Morris Minor Owners Club

I have recently fitted a new head gasket to my 1098. First run after was fine but as I have been using the car more it seems to have developed a firing issue. With no apparent loss of performance it appears to be firing incorrectly. I made sure labelled the plug leads but I am now starting to doubt my sanity. I will be changing the plugs although the current ones seem to be reasonable. I am also getting an oil light at idle, which goes out at higher revs, then comes back on (this only happens once the engine is fully warmed up and the oil level is good). Any thoughts would be well received.

I doubt that you have mixed the leads, if you could start it, it would run on 2 cylinders and you would really lose performance. Have you dislodged some dirt in the carb when doing the head gasket? Have you checked timing/points, etc?
As far as the oil light goes, this usually indicates worn big ends and mains.

Did you re-torque the head down?
Random firing could indicate a cracked dizzy cap.
Check the leads are secure in the cap and on the plugs and coil
Pull the plug leads off one at a time to see which cylinder is causing the problem. Use insulated pliers and do not touch the car.

all fine. just fitted new coil, plugs and points. head was torqued to 40lbs, rockers 25. just running very lumpy, not random. also got poor oil supply to rockers.

Poor oil supply to the rockers can be caused by the oilways in the pedastal and rocker shaft not being lined up correctly

did you do the condenser as well, horrace was back firing and running awful until i repalced the condenser then it ws like someone flicked a different switch, for £3 tis worth a bash

thanks for all the advice. problem appears to be either a blockage, compressed air wasn't even reaching the pressure switch, or a more mechanical issue resulting in low pressure.

Various things can happen with headgasket failure including overheating and water in to the oil - water in oil can create its own sludge, and the excessive heat is good for dislodging old sludge and debris as well as creating burnt oil debris.
Also it's easy to get headgasket debris into the oilways when cleaning the head surface.

The minor oil pick up strainer is pretty large, but if your headgasket failure had cause overheating then a lot of sludge can be dislodged from its long term resting places etc... this can create a restriction at the strainer.
This is much more common on 80's engines (especially ones with very small strainers).

have you changed the oil when doing the headgasket (should do) and if so, what oil viscosity and rating have you used?

Back to the beginning - why did you change the head gasket - you don't mention it blowing - did it ? Did you grind in all the valves when the head was off ?? When you refitted it all - did you set the valve gaps up correctly and (as mentioned above) did you torque it down again after the first heat cycle - and then reset the valve gaps again ?? An engine compression test would reveal the general condition and could point the best way forward.

Thanks for all the suggestions. The head gasket blew and up to that point the engine was running ok. I dabble in the stuff that i can do with limited time and tools and knowledge and the advice I have received from a local specialist points at the likelihood of a blockage, but who knows. It runs well (just did a 200 mile round trip to Goodwood), keeping the rockers lubed with an adhesive oil. I may just go down the engine swap route for simplicity.

Is the general oil pressure high enough ?? Remove the rocker shaft (DO NOT LOOSEN THE HEAD NUTS) - and then crank the engine (with all plugs out!) to see how much oil comes up through the first pillar.

Oil pressure 35psi and a woeful 4psi at idle. Running the engine with rocker cover off there is no oil making it through. On the first run after the head gasket change the tappets were squeaking after about 10 miles.

Well - that oil pressure is hopeless...... Could be stuck relief valve - certainly worth checking. At 35 psi it should have appeared at the rockers. The main parts that MUST be lubricated up there are the valve stems. I suggest you don't run it till you find out why the oil isn't getting up to the rockers- although that 35 psi won't be helping - it should still make it!