Decent Spark Plugs

[L4RRY]

Can anyone reccomend any reliable, good all round spark plugs?

I have a 40hp Mariner and I was wondering if they're all pretty much generic or whether some are better than others for various reasons...

All help welcome


Thanks, Laurence.

[codprawn]

Square ones would be hard to get into the holes..............

Many people claim all sorts for plugs but they are all pretty much the same as long as you get the right spec for your engine.

[Limey Linda]

Here is a tip I got from a friend. Note down the make /number of the factory recommended plugs and go to a friendy auto parts shop and ask if they can order them for you. For his Optimax V6 it cut the price in half compared with an outboard shop.

[Nos4r2]

OR try buying them from a bike shop as long as you know the right grade.

You need the recommended plugs for your motor. Don't deviate from that if you can help it.

[PeterR]

I took the number of the plugs for my 90 mercury to our motor factors they ordered them for next day ngk plugs £2.65 each

[Locozodiac]

Originally Posted by L4RRY

Can anyone reccomend any reliable, good all round spark plugs?

I have a 40hp Mariner and I was wondering if they're all pretty much generic or whether some are better than others for various reasons...

All help welcome


Thanks, Laurence.

If your engine is like this one, the standard factory plugs are : NGK BTHS-10 (no resistor) or BR7HS-10 (with resistor) both work very well, use resistor type is you have radio on board to eliminate sound interference while cruising. The correct gap is 1.0 mm. It's a medium term heat rated plug. Bike stores, a good place to find them, if opting for Champion ask for the correct NGK equivalency and regap tight as specified if required. Costs about $ 2.5 to 3.0 each. For best performance and duration, clean & regap every 50 hours use. Both brands are standard, easy to find plugs.

Happy Boating

[Nos4r2]

Originally Posted by Locozodiac

If your engine is like this one, the standard factory plugs are : NGK BTHS-10 (no resistor) or BR7HS-10 (with resistor) both work very well, use resistor type is you have radio on board to eliminate sound interference while cruising. The correct gap is 1.0 mm. It's a medium term heat rated plug. Bike stores, a good place to find them, if opting for Champion ask for the correct NGK equivalency and regap tight as specified if required. Costs about $ 2.5 to 3.0 each. For best performance and duration, clean & regap every 50 hours use. Both brands are standard, easy to find plugs.

Happy Boating

BR7HS-10 are exactly the same as BR7HS (available in any bike shop off the shelf) but you need to regap the BR7HS to .0040" (40 thousandths of an inch). That's all the 10 stands for.

They are a good plug to use as you can find them really easily in an emergency.

[Locozodiac]

Originally Posted by Nos4r2

BR7HS-10 are exactly the same as BR7HS (available in any bike shop off the shelf) but you need to regap the BR7HS to .0040" (40 thousandths of an inch). That's all the 10 stands for.

They are a good plug to use as you can find them really easily in an emergency.

About re gapping BR7HS to .040, sorry to say but this info is quite not accurate. Had plugs purchasing problems down here. BRTHS-10/B7HS-10 were out of stock, but B7HS was available , so wrote the NGK Company asking if it would be possible to use on 2 strokes outboard engines, this is their answer. "quote"

"You could use the BR7HS, you will just need to adjust the gap open to .032 / 0.8 mm to operate correctly as the ones you have been using previously as BR7HS is .028" / 0.7 mm factory gapped. Both BR7HS-10 & B7HS-10 are factory .040 / 1.0 mm gapped". The ending number stands for the factory 1.0 mm gap.

Hope this info helps, thanks for inquiring.
NGK Technical Support /Aftermarket Division

The alternatives to BR7HS-10 or B7HS-10 in Champion brand are: RL-82C or L-82C, and must be re gapped to 0.40 or 1.0 mm to perform well.

Happy Boating

[Nos4r2]

Whoops-didn't notice the extra 0 in there. D'oh!

[Locozodiac]

Originally Posted by Nos4r2

Whoops-didn't notice the extra 0 in there. D'oh!

The plug ending number was also a new issue to me, have tested both settings 1.0 mm and 0.8 mm, with the second re gapped BR7HS plugs had a better engine response & performance. In theory you could re gap to 0.40/1.0 mm but don't have the technical issue of why you need to regap to 032/0.8mm, probably a heat matter. If easy to find, go for the originals KGK or Champion brand plugs.

Happy Boating

[J.W.W.]

If your Mariner is the newer type (the "Mercury" type, with a cilinderblock without head gasket), the O.E.M. spark plug would be NGK BP8HN-10 or BPZ8HN-10.

[Locozodiac]

Originally Posted by J.W.W.

If your Mariner is the newer type (the "Mercury" type, with a cilinderblock without head gasket),

By cylinderblock without head gasket, you mean a one piece compact engine block with no removable cylinder head ? If so, thought this was an old tech issue not found in new engines.