Porting a MS660 w/BB Kit

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I've got a brand new 066BB here that I'm porting, and thought that I'd share it with you guys. This is the first one I've seen since installing the prototype of this generation on my personal saw. These kits have a come a long ways.

Let's start with the exhaust. The biggest problem I have with this cylinder is the exhaust port roof. It's still completely flat, with no curvature to it at all. This is not good for the rings. However, it does have a HUGE bevel on it, and will likely not be a problem. I'm going to massage this one a little, just to get a little curvature to it. I can't do much at all though, becaust the exhaust port timing is very high, at 96° ATDC. I would much rather see this at 100-105. 100 would be fine it weren't flat, but 105 would give me a little play room. As far as port width is concerned, it's already nearly as wide as the skirts will allow. My outer marks are the skirt edge, and the inner lines are where I'll be taking it to. Not a deal breaker here, but the biggest place for improvement in the cylinder.

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The shape of the intake isn't pretty, but isn't a concern at all. No rings travel across it. There is lots of room for improvement in port width here. Again, port timing is very agressive. It's an amazing 86° BTDC. However, that's how the one on my saw is, and it runs incredible and still idles good with good throttle response.

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I see no issues with the transfers. The furthest line is the ring end. The closest is where I'll be taking the transfer to. You can't see it in this pic, but there's a HUGE bevel on these transfer, probably clost to .040" tall. The port timing is a 125°, giving me a blowdown of nearly 30°, so I'll be raising these to 120°, basically raising them the amount of the factory bevel.

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I won't be doing a popup on this saw, but if I were, there might be an issue here. It appears to me that the NiSi may not go to the top of the bore, by approxiamately .170". Subtract a squish of .020", and that's still .150". That will still have the rings riding onto this area .030". Hopefully this is simply unhone NiSi. I can feel no ridge whatsoever, so hopefully that's the case.

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Bottom line, these kit's make a good replacement for a stock topend. With the aggressive port timing, it should make great power, even in unmodded form. Once ported, my 066 is a monster. I've had multiiple topends on it, and this was the first one that made me say wow. Hopefully this one will run the same. I'll post more as I go along.
 
Initial grinding work is done. Ports are widened and reshaped. Since not wanting to lower the intake, there are still irregularities from the initial shape. You can see that I raised the exhaust only by the amount of the factory bevel. All ports still need rebevelled, a critical step.


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The factory exhaust outlet is tiny, mayby 3/8" at most.

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This "cage" was completely closed on the end. All exhaust has to go through the small holes on the sides. I opened up the cage so that it's a straight shot through.

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I then opened op the outlet as far as the deflector covers.

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I then added an additional port. This port wouldn't have been required for a work saw, but added it anyway. A spark arrestor screen can be added if need be.

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Here's the first of a few heat cycles. This is to break in the piston mostly. I'll let it cool off and cycle again. I'll do this a few times before putting it in the wood tomorrow. I'll not tune in the H needle until tomorrow as well. Starting, idle, and throttle response are in excellent.


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Hi Brad..

There is something I hope you can explane for me cause im pretty dumb on understanding porting the tranfers...I know about exhast and intake,,but with porting the transfers, im kinda lost on figuring out how much you can get by with in timing. Thanks... Jess...
 
There is something I hope you can explane for me cause im pretty dumb on understanding porting the tranfers...I know about exhast and intake,,but with porting the transfers, im kinda lost on figuring out how much you can get by with in timing. Thanks... Jess...

It depends on the saw. Some need more blowdown than others. Blowdown is the number of degrees from when the exhaust first starts to open until the transfers start to open. This saw currently has 28° of BD. That's a lot, too much IMHO. I left it that way just to see how it would respond. I just got home from putting a tank of fuel through it. It runs great, but as expected, didn't turn the RPMs I wanted, even with the high exhaust. I've got the cylinder back on the bench and will be raising the transfers about 5°. That should help feed the cylinder at high RPMs. Other saws would like this much BD. The 7900 comes to mind there.
 
Typically I don't adjust the height on the transfers, it's just to easy to mess up the timing, as Brad indicated.
But every saw has some inherited blockage in the transfer ports, humps, rough castings etc. The point is to make them flow smoothly and give them more flow. So widening, going deeper and smoothing out the rough spots tends to help more than moving them.
Another tip I picked up was to radius everything, not take anything to a knife edge. I can't and wont even try to explain it, but somehow the knife edge disrupts flow more than a radius. It also eliminates the possibility of having the edge get hot and melt.
 
The wood is frozen Oak. The chain is a round filed Stihl RSC, 7-pin rim.

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I just tuned it after putting it back together again. Initial results looks like I picked up 300-500 RPMs. I'll get another vid of it in the wood and see what I gained in the cut.
 
It looks pretty strong. It will be interesting to see how the blowdown will change it.
 
You got a good running 660 there mr Snelling,the engine sounds like music in my ears.
 
Do you ever strap a tach on so you can be accurate with in the cut measurements?

I usually bungee mine on.

Saw sounds good.
 
The muffler opening has not been opened up enough to give you a clean port match to the cylinder, as you can see. You still have an over-lap unless you grind further out on the muffler opening, and then braze a plate to the inside of the muffler for a "perfect" port match. This will give you maxium exhaust flow. Added work forsure, but those are little things you have to do for excellent performance. "Some win some lose but we all play the game" :moneymouth:

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