18 replies to this topic

[lewBlew]

Found out cylinder no. 2 is hardly firing - new plugs, leads etc but if I take the lead off there's hardly any change in engine running. The lead is working, and I've tried different plugs but it's the same. Weird thing is the other cylinders are working perfectly so I don't suspect it's the head gasket (also the car drives ok!).

Made the carb a little richer and just about started to notice the tinest of differences when I took the lead off, however nowhere near enough what it should be. Could it be a valve or something? I'm pretty new to the internals of engines so still learning...

Edit.. oh and compression test showed ok, although a little less than desired and the engine was warm-ish.

Edited by theboybradley, 12 June 2012 - 10:13 PM.

[Alex_B]

I would get a compression tester on all your cylinders, may find that no2 has lost compression then may find no 3 is low as well meaning head gasket has gone between cylinders, or if its just 2 low piston ring has snapped, or if compression is fine and about the same on all cylinders it may be a weaker spark or carb issues but im no expert but thats where i would start. :)

[lewBlew]

Eek, doesn't sound easy! I've never taken a head off before. The other cylinders produce very noticable downturn in performance when I take the leads off, so not thinking head gasket..

[Alex_B]

well a compression tester dosnt envolve taking the head off, so thats a plus! and my money would be on a weak spark, have you tried moving the no2 lead off and swap lead and spark plug over with another cylinder see if it runs better, and try one at a time so you can either rule out a dodgy plug or a dodgy lead, if either then i would replace all the plugs and leads as if one has gone then the others cant be far off, thats my thinking anyway.

[lewBlew]

Thing is the plugs and leads are new. I tried a different plug in no. 2 and the problem remained the same. I will continue fiddling

[Alex_B]

check the plug gaps! i managed to fling a spark plug across the road the other day (got stuck in the rubber bit of spark plug socket and pulled it out a bit quick, nearly hit my mum with it! ) anyway it closed the gap up a bit and the car ran horribly on that cylinder, checked the gap, adjusted and runs beautifully again.

[lewBlew]

Ok. Best to check the silly things like that first I guess before I get my hands too dirty or break it even more

[Alex_B]

yeah well I was driving to work and had lots going through my head, it felt like it was almost misfiring but not, and also felt like either engine steadies or subframe mounts were loose, all it was, was about a mm less gap than it should have been making the car feel completely different, all because of that silly spark plug.

when you have a problem always check the silly little things first as they are usually the cheapest! also they are usually whats wrong. :)

[dklawson]

After checking and setting the plug gaps makes no difference, try swapping the plug leads around. (For example, completely remove the spark plug wire for #2 from the dizzy and plug, Then completely remove the wire for #3. Now put the wire for #3 where #2 was and then fit the remaining wire. If the problem changes to cylinder #3, the problem is the wire. If the problem stays on #2, it is not the plug or plug wire. Oh... mark the dizzy cap before removing the wires so you get them back in the right position.

Regarding plugs, if they are new, they do not come pre-gapped for the Mini. Always check and adjust the plug gap when fitting new plugs.

Another thing to check is the distributor cap itself. If there are any craze cracks or carbon tracks on the inside or outside of the cap, that could be your problem. Try cleaning first but if any evidence of cracks or tracking remain, replace the cap.

[bmcecosse]

Check the valve gaps - may have closed up. Can you list up the compression test figures for us?

[lewBlew]

Will do so (might be a few days). I'll be back.

[tiger99]

If you do all the suggested checks, including the HT leads, and a new distributor cap, and still have the problem, be aware that the cylinder head on the Mini is far simpler to maintain than any modern car, as it has no complications like overhead camshafts. In other words, don't worry if it does have to come off. The Mini is almost the ideal car for your first venture into cylinder heads.

If you have to go there, please read the relevant section of the Haynes manual carefully, and then ask as many questions here as necessary.

[lewBlew]

Will do! I knew the time would come I'd have to delve inside the beast.

Can I just ask, with the compression test, do I have to disable fuel as well as the coil? Or can I just plug in and go? It's a standard 998.

[ian2000t]

Have you ever done the tappets/valve gaps? Definitely get a compression test done. If just that cylinder is low, then:

- Piston ring - not heard of many snapping though.
- Tappet/valve gap too tight on that clinders ex/in valve
- Damaged valve/seat

My money's on the latter 2. My mate had a valve burn out on his Triumph (after 7 years and 50,000 miles of running unleaded in a leaded engine, so it did well) - the compressions were ~120psi all across, apart from that one which was 5psi. Took the head off and found a peice of the valve seat had burned/broken away.


Edit: Compression test:

- Take out all 4 plugs (numbering plug leads first)
- Disable coil
- No need to disable fuel
- Put compression tester in plug 1 hole, foot to floor, crank over for 5 seconds, note the reading.
- Do the same for 2,3,4.

I would also possibly do it once when engine is stone cold, and once when fully warm and compare the readings. Mine scared me once giving 0psi on one cylinder when cold. When it was warm it was absolutely fine (~150psi) - think I've got a sticky valve that's not fully closing when cold, but is fine once it warms a little.

Edited by ian2000t, 13 June 2012 - 12:02 PM.

[lewBlew]

I think when we did a compression test last week on just that one cylinder it read 130, but we weren't pressing the throttle. I'm going to check them all again anyway and compare.

Haven't done tappets or valve gaps, no. Not yet...