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MG Midget and Sprite Technical - Cord piston rings


Does anyone have first hand experience of using Cord ring sets?
How effective?
What information is needed in ensuring the best size/ fit and type to try?
Posted 25 September 2014 at 19:06:47 UK time


REPLY:
Lawrence Slater, Kent, United Kingdom, slaterlpj@btconnect.com

Guy. http://www.mayphil.co.uk/ now own cords.

http://www.cordsduaflex.com/

I have cords in my engine. Easy to fit. They come with good instructions. Great if you don't want to rebore.

My current Sprite engine had done over 100k miles. It was smoking. I put cords in and it stopped smoking and runs very well. -- Except that that was back in 1998, and I need to do the big ends now. One reason why my Sprite is off the road.

But the top end is still good, still has good compression, and doesn't smoke.



REPLY:
Posted 25 September 2014 at 20:52:25 UK time
Guy Weller, Cumbria, United Kingdom

Thanks Lawrence, I thought I remembered that you had used them. Bit that puzzles me is the plethora of different pistons on different engines. Rebore isn't an option for me as its already on a 60,thou rebore I think. Or maybe its 30 thou. Never did understand rebore sizes, whether they are quoting the diameter or the radius.


REPLY:
Posted 26 September 2014 at 00:09:19 UK time
Dave O'Neill 2, West Midlands, United Kingdom View vehicle profile

Rebore size is the diameter.

I used some Cords rings on a Mini 1275GT engine many years ago. It was using 1 litre of oil per day.

The rings didn't cure the problem, but I think it was caused by something other than worn bores/rings.


REPLY:
Posted 26 September 2014 at 09:05:45 UK time
Lawrence Slater, Kent, United Kingdom, slaterlpj@btconnect.com

Hi Guy. Standard 1275 bore size is 2.78" (70.6mm). Over sizes are added to that, in thous". 10,20,30,40 60.

If you are at already +060", you can sleeve it down, or offset the bores (2/3? I think) and go bigger. Pistons circa 90 - 250 quid, boring cost?

Cords rings, - if they have them in +060" -- will cost circa 100 quid, or maybe only circa 50 quid if off the shelf. I know because by chance, I've just had a conversation about similar for my pistons.

Are your pistons a standard pattern OE Spridget piston, albeit +060? If so, then the cords set you need is designated 0827 060. It may be a 3 or 4 ring set, depending on your pistons.

If it's only +030, then they (cords) can definitely sort you.

But you can also rebore from there without offsetting. But I'm told -- yet to confirm -- that you'd have to go to 060, because going to 040 wouldn't be enough to remove all wear and ensure the bores weren't oval.

If the bores are worn evenly, not too ovalled, and only have a reasonable top lip, then cords will sort it.

I've used cords on several engines other than my Sprite, and they've always worked well. They used to be called/thought off, "re-bores in a box". But they can't work miracles. If your bores are more than simply worn, your looking at a rebore.
Guy Weller

I have just checked what the pistons are in this engine. It was rebored when I rebuilt the engine during its re-incarnation back in the mid 90's. The company who did the work gave me a free spare piston and rings "in case I broke a ring when assembling". So, this piston has 4 top rings and a composite style oil ring. The box is marked as 71.37 and the piston crown has +03 stamped on it. Its a TRW piston.

The engine goes well starts instantly, doesn't oil the plugs, but does blue-smoke pretty well continuously. I have tried renewing the valve stem seals but that made no improvement. I have been meaning to get round to doing something for about 18 months and eventually the embarrassment level when driving of polluting the clear autumn air has finally got to me.
Guy Weller

I picked up a set of Cords for the B last year, for the princely sum of £13.99 - just in case!

Their website doesn't seem to give much information.
Dave O'Neill 2

Guy,
Trawling around online I found this useful chart on a Mini site.

All quoted using stroke length of 81.3mm and a nominal bore size.
+020" - 1293cc bore - 2.801"/71.145mm

--- +030" - 1302cc bore - 2.811"/71.4mm -----

+040" - 1311cc bore - 2.821"/71.65mm
+060" - 1330cc bore - 2.841"/72.16mm

--------------------

So that ties in. You are .030" oversize as stated on the piston crown.

Until you pull the head, you won't know if you really need cords. If the bores are worn -- as they must be to some extent -- then so are the rings.

Cords were mostly used when a standard re-ring wouldn't do it, and you didn't want to rebore.

But if your bores are pretty good, -- small lip at the top and no scores --- you could get away with just a new set of regular rings. You can probably get them for circa 30 quid. Grants for example.

I've ringed pistons with std type rings in the past and had good results. The only caveat is that you might need a stepped top ring (ridge dodger), and there aren't many regular ring sets out there these days with a ridge dodger top ring. Cords are one of the exceptions. But you can get over that if you carefully remove the lip yourself. Esp if it's only on the thrust side, as it might be with very little wear in the bores, in which case you might not even need to bother. I've done that before and haven't broken the top ring or ring land.

Look inside your piston for some numbers to id the exact piston you have. That way you can determine the ring width/depth.

My guess is that it will be standard 1275 Spridget spec.

Ring widths Top 1.59mm, 2nd 1.59mm, 3rd 1.59mm, 4th 4.00mm.

If so, then Grants P1280030, or Cords 0827030 will both fit. Grants cheaper (circa 35 quid) and for bores with very little wear. Cords more expensive from cords (97 quid inc vat and postage) for more wear but you don't want to rebore, and you get a ridge dodger top ring.

How do I know all this?

I have Hepolite 19320 +030 3 ring pistons. They're obsolete 1300GT and S pistons, but they have standard ring widths. I've got one broken ring. Bummer. Cords quoted me just the other day. But then I discovered that grants do a 4 ring set with the same widths. So I can just discard one of the top 3 rings -- which are all the same type of compression ring. I just have to deal with the very small wear lip at the top of my bores.

I'm still deciding.

Ring cords on 01685 353220. theit website tells you now't as Dave pointed out. You have to call them for info.

They might be surprised to get another caller in the same month, enquiring about a +030 Spridget engine ring set.


Lawrence Slater

PS to my last post.

I dug out the cords box and receipt from the last time I used them back in 1998.

Ring set 827+020. Price inc vat and postage £35.78.

Basically the same ring set, but in +020" and cheaper than today.
Lawrence Slater

Thanks Lawrence, lots of useful info there!
Cords are way more expensive than I had imagined!
When I rebuilt this engine all the machining work plus supply of all shells and new pistons (with rings)came to just under £200 total. That was a rebore, crank balance, lightened flywheel, line bored and ground crank, and a replacement and balanced front damper pulley. But I suppose it was a while ago!
Guy Weller

Yup. That's pretty much why I started that thread in general, about machine work prices. The last time I had anything done was over 15 years ago, and it's taken me by surprise just how expensive it's become. Parts are still relatively cheap, but labour has become a much more significant cost.

Cord were alway more expensive though. Other than cords, rings back in 1998 were probably less than £10/15.

It doesn't help that +030" is an odd size for a rebore today. So finding a cords set(cheap) in that size, other than direct from Cords, is unlikely. And that means paying Cords direct prices.
Lawrence Slater

After typing that, I thought that price looked too unrealistic so I went and dug through a file box full of receipts. Somewhat surprisingly ( I am NOT an organised sort of a person!) I did find the receipt dated Jan 1998

It doesn't include the flywheel lightening, which I must have done at anther time, but it does include all the rest.
Rebore, and line bore - £32,
a damper pulley - FOC,
a set of pistons - £45.93,
ground mains and big ends £38.40 (I don't think this can have included the shells, which I think were £12 a set at the time)
and supply, fitting and reaming cam bushes. total £160.19 inc VAT.

I think the figure of just under £200 that I was remembering was the total that it cost me to rebuild that engine.

Guy Weller

I wonder how much all that would cost today Guy.

"a set of pistons - £45.93, ". Yup cheap compared to today.

You can get pistons from Sussex for circa 95 quid. I don't know what brand they are, maybe County. I'm sure they're pretty good. But for other brands I've been quoted 250 quid.

I've never heard of TRW. Who makes them? You may find those are the 150 quid variety.

BTW. If you have the box, presumabley the model number is printed on there somewhere. And for the ring widths you only need to measure the ones you have on the new spare piston.
Lawrence Slater

According to the box, back in 1998, TRW were part of the Federal Mogul group
None the wiser. The box contains piston and cotter pin and rings individually wrapped in oiled paper sleeves. And there is a printed table of dimension ramges and options with illustrations for correctly fitting the rings.
Guy Weller

TRW took over the old Lucas Research centre in Shirley, Solihull.

They also had a factory in Birmingham, producing power steering racks, I believe.
Dave O'Neill 2

Sounds like they might be SpeedPro pistons.

How about numbers on the inside of the piston? Then you could email Fed Mogul for the ring specs.

Otherwise measure the ring widths and depths. I'll bet that Deeves or Grants will have a ring set to match.

Any US chappies out there reading this?

Since FM is a US brand, someone like Norm might know how to ID the Pistons?

How about you Prop?
Lawrence Slater

The piston crown is stamped TRW 175-9335 and +03

The accompanying table lists that number (amongst a couple of hundred others) but that doesn't get me any further as the table only then confirms it as a + 30 thou bore.

The underside of the piston has AC cast into it. AC as in the logo for AC cars I think, which would be appropriate, with the the curved letters.

Not much else to learn from the box, other than the leaflet print date is 1993, so as I bought them in 1998 they may have been old stock. And the companies are listed as TRW Inc, and Federal Mogul SA. Does that make them American owned?

Anyway, its diagnosis time.
SYMPTOMS: The car runs well and behaves itself as I would expect, other than producing continuous visible blue smoke. On tickover this is visibly pumping from the exhaust, and when driving at modest speeds (30 to 40mph) there is sufficient to be visible in the rear view mirror.

So I removed the plugs. See photo. These are as they came out after a 10 mile run at normal A road speeds with little other traffic., followed by a few hundred yards at 20 or less down the lane to the village. Cut the engine and removed the plugs.


Guy Weller

I took the plugs out to do a compression test:

cyl dry wet
1 195 215
2 175 215
3 180 220
4 185 220

I should add, its an MG Metro head skimmed to give 10.5:1 compression ratio
Guy Weller

Guy. Your pistons come up a lot on Mini Forums. They seem to have been fitted to Metro Turbos.

Telephone FW Thornton, Shropshire. 01952 252892 They should be able to ID the ring set you need.

Have you rung Cords?

On the performance re - oil smoke.

You did stem seals, but how about valve guides?

The trouble with seals on the ex-valves is that they soon go brittle. I know some people recommend them, but I don't think it achieves much for very long. And if you're guides are too worn, then you're expecting a lot from the seals anyway, both on the ex's and the inlets.

Looking at the compression values and the description of performance, it seems to me that one or more oil control rings are likely worn, broken or clogged. But the compression rings are probably good. Or, you may have a broken comp ring, and a scored bore. Until the heads off, it's all a guess.

The top plug in your pic suggests to me to look at No.1 or No.4. --- Assuming that you kept them in order. Definitely oil residue there. The others look pretty clean to me.

Clean them all to spotless, and then take a shorter drive. Then pull them again and see which one is "oilier" than the others.

Lawrence Slater

Thanks Lawrence. I was waiting for some other expert analysis before declaring my interpretation. But seems no-one else other than you is prepared to hazard an opinion.

I agree, there may be some slight oiling on plug 1, but its very little, and itself doesn't help although it could be a pointer to look more closely at that cylinder.

As for the compression test - the wet figures, with a bit of oil added to help seal the rings, are good at 215 - 220. This indicates that valves are seating well. The guides were replaced about 18,000 miles ago. They should be ok, but you could be right about the valve seals; they may have hardened up a bit by now. I do fit them on exhaust valves too.
But smoking resulting from poor valve stem seal is predominantly on overrun, whereas mine is smoking all the time.

The difference between wet and dry tests suggests some problem with the rings, especially on cyls m2 and 3. And this is in line with he blue smoke signals. But the differences at around 10% not excessive, so I doubt it is broken rings. To me, it signifies moderately worn rings/ bores, rather than a breakage as such.

Time to remove the head I think!

Guy Weller

I'm surprised at the lack of comment too Guy.

And where are the US chaps? Come on comrades. One of you must have the exact specs on these Fed' Mog' pistons at least.

Anyway. 18000 miles guides. Yup I would say that rules them out and points at the bores/rings.

I suggested a broken ring, if it's only one bore/plug oiling up.

As you say, moderate wear rings/bores is most likely.

How many miles on this engine? 100K+?

My sister had a Mk1 Escourt. Had abouut 70K on the engine. Ran well, started first time, and smoked like a chimney. All I did was put a new set of rings on it, - not even cords, -- and the smoking was cured.

Off with it's head.

Are you any closer to a ring set?
Lawrence Slater

Have you made any progress on this Guy? Have you found a set of rings, cords or otherwise, that fit your pistons?
Lawrence Slater

This thread was discussed between 27/09/2014 and 14/10/2014

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