This 'How To' is a bit specific to the Honda CB125 'Twin', but I suppose it applies to most of the other 'Benley' series engined bikes as well.
ANYWAY, this little widgimo is the engine's 'Achilles heel'. Mainly because its a case of 'out of site, out of mind', and when it DOES come to mind, in one of those rare bouts of 'I know, I'll treat the bike to an oil & filter change', few 125 riders seem to have very often, it causes some consternation, because they cant FIND a 'filter'....
This is it. TINY little thing. Thats an 8mm spanner next to it, so you can see just how small it is. Its hardly any bigger than the front of a matchbox. a SMALL matchbox!
And its neglecting this ONE tiny little thing, that is probably the most common 'killer' of Benley series engines.
It sits on the intake of the oil pump, and all the oil from the sump that is pumped around the engine, gets sucked through it, and its fine mesh is supposed to filter out all the crud in the oil so it doesn't get shoved into the oil ways to block them, or into the bearings and stuff to help wear them out.
And the 'Problem' is that its hidden 'inside' the engine. Many owners cant find anything that looks obviously like a filter, so shrug, and carry on, or they find the book, see the filter is inside the engine. Grimace, and decide that its best not to disturb it, because it looks 'complicated' and 'scary' and they might not be able to put it back together again!
But it is TINY, its about 25mm by 50mm in area. Give you an idea, a more conventional 'canister' filter, is a drum, usually about 50mm tall, perhaps 75mm in diameter, so if it was simply a drum, it would have a surface area something like 60cm sq, compared to this thing which is about 12cm sq. Only in a cartridge filter, the element is actually folded into pleats, to increase the surface area to something like ten times a plain drum.... so something like 50 times the filtering area this thing has.
So, as you can imagine, this little filter can get clogged up with muck and sludge RATHER quickly. Book says to do Oil Changes every 1,250 miles, and to inspect and clean the Filter Screen every two oil changes. Personally I advice changing the oil in these engines every 1000miles, and until you have had the bike a few thousand miles, worth doing the filter screen EVERY oil change rather than alternate ones.
Because if you DON'T keep this little strainer clean, it clogs up. And when it clogs up, it restricts the flow of oil to the oil pump, and thence to the rest of the vital bits inside the engine, which all start to wear out, much faster than they should, starting with the oil pump itself, which looses efficiency. Cylinder bores are first to display the signs of premature wear, and the engine will gradually start burning oil, as the piston rings stop sealing so well. This reduces the amount of oil in the engine, making matters worse, but worse still, lets combustion contaminants, or 'sludge' into the engine oil, making it thicker, blacker and generally harder to shove around the engine, and even more clogging to that strainer! Eventually, something 'gives' and on these engines, its usually the cam shaft bearings. The crank shaft is supported on needle rollers, and its not unheard of for them to suffer wear and seizure through poor lubrication, but not entirely reliant on an pressure oil feed, and sitting close enough to the sump oil they get some 'splash' lubrication, its normally the cam shaft bearings that are 'plain' and need a pressurised supply of oil to keep the journal 'floating' in the bearing, and that are also furthest away from the oil pump, that starve and seize, often chewing up the cylinder head when they 'go'. It is NOT nice, wither which way, so pay heed, and give this little thing some attention!
It is NOT difficult to deal with.
You will need:
Oil. Engine takes just under two litres. Primary Drive Gasket. Or Gasket Paper. Do NOT use 'Gloop'. You don't need to buy a new filter, so splash out, spend 50p on some proper gasket paper or maybe £1.50 on a proper gasket! (If you are really DESPERATE you can even use an old cereal packet! As The Cornflake Packet Gasket Trick), Some Detergent, and an old Toothbrush. Oh, and an 8mm spanner, and 17mm socket, and an old washing up bowl or similar, 'receptacle'! This is not high tech mechanics.
Locate and identify the Sump Drain Plug. It is on the right hand side of the engine. If you find the Generator Rotor nut cover, the round slotted one in the middle, (missing in this photo!) and go directly down, it is recessed just ahead of an beneath the Engine Number boss, in front of the gear shift assembly.
Start and warm the engine, if possible. Warm oil is more runny than cold oil, so if you get the engine warm before changing the oil, more of it will come out, more easily. Once warm, be careful of hot exhausts and 'stuff', and turn the engine off before going any further! Often worth removing the battery lead, so you cant accidentally turn the engine over with no oil in it.
But, now you can put plastic washing up bowl, or you preferred container under the sump plug. Undo the sump plug, trying not to drop it in the container, and as it comes out, in a gush, get oil everywhere but in the container!
Sometimes helps if you can tilt the bike a little when its coming towards the end of draining. If you have a side stand you can prop it on that. If not, just tilt the bike, it wont take long to drain, there's not that much oil in there.
When the oil has cooled down.... you can undertake the oil change ritual of fishing for the sump plug in the ice cream tub!
REPLACE SUMP PLUG. it saves it getting lost and answering stupid questions later.... like "Why's it taking so much oil to fill it up?" and "Oh!? I seem to have an oil leak, where's that coming from?" Before you put two and two together, and remember, you forgot to put the plug back in!
And dispose of old engine oil in an environmentally friendly manner. Here its being tipped into an empty oil can, where it will be disposed of in an environmentally friendly manner, mixed with a little old stale petrol or something, and probably used to environmentally dispose of ants nests in the garden. You may prefer to simply take it to the local tip, and put it in one of their big reclamation tanks!
On the other side of the engine, we have one casing, covering the oil pump and primary drive. You will need to disconnect the Tachometer Drive, and the clutch cable. Then you can undo the bolts around the flange of the casing to remove it.
This is what it looks like behind that cover. NOT scary at all! Big drum thing at the top is the clutch. while our in here, you may want to have a look at that. If not, just take note, if/when the clutch plates need replacing, that isn't all that scary either! Gear in the middle is the primary drive gear on the end of the crank shaft, and that is driving the oil pimp in the alloy housing underneath. The trumpet on the very bottom with a black rubber bit on the bottom, Donna is pointing at with a cable tie, is the oil pick up, which is where this elusive strainer thingy lives!
Lifting up the rubber rim of that upside down trumpet, reveals and releases the oil strainer.
which will probably look something like this. VERY mucky and covered in crud!
The very worst of the crud can be carefully scraped off, with something NOT hard, like a wooden chip fork.... or lolipop stick, or an old scrap of plastic.
Once the worst of the crud has been removed, the strainer can be thoroughly cleaned. I used an old toothbrush and washing up liquid. You could use a solvent, but detergent's easy enough!
Before putting everything back together, the casing faces need cleaning up to remove all the old gasket material, before they can be put back on.
A lot of the old gasket may simply tear off by hand, but more stubborn bits will probably need carefully scraping. Care needs to be taken not to damage the gasket faces. A carpentry chisel can make a good scraper, as they are often wider and stiffer than Stanley blades, which can often gauge and scratch the soft aluminium.
Both the crank cases And the faces of the primary drive cover have to be cleaned. Then before the strainer can be refitted, the sump could do with a bit of a wipe out with tissue, and something soft and pokie, like a lollipop stick to get any gloop or debris out, so it wont just clog the strainer straight back up. Especially if you have dropped any old gasket material in there while scraping.
The strainer can now be replaced into the mouth of the oil pump.
In this instance, while the primary drive was exposed, the clutch was also replaced (See HOW To: (Honda CB/CD/CM 125/200 'Benley' Series Engine) Clutch Replacement) But if no other work is to be undertaken, a new gasket may be fitted, and the primary drive cover put back on..
DO NOT USE ANY KIND OF GLOOP!
Silicone sealant, hylomar, RTV, 'Squeezee Gasket' are NOT a good idea here, instead of a paper gasket. first you have just cleaned that strainer, and any gloop you use to glue the casing back on with will squeeze out the joint and bits of it will float about in the new oil, and get dragged to and clog that nicely cleaned mesh! NOT GOOD! Worse, one of the oil pump galleries is formed between the crank case and the primary drive cover flange. if you use gloop, its likely to squeeze into that gallery and clog THAT up starving oil flow to the top of the engine! EVEN more NOT GOOD!
NEW GASKET..... bolt cover back on, re attach clutch cable and tacho drive, refill with oil, and jobs a good'n for another 2,000miles or so!