Hi All,

I have a 59 (2009) plate Zetec 1.25 and I am changing the spark plugs, I bought a set of Bosch HR8MCV+39 but can't find the correct gap setting anywhere...after an internet search there were posts saying they should be set at 1.0mm and others 1.3mm so I am confused, I have read they are pre-set but I would like to check the gap is correct before replacing, can anyone confirm what is the correct gap setting?

 

Thanks in advance,

James.

25 thou for us oldies 😀

On 5/25/2018 at 3:55 PM, pragmatix said:

25 thou for us oldies 😀

While I am old (Thanks for reminding me) you have confused me I don't know what 25 thou is...I have always set the plugs on my previous cars in mm, I presume "thousands of an inch", which would give me a setting of around 63.5mm but that seems low. Did you mean 50 thou which is 1.27mm and therefore closer to 1.3mm.

BTW Thanks for replying Pete I posted on a few forums and got no replies.

Kind regards,

James. 

As someone relitavely new to the engineering world, I can confirm we still use thou quite a bit, especially for precision stuff such as shimming gearboxes etc. 1 thou = 0.025mm (or 0.0254mm if you were being anal). 4 thou = 0.1mm. So 25 thou is 0.625mm (so 0.63mm). 

As you say that's very small, and should be more like double that.

Just got my Haynes manual out to check for you... No mention of it, they really have gone down hill dramatically.

1.3mm according to Google though.

34 minutes ago, Luke4efc said:

As someone relitavely new to the engineering world, I can confirm we still use thou quite a bit, especially for precision stuff such as shimming gearboxes etc. 1 thou = 0.025mm (or 0.0254mm if you were being anal). 4 thou = 0.1mm. So 25 thou is 0.625mm (so 0.63mm). 

As you say that's very small, and should be more like double that.

Yes I meant 50 thou trying to be too clever or the thickness of a ***** packet cardboard ( old type packet can't speak for new ones as I don't smoke) 😁

23 hours ago, Luke4efc said:

As someone relitavely new to the engineering world, I can confirm we still use thou quite a bit, especially for precision stuff such as shimming gearboxes etc. 1 thou = 0.025mm (or 0.0254mm if you were being anal). 4 thou = 0.1mm. So 25 thou is 0.625mm (so 0.63mm). 

As you say that's very small, and should be more like double that.

 

22 hours ago, BP2411 said:

Just got my Haynes manual out to check for you... No mention of it, they really have gone down hill dramatically.

 

22 hours ago, BP2411 said:

1.3mm according to Google though.

 

22 hours ago, pragmatix said:

Yes I meant 50 thou trying to be too clever or the thickness of a ***** packet cardboard ( old type packet can't speak for new ones as I don't smoke) 😁

Thank you for all your replies, so 1.3mm it is then, I can and have done do a lot of jobs on my car but shimming a gearbox is out of my league, I have the Haynes manual and it doesn't give a setting, and when I did a Google search some posts gave 1.00mm and some 1.3mm hence my post.

At least my post will help others when they aren't sure of the correct setting.

Thanks again for your replies kind regards,

James. 

it is definatly 1.3mm 

in the old days (eg 1970s )  25 thou could have been a spark plug gap, they were smaller in the days of battery/coil/contact breaker ignition. They have got bigger over the years with decent electronic ignition systems 

33 minutes ago, isetta said:

in the old days (eg 1970s )  25 thou could have been a spark plug gap, they were smaller in the days of battery/coil/contact breaker ignition. They have got bigger over the years with decent electronic ignition systems 

25thou for sparkplugs and 15thou for points with a dwell angle of 48-52 degrees, and 12thou for tappets. co 3.0-4.5

those were the days. 

Fiesta 1.25 2004 petrol. I had a misfire on cyl no 2. Juddered during acceleration and idling. Code reader diagnose a misfire on cly no 2 p0302. I changed the plugs. Took out Bosch 1.3mm gap and put in ngk, which had a 1.0mm gap. It fixed the fault. I also changed the coil pack. Runs ok. The 1.0mm gap needs a spark of 3kv, the 1.3mm gap needed a spark of 3.9kv, which I think stressed the coil pack. I will be using a 1.0mm gap even though the manual says 1.3mm. Kevin