(engine) grounding question - 74 Mk2

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joe czech

joe czech

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(replacement lucas harness assembly) on the main wiring harness, there is a two-wire grounding lug in the proximity of the head steady - i'm assuming for an engine ground. what is the factory location for that ground - the head steady iso bracket, or directly beneath one of the mounting cap screws on the head steady bracket? since the head steady bracket is painted, it seems the only ground path is the internal tooth washers of the head stead bracket to head bolts, and the lock washers of the iso brackets. BTW, during repaint, I masked the paint from the bracket where it mates with the head. it seems to me, that grounding lug would best connected to one of the head steady bracket cap screws for a good engine ground. when I got the bike, the original ground was connected to the iso bracket. the original wiring was a mess, and I have no idea what's correct, or the best ground point. any benefit to adding a secondary engine ground strap? TIA....
 
joe czech said:
what is the factory location for that ground - the head steady iso bracket,
Click to expand...

The factory position was the rear head steady stud:
(engine) grounding question - 74 Mk2


joe czech said:
or directly beneath one of the mounting cap screws on the head steady bracket?
Click to expand...

That would seem to be a more suitable location for the terminal, however, for some reason they chose not to.
 
jan nelder said:
could put it under the headsteady, and add washers on other positions.
Click to expand...
No don't do that , you need the head steady bracket attached firmly to the head imo
Just put it under the head of one of the Allen screws
Cheers
 
L.A.B. said:
The factory position was the rear head steady stud:
(engine) grounding question - 74 Mk2




That would seem to be a more suitable location for the terminal, however, for some reason they chose not to.
Click to expand...

BINGO! that clears up the ground PLUS that little clip for the oil line. I had the clip in the parts bag, but wasn't sure of the exact mounting location. BTW, I saw an on-line youtube video by Mi Ty (Oregon Norton) - he was doing something on his Mk2a, and I vaguely recall his ground was in that exact location. it may be redundant, but I may add a secondary ground from the iso bracket to the head steady cap screw. figure, it can't hurt - ??? as I remember, my original ground was on the RH head stead rubber iso stud. my original wiring was an absolute mess - so much so, I couldn't trust anything. thanks LAB!
 
As others have done, I installed an additional ground to the engine itself, a ring terminal on one of the bolts where the upper head steady bolts to the engine. I like the idea of the most "positive" (NPI) ground possible directly to the engine. The more fittings there are between the ground wire and the engine, the more possibility for a poor/corroded connection.
 
L.A.B. said:
(engine) grounding question - 74 Mk2




That would seem to be a more suitable location for the terminal, however, for some reason they chose not to.
Click to expand...

there may be a reason for the factory location. it probably has to do with the manufacturing process. obviously, the engine assembly was built and prior to installation in the frame, and the front and rear isolastic mounts were installed along with the head steady bracket prior to mating with the frame. i'm thinking this is due to the torque requirements of the bracket screws, especially the center screw - much easier off frame. the frame assembly probably came through with the main wiring harness installed. the engine assembly, with the head steady bracket, were installed in the frame and the engine ground would attach to the factory location at that point. the assembly line would not have un-done the head steady bracket cap screw to ground the engine. that would have required several extra steps at that process and tooling at that assembly station. the location on the iso bracket was on the inner side due to the curved edge on the bracket itself. I agree, not the best location, but I guess it works OK. I would say there needs to be a grounding washer under the harness ground lug. nothing's called out in the parts book, so not sure how one figures out some of the details. ;)
 
joe czech said:
there may be a reason for the factory location. it probably has to do with the manufacturing process. obviously, the engine assembly was built and prior to installation in the frame, and the front and rear isolastic mounts were installed along with the head steady bracket prior to mating with the frame.
Click to expand...

The power unit (engine, cradle, gearbox & primary) was certainly assembled first, but factory photos show they laid the power unit on its side and then lowered the frame onto the power unit.

No evidence the front Iso. or head steady were attached to the engine at this point or the wiring harness being attached to the frame at this stage of the assembly process.
 
I had issues with the factory ground and added in a new one direct from a head steady bolt screwed into the head and back to the battery, the old one would only pass enough current for one spark, not much good on a wasted spark Boyer. Not an issue if you use a dual coil as the spark current passes from one plug back to the other.
 
L.A.B. said:
The power unit (engine, cradle, gearbox & primary) was certainly assembled first, but factory photos show they laid the power unit on its side and then lowered the frame onto the power unit.

No evidence the front Iso. or head steady were attached to the engine at this point or the wiring harness being attached to the frame at this stage of the assembly process.
Click to expand...
on it's side - seems odd - ??? i would have thought the frame and engine would have been in it's normal orientation. anyway, just speculating on my part - :) any kind of public access to those photos you're referring to?
 
joe czech said:
on it's side - seems odd - ???
Click to expand...

It's by far the easiest way to do it as the frame is much lighter than the power unit.

Once the power unit and frame had been joined together by the main Iso. stud and the front Iso. probably fitted at this time then the assembly would have been set upright and placed in the assembly cradle.
 
The original head steady probably just about ok to earth through as the thin layer of paint would possibly give a little
But in these days of powder coat it could end up isolated
So an earth to one of the head steady cap heads would be a good idea IMO
 
baz said:
The original head steady probably just about ok to earth through as the thin layer of paint would possibly give a little
But in these days of powder coat it could end up isolated
So an earth to one of the head steady cap heads would be a good idea IMO
Click to expand...
I agree. the original ground should suffice. I went ahead and made up a short jumper as a secondary ground - just a piece of 14 awg. this may be overkill, but I feel better about it. the ground lug in the replacement harness wasn't quite long enough to go directly to the head steady cap screw.

(engine) grounding question - 74 Mk2
 
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"just a piece of 14 awg. this may be overkill,"

Heck, I used 12AWG! :)

No such thing as "too good" for grounds!
 
MexicoMike said:
"just a piece of 14 awg. this may be overkill,"

Heck, I used 12AWG! :)

No such thing as "too good" for grounds!
Click to expand...
i agree - definitely no argument here. my thought process - it appears the lucas harness is two, parallel, 18 awg wires. if i'm not mistaken, current capacity of two 18's is the approximate equivalent of one 14 - ??? :)
 
joe czech said:
it appears the lucas harness is two, parallel, 18 awg wires.
Click to expand...

If Lucas (Wassell Classic Lucas) then the wiring is almost certainly Edit: (two) 14/0.30, 1.0mm² (14 strands of 0.30mm dia.) as Edit: automotive wiring (at least outside the USA) has been 'metric' for some years.

https://www.autoelectricsupplies.co.uk/product/66/category/11

The equivalent original Lucas British Standard harness wiring would've been Edit: (two) 14/32 SWG (14 strands of 0.274mm).
 
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L.A.B. said:
If Lucas (Wassell Classic Lucas) then the wiring is almost certainly 14/0.30, 1.0mm² (14 strands of 0.30mm dia.) as wiring (at least outside the USA) has been 'metric' for some years.

https://www.autoelectricsupplies.co.uk/product/66/category/11

The equivalent original Lucas British Standard harness wiring would've been 14/32 SWG (14 strands of 0.274mm)
Click to expand...
not sure i'm following you here. unless I checked the wrong ground path, it appears the original harness to be two parallel 18 ga/14 strand conductors. not sure of the metric equivalent. now I can't say for sure if the twin, parallel conductors within the harness, goes back to a single battery ground point, or one of those conductors is somehow daisy-chained, within the harness, for another ground, but either way, still pretty sure one 14 is equivalent to two 18's - :)

I think we're talking the same thing, only apples and oranges - that is metric vs AWG. been dealing with AWG most of my life - not so much with metric - ;)
 
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joe czech said:
not sure i'm following you here. unless I checked the wrong ground path, it appears the original harness to be two parallel 18 ga/14 strand conductors.
Click to expand...

The original harness would have had two parallel 14/32SWG wires, not two '18 gauge' as the original British wiring wasn't 'AWG gauge' standard which was what I was attempting to point out that they're two different wiring standards and metric is a third standard now used in most of the world.

Modern harness wiring is metric. 14/0.30 which is approximately equivalent to US '18 gauge'.

joe czech said:
not sure of the metric equivalent.
Click to expand...


The Wassell Lucas harness wire is almost certainly metric 14/0.30mm (as I said) and not '18 gauge' as that's a different (US) wire standard.

joe czech said:
now I can't say for sure if the twin, parallel conductors within the harness, go back to a single battery ground point, or one of those conductors is somehow daisy-chained, within the harness, to another ground, but either way, still pretty sure one 14 is equivalent to two 18's -
I think we're talking the same thing, only apples and oranges - that is metric vs AWG. been dealing with AWG most of my life - not so much with metric -
Click to expand...


Yes, in US terms. "14 gauge" metric equivalent would be 28/0.30, 2mm².
https://www.autoelectricsupplies.co.uk/cms/files/awg_to_mm2_conversion_data.pdf
 
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