Stihl MS660 woods port build thread

[yldflight]

That cylinder does look like it's had a seriously heavy duty honing. Makes me wonder how much of the original plating is left on the bore.

 

[dozerdan]

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 are used to working with iron cylinders and chrome rings.
Modern two stroke use Nikasil or hard Chrome plating.
Some of the Chrome plated bores are smooth from new, no hone marks and yes new rings in those smooth bores worked well.
I have worked on many types of cylinders also from 1970 to present day. I have even had one or two saw engines apart.
The German engineers at Porsche would have kicked my ass for honing a chrome ,nikasil or alusil plated bore.
I have worked on many silicon impregnated aluminum cylinder bores on the Chevy Vega. When the engine would over heat the silicone would migrate away and the rings would run on the aluminum. You had to hone them to get down to the silicone again. On those cylinders you used an etch hone.
Gm engineers would have kicked my ass for honing a Vega bore with a normal hone. Yes the Vega used chrome rings.
I would never use anything over 320 grit on Nikasil or Chrome. Your best bet is if you have to hone it is use scotch brite.

I also agree to disagree.

Later
Dan

 

[srcarr52]

You are used to working with iron cylinders and chrome rings.
Modern two stroke use Nikasil or hard Chrome plating.
Some of the Chrome plated bores are smooth from new, no hone marks and yes new rings in those smooth bores worked well.
I have worked on many types of cylinders also from 1970 to present day. I have even had one or two saw engines apart.
The German engineers at Porsche would have kicked my ass for honing a chrome ,nikasil or alusil plated bore.
I have worked on many silicon impregnated aluminum cylinder bores on the Chevy Vega. When the engine would over heat the silicone would migrate away and the rings would run on the aluminum. You had to hone them to get down to the silicone again. On those cylinders you used an etch hone.
Gm engineers would have kicked my ass for honing a Vega bore with a normal hone. Yes the Vega used chrome rings.
I would never use anything over 320 grit on Nikasil or Chrome. Your best bet is if you have to hone it is use scotch brite.

I also agree to disagree.

Later
Dan

Chainsaws are all bevel ground cast ring engines, they need to wear in for proper sealing. Every cylinder I've looked at has had honing marks from the factory. If I was a chrome ring it would be a different story. I'll agree with you if the fact that there are some engines that you do not want to hone, but chainsaws are not one of them. Scotch brite is great for removing aluminum transfer but it won't create the surface needed, like a hone does, to properly seat rings and hold oil.

That cylinder does look like it's had a seriously heavy duty honing. Makes me wonder how much of the original plating is left on the bore.

As stated before, it takes less than 6 seconds at low speed to make a cylinder look that nice. I recently purchased a digital bore gauge (0.00005" resolution) and there is usually less than 0.0002" taken out. You really have to go after them to remove more than that but I have seen idiots do it with spring hones. This particular cylinder is a little deceiving as it was in excellent shape, not a vertical scratch anywhere and even had some hone marks left from the factory.

Clearly we've covered that is not one solution for all cylinder/ring packages but I'm going to stick with honing a cylinder when using a cast ring.