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BP7HS vs B7HS spark plug
#1
Could someone please advise me? I went to one of the local bike spares shop, looking to buy a NGK BP7HS spark plug. The 
spares guy only had a NGK B7HS on hand. His comment was that it was an equivalent plug and that I could safely use it in my 
stock BWS YW100e. Since I have only used the plug number (BPR7HS or BP7HS) that is recommended in the user manual, I 
expressed some doubt. He called over their resident motor-mach, to settle my query on the replacement spark plug number.
Anyhow, I then asked if I should re-gap the plug differently, due to the electrode length being different. I was told to use the same gap. Now, that worries me!!
Surely the plug with the longer electrode, which sits deeper in the combustion chamber, would have a different timing effect? The plug thread length is identical but the electrode protrudes on the BP7HS, while the B7HS electrode is flush with the top of the combustion chamber. Both clear the piston, but one ignites at the top of the combustion chamber and the other inside the combustion chamber (see pix).
Am I right in having my doubts or what am I missing here?
Another thought, would I have to reset the carb air-mix when using the B7HS plug?


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#2
To add a bit more info to the mix, the spark plug gap for the BWS YW100 (BP7HS) is listed as 0.9 - 1.0 mm, while the Nitro YQ100 (B8HS) is listed as a 0.5 -0.7 mm gap. Note that the Nitro's listed spark plug code is for a colder range plug aka B8HS when compared to the BP7HS / B7HS, being queried in my post above.
The obvious thing would be, to try the plug on a few test rides, then do a plug chop after each test ride to read the condition of the plug. But there will always be the nagging thought, that piston / engine damage could occur, if the incorrect spark plug is used. As you are aware, a very hot or very cold plug can cause fouling, preignition and other fun problems.
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#3
It should be fine, id say test it ,see how it goes and if it runs any differently go back to the old plug model but if your rpm is the same on idle, and if the engine runs the same it should be fine
Matthew Olivier (aka Mat1998)
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#4
Thanx for your reply, Mat.
Here is the reply from NGK Technical Service: "If your service manual calls for NGK BP7HS or BPR7HS (the R just means resistor), I would recommend staying with those part numbers. If you use NGK B7HS this is a non-projected spark plug and might cause fouling. This will not hurt the engine, it will just cause premature spark plug problems if the engine is lightly loaded."

An extract from the NGK catalogue: "Take note wrt heat range: If the tip of the spark plug is too hot, it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shortingout of the spark current (this is commonly called a fouled plug). A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug.
A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with NGK spark plugs, a lower number indicates a hotter plug and a higher number indicates colder plugs."

This info may be old hat to many, but I thought that it is interesting enough to share with the members here. Another thought, if the plug could carbon up at any time and someone tried to take a chance (take a gap), only to have the plug fail on you... Thanx but it would be safer to stick with the recommended plug, listed in the owner manual.
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