Piston rings issues

[swampy42]

I'm confident I can get them all on without another incident. The one that snapped was a freak accident and obviously down to a flaw in the ring rather than my ineptitude!! . Actually, I think that should be the other way around.

[alexmcguffie]

Don't forget to check the ring gap (where the 2 ends of the ring join) in the bore before fitting the rings to the piston. It should be 7 - 12 thou. Also the gap in the piston groove should be 2 - 4 thou with the ring fitted.

[swampy42]

The ring gap I knew about - the other I didn't! Thanks for the heads-up.
Russ

[bmcecosse]

You're re-fitting old rings! The gaps will be fine... Perhaps just check the rings you get from 'win' . Even with new pistons/rings I've never had to increase the gaps....

[swampy42]

I'm assuming as there's only a couple of new rings that there's no need to glaze bust now?

[alexmcguffie]

I OBVIOUSLY meant check the gaps of the new rings. Checking the groove gap on all rings will show up any wear but your piston looks in reasonable condition.

[bmcecosse]

YES - you should glaze bust! And smooth off any ridge at the top.

[swampy42]

Is there a specific groove for a specific ring, meaning with the exception of the oil ring, can any of the top 3 rings go in any of the top 3 grooves? Or are they subtly different?

[philthehill]

To answer your question above - NO.
If you have a 4 ring piston (all above the gudgen pin):-
The top ring is the compression ring.
The 2nd one down is the ring compression - piston 2nd.
The 3rd one down is also the ring compression - piston 3rd.
The 4th one down is the scraper ring - piston bottom.

Make sure that the rings go the right way up.
They should be marked T (TOP) but with a S/H ring the marking may be worn off.
See attached section from BMC wksp manual regarding fitting and installing piston rings.[frame][/frame]

[swampy42]

Hi Philthehill
Many thanks for this. It's slowly becoming clearer.
Some time ago you posted a diagram on mmoc which was similar to the diagram on this link . . . http://www.mmoc.org.uk/viewtopic.php?f= ... 69&start=0
. . . but included all 4 rings and what their profiles were (at least I think that's what it showed, if memory serves). As is always the case I can't find it again. It was really clear and I wish I had downloaded it at the time. Does anyone by any chance have a link? Thanks as always.
Russ

[bmcecosse]

Did you not keep the rings in order and orientation when you took them off each piston?

[philthehill]

Swampy
I have drawn you a new schematic of the piston ring arrangements for a 4 ring (above the gudgen pin) piston fitted to a Minor.
Note that the top ring has square corners (it may be stepped on its outer top edge to overcome any ridge at the top of the bore).
Note that the 2nd & 3rd ring have angled edge against the bore. These do two things - firstly retain the compression and secondly help to scrape oil off the bore walls.
The 4th ring assy - the oil control/scraper ring is the main ring for stopping oil/fumes passing up and down the bore past the piston.
The angle of the 2nd and 3rd ring is much exaggerated on my schematic and you would be hard pressed to determine which is top without the 'T' (TOP) marking but best of luck.
Phil[frame][/frame]

[bmcecosse]

Good drawing! There is a way to tell which way to put the rings by gently squeezing them in your fingers, and the ring will buckle slightly...but I can't remember now which way round that slight 'buckle' indicates....maybe you know Phil ?? I 'think' the concave side of the buckled ring goes top ...but I'm not sure.

[philthehill]

Not sure either about the ring between the fingers.
I think I would rather trust my trusty micrometre or digital vernier.
Attached is a schematic of No:2 & No:3 piston ring and whilst the angle is not so severe in reality measuring carefully should identify the short side which goes to the top.
If you are good with a pair of engineers callipers (with screw adjustment) you should be able to feel and determine the short diagonal.[frame][/frame]

[millerman]

Phil, very well drawn, thanks

[swampy42]

Did you not keep the rings in order and orientation when you took them off each piston?

Yes, but I received some S/H rings and am not sure which they are. A close up pic would indicate perhaps the top ring?[frame][/frame]

Just spotted your comment about measuring both top and bottom, so will do that tonight. Many thanks indeed to all.

[bmcecosse]

Gently squeeze it closed with your fingers -if it doesn't 'buckle' then it is a top ring.

[kennatt]

I've bit my tongue a bit with this ,but If I had an engine in bits,which you have,I think the Last thing I would be doing is using second hand piston rings,and risk having to do it again.The cost of a set of new rings,allthough not cheap ,isn't prohibitive,even if cash is a problem, worth saving up for a couple of weeks and being sure that the engine dosent need stripping again. BUT each to their own.

[swampy42]

I agree. It's quite an important part. I've spent so much on this project, that I've just sort of drawn the line. However, I quite often reverse ferret, so may end up getting a new set (especially if I break more). But, the good thing about this process, which I would have otherwise missed out on, is that I'm learning, about something that I really didn't want to do in the first place (see one of my previous posts), but now I'm enjoying . . . sort of. So, thanks to all for your guidance.

Anyway, I've measured the diagonals and they're all in the region of 0.31 - 0.315. I don't have the most expensive calipers in the world, so I think that's as close as I can get. Looks like they're top rings as there's no buckle either.

[bmcecosse]

The good thing is that if these rings don't work for you - the pistons can be relatively easily popped out and the rings changed for new ones... I would give it a go - even if they are 'top rings' - just put them on the second ring position and give it a try.