piston skirt (166 duration)
exh: 98 deg, RAISE exhaust by .06" (164 duration)
trans: 115 deg, RAISE trans by .087" (130 duration)
blow down: 17 deg

this seems like a lot of material if i go by the numbers. before I cut, does this all seem reasonable?

btw, I used a crank length of 2.5" (63.5 mms) and a stroke of 36mm.

welcome feedback.

 

[Gypo Logger]

If your willing to do it one step at a time you may save yourself a lot of work. I like that your taking a bit off the intake skirt.
Stihl has done a good job on the stock timing I think.
What if you started with skirt clip, a gasket delete and a DP muff mod and a bit of port matching and see what improvements you get.
John

 

[mdavlee]

Too much intake and exhaust for me. You doing any machine work?

 

[Lignator]

The saw has the OEM dual port muffler cover and has the large hole (penny sized) in the primary exhaust port. I was surprised to see that. Thought only 046's ran that muffler. I am going to open the cover up a bit more but leave the other hole alone for now.

I can't pull the gasket, it's at .027" and the gasket is around .015" thick. Saw has 165psi cold comp as is which seemed respectable.

I don't have lathe access any more so i won't be cutting squish or the base, though that would be ideal.

So far I have polished the top of the piston and cleaned up the windows. I have also removed the lip from the lower transfers, though I didn't take them all the way to the base. It seems that would slow down the fuel charge, perhaps not. Either way easier to take it off than put it on.

At the very least I think taking .100 off the skirt will help get more fuel through the saw, but not waste too much. I agree that matching the exhaust to the muffler, polishing and widening/squaring up exhaust and widening intake all are good ideas.

I have read that these saws short blow down duration, hence my thought to change transfer and exhaust durations. Perhaps this has been proven wrong.

 

[cuttinties]

Those numbers are too high for my preference. If you like a peaky saw go for it. But those numbers aren't going to be very forgiving.

 

[Four Paws]

You don't need more exhaust duration.

 

[mdavlee]

If no machine work go to 76 intake and 15 degrees of blowdown.

 

[Lignator]

i definitely don't want it to be peaky. i plan on running a 25" bar most of the time in hardwoods.

 

[Lignator]

If no machine work go to 76 intake and 15 degrees of blowdown.

intake off the skirt? pistons are def cheaper than new jugs.

 

[mdavlee]

If there's a chance you'll cut the jug later then take it off the piston.

 

[Lignator]

so i get .04" off the skirt for intake and raise the transfers .045" for 76 deg and 15 deg

 

[mdavlee]

Sounds about right.

 

[wcorey]

I picked up my first ms460 last Nov for short $'s, decent shape but low comp, piston was mildly scored but everything cleaned up well.
Finally got around to porting it a few weeks ago, cut base/squish, widened/re-timed ports, etc.
Didn't touch the lowers but put some effort into getting a flat roof on the uppers, blended back to the point where I broke through on the ex outside corner, bad habit lately.

I have also read here many times that the one idiosyncrasy to porting these is they like short blowdown.
B Snelling in particular has taken bd and also intake duration to a bit of an extreme and claims good results.
Since I never tried it stock and don't have another to compare to, figured I'd start just a bit on the conservative side (for me) and go back in for more if it seemed necessary.
Haven't advanced the timing yet, have an enlarged hole under the muffler side deflector and a second port on the front cover but not extreme.

Ended up with;
101 ex
117 tr
78 int
.020 sq
Comp 185

Tried it out in 24" oak, I'm not really impressed with it, runs decent but just doesn't Wow me like other saws I've done.
Haven't put it side by side up against the 044 but have some time on that one and in that size wood at least doesn't seem that much faster.
I have another stock cylinder I've been saving for an 044/046 hybrid, may put that on to compare before I do anything else to it.

Otherwise not sure what direction to take with it at this point...

 

[Lignator]

compression and squish numbers look good Bill.

try knocking that lip off the lower transfers. I've done that on other saws with this design of transfer port and had good results. just don't go too crazy. i believe it slows down the velocity of the charge as you enter the combustion chamber.

 

[nmurph]

Lig, I would definitely lose the base gasket and improvise.

 

[Lignator]

I was thinking about trying to make a mandrel and sand down the squish band. could probably get a few thou that way and delete the gasket. other option might be an alternate gasket material.

 

[Four Paws]

I was thinking about trying to make a mandrel and sand down the squish band. could probably get a few thou that way and delete the gasket. other option might be an alternate gasket material.

Now you're on the right track.

 

[mdavlee]

Old piston and sandpaper will work to get a little bit out.

 

[Knobby57]

I found on a 460 most magazine covers make a good gasket . I used a cover from a filson catalog . My final squish was .020


Sent from my iPhone using Tapatalk

 

[Lignator]

good tip.

one thing i picked up recently was using grease on the burr while grinding. creates almost like a lapping compound. cutting oil just gets slung around. oils good on sand paper.