G'day,

I thought it was about time I gave Minnie a birthday and looked at timing and spark plugs just to see how things are going. Minnie has been on the road for about 4 1/2 years now and I've done around 5,000 miles all up. Plugs are NGK BP6ES. Last time they were out was around 3 1/2 years ago when I checked and adjusted the tappets for the 2nd time. The engine is an 850 and has been bored out as it was seized when I got it. Carby is an 1 1/2 SU, running through a water heated inlet manifold (C-AHT770) and a set of C-STR816 extractors.

When I had the engine initially tuned up by a Mini specialist, he made the comment that it was possibly a bit over fuelled with the 1 1/2 SU but said it would be Ok. I don't know anything about the carby other than it was fully rebuilt to suit an 850.

I've just pulled the plugs out and No 2 was fairly tight to undo for about 1/2 the thread compared to the others. Looking at the plugs, Nos 1 and 4 look the same as each other and nos 2 and 3 are the same as each other - i.e. the 2 centre ones are different to the 2 outside ones.

I've got 2 questions about these please:
1/. Going by the attached pics of the plugs for No 1 and No 2, what do these tell you about how the engine has been running?
2/. Given No 2 was a bit tight, do you suggest putting any anti seize on them before I put them back in? I've read conflicting arguments either way.

And a general question, how often should I be replacing the plugs and am I running the right ones?

Thanks Rocky

The mixture seems pretty decent from those plugs

There is a little bit of deposits on the number 2 plug but the electrode seems clean

I’d suggest you go to a hotter plug BP5ES & change them once a year or so. They’re so cheap and easy to replace (and gap them to 25 thou before fitting)

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Thanks Timmy. Good to hear that everything looks ok.

I'll grab a set of BP5ES and whack them in and change them more often. I'm running electronic ignition and not points so is the gap still the same? I was watching a youtube video on timing adjustment and the bloke in that reckons 25 thou for points and 35 thou for electronic but that might be with a fancy electronic dizzy and mine's just got a module fitted inside it in place of the points.

Cheers Rocky

If it’s a drop in module and you have a standard 3 ohm coil you’ll need 25 thou gaps

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Thanks again Timmy. Yep it was a drop in module and a standard coil so I'll go with 25thou.

What do you reckon about using a smear of antiseize? Perhaps if I change them more often, they won't get as tight. Mind you, no 2 wasn't
"I think this is going to end in tears" tight, just a fair bit tighter to undo than the others for about half the thread. Probably a bit of carbon built up on the bottom of the thread maybe?

Cheers Rocky

Having the outer 2 a different colour is a quirk of the a series and its Siamese inlet manifold. For what its worth I would stick with bp6es, I find them best. If you check your plugs 6mths or 1 Yr intervals you shouldn't need any antiserum and they don't need to be tightened by the hulk either.
I found that a good set of spiral wire plug leads helps even out the plug colour, go for sandyto light brown.

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Cheers Dave.

There were 850s which came from the factory with 1-1/2" carbs.

I never notice that much difference between plugs.

That bottom one doesn't look good to me.

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1986 Mayfair (998 auto), 1974 S, 1974 Van, 1972 PMG Van

Too many minis

Thanks Dave. I'll be checking the plugs more often and I'll check out the spiral wire leads as well.

Cheers Rocky

I didn't know 850s came with 1 1/2". When I got Minnie, it had a mismatched pair of 1-1/4" on it with a homemade manifold.

When you say "it doesn't look good" are you thinking there's an issue somewhere or just needed replacing sooner?

Thanks Rocky

All our local 850's had a single HS2

I think it was the automatic MK1 850 in the UK that had an HS4 from factory, and also later 850 engines that we never got here .

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an issue somewhere. The plugs should last a lot longer.



Exactly. It was the autos but what it means is that a HS4 can't really be bad on an 850.

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1986 Mayfair (998 auto), 1974 S, 1974 Van, 1972 PMG Van

Too many minis

Hey 68+86 auto,

Can you throw any light onto what you think the issue might be please?

Thanks Rocky

It could be a lot of things. It is probably running rich but it could also be an ignition issue. I don't normally read plugs.

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1986 Mayfair (998 auto), 1974 S, 1974 Van, 1972 PMG Van

Too many minis

I wouldn't worry too much, put a new set of plugs in, get some spiral wire leads and run it for a while and see how they go.
For the vacuum if the dissy unit is ok you could get an adaptor fitting to screw into it and use vac hose.

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Cheers Dave.

If you get a length of rubber hose you might be able to go over the threaded end on the vacuum can, and then put the other end on the carb. This would let you know if the vac can is working or not

If the metal pipe is leaking somewhere along the length you could trim it and use the end to adapt it to a hose like this

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