10 replies to this topic

[davej]

Evening all

I have been having a few issues with the mini engine recently, in the past couple of weeks I've had the head off and replaced the valve guides and seals, re-cut the seats and a new head gasket. The engine is a 1293cc A+ with a SW5-07 cam in it.

Since I've put it all back together I have not been able to get it running right with cylinder 2 misfiring more than firing. We set the twin carbs (1" 1/4`s) back up and she was running ok, went for a drive and after a couple of miles the misfire came back and lots of smoke behind me. I have had a colour tune on it today and it was running rich so I have weakened it to get a nice bluey colour, I could see at tickover that no 2 was getting a decent spark but not much colour until you give it some revs. The engine has only done just over 500 miles since a full rebuild, I've checked the plugs (very black and wet) with a multimeter and done a compression test which was showing 170psi on all 4 cylinders. HT leads and points etc where all brand new when the engine was rebuilt. Running out ideas as to what it can be now, anyone got any ideas?

Cheers

Dave

[NZMINI1100]

I presume you have done the valve clearances? I'd also check that the H/G hasn't even though you just did it, Though you have good compression so probably not that. Timing been checked? Spark plugs gapped? Points been set properly? Also what colour smoke?

[davej]

Yeah valve clearances set, timing checked, correct 0.8mm spark plug gaps, the points were set properly but I haven`t checked for a while. The smoke is a light blue.

[carbon]

Worth checking that the jets on the HS2s are returning up properly after the choke has been used - they can sometimes be a little sticky. This definitely gives black plugs.

Other cause can be a sticking float valve or a bit of dirt under the seat, allows more petrol in and again can give rich mixture but you also normally can smell the fuel. Do you have an in-line filter?

When you replaced the guides and seals, what condition were the valve stems in? Blueish smoke normally indicates burning oil.

What amount of static/idle advance are you using?

[davej]

How do I check the jets are not sticking? No I haven't got an in-line filter and I can't smell any fuel in the car.

The stems looked fine, gave them a clean and there was no play when they were in the guides.

What do you mean by the amount of advance?

[NZMINI1100]

As "Carbon" has said, Blue smoke is normally burning oil, So if its huffing blue. I would normally say piston rings, but again your compression is good. bad guides can cause this too but you said there was no play, Also bad guides tend to cause smoke with changes in throttle where as rings is more constant, Does anyone know if its possible for the SU's oil pot to leak causing oil to be taken into the combustion chamber?

[NZMINI1100]

I think it would also be worth checking for leaks on the inlet manifold/carb, not that this would cause your smoking issue, but maybe your misfire and smoking issue aren't related.

[davej]

I'm not too bothered by the smoke at the moment as it only smokes when its badly misfiring, so I think if I can stop the misfire it will stop smoking, also I've got some decent oil to go in it now as I've been using bog standard 20-50 while bedding the engine in.

Could it be the coil? How do you check that the spark is good enough?

Cheers

Dave

[NZMINI1100]

It could be the coil, when my coil went, it started leaking the cooling oil from it, so it would heat up the more you drove and start missing more and more. could be worth replacing as they aren't expensive.

[psychobob]

are all the valve guide oil seals still looking okay. i have had a brand new one split and it caused the same symptoms. the oil getting into the bore caused the plug to foul, which in turn, caused a misfire on one cylinder. the excess oil also caused blue smoke from the oil burning off. worth whipping the rocker cover off to check.

[tiger99]

The suggestion was made that oil from the carburettor dashpots might be leaking. Well, it is a good suggestion, but will not normally happen, unless the piston is cracked where the inner tube joins it (never heard of that happening, as there is only minimal stress) but overfilled dashpots will leak oil into the engine for a short time, usually quite harmlessly. The problem is self-correcting within a short time, as the oil level falls, so I think we can discount that.

I am wondering if some minor problem in the breather system (blockage somewhere, bits missing, wrong parts fitted for that particular engine configuration, etc) could be causing oil to be ingested into the inlet tract. There were so many variants of breather system that I would not know where to begin looking, but a careful check of what is fitted against the diagrams on the Somerford Mini web site might be a good starting point.