Stihl MS660: NWP BB port and build

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Just finished up the day completing a MS660 with BB build for a friend.

So I though I'd share some pics. This saw was a PAIN to get appart I snapped BOTH of my T27's off on two of the jug bolts:thumbsup: Ended up busting the fins off to get into there with an T-27 insert and a socket. Broke that too. Then tried to chisel around the head and walk it out. That worked on one of the two that were stuck, but not the other.

Ended up using the die grinder to grind the head off and then get in there with the channel-locks the free it up:confused2: About two wasted hours just tearing it down. Plus, taking the saw farther appart than needed just to get in there.

Anyway, heres some pics. These are the saw all appart, and then a comparison of the stock and BB jug/slug

 

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Exhaust and intake port comparison

 

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Marking and porting the intake on the NWP BB cylinder

 

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Sorry, I forgot to take a before pic of the exhaust port. But here's an after, and one of the lower transfers. I didnt do much with them because dont have a pencil grinder, but I did work them down a little farther ad blended them into the base a little better.

 

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A little muffler work here.

I didnt remobe the barrel because it is spot welded in and too time consuming to remove and make right. So I just made some bigger holes in it.

And the little tiny 7/16" hole for the exit port is pathetic on a 98cc saw:confused2: So we had to take care of that a bit as well:thumbsup:

 

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Thats all the pics. The saw is back up and running now. Allthough on a conservative tune of 12.5k rpm and 32:1 fuel for break-in.

He does think it seems more powerful than before, even though it aint broke in yet.

But my dolmar 8400BB is still faster. And a lot of that has to do with the chain. He is one of them cutters that forces the saw in the cut, therefore he keeps his rakers @ .025. Personally, I like the saw to pull its own self through, so I keep mine @ .050-.060. But he cant run my saw without stalling the chain out, because he feels "compelled" to dawg in and push.

AND he is only running a 7 pin rim. I told him the saw will be a lot faster if he either changed his cutting style and lower the rakers, or if not, jump up to an 8 or 9 pin rim.

Anyways, enjoy the pics:thumbsup:

 

[xyz123]

Only way to really tell is run the same chain on both saws with the same operator running both saws in same piece of wood. Then you still have variables of hitting knots etc.

I tested a 4th gen BB066 kit right out of the box and the port timing was :thumbsup: right out of the box. Couldnt believe it was stock.

I ran stock 7900 and stock BB84-7900 and the BB didnt have the same gains stock for stock like the BB066 did. I think it is because the 7900 is so hot out of the box. Most impressive stock saw I have run to date.

Someday when it is cool out we need to hook up.

I have a stock JD 800v 80cc = Echo 8000 with just tightened squish, Poulan pro 505 82cc stock that I'm not impressed with stock, muffler modded MS660 stock and a woods ported 066 all stock bores I would like to compare with you sometime.

I try and use debarked square cants for saw and chain testing, that takes out most of the variables.

Here is my woods ported 7901

Makita 7901 woods ported Dolmar 7900 - YouTube


Here is stock BB066 on 064 with 9T. The more gear 10T and 11T I gave it the faster it pulled in the cuts. So the torque was there out of the box.

Fred stihl 064 with stock big bore 066 with 9T - YouTube


Here is my stock bore woods ported work saw 066

woods ported stihl 066 8T set at only 14k - YouTube

 

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I was wondering when you'd chime in I figured you'd be the first though.

Impressive videos too:thumbsup:

I cannot say that port timing was right on this one though

I dont have a degree wheel, and I am not a pro by no means, so my methods may seem crude, but they are effective none-the less.

Since I was waiting on you to chime in, I'll post a little more technical detail of the build:thumbsup:

For starters, I measure port timing by measuring from the base to the opening of the ports. (again, no degree wheel) but I do have a depth guage:thumbsup:

In the following pictures, is a drawing of the ports. The first is stock, the second is stock BB, and the last is ported BB. The numbers to the side are the distance from the base of the jug to the port bottom and top. The other #'s outside the port are the width and height. The #'s inside are the squared area of the port (not counting for the rounded sides. Just H x W)

As you know The top of the exhaust port, and the bottom of the intake are the only two that really matter. They determine the timing and duration. The bottom of the exhause only has to have enough to NOT free-port (expose the crankcase). And the upper of the intake only has to have enough to not expose the comustion chamber:thumbsup:

So comparing the exhaust upper and intake lower of the stock vs BB, we have the exhaust pretty much spot on. Within .015. Which got extended another .010 from polishing. But look at the intake. The BB kit is almost a full 1/10 of an inch lower. Which means the intake opens sooner and stays open longer:confused2: And I was also disappointed that the exhaust port was considerabally smaller

So basically what I did, was take the top of the intake up to about where the stock one was. (again, no effect on timing, just increasing volume:thumbsup and the same with the exhaust port floor. And then widened them out to leave about .070 of piston skirt to seal the port.

And the end results you can see:thumbsup: The intake is now about .130" taller and the exhaust is ~ .100.

That last pic is percent difference of the finished job vs BB and stock. The eshaust is 11% bigger than stock and 27% bigger than the BB, and the intake is 20% bigger than stock and 18% bigger than the BB:thumbsup:

Also, in the first 3 pics, the % at the bottom is how much smaller the exhaust is vs the intake. Stock, the exhaust was only 18% smaller. BB was 27%(I covered that up) and finished is 28%. Also, the number at the top is the total height of the cylinder from base to squish band. Stock was 3.188 and BB was 3.194. I would have rather seen it at 3.188, because that would have gave me ~.022 squish, but o-well.

 

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Only way to really tell is run the same chain on both saws with the same operator running both saws in same piece of wood. Then you still have variables of hitting knots etc.

We may have to do that once he gets it broke in:thumbsup:

I am just not a fan of his cutting style. Dawging in and forcing. When I cut with his saw, it just feels like a dull chain even though I just sharpened it for him:confused2: I hate .025 rakers.

Where do you run yours at on these bigger saws?

I ran stock 7900 and stock BB84-7900 and the BB didnt have the same gains stock for stock like the BB066 did. I think it is because the 7900 is so hot out of the box. Most impressive stock saw I have run to date.

Doesnt the BB kit also add a few more CC's to the 066 than the 7900. If I remember right, I was thinking like +5cc on the 7900 and +7 on the 066???

You should compare it to what I did. put the BB on a 6400:thumbsup: +20cc instantly

 

[xyz123]

I think they both got 2mm more bore giving them 5cc and 6cc more. 79cc to 84cc and 92cc to 98cc if I remember right. Could be off 1cc on both.

I just think it is because a 7900 is hot out of the box. Hard to beat it without porting.

You dont happen to have a stock 7900 now days do you? I dont have any of my dolmar or makita stuff anymore.

I dont lower the rakers as far as you and I dont push hard in the cuts either or dog it in and make a dull chain work. I just try and keep sharp chain on and touch up or switch out if had to.

I think you are only 30mins south of me right down there near my vet.