Stihl MS660 woods port build thread

[srcarr52]

This MS660 for fishermanmgv came in a few weeks ago, very clean used saw he picked up but he was looking for a little more out of it.

As measured with a degree wheel the numbers were:
Ex. 172 deg
In. 160 deg
Trans. 112 deg

Now measured with a caliper and the durations calculated:
Ex. 167 deg
In. 155 deg
Trans. 110 deg.

There is a quit a bit of difference between the two because with the caliper method any port chamfering is not taken into account and stock there is a large chamfer on the exhaust and intake sides.

The cylinder had a ring of death at the top so I didn't cut the squish much but I did true it up with sand paper on the mandrel. The final numbers measured with the caliper method.
Ex. 167 deg
In. 160 deg
Trans. 120 deg.

Pretty tame on the intake, lots more duration but not to wide on the ports since the rubber boot intake is the biggest bottleneck in this system.

Not too much lower transfer work, just take the lip off the bottom and square it up nicely. You can't see it but the sides are cut much wider under the bridge to help direct the flow more towards the intake side. The upper transfers were raised a lot and brought towards the intake side. The exhaust side was taken out a little but the entry angle intersection remained the same. Due to the ring pin location you can't go to much more towards the intake side but this is plenty good for a woods ported working man saw.

I trued the squish band, took 0.005" off and ended up taking 0.008" off the base, squish ended up a little larger then I wanted at 0.028" but if it ever needs a rebuild a Meteor piston will fit fine (I've found them to be 0.005" taller on the pin to crown height). You can't go too much wider on the exhaust and I really didn't raise it all, just enough to get the shape and finish I wanted.

The exhaust trumpet was enlarged slightly and the muffler was port matched with the baffle cut out.

Extra outlet on the left side.

 

[NORMZILLA44]

Looking good! Great model choice too!

 

[srcarr52]

We decided on the aftermarket foam filter kit. Looks nice and hopefully will do better then the stock filter.

Exhaust outlet fits nicely under the chain brake handle.

One more view, great condition for a used saw.

 

[srcarr52]

And I know how everyone gets upset when there is no video...

[video=youtube;5-XsNbOitBQ]http://www.youtube.com/watch?v=5-XsNbOitBQ&context=C3cf585fADOEgsToPDskKKWmlGDDkfsAVCw-Uvfrsk[/video]

 

[stihl038x2]

I'm in before the "lock"..............



















Thought I'd put that in, seems to be a common phrase, besides I had nothing to add & wanted to subscribe :jester:

Steve

 

[srcarr52]

You could have just done the classic... opcorn:

 

[NORMZILLA44]

Nice saw, the only thing missing is a wrap handle

 

[asdf4240]

What is the ring of death? And it looks like you honed the cylinder, true or false?

Otherwise nice work. Thanks for the post.

 

[srcarr52]

What is the ring of death? And it looks like you honed the cylinder, true or false?

Otherwise nice work. Thanks for the post.

Ring of death is an unplated ring at the top of the cylinder. If I put the piston any higher in the bore the rings would be in danger of falling into this area and snagging which would not end well.

Yes I always deglaze the cylinder with a ball hone when I put in fresh rings. When I was younger I worked in an engine shop and we would never put in new rings without honing so I've continued the practice.

 

[fishermanmgv]

I put this saw through some big wood yesterday and all I can say is WOW! I would say it is at least 15 to 20 percent faster than muff mod alone. Spools up really fast. Cant hardly get it to bog when pushing hard on a 32 inch bar. Thanks srcarr52!

 

[solarguru]

Very nice work!!! I am working on a MS660 currently and look forward to finishing mine up... Apparently I forgot to ask if I could do it before I got started on it... lol...

 

[Bowtie]

I really dont like the looks of the hone marks in that cylinder. I would be concerned.

 

[srcarr52]

I really dont like the looks of the hone marks in that cylinder. I would be concerned.

You're right... I was going for the proper 60 deg cross hatch with the hone but it ended up more like 57.5.

 

[Bowtie]

You're right... I was going for the proper 60 deg cross hatch with the hone but it ended up more like 57.5.

With all due respect, honing the NikaSil on those cylinders is a bad idea. The plating is very thin, and it looks like you honed it pretty heavy. Possible outcomes are 1) honing through the plating = bad. 2) rapid wear on the piston, especially the skirts = bad, 3) excess clearance between piston and cylinder causing piston slap and, again resulting in rapid wear = bad.

I could care less about the angle of he crosshatch on a 2 smoker cylinder.

 

[blsnelling]

Some respected builders on here hone every cylinder they port. I'm not one of those, but just saying. The NiSi is not near as easy to hone through as most think. I've honed some scored cylinders pretty heavily before, and have yet to go through. I personally reserve honing for the last step of repairing a scored cylinder.

 

[Bowtie]

Some respected builders on here hone every cylinder they port. I'm not one of those, but just saying. The NiSi is not near as easy to hone through as most think. I've honed some scored cylinders pretty heavily before, and have yet to go through. I personally reserve honing for the last step of repairing a scored cylinder.

I have done it before but I will not do it again. Also a light touch with a hone is one thing, it looks like the cylinder posted above was honed quite extensively. I know the camera can make things look different, but that is my take.

Just my opinion, not trying to start a war.

 

[srcarr52]

With all due respect, honing the NikaSil on those cylinders is a bad idea. The plating is very thin, and it looks like you honed it pretty heavy. Possible outcomes are 1) honing through the plating = bad. 2) rapid wear on the piston, especially the skirts = bad, 3) excess clearance between piston and cylinder causing piston slap and, again resulting in rapid wear = bad.

I could care less about the angle of he crosshatch on a 2 smoker cylinder.

From your post I understand that you are a believer in not honing a cylinder. There are two worlds of though on this site about this issue and only one in the professional engine building world. So I will give you the reasons why to do so in rebuttal to your items above.

Item #1: Yes the cylinder plating will be about 0.0015-0.003" thick depending on the original manufacture machine quality and the quality of the plating, it can be more if you've had a cylinder replated since they have to clean the majority of the old plating before replating. What you see in my pictures is a result of a properly oiled ball hone spun for around 3 seconds, 4-5 strokes in either direction, removing maybe 0.0002-0.0004". I don't own a dial bore gauge that reads small enough to accurately quantify it so evidently it's less then 0.0005". A very light honing can produce an extremely nice finish but more importantly remove the glazed surface of the cylinder. I would say it would take around a minute spun much faster then I did to hone through the plating with a ball hone, probably less time with a fixed stone style cylinder hone and don't ever use a spring style cylinder hone because you're almost guaranteed to hone the base side of the cylinder more then the combustion chamber side. Sounds like a good experiment for a junk cylinder.

As for item #2: Do you think the bores come pre-worn into a shinny surface from the factory? No, they are finished honed similarly to what you see above. What you don't realize is that rings come with a slight bevel ground into the outer diameter. This bevel is designed to help scrape the oil off the cylinder as well as provide a forgiving area for wear to occur such that the ring "seats" into the cylinder. Since no cylinder is perfectly round and no ring is either, it's imperative that a slight amount of wear happens such that the ring wears into the imperfections of the cylinder profile. This same reason is why most engine manufactures recommend you use a break in oil or a non synthetic oil during the break in period. Because synthetic oil is actually too good at it's job and will stop the rings from seating properly.

And finally on to item #3: Yes excessive bore clearance can cause lots of issues all resulting in complete engine failure. As stated in response to item #1 the couple of ten thousands of an inch will not even effect cylinder clearance since all manufactures recommend clearance in the range of a few thousands of an inch, which is a decimal place away to be greatly worried about.

As stated above in this thread I was an engine builder while working my way through engineering school with emphasis on vehicle dynamics and fatigue of metals. I've continue to dabble in higher level racing while I pursue my career as a consultant for a multibody dynamics software development firm. I've stay in touch with many of my former colleges who now work for very respected racing engine manufactures, who would undoubtedly kick my a$$ for putting new rings in an engine without honing it first.

I'm not expecting you to change your opinion, so maybe we should just agree to disagree.

 

[Bowtie]

From your post I understand that you are a believer in not honing a cylinder. There are two worlds of though on this site about this issue and only one in the professional engine building world. So I will give you the reasons why to do so in rebuttal to your items above.

Item #1: Yes the cylinder plating will be about 0.0015-0.003" thick depending on the original manufacture machine quality and the quality of the plating, it can be more if you've had a cylinder replated since they have to clean the majority of the old plating before replating. What you see in my pictures is a result of a properly oiled ball hone spun for around 3 seconds, 4-5 strokes in either direction, removing maybe 0.0002-0.0004". I don't own a dial bore gauge that reads small enough to accurately quantify it so evidently it's less then 0.0005". A very light honing can produce an extremely nice finish but more importantly remove the glazed surface of the cylinder. I would say it would take around a minute spun much faster then I did to hone through the plating with a ball hone, probably less time with a fixed stone style cylinder hone and don't ever use a spring style cylinder hone because you're almost guaranteed to hone the base side of the cylinder more then the combustion chamber side. Sounds like a good experiment for a junk cylinder.

As for item #2: Do you think the bores come pre-worn into a shinny surface from the factory? No, they are finished honed similarly to what you see above. What you don't realize is that rings come with a slight bevel ground into the outer diameter. This bevel is designed to help scrape the oil off the cylinder as well as provide a forgiving area for wear to occur such that the ring "seats" into the cylinder. Since no cylinder is perfectly round and no ring is either, it's imperative that a slight amount of wear happens such that the ring wears into the imperfections of the cylinder profile. This same reason is why most engine manufactures recommend you use a break in oil or a non synthetic oil during the break in period. Because synthetic oil is actually too good at it's job and will stop the rings from seating properly.

And finally on to item #3: Yes excessive bore clearance can cause lots of issues all resulting in complete engine failure. As stated in response to item #1 the couple of ten thousands of an inch will not even effect cylinder clearance since all manufactures recommend clearance in the range of a few thousands of an inch, which is a decimal place away to be greatly worried about.

As stated above in this thread I was an engine builder while working my way through engineering school with emphasis on vehicle dynamics and fatigue of metals. I've continue to dabble in higher level racing while I pursue my career as a consultant for a multibody dynamics software development firm. I've stay in touch with many of my former colleges who now work for very respected racing engine manufactures, who would undoubtedly kick my a$$ for putting new rings in an engine without honing it first.

I'm not expecting you to change your opinion, so maybe we should just agree to disagree.

You stated your case well. I do understand about engines however, been working on them myself for quite a few years.

The port work looks fine, I just disagree about the honing, but its all good.

 

[tlandrum]

seems as if ive said this before..... CAN'T WE ALL JUST GET ALONG

 

[srcarr52]

You stated your case well. I do understand about engines however, been working on them myself for quite a few years.

The port work looks fine, I just disagree about the honing, but its all good.

No worries. I start build threads to provide a place for discussion such as these, although I've seen this subject on a few threads lately so I finally gave my $0.02 on the subject. Plus words like "concerned" on a build thread forced my hand a bit.

Anyone with comments on the port numbers??? I tried more transfer timing then the last 66 I did and this one seems to be a bit stronger.