Engine Maintenance - General Notes
- Details
- Written by B.S. Fine
REGULAR SERVICING
The factory workshop manual contains full details of the service intervals and what is required at each. As far as the engine is concerned, the schedule recommends checking the oil level every 1,000 miles (1,600km), changing the oil every 3,000 miles (4,800km) and changing both the oil and the filter every 6,000 miles (9,600km)and flushing the engine every 12,000 miles (19,200km). Interestingly, there are no recommended time intervals that over-ride the mileages. Modern developments in oil technology since the fifties allow us to take a broader view of these recommendations. Firstly, modern oil withstands degradation in use better than older oils, so the distance between oil changes can probably be extended without adverse consequences as long as the car is in normal use and not subject to particularly adverse conditions. Secondly, modern oils tend to be more detergent than their forebears, which means that the oil holds the by-products of combustion in suspension rather than allowing it to settle out as sludge. Modern detergent oil quickly becomes “dirty” on the dipstick but it reduces the need to flush because the contaminants are more effectively disposed of at every oil change.
In practice, most Magnettes are now owned and used as classic hobby cars, so mileage is far less significant as a guide to servicing. More relevant now is how the car is used, because infrequent short journeys and long lay-ups will make it sensible to change the oil and filter more regularly. The typical cycle of use for a hobby car is that it has an active summer but an idle winter, so it makes sense to gear the oil changes to this by starting the season in spring with new oil and filter, then draining it if the car is to be laid up over the winter. The expense will be repaid many times over in engine longevity.
Changing the oil filter can be made easier by fitting a spin-off canister filter in place of the standard item, which is messy to change and clean.
ADJUSTING THE TAPPETS AND RELATED ISSUES
The ‘B’ series engine has a reputation for sounding “tappety”, so there is a temptation to reduce the rocker clearance to make it quieter. This is misguided because, with too small a gap, the valve may not fully close when hot. This allows gas blow-past, which will quickly damage the valves, especially the exhaust valves.
The recommended clearance is .015” (or “15 thou”) when set hot. An additional .001” must be added if adjusting the setting on a cold engine. The quick way to set all the clearances is to use the “rule of nine”. So you adjust valve no.1 when valve no. 8 is just about to open (i.e. the rocker begins its downward movement), valve no.2 when no.7 is opening and so on. Rather than doing the valves in numerical order, you just watch for the opening valve as you slowly crank the engine and adjust the appropriate partner valve. Cranking is easier of you take the spark plugs out, which also gives you the opportunity to check their condition and clean them.
Unless you built your engine yourself or you know the engine has been properly rebuilt in recent history, it is worth removing the rocker shaft for a proper inspection of the working parts. The impact of the rocker on the valve stem can cause an indentation in the lobe face of the rocker. If you use a feeler gauge to set the clearance, it will bridge this indentation and give a false reading. The clearance will be greater than the false reading, making the engine noisy and changing the valve timing, with adverse effect on performance. When removing the rocker shaft, follow the workshop manual guidance on draining the coolant and loosening the head nuts to avoid distortion of the head. The oil supply to the rocker shaft is narrow and can become blocked. The shaft itself may also suffer from sludge after protracted use and there is a large screw plug at the end which can be removed so that the internal oil-way can be flushed through.
Problems with tappet settings can also arise if the rocker shaft itself is worn. In use, the rocker is subjected to significant upward pressure when the push-rod is forcing it up against the resistance of the valve springs. In a high mileage engine it is not unusual to find major wear on the underside of the rocker shaft and in the rocker bushes. This will distort the rocker clearance and adversely affect the valve timing. It becomes impossible to achieve a good state of tune and even running. Check visually for a depression in the shaft and even if this looks sound, slide the rocker back on and try to move it laterally to check for wear in the bush. If in doubt, replace shaft and bushes. The cost will be repaid by the ease of tuning and the smoother running.
When re-fitting the rocker shaft, make sure the oil feed hole matches with the hole in the rear turret. Before you refit the rocker cover, run the engine briefly to check that oil is flowing freely out of all the rocker pivots.
OIL CONSUMPTION
The rate of oil consumption will depend on the state of wear of the relevant components. If your engine is high-mileage, then it may be expected to need regular top-ups as a quantity of oil will be burnt along with the fuel. General wear will also cause poor oil pressure when the engine is hot. As the wear becomes more serious, the engine will be burning significant quantities of oil and the exhaust will contain blue smoke, especially in conditions when there is low induction manifold pressure (see below).
If your engine needs regular top-ups but is maintaining good pressure and is not smoky, the oil loss may be arising from leaks. Generally these are visible on the outside of the engine or as drips under it. The engine has two weak points: the oil-seal in the timing cover, behind the crank pulley, was a simple felt ring that tends to shrink with use and allows oil to pass; at the rear of the crank-shaft, the seal is a reverse scroll in a tight housing. Only on ther later B-series engines was a modern neoprene oil-seal fitted. In the Magnette engine, theoretically, oil escaping past the end of the crank is carried backwards in the scroll before escapes into the bell-housing. However, if other wear issues generate crankcase pressure (discussed below), the oil can be forced past both these ineffective seals. Drips from the front will tend to be sprayed over the engine by the fan, causing a generally dirty front end, though tell-tale marks will also be seen on the garage floor. At the rear, escaping oil enters the bell housing and escapes via the small hole at the bottom designed for the purpose. The hole carries a split-pin so that vibration of the pin during movement will ensure the hole is never blocked by road dirt. (The designers of the engine seem to have concluded that since some oil loss is inevitable, it is better on the road than on the clutch!)
A poor fit of the rocker cover gasket and perished rubber washers in the fitting holes can also be a sources of leaks. Again, crankcase pressure will exacerbate the problem, which may be detectable as an oil-mist staining on the underside of the bonnet and drips down the side of the cylinder head. When fitting a new cover gasket, I find it beneficial to stick it in place on the cover with Hermetite or a similar gasket cement. This ensures it does not get displaced during fitting, which can be fiddly because of the heater water pipe that tends to get in the way. I do not use the cement on the cylinder head face; this makes subsequent removal easier. When faced with a leak from the rocker cover, it is tempting to over-tighten the two fixing bolts but this makes the problem worse because it distorts the cover and prevents a good seal round the edge.
Although general engine wear can cause low oil pressure, it will also be caused by a worn pressure release valve. The valve is situated on the rear, left-hand side of the engine and is held in place by a domed nut. It comprises a cylindrical cup that sits in a concave machined housing and is held by a spring. The cup can be worn by the passing oil and the spring becomes weak with age. It is possible to shim the spring to take up wear, but it is far better to replace both cup and spring with new components. If the housing appears to have worn unevenly, lap the cup into its housing with a bit of grinding paste, but only if the engine is out and is going to be flushed out later to remove swarf etc. If you are replacing it with the engine in situ, you don't want to risk contaminating the oil.
If your engine is smoking badly then it is likely to need a full overhaul. A smoky engine will soldier on for a fair distance but the oil in the combustion chambers will change the combustion characteristics of the engine, risking damage to pistons and valves. It may also fail its annual technical inspection (the MOT Test in the UK) because of poor emissions. It is best to deal with the problem early rather than put it off. The main causes of a smoky engine are:
1) Worn valve guides that allow oil to be sucked down the valve stem.
2) Valve oil seals that have perished or hardened and are allowing oil down the valve stem.
3) Worn piston rings and cylinder bores that allow oil to be blown or pumped past the rings and up into the combustion chamber.
4) A blocked crankcase breather that causes high crankcase pressure. This leads to blow-past as in item 2).
You can try to establish the source of your smoke problem by carrying out a road test. Find a long steep hill and drive down it with your foot off the throttle, so that the engine is being turned by the motion of the car rather than propelling it under load. This will cause very low pressure in the induction system and if your valve guides, stems or seals are at fault these conditions will maximise the symptoms. At the bottom of the hill, accelerate away hard and if you get a big puff of blue smoke from the exhaust, then it is the valve gear that needs attention. You might need a friend in a following car to observe the smoke.
If you get a puff of blue smoke when you accelerate after leaving the car for a long spell at idle, this may also point to piston ring pumping. This phenomenon arises when the rings and their grooves are worn. The rapid up and down movement of the pistons turns the loose rings into a very effective way of pumping oil up the cylinder into the combustion chamber. The downward-moving ring scrapes oil from the cylinder wall. This is held in the wear gaps between ring and groove. Then when the piston changes direction at the bottom of the stroke, the ring is forced to the bottom of the grove and the oil passes upwards into the gap between the rings. The next downward movement takes it into the next ring gap and so on until a series of miniscule amounts of oil moved this way add up to a significant quantity burned with the fuel. Hence the blue smoke.
Before removing the engine for overhaul, it is best to check that the crankcase breather on the tappet cover is clear of blockage. Later engines had a breather pipe that was angled upwards like an upside-down hockey stick. This modification was intended to avoid casual oil loss down the pipe. The rubber breather that links the rocker cover to the air cleaner can also be blocked even though it looks sound. The inside of the pipe may have collapsed. If the engine cannot breathe properly, pressure will build up with the downward movement of the pistons, forcing oil to find its way out of the engine.
If you are satisfied that there is no breather blockage, then removal of the cylinder head (see workshop manual) will allow you to check the valve gear for wear and also measure the bores. A “finger nail test” will reveal significant bore wear . A ridge at the top of the bore occurs where the piston ring reaches the top of its stroke. No wear occurs above this so a ridge between the worn and unworn bore surfaces can be detected by simply feeling for it with your finger nail. If there is no ridge, then a rebore may not be required and new rings may do the job. However, bore wear happens in an irregular pattern because of the reciprocating path followed by the pistons. Even with no discernible ridge, proper measurement of the full swept area is needed to establish how bad the wear is lower down.
A Magnette’s pistons cannot be removed with the engine in situ because the suspension cross-member prevents sump removal. If you are removing the engine anyway then it is probably a false economy to do so just to replace the piston rings. While the engine is out and dismantled, the obvious opportunity arises to get a hot-dip to clean it out, a rebore, new camshaft bearings, a reground crank and new big-end and main bearing shells at the same time. Most owners who split the engine and gearbox also renew the clutch cover, driven plate and release bearing as a matter of course. There are obvious cost implications to all this work but the benefit is an engine that is a known quantity and, with a careful maintenance regime, should reliably give you another 100,000 miles or so before another major overhaul.
Engines that have already been rebored several times may need cylinder liners. There are also limits to the number of times the crank journals can be reground. If they are within permitted limits (see workshop manual) and not ovalled, new bearing shells will be all that is needed. This is where regular oil changes will pay you back, because crank wear is usually a result of high mileage with poor oil and the contaminants that it carries. The condition of the old shells will give you a good indication of the quality of previous maintenance standards.