Removing all ancillaries from Miffi last weekend left me undecided if I am going to just try a headgasket and cylinder-head exchange right now or do a full engine overhaul. Either way the head needs to come off. And as a small fridge for cold drinks and a reclining garden chair were recent garage upgrades – a job like this is the best way to relax after a hot day in the office 😀
Equipped with the Mini manual, an ice-cold beverage a short double check of the head nuts release sequence while watching the sun go down was a good start. After removing the rocker assembly I was surprised about the great condition after 112000km. There is almost no wear on the rocker arms. I still need to check the shaft thoroughly – but I am quite certain I will reuse this as it is.
What I already knew is that the piston rings are most likely not the problem. When I did the compression test on Cyl 3 and 4 last weekend, I repeated the same with a tea-spoon of oil in each cylinder. The pressure loss was the same – so I expected a gasket failure or valve failure. The lack of a compressor and leak-down tester in my garage (yet) did not allow me to diagnose this at this point. After taking the head off it was immediately clear that it is not a head gasket failure. When I bought the car a few years back, I was told that the engine had never been opened. I tried to research if this unknown white head gasket could be the factory one – but I doubt it. Pistons are factory default as far as I can tell.
With the cylinder head upside down on the workbench and spark plugs back in, I filled some petrol into the chambers. and sure enough – all four valves on 3 and 4 do not close correctly and leak. This is caused by carbon build-up which can have a number of reasons. Worn valve stem seals or play in guides might be a reason. This would cause oil to leak onto the valve head. I will take the valves out next to investigate this.
A defective PCV might be another cause. Back in 2019 I cleaned out the breather as good as possible with break cleaner. As a new one is not expensive and available from MiniSpares – I will replace the old one just in case. Another reason could be bad oil. But as I am using Castrol 20W-50 and do regular oil changes – I can rule out this as issue.
The main culprit I suspect is the carburetor fuel mixture setting. My car is running a somewhat rare Gutmann GKat (regulated catalyst) setup. While the care was build in 1991 (last HIF44 carb model) it apparently was sold and first registered in 1992. Whether the GKAT was fitted back then (when the SPI mini’s where released) or retrofitted later is something is unclear. During the last TÜV emission test we already had issues getting right Lambda and CO values. With the device we were running too lean. Without the device connected – the fuel mixture was too rich.
To counter this for the test I had to enrich the HIF44 quite a bit for this. We somehow passed the test – with Lambda 0.98 but I did not change the setting back afterwards. I suspect the device has failed in the meantime and I was running too rich. Paired with mostly short trips this is a combination prone for carbon build-up.
After flipping the coin it shows “Head only” for now. I will just replace the head with a completely overhaul spare from Peter Burgess which I already have. New breather, GKAT removal and MD-Lambda View along with a HIF44 clean up and check are the next steps.
Fixing C6622 
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