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MG Midget and Sprite Technical - Big Ends and Mains

Ongoing saga, really.
I am slowly "refreshing" my 1275 engine as a (chilly) winter project. That means I am doing it outside, with the engine still in the car as I cannot get to my chain hoist in the garage.

Anyways, I have a question. I had assumed that I would be able to renew the Main bearing shells with the engine in situ, as I used to with my 1500. Centre main was easy enough although the shells were barely marked. But after removing the bolts neither the front nor the rear cap wants to come away.

The front one feels solid and the back, though loose, doesn't look like it will clear the hole in the backplate. It looks like I cannot get the caps off a 1275 with the engine in the car. Is this right?

If that is the case, then I will just tighten the mains back up again and leave the existing shells in there - there was very little evidence of any marking on the centre one so I guess the others will be OK.
GuyW

Guy,

I don't remember absolutely, but I think you are right that the front and rear caps can't be removed with the front and rear plates in place.

I do agree with you that if the center is good, the front and rear likely are as well. In the large truck engines that I used to run, the maintenance schedule called for rod bearings every 100,000 miles and main bearings every 300,000 miles. So, there is some precedent for you.

Charley
C R Huff

Thanks Charley,

I have an idea (from memory, I haven't checked)that there are 2 set screws at the front that go through into the front cap from inside the chaincase. That would account for it remaining solid, even with the 2 big bolts removed. At the back, it just seems there is not quite enough clearance between the crank and the backplate to squirm the bearing cap out.

If anything, on a 3-bearing crank, one might expect the centre mains to wear more than either end if there is a bit of "whip". Although that may just be theoretical on a well balanced, line bored, engine that isn't run at race speeds.

Another question. The main bearing cap bolts don't have lock tabs and don't appear to have any threadlock either. I built this engine so that is how I put it together, right or wrong! Some of the drawings show little square locking tabs. Some show a strap type one that goes between the bolts. What's best? My inclination would be to use Locktight and no locking tabs as they are soft and I suspect would hammer thinner in time, reducing the bolt pre-load
GuyW

Hi Guy

Your right the front one has two set screws behind the crank timing sprocket. Even if you remove the screws the chances are you will damage the gasket between the cap and the front engine plate trying to get the cap out. At the rear there is not enough clearance at the back for the rear cap.

The Main cap bolts don't have lock washers and I used Locktite!
Bob Beaumont

Thanks Bob
GuyW

Guy, those lock tabs are a nightmare - don't bother! They are too soft for a start and the high torque just pulls the bolts into them - thats if you can stop them from turning.

I don't use lock tabs or loctite on the mains and they've always been fine. I use loctite on the big ends but only because they are ARP ones that aren't stiff nuts like the standard ones.
john payne

Thanks John. So that's 3 votes for no lock tabs! Yes, l thought it was a wrong application for soft metal washers too. I will probably still use Locktight though as l cannot see any downsides to that.
GuyW

Not wishing to question your wisdom, Guy, in assuming the two ends will be good if the centre shells are OK, but wouldn't the front be more susceptible to wear, with its eccentric loads?

I made exactly the same assumption as you, when I took the main centre cap off, sniffed the shells, and shut the engine up again. My question is asked purely in the name of science.
Nick and Cherry Scoop

Nick, I don't know the answer to that. But I cut my first teeth on Austin 7 engines. Early ones were 2 bearing and were said to suffer from crank whip so the later ones have a three bearing crank. But then with that the middle bearing used to wear more than either of the other two.
What eccentric loads are you are thinking of on the front bearing - The tug of the timing chain I suppose? I wonder if that would make sufficient difference on a whirling heavy crank? I don't know.

In this instance I am working on the engine in situ in the car, so, as I have learnt, it isn't really possible to change the front and rear shells at this time. Given that the middle one was so good I am going to risk it and leave the other two. It does mean I can progress with re-fitting the pistons and new big-end shells whilst the sun is shining and snow isn't falling!
GuyW

Rather than doing half a job Guy, would you like to borrow my fold up portable engine crane, it fits into the back of a hatch back, and I am in Kendal.(but I am not in today) A.T
andy tilney

Thanks Andy, but not this time. I am pretty confident that the main bearings are OK. I would have put the centre bearing shells back in, they were that good, if I hadn't already bought the replacement set. The main objective was to re-ring the pistons and get it back on the road asap.

Didn't realise you were in Kendal as well! ;-)



GuyW

My experience is that the centre main does tend to wear more.

I have also replaced just the centre main with the engine in-situ.
Dave O'Neill 2

Guy I passed a blue midget up on stands today, if that's yours I am only five minuets from you, in fact I pass it every sunday, Andy
andy tilney

Andy, not actually in Kendal, 1.5 miles out. But there cannot be that many blue Midgets (actually its a Sprite) in Kendal. In fact I thought I knew all of the "local" cars - or at least the few that are in reasonably regular use which is why I was surprised when you said you were in Kendal
GuyW

Guy I am sorry but my MG is a B not a midget/sprite, Andy
andy tilney

Ah, I have seen a couple of Bs around, but not that often. John in the village restored a green BGT a few years ago, but didn't keep it for long after he finished it.
GuyW

On my arp set they used nyloc nuts.. no shims... just there own thread paste

prop
Prop and the Blackhole Midget

Yes Prop. That is what I have for the big end caps. New Nylocks. It is the mains that I was planning on using Locktight on.
GuyW

Very early 12CC engines did use locktabs, similar to the small-bore engines, but later ones did not.

I've never used Loctite on them. Just tighten to the correct torque.
Dave O'Neill 2

Guy I have just read your post on replacing your big end nuts with nylocks, these nuts rely on the bolt stretch to keep them tight, to check if the bolt is not overstretched, you need to be able to spin the nut up the bolt with out it binding, if you use nylocks you cant check this, if you cant spin the nut up the bolt then you need to replace the bolts as they have stretched and wont work as they should, just something to think about, Andy
andy tilney

Thanks Andy. So if I just test them with a standard fresh half nut would that be sufficient to check them before fitting the (new) nylocks that I have?
GuyW

as a standard 5/16 unf nut is not as deep as the correct big end nut I don't know, but if your standard big end nut spin up why would you not use them, as there is nothing wrong with them, Andy
andy tilney

Sorry Andy, you have me confused now. The standard big end nuts are nylock, so cannot be used to test as you describe. I need to use a non-nylock variant.
GuyW

Big-end bolts are 3/8, not 5/16.

Although they are nyloc nuts, they aren't 'ordinary' nylocs, they are HT versions.

Marina engines and, I believe, A+ used 5/16 bolts with 12-point nuts.
Dave O'Neill 2

Thanks Dave, I have the correct bolts. And I have a new set of the correct HT Nyloc nuts. The issue was just one of testing the bolts for stretch, by using a standard nut.
GuyW

Just checking.

Expensive little blighters, and they seem to vary in price quite considerably, depending on supplier.
Dave O'Neill 2

Mine came from a 2proper" supplier so should be the correct ones. But you have got me thinking. How would one tell them apart from normal ones? And does your "HT" mean high tensile, or high temperature? Presumably the nylon insert is different as it needs to retain its composition under high(ish) temperature.
GuyW

I think the nut material is different and I think it refers to high tensile. Certainly comparing the HT big end nut with a standard nylock the actual nut depth is larger on the HT ones and they don't deform as easily.(I tried putting 40lbs torque on a standard nylock and it didn't like it!)

Bob Beaumont

Guy I am sorry if I confuses you, that was not my intention, but I have never seen any nylocks on big end bolts on any A series engines, that I have worked on, Andy
andy tilney

LOL Andy, Now having re-read your post, I can see that you thought I was trying to replace standard nuts with Nylock ones. Whilst I thought you were suggesting that I test with ordinary nuts before replacing with the correct Nylock ones. It all makes sense now!
GuyW

Been away a few days, but back to re-assembling my 1275. And I have a problem with these big end (con rod) bolts. Or rather the nuts.

According to Haynes they should be tightened to 46ft Lbs. So I set my torque wrench to 42 for a first tightening, and all OK. But when I then increase to 46, 3 out of the 8 nuts have stripped their threads. And given that, I don't feel confident about the others so far tightened.

My suspicion is that I have been supplied with standard Nylock nuts. The ones taken off have a line with 2 cross hairs stamped on one flat. I presume that designates them as HT nuts. The supplied ones have no markings at all. Does anyone know if the HT ones should have a mark on them these days?
GuyW

Hi Guy

My manual says 32-34 lbs ft for nyloc nuts . I tend to use Binx nuts or Philidas nuts these days to replace the Nyloc ones. Did you read 45 NM as 45lbs/ft?

Peter
Peter Burgess Tuning

Here's the evidence.
IN the photo the two at the left are the nuts removed. You can see the double cross-hair marks on one flat.
The middle pair are two of the new ones supplied as Con Rod nuts. They have no markings at all.
The right hand pair are actually standard SS Nylocks (not HT) and apart from the greater depth apparent in the top row, they seem identical to the newly supplied ones.

The other differences are the colour of the nylon insert - black on my old ones and white on both of the new ones. And the Nylon insert is held with 2 punch marks as against 6 on the replacements. And rather more subtly and maybe not apparent in the photo, but the old ones are just slightly "crisper" to look at, like machined nuts always used to be. The replacements have a slightly more rounded appearance to their edges.

You can tell I am doubtful, but does anyone KNOW what I should be looking for?

GuyW

Thanks for your quick response Peter.
No, the figure I was reading is in ft-lbs. But I now see I was on the 1500 page! Dohh!
You are quite right - for Nylocks it should be 32 to 34 ft Lbs. (page before in the manual!) Doesn't seem to be a lot though.

Thanks, that gives me rather more confidence. Though I would still wonder how one tells the specials apart from standard Nylocks.
GuyW

My friends have always said I am special :)
To be honest I didnt like the replacement nylocs so I went for the Binx nuts last build.

Peter
Peter Burgess Tuning

I've not heard of the term Binx nuts before Peter. I had to look it up on't net!

Next problem - The thread on one of the con rod bolts is a bit knackered now, so I need a replacement! Its one of those special ones with "ears" the top instead of a hex head. And so far wherever I have looked they are NLA!.....

Oh dear, I am beginning to feel a bit like Prop - like the Spridget spirits are ganging up against me!
GuyW

My BMC WSM says 45 lb/ft for 1275 conrod nuts.

As you say, they look like standard nylocs.
Dave O'Neill 2

Are you sure that isn't 45 Nm Dave? The early style A series rods were 40 lbs/ft.

Peter
Peter Burgess Tuning

Guy,

ARP sets are available - but expensive, Moss do list the nuts individually.


http://www.moss-europe.co.uk/competition-big-end-bolts.html

richard boobier

The "Leyland" WSM lists 32-34 for Nylocks, 40 for normal nuts.

Anyway, I am annoyed at myself for creating totally unnecessary problems! Richard, thanks for the link. I really don't want to fork out that sort of money for a full set of ARP bolts. I just want to find a supplier of a single bolt, or maybe 2, to match the others.

Anyone know the correct part number for the "eared" style bolts. Its not clear from illustrations, which ones are hex head and which ones eared.
GuyW

Send me your email address Guy, I'll see if I have any spare ones.

Peter
Peter Burgess Tuning

I have sent you a PM, Peter. Thanks!
GuyW

I have been thinking about this a bit more. And OK, my fault for looking up the wrong torque data, but even so l am a bit surprised that proper HT Nylock nuts would strip at just 40 ft lbs. That's only 6 above the correct torque. That leaves me still puzzling over whether l was supplied with the correct ones and if so wouldn't they have some identification markings.

I did ring the supplier - a well known company - to ask if the nuts should have any identifying marks and also if the ones l have may have inadvertantly been 'picked' from the wrong bin by mistake. I got a fairly hostile response. he said the HT ones "look different" but couldn't explain in what way. Apparently they couldn't mistakenly pick the wrong ones as they are stored "in a completely different part of the building" (slightly surprising?). I did ask if l gave him a mixed hand full of HT and standard Nylocks could he separate them out. His answer was only by knowing the supplier. He didn't offer a solution and l don't think he was very convincing.
GuyW

It would be interesting to know who the supplier is!

As the 1275 Midget uses Cooper S rods and bolts, it might be worth trying Minispares.

Peter, it definitely says 45 lb/ft.

Which rods are you referring to as 'early style'?

I've just looked in a Haynes Mini WSM and it says 33 lb/ft and 45 Nm for conrod nuts, but doesn't differentiate between Cooper S and 1275 GT. The former having 3/8" bolts/nuts and the latter being 5/16".
Dave O'Neill 2

Dave, odd! I agree with Guy - or rather my Leyland workshop manual does!
AKD4021 15th edition, General data p.18
40 lb ft
Nyloc 32-34 lb t.
David Smith

Hi Dave

The only info I could find specific to the Cooper 970/1071 and 1275 S rods were to tighten to 40 lbs/ft dry. So I assume the early nuts in my wsm refers to the Cooper S spec ones not the later nyloc which I have also seen on S rods ( I know the late Midget rods are same spec as the last Cooper S ones). My manuals do not say the 40lbs/ft dry though.

Guy
, you did get to 42 on a non calibrated torque wrench (when did you last have it tested or buy a new one). If it did take 46 to strip some of them you have used a 35% overload at 34 lbs/ft starting point if your wrench is spot on and 38% failure rate.

Peter
Peter Burgess Tuning

Peter, yes you are right. The torque wrench is a good one and has been away for recalibration a couple of times, but not recently. Its for those reasons, and the fact that the fault was clearly my own, that l am not naming the supplier. They have always been reliable in the past and it was just a slightly unhelpful response l got this time, that is all.

The real missing bit of the puzzle to me is how to identify currently supplied HT nylocks from standard ones. No one seems to know! And if they cannot be differentiated how does the retailer know what he is sending out?

The other possibility is that at the correct torque of 32 - 34 ft lbs, standard nylocks are all that is required, and that is what is being supplied. In which case my complaint would be on the prices being charged for "specials" that are in fact standard nuts! And that seems unlikely too!
GuyW

All the Nylocs we saw looked poor light duty affairs so we went to the Philidas or Binx ones which look 'proper'. I would have thought your OE nylocs would be ok to reuse with bearing retention Loctite.

Peter
Peter Burgess Tuning

Peter, yes that is what I plan to do - re-use the old ones + locktight. They look like a much better quality anyway.

I do find it surprising that my supplier said they knew which ones were HT by which bin they picked them from. When I asked how they know which bin to put a fresh re-stocking delivery in, he said because they came from a different supplier. That's Ok, if you have 100% trust in your suppliers and never contrive to mix up ANY of the stock after opening the delivery! All of which seems most suspect to me!
GuyW

Now reading up on the internet it seems that different grades of Nylock ARE available, and "usually" carry different markings. No markings (like mine) means either ungraded or GR5. GR8 have either a single notch half way down the nut corners and/or a number 8, or a ++ stamped on the contact face of the nut.
But there is a caveat saying that manufacturers don't necessarily mark the graded nuts unless the specifier requests it, so unmarked nuts COULD be of a higher grade.

Clear as mud!
GuyW

I re-used the original nylocks with Loctite and took them to 40ft ibs. No trouble at all. As I said the 'modern' nylocks deformed at about 35ft Ibs and I had no confidence in them.

In the old days when I was racing I renewed the bolt and the nut after every strip down just for safety. I have a fair number of them still knocking around. I also used to renew the FW bearings at the end of each season as a precaution!! Imagine doing that now!!
Bob Beaumont

My WSM is AKD4021 F.

Dave O'Neill 2

This thread was discussed between 05/03/2016 and 16/03/2016

MG Midget and Sprite Technical index

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