Spark plug

[dublin005]

Hi I'm wondering if anyone can help me from the manual for my 2006 5hp 2stroke 5CMH engine as per the manual it says to use spark plug type br7hs after ringing two different dealers one said I should be using br7hs and the other said use a br7hs -10 both are ngk and the difference is the gap was hoping someone could shed some light on this why use a bigger air gap or does it matter which plug I use.

[zenoahphobic]

No no not the gap it is set the same. The number difference refers to the length of the spark plug thread ; the heat range is the same. You will need to see how deep the thread is in the head. (easy to do with head off but you are not going to do that).

If the plug is too short then the spark tends to be more "hidden" within the thread.

If the plug is too long then there is a small chance that it be hit by the piston. But the advantage is that the spark is more exposed.

Having a too short a thread exposes the remaining thread to combustion deposits and when a longer plug is put in it can jamb on this not seating properly, if not cleaned beforehand.

[TownsendsFJR1300]

Adding to the above, you should be able to see/measure how deep the threads are. Just use say a coat hanger, with masking tape and marks on it.

**Your owners manual should say what size plug YOUR engine requires...

[bajakeith]

The Proper term..

Its called "Reach" and I can write a book about it..wont bore ya tho...

[zenoahphobic]

Its called "Reach" and I can write a book about it..wont bore ya tho...

No don't make anyone reach

[zenoahphobic]

I think here the plug only has the term "reach" referred to it, but the head has depth of spark plug thread. If you had a cylinder in front of you what terms do you attribute to this hole? ( thread diameter , thread size and thread depth).

Incidentally the OP has no manual, so I guess he still needs to know whether - 10 and the gap required.

[Sequoiha]

The plugs are exactly the same, the BR7HS-10 is pre gapped to 1.0mm (.040) but still check the gap, and do not use a wedge type gapper to adjust it, the wedge can move the electrode on the tip and change the resistance value.

[99yam40]

The plugs are exactly the same, the BR7HS-10 is pre gapped to 1.0mm (.040) but still check the gap, and do not use a wedge type gapper to adjust it, the wedge can move the electrode on the tip and change the resistance value.

Well someone finally answered the OP question
Apparently the BR7HS is not pregapped as the BR7HS-10 is from this statement

Thanks Sequoiha

[Sequoiha]

Your welcome