Hi Folks, Got a Stihl chainsaw with a Bosch R10, USR 4AC spark plug. Is there anything else available as a replacement plug; I cannot cross the part number? Or am I married to this very one? And if so, is it back to the dealer for these plugs or are there any other viable sources available? Thanks, Brian
Is that the number on the porcelain part of the plug or on the metal part of the plug. I believe the number on the metal part of the plug is what you can use to cross reference.
The steel body just below the porcelain. It does cross to a Champion Rz7C but that too seems to be a bit unusual. Thanks. Brian
What saw is it? Like said most stihl isese the NGK BPMR7A I think the common champion plug is different than what you listed. I crossed the NGK # and found this site. Spark plug cross reference
Going by memory here but I think it is a 211 model. Only a couple of years old and currently manufactured. As it is a metric plug, and a little unusual in size and length, I am having a hard time crossing it (should have put a couple of Easy Boys! in that sentence....). I am sure I can go to the Stihl dealer but it is a long way from here, at least by RI standards, and I am assuming it will be expensive there. Maybe not though. ?? Brian
MS211 takes an NGK CMR6H http://randallequipment.com/wp-content/uploads/stihl-spark-plug-guide-081413-proof-1.pdf
NGK CMR6H looks like the plug for a MS211. I know your not sure but it is a different plug useing that number. Arent all stihls metric thread since they are a german saw? I know now its produced in america but they still use metric fastners??
OK, looked at that page and that NGK number looks like the one. Then using this page: Spark plug cross reference It looks like the NGK crosses to a Champion RZ7C. I do not have any brand preferences, just looking for a plug I can pick up locally, ideally at an auto parts chain w/out having to order one. Thanks for the info., I should be able to get something from one of those brands. Brian
All common spark plugs are metric thread as they were developed by Bosch in Germany. There are a few antique threads but the last one used, AFAIK, was the 7/8-18 which a neighbour's 1950 Minneapolis-Moline U runs. I wouldn't try a Champion with a Y suffix in a small engine as they have an extended tip that doesn't have enough piston clearance. Spark Plug Standard Thread Form
Interesting! I never realized that common 'American' spark plugs in cars built in the US always (or virtually always) used metric threads- thanks for posting that tidbit of info.. Must have driven the manufactures of US engine nuts for decades being either the only or one of the extremely few metric threads they used on the entire car. Sort of like one of the very few English standard threads found throughout the world is 1/4-20, which is and apparently always has been used for camera tripods; I always though it must confound the German, Japanese, Swiss, etc. countries where metric is the only measuring system in use. As for using a Champion plug in the Stihl saw, I will compare the projected length of both before installing the Champion. Thanks for the 'head's up' on that. I have tripped over this before with motorcycles regarding tip projection.... into the piston if one is not careful / aware. Brian
The "P" in the NGK plug would designate a projected insulator. I would be just fine with doing away with U.S. imperial fastener sizes. Metric works fine and would save future mechanics a ton of $$ not having to buy duplicate tools in both systems. Things like miles, gallons, and Fahrenheit would be harder to switch but no real harm or hurry there. Car wheels are measured in inches all across the world too.
And my brain knows 19mm is bigger than 17mm a whole lot quicker than 3/4 is bigger than 23/32. Let's see: 8 guzinta 32 4 times.....
'Measured in inches' perhaps but any size can be stated in either system. That is one big stumbling block in our converting to the metric system; many believe that 'everything' has to change to use a different measuring system. Some of that is true but in fact, we are unlikely to get taller or shorter, for example, no matter how we are measured or what system is used. And a lot of things are a mess in either system; .223 inches is as odd a measurement as is 5.56 mm and yet are the same size. As a toolmaker and mechanical engineer, I know, use and am perfectly comfortable with the version of the English system we use; I knows me fractions and their equivalent decimals, all the usual and quite a few odd thread sizes and tap drill sizes under an inch and so forth. That said, I am absolutely convinced that the metric system is the way to go for two really important reasons. The first is that there is only one unit of measurement for all things in the metric system and it is simply scaled up or down to suit. Length for example, in the metric system it is the meter (about 40 inches) and is just scaled down (microns, or millionths of a meter for all extremely small but non- nuclear measurements) or scaled up (1.5 billion meters from the Earth to the Sun). Easy to divide or multiply any length into any other length measurement. Compare to the system we use: inches, feet, yards, miles.... quick, how many inches in a mile?. And then the 'wacky' measurements such as wire sizes, wire gauges (not the same thing), thread sizes (how big is a 6-32 and what is the tap drill for it?) and so forth. The second huge advantage the metric system has is that all things are done in divisions of 10, like the whole rest of our numbering system. The system we use has no base: 12" to a foot, 3 feet to a yard, 1760 yards in a mile, etc. (quick, how many inches in a mile.... still?) As another poster mentioned, everyone can instantly tell that 19 mm is larger than 17mm but how many instantly what standard drill size is slightly smaller than 49/64" ? A sane measuring system has other benefits not obvious too, for example threads (like spark plug threads) are easy to calculate tap drill size: for a 70% thread, just remove the pitch of a thread from the major diameter. In metric, a tap drill for an 8 X 1.0 thread is (8 - 1) 7 mm. Same thing works for our system but is far tougher to spit out the answer: a 1/4- 20 has 20 tpi, so 0.050" pitch, and 1/4" is 0.250, so subtract pitch from major dia. (0.050 from 0.250) and you have .200", which is NOT a standard size in our system. So we use a number 7 drill, which measures .201", and none of this makes sense, it is just the way it is. Humans all over the world have made an absolute mess of all measuring standards and that is to be expected and makes perfect sense over time. But the French stopped and took a huge step in fixing it, and did a very good job of that. We just do not want to hear it. Now, as it all applies to chainsaws: how many 16" chains are there on a 30 yard roll of saw chains: gentlemen, start your calculators. Brian (who stands 39/99 or 0.373737373737..... Rods tall)
.223 and 5.56 are NOT the same. If a gun is chambered in both that's ok but you can't shoot 5.56 in .223 , the head prussure from slight shoulder differences.
Yeah, everything I use goes through a Wylde chamber though. But I can dance in that hall too if you want: 223 Remington and 5.56 Nato are exactly the same BORE SIZE. Same intent and more correct if required. Brian
