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MG Midget and Sprite Technical - Valve Rocker Locknut Size

Hello members,

can somebody help me?

When I adjusted the valve clearances yesterday, I found out that on rocker #8 the locknut was a different size and seems to be a loose fit (turns endlessly).

What would be the appropriate size and dimension for a correct replacement? According to John Twist they´re metric (can you verify this?) - but which size?

Thank you!
WB Bankowski

I think they are 9/32 BSF, not metric.

Peter
Peter Burgess Tuning

Thank you Peter.

Where can I buy a replacement?
WB Bankowski

A series engine?

Part number 51k1178, or nt605062.

Depends which rocker you have, cast or pressed.
Lawrence Slater

Lawrence,

it is a 1098cc, midget Mark2.

How would I know the difference between cast and pressed?
WB Bankowski

Some confusion here.

Under the 948/1098 engine, Moss list 51K1178 as being for the sintered or forged rocker, neither of which were fitted to these engines.

They don't mention the pressed rocker.

They list 6K654 as being for the cast rocker only, although they show a picture of a pressed rocker. They list the same part number under 1275 and say it is for the pressed rocker.

The 1098 pressed rocker is different to the 1275 pressed rocker and, from memory, I think the nut is a different size.
Dave O'Neill 2

Ok.

Is there a way that I can verify which thread size it is? Or would a photo be more helpful?
WB Bankowski

I have an older parts book from 1983. -- Not Moss, but Sprite and Midget Centre Richmond -- long dead.

For the 1098 engine, it lists:

51K1178, against CAM289 pressed rocker. Adjusting screw, 12H3376.

NT605061, against 12G1221 cast rocker. Adjusting screw, AEG167.

I guess an official BMC parts book would be useful here.

I can look at an old rocker screw/nut later, and see if I have a tap/die to fit the thread.
Lawrence Slater

The locknut for the 948/1098 pressed steel rocker is 6K 654 according to the BMC Parts Manual. I also believe that the thread is 9/32" UNF.

Richard
Richard Wale

IIRC one of the differences in the part number of the adjusting screw may be due to the early ones having a lubrication hole and the later ones not.
David Billington

WB

Take the nut to your local hardware store... they should have a cheater board that you can screw the nut onto and that will give you the spec

Id replace the adjusting screw also...if there is damage to the nut its safe to assume damage to the adjusting screw also
Prop and the Blackhole Midget

Best thing I can suggest at the moment without a conclusive thread identified is to measure the OD with a micrometer or calipers and measure the crest to crest distance of X number of threads to work out the pitch. BSF and UNF have been mentioned and are not compatible pitches so it should be easy to determine what it is. Prop's idea might work if you can find a specialist in Austria dealing in inch fasteners, maybe an old British bike or car place that might have suitable taps or dies. nuts etc to match up.
David Billington

Thank you all for your support, I think I have now enough information to find a solution!
WB Bankowski

Wolf

See:
http://www.minispares.com/shop/classic/Engine/Cylinder~heads/Rocker.aspx?100408

Mike
M Wood

Well spotted that man.
Lawrence Slater

Prop...most of our "Hardware Stores"..wouldn't have a clue...
I seem to remember there are two different sizes...5/16" UNF and a BSF size (Not sure what)..depending on the age of the engine.
Definitely not Metric..
j hall

Prop...most of our "Hardware Stores"..wouldn't have a clue...


Sadly thats becoming the norm here as well...and its not just hardware, it seems we have become a slave to the putter box and kids reading the back of the package for the ansewer... gez, I wish I had thought to read the package before wasteing 20 minutes of my time looking for a store employee hidding in the break room.

Prop
Prop and the Blackhole Midget

I have just measured one and it's definitely 9/32" thread diameter, and also 26 tpi. Since the engine is basically 'Unified' threads, that would make it a UNS thread, i.e. Unified Special. The 26 tpi says it is in effect a 9/32" UNF, but that does not exist, hence 9/32" UNS!

A remote, remote alternative is 9/32" BSC (British Standard Cycle), which does exist as a standard thread, but I would be very surprised if it is that.

I can't tell with standard thread gauges if the thread form is 60° (Unified) or 55° (Whitworth), but would plump for Unified.
Richard Wale

Richard,

My copy of Machinery's handbook (21st edition, 5th printing 1982) does list 9/32" BSF x 26TPI but does have the proviso that it should be dispensed with wherever possible. I think that still leaves it in the race as a contender. Looking further it doesn't seem that the same book lists any UN? series thread of 9/32".
David Billington

Oddly enough Richard, I think my engineering mate did mutter something about cycle threads. I'll check up Monday as I think he made me some in case I need them one fine day.

Peter
Peter Burgess Tuning

David/Peter,

Curiouser and curiouser! So a 3rd possible option - 9/32" x 26 BSF?

In practical terms the 9/32" x 26tpi BSC and UNF would be virtually, if not actually the same actual thread, as both use the 60° thread form, unlike BSF that uses the 55° Whitworth thread form

What IS the right answer for this thread???

Richard
Richard Wale

Richard

I posted 9/32 BSF at the start of the thread :)

Peter
Peter Burgess Tuning

Peter

Does this look the 7/16 inch AF spanner sized locknut in question for early pressed steel A Series rocker arms?:
http://www.minispares.com/product/Classic/Engine/Cylinder_heads/Rocker/6K654.aspx

(and later type for forged, sintered and pressed steel rocker arms in other A Series engines, another non-UNF nut but this time a 1/2 inch AF spanner size:
http://www.minispares.com/product/classic/NT605061.aspx)

Spanner size and diameter of the rocker arm adjuster screw would be a good clue between the two.

Cheers
Mike


M Wood

Rocker adjusting screws:

http://www.minispares.com/product/classic/12A1215.aspx


http://www.minispares.com/product/classic/AEG167.aspx
(Genuine:
http://www.minispares.com/product/classic/12H3376.aspx)

Mike



M Wood

A quick check showed that Tracy Tools does list 9/32" UNS tap and dies.
David Billington

Peter,

Oops, sorry missed that!

Richard
Richard Wale

Hi Mike

I reckon it would be safe to go with the nut size to guess what one has. I seem to think most of the ones we do are 7/16 spanner size even on 1275s.

Cos its you I'll forgive you just this once Richard :) I usually miss what folk have written, spend ages typing, give it one last check and realise I talking rubbish!

Peter
Peter Burgess Tuning

Confused? You will be.

In the garage this afternoon, I found a couple of sets of 1098 pressed rockers. The nuts are 7/16" AF.

I also have an MGB head. The rocker nuts on that are 1/2" AF.

Moss list 51K1178 for the MGA and MGB.

As Nigel often says, you need to cross-reference.

I haven't had time to look at any printed parts books that I have, unfortunately.
Dave O'Neill 2

Dave

The 1/2 inch spanner sized rocker locknut has the same part number for MGA engines and A Series engines: NT605061

See:

http://www.mgrovermerchandise.com/product.aspx?CID=a50709b2-a969-4cce-a883-ab5908543e80&SID=3fb67a98-ed81-45c0-8cef-884a8160e109&PID=26f34fca-193d-43ed-b055-47c831ddba1b

&

http://www.minispares.com/product/classic/NT605061.aspx

Mike

(both listed at:
http://www.sussexclassiccar.co.uk/shop_factory_hazel/contents/en-uk/d1272.html

As well as at:
http://www.minispares.com/product/classic/NT605061.aspx
& http://www.minispares.com/product/Classic/Engine/Cylinder_heads/Rocker/6K654.aspx)
M Wood

Hi Dave

7/16th" and 1/2" spanner size for nut not thread of nut.
MGB rocker adjusters are 5/16th UNF.

As I said I'll have a quick check with my mate today who was probably young when they developed the threads in the first place :)

Maybe the factory misordered the nuts/adjusters...
some USA road cars had left hand thread wheel nuts/lugs...On the absurd side, some say one of Chrysler’s fastener sub-contractors screwed up (pun intended) with an un-related industry customer and cranked out several million left-hand studs and nuts when the order called for standard right-hand threads. Chrysler supposedly got a screaming deal on a zillion parts and adopted the fasteners for production until the supply finally ran out in 1970.



Peter
Peter Burgess Tuning

Peter

Moss are quoting the same part number for some A-series and B-series.

From memory, I think the 1275 pressed rockers have a 1/2" AF nut, so may be the same thread as B-series.
Dave O'Neill 2

Just checked 2 x 1275 thick flange Midget engines I stripped to do a race engine. 7/16th" spanner size fits rocker adjusting nuts. I am not sure if the 1/2" spanner size ones aren't the sintered ones but I will keep checking . All the pressed ones I have are 7/16 but I cannot guarantee what they came off originally, so I can only really report on original engines I have stripped.

Peter
Peter Burgess Tuning

My mate says 9/32" BSF for the 7/16th spanner size adjuster.

Peter
Peter Burgess Tuning

This thread was discussed between 14/04/2015 and 20/04/2015

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