23 replies to this topic

[1984mini25]

This morning I rolled the mini out of winter hibernation, gave it a good wash and drove off to fill the tank (witch was so low it wasn’t registering on the gauge) and then onto a 20 mile round trip of local b roads. Upon getting back I quickly whipped out the freshly fitted plugs. No1,2 and 4 look ok to me except No3, It’s black but not wet.

But all the ignition is new from the plugs, ht leads, dizzy cap, points and condenser. And it’s a 998 with single hs4 and combined cast inlet and exhaust manifold.

 

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[DeadSquare]

The best time to examine plug colour, is after 50 miles on a motorway.

 

The colour of those plugs indicate too rich a mixture.

 

If you want to feel that you are 'doing something about it' , swap 1 and 3 and look again after 100 miles.

[MiniMax1984]

Addition: if you really want to read something from the plug-color, you would have to switch off the engine at the revs / state you want to check the mixture for., and then look at the pluds. If you drive it 50 miles at full load at 4500 RPM and then cruise home, the color will tell the mixture from your cruise, not from the 4500 RPM session.

 

So this could be too rich in idle but fine at driving, you could not tell.

Easy and inexpensive check I always got good results with (verified via lambda while driving): Colortune.

[1984mini25]

Well seeing as for the best part of last year I was chasing an intermittent misfiring, rough running and cutting out issue and then throwing some less than satisfactory new parts in to confuse things. So during its winter layup I removed and flushed though the fuel tank and internal filter.

 

And considering it would have been lucky to make it to the end of the road without misfiring or cutting out, and hasn’t moved for 5 months I’ll take it a success. (I was also bloody knackered having forgotten how heavy the steering and brakes were)

 

I’ve brushed the plugs off and adjusted/leaned off the mixture two flats and I’ll see how it goes. What I was more concerned with was the plug for no3 (second on the left) as although it’s a been a little smoky on start-up (could well of been down to old fuel) it doesn’t appear to be burning too much oil.

[1984mini25]

I cleaned off the plugs, readjusted/leaned off the mixture 4 flats and have done a few sort trips out, upon pulling the plugs (wile also doing an oil change) I now have this... 

 

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I've since cleaned them off again and swapped 2 and 3 round. As other than an occasional miss under part throttle it seams to be driving ok. 

[StefanMini]

If you want a proper tune up then contact ACdodd, he will make your Mini running perfect.

[Lplus]

Well seeing as for the best part of last year I was chasing an intermittent misfiring, rough running and cutting out issue and then throwing some less than satisfactory new parts in to confuse things. So during its winter layup I removed and flushed though the fuel tank and internal filter.

 

And considering it would have been lucky to make it to the end of the road without misfiring or cutting out, and hasn’t moved for 5 months I’ll take it a success. (I was also bloody knackered having forgotten how heavy the steering and brakes were)

 

I’ve brushed the plugs off and adjusted/leaned off the mixture two flats and I’ll see how it goes. What I was more concerned with was the plug for no3 (second on the left) as although it’s a been a little smoky on start-up (could well of been down to old fuel) it doesn’t appear to be burning too much oil.

What colour is the smoke on start up?  How much oil burn is "too much oil"?  The fact that no 3 is still showing darker than the rest suggests a possible problem with compression or oil control rings on that cylinder.  Is there any chance you can get a compression tester on it?  That said, even a worn engine with even  compression on all cylinders can be a smoke bomb if the oil control rings are shot.  Ask me how I know...

[bpirie1000]

Have you had rocker off to look at valves? Make sure all moving correctly.?

Compression check all in order?

[1984mini25]

Well seeing as for the best part of last year I was chasing an intermittent misfiring, rough running and cutting out issue and then throwing some less than satisfactory new parts in to confuse things. So during its winter layup I removed and flushed though the fuel tank and internal filter.

And considering it would have been lucky to make it to the end of the road without misfiring or cutting out, and hasn’t moved for 5 months I’ll take it a success. (I was also bloody knackered having forgotten how heavy the steering and brakes were)

I’ve brushed the plugs off and adjusted/leaned off the mixture two flats and I’ll see how it goes. What I was more concerned with was the plug for no3 (second on the left) as although it’s a been a little smoky on start-up (could well of been down to old fuel) it doesn’t appear to be burning too much oil.

What colour is the smoke on start up? How much oil burn is "too much oil"? The fact that no 3 is still showing darker than the rest suggests a possible problem with compression or oil control rings on that cylinder. Is there any chance you can get a compression tester on it? That said, even a worn engine with even compression on all cylinders can be a smoke bomb if the oil control rings are shot. Ask me how I know...

The colour of the smoke on start up is blue, worse if it has been left for a few days. It doesn't always but it's the first start from cold on choke and first run under load, which as I live on a bit of a hill is unavoidable. Once warmed up from driving (not sitting idling) and off choke there's no noticable smoke of any kind while driving.

It must be using some oil (it's also got the mini gear selector seal dribble) but it never seams to show a noticeable amount used on the dipstick, too the point topping it up could lead to accidental overfilling. But as I've just done a fresh oil change I'll check it again after a set mileage.

I had thought about rechecking the valve clearances, even though I've only recently just done them. As I have noticed (it could just be me though) that when hot and idling (nice and smooth around 850rpm) on the drive while I'm unlocking the garage there's a light metallic rattle/knocking. Which could be nothing, or if one of the plugs isn't firing properly...

And the other reason for doing the oil change is when hot and idling the oil pressure gauge (if it wasn't fitted I wouldn't worry about it) instead of sitting steady flutters about normally just below 40psi, even though the idle is smooth and not at all lumpy.

[Lplus]

 

 

Well seeing as for the best part of last year I was chasing an intermittent misfiring, rough running and cutting out issue and then throwing some less than satisfactory new parts in to confuse things. So during its winter layup I removed and flushed though the fuel tank and internal filter.

And considering it would have been lucky to make it to the end of the road without misfiring or cutting out, and hasn’t moved for 5 months I’ll take it a success. (I was also bloody knackered having forgotten how heavy the steering and brakes were)

I’ve brushed the plugs off and adjusted/leaned off the mixture two flats and I’ll see how it goes. What I was more concerned with was the plug for no3 (second on the left) as although it’s a been a little smoky on start-up (could well of been down to old fuel) it doesn’t appear to be burning too much oil.

What colour is the smoke on start up? How much oil burn is "too much oil"? The fact that no 3 is still showing darker than the rest suggests a possible problem with compression or oil control rings on that cylinder. Is there any chance you can get a compression tester on it? That said, even a worn engine with even compression on all cylinders can be a smoke bomb if the oil control rings are shot. Ask me how I know...

The colour of the smoke on start up is blue, worse if it has been left for a few days. It doesn't always but it's the first start from cold on choke and first run under load, which as I live on a bit of a hill is unavoidable. Once warmed up from driving (not sitting idling) and off choke there's no noticable smoke of any kind while driving.

It must be using some oil (it's also got the mini gear selector seal dribble) but it never seams to show a noticeable amount used on the dipstick, too the point topping it up could lead to accidental overfilling. But as I've just done a fresh oil change I'll check it again after a set mileage.

I had thought about rechecking the valve clearances, even though I've only recently just done them. As I have noticed (it could just be me though) that when hot and idling (nice and smooth around 850rpm) on the drive while I'm unlocking the garage there's a light metallic rattle/knocking. Which could be nothing, or if one of the plugs isn't firing properly...

And the other reason for doing the oil change is when hot and idling the oil pressure gauge (if it wasn't fitted I wouldn't worry about it) instead of sitting steady flutters about normally just below 40psi, even though the idle is smooth and not at all lumpy.

 

Blue smoke on start up could be valve guide/seal or tired oil control rings, possibly just on the one cylinder.  A ticking/rattle on tickover sounds likely to be valve gear/tappets.  A variable oil pressure at tickover sounds a bit odd, but if it's a solid 60 psi at 3000 rpm hot then it's within spec.

[1984mini25]

I've changed the oil, left the fuelling as is, readjusted the tappets on No3, cleaned up the inside of the dizzy cap and rotor arm (although both are new) swapped No3 and No1 sparks plugs round and swapped N03 and 4 ht leads over. 

 

With another longer run (mostly b roads at 50mph to whatever 3.5k is in 4th with a 2.9 diff) I stopped half way to check the plugs, No3 and No1.

 

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As I wasn't going to mess around with hot plugs, I swapped No3 and No1 back round and this is all 4 plugs after the return journey home.

 

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So No3 cylinder/spark plug is getting better but still looks to be having issues. 

Edited by 1984mini25, 02 May 2023 - 02:07 PM.

[1984mini25]

Recently replaced the dizzy cap (the little spring on the 'new' cap had gone rusty) and new red rotor arm, done a few more miles and whipped the plugs out....

 

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What am I looking at with regards to doing a compression test? 

[Alex_B]

It's hard to tell from your photos, but are the plug gaps all the same? 

I have been chasing a single cylinder issue with mine, funnily enough #3 for me too and it was just the gap was too tight resulting in a poor burn and it stopped the plug from being able to self clean during operation. 

But any slight variations on that cylinder vs the rest can have the same result, so I would personally check all the tappets are equal (sounds like you have already done this), do a compression check ensuring you can reliably repeat the results (throttle wide open, no plugs in, same number of rotations of the crank, same engine speed etc). You're looking at compression results to be within 10% of each other. Check plug gaps are all the same, HT leads are all within spec for resistance, cap & arm are all good. No intake leaks (doubt that's the case here though as its showing as being too rich) 

Another test you can do is a leak down test, this will tell you more than a basic compression test by giving you a tangible leak down figure as well where you are loosing compression i.e through your intake / exhaust valves or past the rings. 

[1984mini25]

Over the weekend while I had the fuel tank out to give it a through cleaning with citric acid, changed the filter under the boot floor and the filter in the pump. I thought I'd give something a try as it wasn't going anywhere for a few days. I removed the plugs and poured some redex directly into no3 cylinder and left it to sit on top of the piston. After refitting the freshly cleaned and painted fuel tank, popping the regapped plugs back in (25tho but do look a little close in some of the pics) and starting it up to limp to the nearest petrol station (once the smoke had cleared a bit, although a lot less than it has been) and then off on the usual run, hear are the plugs after getting back home. 

 

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[Lplus]

Pretty evenly coloured.  I'd be leaving well alone for a while and see how they look after a few more runs.