Author Topic: Sachs Dolmar 166 big bore  (Read 467 times)

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Offline Al Smith

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Re: Sachs Dolmar 166 big bore
« Reply #50 on: November 10, 2014, 09:02:47 pm »
It would make sense you can't use a tool steel ring on hard nickle alloy plating like "nicasil".However and for example older engines such as the 125C Mac which had a chrome bore the rings are exactly the same as used on the cast iron bore MC 101 kart engines .Explain that one .

I would have thought that with chrome that's about as hard as you can get .Evidently the alloy plating is harder .Of course with cast iron and its properties it has the ability to absorb oil where hard linings do not .Which in my pea mind does not explain the chrome and not the nicasil .

I would assume then that rings for nicasil are some type of cast iron alloy .I can't ever remember breaking one but I have some old ones in the drawer I could break and see for myself .

Offline EHP

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Re: Sachs Dolmar 166 big bore
« Reply #51 on: November 10, 2014, 09:27:00 pm »
Al, the chrome bore in most of the saws today are pretty soft and not a true chrome but thats what they call it , some chrome bores are so soft you would almost think you can scratch it with your finger nail , dolmar is one of those companies . Nicasil plated bore is by far alot harder , you can see a huge diffence when your porting either , the chrome bore the burrs last a long time , in real nicasil they donot last long at all

Offline srcarr52

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Re: Sachs Dolmar 166 big bore
« Reply #52 on: November 11, 2014, 11:54:00 am »
Nicasil is much harder than chrome, but it also has little voids to hold oil this is why you can use a harder chromed or tool steel like rings.  Chrome doesn't have the voids to hold oil and chrome on chrome has a tendency to gall, this is why you have to use a cast ring.

Offline 660magnum

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Re: Sachs Dolmar 166 big bore
« Reply #53 on: November 11, 2014, 12:27:35 pm »
In other forums I've seen many instances of people putting cast rings in Nikasil bores.

My observation is that the cast rings seat and seal OK. They just don't last as long as the hard rings.

The people like them as these engines eventually get crashed and broken up within 100hrs actual run time.

I would venture to say that they would be fine on a cookie cutter or race saw but not for production felling.
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Offline 660magnum

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Re: Sachs Dolmar 166 big bore
« Reply #54 on: November 11, 2014, 12:36:00 pm »
These are model airplane engines. Some planes are as big as a pickup truck.

The people like to see the rings have a good vertical wear pattern within an hour's running time. The cast rings do this well.

The hard rings, you can run them a whole season and they will only show a vertical pattern half way - usually from the top. The pilots feel they are loosing compression.

Typically by the time the hard ring is fully seated, it's time for a new piston/pin bearing, crank/rod, bearings/seals
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Offline EHP

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Re: Sachs Dolmar 166 big bore
« Reply #55 on: November 11, 2014, 01:44:22 pm »
I seen a 3120 alcohol saw that someone put a ring that was meant to run on nicasil instead of chrome bore , it had about 45 seconds on it and the chrome was in bad shape in that short of time , it was to bad to run any longer

Offline srcarr52

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Re: Sachs Dolmar 166 big bore
« Reply #56 on: November 11, 2014, 04:18:06 pm »
These are model airplane engines. Some planes are as big as a pickup truck.

The people like to see the rings have a good vertical wear pattern within an hour's running time. The cast rings do this well.

The hard rings, you can run them a whole season and they will only show a vertical pattern half way - usually from the top. The pilots feel they are loosing compression.

Typically by the time the hard ring is fully seated, it's time for a new piston/pin bearing, crank/rod, bearings/seals

Vertically gas port the piston.  It will help those low tension rings seal better, been doing it on alky karts for a long time to control blow by.

Offline ej

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Re: Sachs Dolmar 166 big bore
« Reply #57 on: August 24, 2015, 08:33:50 pm »
lee would it be hard to put the 3120 piston instead of the stihl piston how close are they

Offline Cut4fun .

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Re: Sachs Dolmar 166 big bore
« Reply #58 on: August 24, 2015, 10:36:43 pm »
lee would it be hard to put the 3120 piston instead of the stihl piston how close are they

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