oily bores

[Bob Culver]

From limited but observant experience with other engines, relative oil consumption can be puzzling, Some engines with broken rings, basic oil rings, use little. Others with multi section oil rings use ample.

Eons ago with the original wide ring pistons my car moderately worn used almost no oil. A similarly worn engine but with thin ring split skirt pistons used lots. Even after a rebore the 4 ring pistons used a pint per 300 miles of hot main road running. This with the split ending in a relief below the top oil ring.
Some years ago I asked about typical consumptions; few replied and as I recall only Ruairidh claimed a  low figure. Some claim reasonable consumption without baffles.

If, as the photo implies, RRs observation is correct, could explain  much. Top rings with thick chrome plating often had large bevels both edges.

I assume the rings are not some gross oversize gapped down.
I presume the land below bottom ring is reduced dia.

If desperate could turn/file a slight relief below top oil ring and drill holes breaking in to. One rail of oil rings can have tiny 5 deg taper filed onto outer edge and fitted upward. If can locate a source or good used ones, wavy spacers behind oil rings will help, assuming room. If not already tapered or bevelled can also chamfer top edge of comp rings, stopping near gap.

Are the very heavy multigrades so thick when cold that the rings cannot handle? (In conventional engines less is thrown about to compensate)
Do others adopt the huge oil trenches in the cap?
Is the piston illustrated the common pattern? The last ones made here had the slot below the ring groove.

[steve davidson]

Hi Bob and all,

I met with an experienced engine builder this morning (about another issue) and asked for his opinion. It looks to RR and Ruaridah were on the right track.

When I built the engine the advice I got was that, if there were dots on the rings then the dots face up, if there were no dots and just marks (mine had .030" marks), then the marks go up, if no marks and not dots then do as you please. Well it seems that this mantra is only partially correct. If there are dots then, dots face up, but the other marks are meaningless in terms of orientation. My rings have an external chamfer (opposite side to the 30" markings) and these must face down and I had them facing up.

It makes sense now that it's been explained to me. If the chamfer is facing up it acts as a face for the expanding gas to act against and compress the ring thus pulling it off the cylinder face.

I went back and checked the old rings, no dots or chamfers but it’s very conceivable that the chamfer had been worn away as the ring gaps were along way out of spec when I stripped it down.

Thanks for all your input, will let you know how it goes when I get it back together in a few weeks. But feel free to keep the ideas coming.

[Bob Culver]

It is not  primarily reduction of gas pressure but the ring planing  on the oil wedge on the upstroke which reduces pumping.
If large enough to admit significant gas, reduction of ring pressure would occur in both directions.

It means further loss of already very short skirt but a very small relief below ring could be added. Your club likely has old pistons to copy. With modern oils small drillings do not block.

[Ruairidh Dunford]

Looks like you may be getting closer to finding a cause, good luck.

[AllAlloyCup]

For what it’s worth I once replaced pistons on my Morris Eight
1934, plus reground the valves, but did not change those or the valve guides.
Result : a smoky engine and I was told that the improved pistons
we’re sucking oil up the very worn valve guides( (( I was 18 and it was my first car!)

I had no garage and can still remember how cold my fingers got
changing the valve guides in situ, with a brass drift,in the street, one
very cold March day. After all this the rusty M8 Tourer failed it’s
10 year test as the examiner did not like my Dexion repair to the chassis!

Just as well there’s no emission tests for A7’s or M8’s....

Bill G

[Ray White]

Question... I can see why you would fit the ring with the chamfer facing down - so compression doesn't close it inwards - but why is there a chamfer at all?

[Ruairidh Dunford]

This type of ring (tapered) is called a wiper ring, I think.

I understand that it’s job is to seal and wipe the bore clean of excess oil. If fitted upside down it wipes oil up into the combustion chamber rather than down into the sump with obvious results.

["Slack Alice" Simon]

This type of ring (tapered) is called a wiper ring, I think.

I understand that it’s job is to seal and wipe the bore clean of excess oil.  If fitted upside down it wipes oil up into the combustion chamber rather than down into the sump with obvious results.

I think the chamfer decreases the area of the ring in contact with the cylinder, so increasing the pressure on the cylinder wall, so making it a more effective "wiper".

Simon

[steve davidson]

It is not  primarily reduction of gas pressure but the ring planing  on the oil wedge on the upstroke which reduces pumping.
If large enough to admit significant gas, reduction of ring pressure would occur in both directions.

It means further loss of already very short skirt but a very small relief below ring could be added. Your club likely has old pistons to copy. With modern oils small drillings do not block.

thanks Bob, good idea, I'll have a hunt around for some old ones and see what they had

---

For what it’s worth I once replaced pistons on my Morris Eight
1934, plus reground the valves, but did not change those or the valve guides.
Result : a smoky engine and I was told that the improved pistons
we’re sucking oil up the very worn valve guides( (( I was 18 and it was my first car!)

I had no garage and can still remember how cold my fingers got
changing the valve guides in situ, with a brass drift,in the street, one
very cold March day. After all this the rusty M8 Tourer failed it’s
10 year test as the examiner did not like my Dexion repair to the chassis!

Just as well there’s no emission tests for A7’s or M8’s....

Bill G

Hi Bill,

Great to hear that these problems have haunted all of us!  I've heard similar theories before but it's always struck me that for this to be the case the piston must be on the down stroke (creating a negative pressure) so either there has been detonation and all the valves are closed or the inlet valve is open and any oil being sucked in from the valve stem is "competing" with air/fuel from the inlet port.  To me that would seem more likely if it was an OHC engine. But I'm a simple civil engineer, the mech guys know more than me!  Thanks for the input.

[Colin Wilks]

This description of scraper rings seems relevant:
http://korihandbook.federalmogul.com/en/section_19.htm