Magnets on your oil Filter?

Dureth said:
I don't know about cars but in my Ducati 750SS twin the pistons most certainly do not touch anything but the rings and the small end bearing.

They may move side to side but they sure as hell don't touch the bore. I thought the whole point of the rings is to accomodate this movement without the piston needing to come in contact with the bore and to seal the resultant gap needed to allow this to happen.
Click to expand...

Rings are to seal against the bores not stop piston rock. Piston slap is the cold 'smaller' pistons hitting the bores as they rock, when they expand as they warm up the clearances are smaller and they quieten down. This varies from engine to engine depending on the material of the piston and tolerances. Also rings are effectively springs, they are not solid against the piston but rather the piston land.

One of the main purposes of engine oil is to lubricate the interface between the bore and cylinders. The honing of the bore at the factory is not only to allow the rings to bed in but also 'hold' the oil.

Several industy engine tests rate the piston skirts on the amount of scuffing evident, this scuffing varies between oils and is purely a wear mechanism between piston and bore.

Camshaft bearings also suffer from wear and contribute to aluminium is used oil analysis
 
Of course pistons touch the bores, they dont float on the rings. The rings are in the grooves and are no way held, just by the groove and the bore. Pistons do wear without a shaddow of a doubt, its just that they are oiled and the bores are super smooth thus the piston just glides straight over the bore not wearing much at all.
 
really no. bores are actually machined not to be smooth, if they look polished they are worn they should look matted, the tiny scratches is what holds the oil coming from the oil control ring.

i don't know what you mean by ''The rings are in the grooves and are no way held, just by the groove and the bore.'' because that's kinda the case.

if the piston touches the bore the rings are probably worn.

the distance between the rings is carefully considered for the exact reason of controlling/limiting as much as possible piston rock.
 
dalin80 said:
the distance between the rings is carefully considered for the exact reason of controlling/limiting as much as possible piston rock.
Click to expand...

Why are they all above the gudgeon pin then?

Its obvious you are just guessing about this without any actual knowledge on the subject.
 
Dogbreath said:
The rings are all at the top end of the piston, they can not possibly stop the piston skirt from contacting the bore.
Click to expand...
How so?
Surely, and i'm nowhere near as knowledgable as you or simon on this, if the gudgeon pin is the pivot point and the piston crown is held in an upright position by the rings, then by design the opposing end of the piston can't move right?
Like a see-saw, you can't have one end fixed but have the other moving.
 
The_Dark_Side said:
if the gudgeon pin is the pivot point and the piston crown is held in an upright position by the rings,
Click to expand...


This is the point, the rings dont hold the piston upright. Next time you see an engine with the head off you will be able to rock the pistons in their bore with just a finger.

If the rings were solid against the piston 'cylinder' they would help stop the piston rocking, but then you wouldn't be able to fit them and the piston would sieze when it warms up
 
You normally have two sets of piston rings , the top set are for keeping the gases in the combustion chamber (for compression) and the bottom set (sometimes known as scrapers) are to keep the oil out of the combustion chambers.

The pistons slide up and down with a very thin layer of oil between them and the bore wall. Too small a gap & the piston seizes , too big and the piston rocks then seizes.

The tolerance is so tight that in some racing engines hot water is pumped through the system to pre-heat the engine and allow exapansion tolerances to settle otherwise it would go pop-bang-whimper

//edit//

When tolerances went wrong on my bike :D :-

seized.jpg
 
Last edited:
The_Dark_Side said:
Yep i know they don't hold them rigidly in place, but surely there's not enough play to allow the piston skirt to hit the bore?
is there?
Click to expand...

Of course there is, if there was no play then the pistons would seize as soon as they warmed up.

Ignore the rings they only seal, just imagine any piston in a bore.

This is why massive ship engines use cross heads to remove the side loadings, provided by the conrod, from the cylinder walls, also assists packaging. Can just about see here

http://www.sf.hs-wismar.de/~griffel/mscw/gif/Sulzer.gif
 
If the piston skirt touches the bore you have problems. End of story. Sorry to all people who have posted disagreeing with this but its true. If your piston skirt touches the bore, it's going to cause very nasty score damage to the cylinder walls. Period. With the forces involved inside the engine, the piston itself is supposed to float in the middle of the cylinder, causing no mechanical contact at all. You usually have three piston rings, an oil spreader, an oil scraper, and a seal ring. these are only supposed to make the tiniest possible contact with the cylinder walls.

Anyway, back on to topic, Magnets in the oil filter are a good idea, just for piece of mind and ultra care on engines, but i agree with other people, a magnetic sump plug would be better. You can actually buy sump plugs with REALLY strong rare earth magnets in them as aftermarket parts. Or, alternatively, surround a few around the base of the sump plug, and take them off at oil change time. I've rebuilt hundreds of engines in various vintage/sports/cherished vehicles, the odd gearbox, and loads of diffs. Done a couple of land rover transfer cases too. Any vehicle part which is likely to wear, like these, and get shards of metal will benefit from having a STRONG magnet either around the drain plug, or the drain plug itself. I usually fit aftermarket magnetic drain plugs to anything i can find them for. Failing that, i get rare earth magnets and place them in the vicinity of the drain plug, recommending removal just before oil change, so that any swarf stands maximum chance of drainage.

a
 
Skree said:
If the piston skirt touches the bore you have problems. End of story. Sorry to all people who have posted disagreeing with this but its true. If your piston skirt touches the bore, it's going to cause very nasty score damage to the cylinder walls. Period. With the forces involved inside the engine, the piston itself is supposed to float in the middle of the cylinder, causing no mechanical contact at all. You usually have three piston rings, an oil spreader, an oil scraper, and a seal ring. these are only supposed to make the tiniest possible contact with the cylinder walls.
Click to expand...

Its no way as bad as you make out. My car suffers from piston slap when cold, its done 62k miles and still makes decent power. Its always done it from new as have quite a few late models and is a known problem with Nissan.

With regular intervals in oil changes the piston shouldnt cause damage although Im sure it will probably wear the bores quicker, by how much I wouldnt know. Also surely the rings make more than the tiniest contact, they must make damn good contact or else you would suffer with major blow by.
 
Last edited:
Skree said:
If the piston skirt touches the bore you have problems. End of story. Sorry to all people who have posted disagreeing with this but its true. If your piston skirt touches the bore, it's going to cause very nasty score damage to the cylinder walls. Period. With the forces involved inside the engine, the piston itself is supposed to float in the middle of the cylinder, causing no mechanical contact at all. You usually have three piston rings, an oil spreader, an oil scraper, and a seal ring. these are only supposed to make the tiniest possible contact with the cylinder walls.
Click to expand...


Arrrrrgggggh!
 
Simon said:
Arrrrrgggggh!
Click to expand...

Thirded!

The pistons in my coupe have a black anti-scuff coating on them from new. The 72,000 mile old ones I removed had consdierably less anti-scuff coating left tham the new one. How could that possibly have happened if it didn't touch?

If you simply held a con rod and piston in your hands and noted the degrees of freedom the gudgeon pin and big end allows, it would be utterly and undeniably obvious that nothing stops the piston skirts touching the cylinder walls other than whatever lubrication film exists whilst the engine is running (which will be very thin indeed on the rising stroke if the oil control ring is working).

On the firing stroke the piston develops large sideways thrust forces due to the angle of the conrod, this thrust is obviously countered by the cylinder wall. It is simply inevitable that the skirt will touch the cylinder at some stage, especialy at cold start after oil has drained off the cylinder walls.
 
Your arguments are both wrong and right to points. no one want's any contact between piston,rings or bores and modern engines have very little, but it cant be avoided as it's a mechcanical cost.

ware = piston slap/poor combustion = bad

no ware = prefect world = no oil changes = no thread about oil filter magnets

anyway are these the one's that look like half a coffee mug and wrap around the oil filter ? i tend to just go overboard on oil changes to keep ware down.
 
You must log in or register to reply here.
Back
Top Bottom