01-06-2012, 02:59 PM
Royal Enfield Bullet Engines and Wet Sumping
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Wet sumping is probably the most frequently occurring lubrication problem with Bullet engines.
Wet sumping refers to the problem of too much oil accumulating in the sump. It will be most
noticeable when the engine is started after standing for a period, with clouds of smoke being a
sign that the engine is burning oil.
Description
In the majority of traditional British motorcycles the oil tank was located below the seat and
attached to the frame. Royal Enfield had a different arrangement, locating the oil tank in a
discrete compartment within the engine crankcase.
Oil is pumped from the oil tank around the engine by the
unique double-ended eccentric plunger type oil pump
assembly, located in the right-hand crankcase cover, just
above the oil filter housing. The pump plungers are driven by
a spindle, which itself is driven by the crankshaft worm gear.
The oil pump features two main compartments, one at the
front and one at the rear. The rear compartment is a feed
pump. This draws oil from the oil tank, pumps it through the
oil filter and timing shaft and along the internally drilled
crankshaft directly to the big-end bearing. Oil is then flung
from the rotating flywheels, splash-lubricating the main
bearings, cylinder walls, the underside of the piston and the
small-end bearing. The front compartment is a scavenging
pump, with a greater flow rate than the feed pump. The
scavenging pump sucks oil from the sump, where it gathers after lubricating the big-end bearing,
sending oil to the rockers through the external oil pipe. Under gravity, oil drains down through
the push rod tubes to the timing chest. From the timing chest, oil finds its way back into the oil
tank through a strategically placed drilling, leaving the timing chest about ¾ full.
When the engine is running, and if the pump is functioning correctly, only a very small quantity
of oil should collect in the sump, just about 30 cc’s (less than an egg-cup full).
Diagnosis
On a Bullet engine, the lowest point is the sump. If you imagine the oil tank as one ‘section’ of a
U-bend and the sump as the other, oil will try to fill both sections of the ‘bend’ equally. If it can,
oil will find a way to settle in the sump. Normally the scavenge pump will clear the sump, but
when the pump fails to do so, wet sumping occurs.
A number of features of the Bullet engine may contribute to wet sumping:
1. a worn crankshaft oil seal may leak, allowing oil into the
sump from the big-end bearing (remember, the timing chest
is about ¾ full of oil). In this case oil will pass through the oil
ways from the filter, through the ‘quill’ to the big-end
2. the scavenge pump or oil ways may be inefficient, badly
worn or partially blocked
3. a leaking crankcase joint will allow oil to seep from the oil
tank to the sump
4. if the pumps are fitted the wrong way round, the larger scavenge pump in place of the feed
pump, oil will not be effectively cleared from the sump.
Feed
Scavenge
There are three likely consequences from wet sumping: 1. the flywheels may splash so much oil
onto the cylinder walls that the piston rings will not be able to wipe the oil away. This allows oil
to reach the combustion chamber, burning off in clouds of bluish-white smoke to annoy your
neighbours. 2. in extreme cases, oil in the combustion chamber may foul the spark plug. 3.
excess oil will be forced through the crankcase breathers – over the back end of your bike.
Prescription
All that most owners will need to do to ensure long
trouble free service is to change the oil and filter at
regular intervals. At the same time clean the filter plugs
and replace the cork oil feed seal (in the pump worm).
On later Bullets, the oil feed seal is bonded neoprene in
the oil pump worm. This type of seal only needs to be
replaced if there are signs of wear. (The earlier, cork
seal and worm, may be replaced with the neoprene
sealed worm part number 144452).
NOTE: the thread on this worm nut is LEFT HANDED.
In most cases the oil pump will normally return the
excess oil to the tank after a few miles of running. If the problem is more persistent, there are
steps you can take to help minimise the annoying effects of wet sumping.
1. leave the engine with the piston near TDC when idle – this will leave the big-end higher in
relation to the oil tank, making it less likely for oil to trickle into the sump through the bigend
2. don’t overfill the oil tank – the lubrication system ‘breathes’ more easily if the oil level is
not too high. Good advice is to refill with about 2 litres of oil at an oil change (rather than 2.25
litres some recommend). Checking the oil level by placing the oil filler cap on the filler neck
(not screwed down) and keep the oil level midway on the dipstick. (For your peace of mind,
even with oil below the low mark there may still be enough oil in the system. That is not,
however, a reason to allow the oil level to drop so low!)
3. ride your Bullet more! – frequent use is often the best treatment for this problem,
preventing the accumulation of oil that may occur where the bike is left standing for long
periods
4. if you remove the sump drain/filter plug (the most forward of the drain plugs) take extreme
care when refitting the plug that you do not obscure the oil way that is drilled only a little
distance above the thread in the sump plug hole, (due to tolerances, some engines may need 2
washers to prevent this).
Intensive Care
If you find that in your engine the primary cause of wet sumping is an inefficient timing shaft
seal, (different to the oil feed seal), this will need to be replaced. Changing the timing shaft seal
is a relatively easy job. Remove the timing cover and timing pinion to gain access to the seal.
Ensure the seal has been fitted the correct way round. TIP – an oil seal should always be fitted
so that its spring is on the side you want to prevent oil escaping from. Most Redditch Bullets
featured a bronze bush for the timing side oil seal, calling for a complete engine strip down to
replace. This bush requires very careful fitting, and must be reamed precisely, the flywheels
must then be checked to run perfectly true. Early Indian models did not use this bush, and
therefore no easy cure if the crankcase wears at this point. If the cause of wet sumping is a
leaking crankcase joint, then again the only thorough solution is a complete engine strip.