Spark plug gapping

JezF · Mar 5th, 2009, 09:32

I'd be interested to know what gapping you have your spark plugs set at? I was told by my LPG installers to reduce gaping, maybe by .4mm, can't quite remember though.

Also I'd be interested to hear how regularly you change your plugs and what type you use.

I've had some problems with my BRC system and on my side of the net, the only thing I can think of that might be causing a problem is the plugs.

Thanks,

Jez

GavinC · Mar 6th, 2009, 09:59

On my '95 960 I use NGK BCPR6E **single electrode** plugs gapped to .7 mm - which means closing them by .1mm. I think it's simply the standard petrol .8mm gap plug for a 960 closed by .1mm. I'm lucky to get 15,000 miles from the plugs - often 10,000 miles or less; no standard time 'cos I change 'em as soon as I notice the idle as less than silky smooth. A very intermittent, very slight 'miss' is my signal to change the plugs - albeit switch to petrol and it'd idle smoothly.

Others may recommend Bosch or insist on Volvo plugs. NGK also sell plugs specifically for LPG but they are a lot more expensive and I've never tried them. Some say that the plugs don't need closing which could be correct as .1mm is tiny. Some say use a plug specified one grade cooler. It is important however, I believe, to use single electrode for LPG.

If you've got running problems, ignition is almost always the best place to start - plugs first as you are doing. You might know that LPG is trickier than petrol to ignite and so your car may run fine on petrol and it's only when you switch to LPG that the ignition weakness becomes apparent. P'raps with deterioration over miles that very same fault - eg. a failing coil - would eventually reveal itself on petrol, too.

capt jack · Mar 6th, 2009, 13:17

100% agree with GavinC. I use Bosch single point super plus plugs, set at 0.7mm. They will last no more than 10k miles. The car is a 97 V70 2.5 10v.

Single point is vital - the multi ones will give you problems.

I tried plugs a grade cooler, but they didn't last so long, and gave rough running on petrol.

I've tried others, including NGK, Volvo, and Champion, but Bosch super plus last the longest. The others needed to be re-gapped at 5k.

Motor factors are way cheaper than Halfords - and they will sell you 5 at a time. Halfords do them in packs of 4 only!

Cheers

Jack

GavinC · Mar 6th, 2009, 15:05

Thanks capt jack - I'll bear your reco re Bosch Super plus in mind for future. Your experience trying cooler plugs is useful, too.

Mar 5th, 2009, 09:32	#1
JezF Senior Member Last Online: Nov 1st, 2012 19:19 Join Date: Feb 2008 Location: Horsham	Spark plug gapping I'd be interested to know what gapping you have your spark plugs set at? I was told by my LPG installers to reduce gaping, maybe by .4mm, can't quite remember though. Also I'd be interested to hear how regularly you change your plugs and what type you use. I've had some problems with my BRC system and on my side of the net, the only thing I can think of that might be causing a problem is the plugs. Thanks, Jez __________________ Skoda Octavia VRS + Lotus Elise S1

Mar 6th, 2009, 09:59	#2
GavinC GavinC Last Online: Oct 13th, 2012 18:51 Join Date: Dec 2003 Location: Harrogate	On my '95 960 I use NGK BCPR6E single electrode plugs gapped to .7 mm - which means closing them by .1mm. I think it's simply the standard petrol .8mm gap plug for a 960 closed by .1mm. I'm lucky to get 15,000 miles from the plugs - often 10,000 miles or less; no standard time 'cos I change 'em as soon as I notice the idle as less than silky smooth. A very intermittent, very slight 'miss' is my signal to change the plugs - albeit switch to petrol and it'd idle smoothly. Others may recommend Bosch or insist on Volvo plugs. NGK also sell plugs specifically for LPG but they are a lot more expensive and I've never tried them. Some say that the plugs don't need closing which could be correct as .1mm is tiny. Some say use a plug specified one grade cooler. It is important however, I believe, to use single electrode for LPG. If you've got running problems, ignition is almost always the best place to start - plugs first as you are doing. You might know that LPG is trickier than petrol to ignite and so your car may run fine on petrol and it's only when you switch to LPG that the ignition weakness becomes apparent. P'raps with deterioration over miles that very same fault - eg. a failing coil - would eventually reveal itself on petrol, too. Last edited by GavinC; Mar 6th, 2009 at 10:05. Reason: Oversight - addition needed.

Mar 6th, 2009, 13:17	#3
capt jack VOC Member Last Online: Yesterday 22:55 Join Date: Jun 2006 Location: Selby, North Yorkshire	Sparks 100% agree with GavinC. I use Bosch single point super plus plugs, set at 0.7mm. They will last no more than 10k miles. The car is a 97 V70 2.5 10v. Single point is vital - the multi ones will give you problems. I tried plugs a grade cooler, but they didn't last so long, and gave rough running on petrol. I've tried others, including NGK, Volvo, and Champion, but Bosch super plus last the longest. The others needed to be re-gapped at 5k. Motor factors are way cheaper than Halfords - and they will sell you 5 at a time. Halfords do them in packs of 4 only! Cheers Jack

Mar 6th, 2009, 15:05	#4
GavinC GavinC Last Online: Oct 13th, 2012 18:51 Join Date: Dec 2003 Location: Harrogate	Thanks capt jack - I'll bear your reco re Bosch Super plus in mind for future. Your experience trying cooler plugs is useful, too.

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