Oil control rings- thoughts?

[goandy]

The oil control rings in my motor are well worn past their limits. New ones simply aren't available unless you're really lucky so I have to consider some options and would love to hear some opinions on ths matter.

The motor as a whole is definitely rebuildable, with plates that can be lapped if scored and the rotor housing itself has very hard chrome so you're unlucky if that's no good. I would be surprised if that wears out with our use. Apex seals will last a fair while but if worn out there may be remanufactured NSU versions available (Hurley).

The oil control rings are unique to this engine (not sure if they are the same as the NSU wankel) afaik. There's two options that I can see open to us for rebuilding:

1. Regrind the angle on the rubbing surface of the oil control ring. This would doubtless require a jig of some sort and a flat surface on which to grind. My thoughts were that it could be done on a lathe or have a standalone jig that works on a flat surface such as glass with wet&dry paper on it to act as the grinding medium. It does need to be a smooth finish so maybe the lathe is not the best. I might end up making some ghetto style cordless drill operated jig!

2. Machine the rotor side faces to accept Mazda oil control rings. The Mazda seals are deeper and their diameter is about 1.5mm greater. This would involve machining a deeper and larger groove in the rotor and also manufacture a spacer ring to fit into the part of the old oil control ring groove so that the inside of the Mazda seal has the correct diameter surface to locate onto. From what I've read, Hurley Engineering in the UK does this to NSU rotors when they rebuild them.

So, thoughts?

[t140v]

Hi, have you any photos of the parts? there may be something out there used for something else.

Regards Stuart.

[bdalameda]

Do you know what material they are made out of???

[jm0406]

Metal spray the old groove to fill in, then re machine to accept the new oil control ring. I do this kind of thing on bearing surfaces all the time to build them back up.

[pmcburney]

If it were me...


As it's highly unlikely a supply of the original control rings will suddenly appear in the future, I'd machine the rotor to accept commonly available parts.

If you ever decide to rebuild again, you'll have a good chance of getting those parts.

Honing/dressing the originals is a hiding to nothing.

It's a big job to refurbish a proper unit, making it as easy and simple as possible in relation to spare parts would be high on my priority list.

[goandy]

I think everyone is saying what I know has to be done! I'll look into the metal spraying- hadn't even considered that.

[gerryggg]

Do you have the specs for the rings? i can't seem to find them in my manual. I have the ones from my proper and since the side plates are garbage, maybe I can help you out.

[goandy]

Sorry. Forehead slapping moment coming up. I just went out to take photos of the bits and I had the measurements wrong. The Mazda seal is smaller diameter but deeper. That would mean metal spraying and machining the rotor outside lip of the oil control groove and also machining the inner face of the Mazda oil control ring. There isn't enough metal on the rotor to enlarge the inner face of the groove. I'm not sure if there's enough metal to machine the inner part of the Mazda ring.

Here are some pics- the bare rotor


Here's the suzuki oil control ring rubbing face (the shiny bit is the wearing portion that you measure the width of):








Mazda ring (lighter silver) and Suzuki ring side by side:


Suzuki ring in the rotor:


I couldn't tell you what they are made out of other than they are magnetic steel/iron. Some people have said they may be made of cast iron- the Mazda ones are quite brittle and the broken edge is very grainy.

Gerry- very kind offer, but maybe you should consider keeping them if they're good- you might need them in the future!

[goandy]

After discussions with a learned old engineer uncle, I will look at remaking some oil control rings out of fine grain cast iron stock. I have the lathe so may as well justify it! It will take a bit of time so I'll update the thread when I get organized.

Using Mazda ones is just not the solution. You have to fill and remachine the groove in the rotor- or machine a lip/insert which fits into it, and also machine the inner edges of the Mazda ring to fit. Once you've taken around 1.5mm off it would be worried that the ring is then too thin and fragile.

If I can find a short length of 130mm diameter tube with a wall thickness of at least 10mm I should be able to do it!

[goandy]

Some ring measurements for reference:
Outer diameter 127.45mm
Inner diameter 121.50mm
Thickness on outer edge 3.80mm
Thickness on worn inner edge 3.85mm. Given this is pretty much measured half way across the width of the ring where the bright wear portion begins, a new ring probably has an inner thickness anywhere up to 3.90mm

Inner o ring channel is 1.6mm deep, 2.4mm wide and wall thickness around 0.7mm.

Just remember these measurements are taken off a worn ring but the diameters should be pretty close. There's around .1mm clearance between the ring and rotor when it's in its groove.

[goandy]

Just a quick update. No NOS rings anywhere, so whilst I intend making some to see if it can be done easily, until I get the materials and make the tooling, I've reground the ones I have. I made up a plate to hold the seal, which is mounted on an electric motor. That motor has two adjusting bolts which allows you to adjust the angle of the motor assembly and therefore seal on the grinding surface to get roughly the right angle for grinding.



To grind I used wet and dry sandpaper in 400 to 1200 grades to grind and surface finish the seals, mounted flat on a sheet of glass. Didn;t take long as the cast iron is fairly soft and the result looks ok. The proof will be when it's back together, No massive smoke screen will equal success!

[raychappo]

They look fantastic! A very resourceful solution.
As you have ground the control ring, will there still be enough so that the spring behind gives enough pressure on the ring against the end plate?

If all goes well and it works will you be willing to regrind other members seals? My proper unit has good compression but it gets through sump oil so I imagine the oil control ring could be to blame. I have a set of NOS rotor ring seals (6 rings) so if I dissasemble the proper to fit those it would be nice to do a full job and recondition the control ring as well.

Your services would of couse be rewarded

[jm0406]

I would think they could be machined if you knew what material to make them from. The Mazda people should have information on what materials work. It might even be an improvement over the original ones. Jeff

[goandy]

Ok, the way I ground the seals, I pretty much go up to the original inside edge so am only taking material away from the outside in effect. On these I removed around 0.1mm in height to regrind them so there is no issue with there being enough seal material left.

I may have a look at using newer Mazda oil seal backing springs if my springs are out of spec- I'll see how they look back in the rotor.

If it's successful, I'll be more than happy to regrind some for other people for the price of postage. Obviously this will be a "use and don't abuse" service so one or two sets per person is ok but not 10! I figure that anyone who is a. mad enough to own a RE5 and b. Crazy/stupid/ambitious enough to rebuild a proper unit needs all the help they can get!

The oil control rings as far as I know are made out of cast iron but obviously high quality. The best sort to use is what model engine ring makers use- cylinder liner cast iron as it is centrifugally cast and has an even grain structure. I have heard in the past that the Mazda rings are chrome coated but I've never seen anything that looks like chrome.

When you snap a Mazda oil control ring it's fairly brittle and has a grainy edge to it.

The plan is still there to manufacture some but it's low on the priority list now. If the reground rings work then I may not even bother with remanufacturing and stick with regrinding.

[goandy]

I coated the reground rings with marking ink and rubbed them on the side plates. The rubbed part of the oil control ring surface measured up around 0.2-0.3mm so is perfectly in spec.... Give me another six months and I hope to have the motor back together and running in the bike!