Friday, 28 February 2014

Valentine's Day startup!

19 Jan14
Battery connected and testing started. Lights look OK with the exception of the headlamp dipswitch, windscreen wipers don’t work and the heater fan blows a fuse! Altogether at least as good as I expected! Troubleshooting begins ….
09 Feb
Managed to sort out most of the electrics. The fan wiring was messed up, I’ve now got it running but only on a single fast speed. The wipers didn’t work properly with the rotary switch I was using (advantage being it’s marked ‘wipers’) but after changing the brushes, fitting a new park switch and 130 degree wheel to the motor unit, it’s now working with the two-speed-and-park switch supplied with the loom. I need to check the speeds are OK for IVA.
I’ve adjusted the float in the tank sender, after it was obvious it was bottoming and giving a reading of quarter full when empty.
I’ve spent some time on the exhaust – not a great pleasure given the recent poor weather and cramped garage access, but now much happier with the fit-up, though getting a ground clearance of much over four inches is challenging.
I’ve been focussing both on getting the engine ready for starting, and on the IVA requirements. The engine’s now about ready – I’m not happy with the arrangement of the cooling system really, having seen how many joints I’ve ended up with. It’s now almost leaktight (at least unpressurised). The sump’s filled with Halfords Classic 20/50 – which looks remarkably like Duckham’s – and I’ve primed the pump with an electric drill until 40psi on the gauge.
I’m just waiting to sort out the ballast resistor ignition circuit. I looked at a number of diagrams on the net, but only one (MGB-V8 site) correctly showed the need for a diode bridge. Without this, the starter runs as soon as the ignition key’s turned to the first position. It’s actually obvious from the various circuit diagrams I looked at, that as soon as the ignition’s on, the current runs to the starter solenoid, but I made the mistake of wiring it that way first. The kit needed is a 35A Diode Bridge KBPC 3504, which costs buttons from Maplins. I’m just waiting for this and then – fingers crossed – should be able to fire up.
I called at the petrol station to fill my two-gallon Valor can with petrol (I do this every year for the lawnmower – always half expecting to be refused, as although the can has held petrol continuously for over 75 years it’s considered ‘non-PC’ these days!) which has been transferred to the tank. I’ve run the pump to prime the filters and carburettor, fixing the inevitable couple of leaks. Also turned the engine over a few times – without plugs – on the starter motor.
16 Feb
Diode bridge arrived and I fitted it onto an aluminium backplate with the ballast resistor, wiring it to a piggyback connector to the ‘start’ terminal of the ignition switch.

Valentine’s day – 14th – was historic, I reset the ignition timing approximately, and the engine fired up quite readily, though with blowing exhausts, water drips from hoses and a biblical oil leak from the oil pressure gauge connection. Also a bit of an intermittent misfire from the left bank. All in all, no worse than expected!

Next job is to get the clutch working. I’ve got a 5/8” master cylinder with the Rover 7/8” slave cylinder, which means the stroke at the slave is approximately half the stroke at the master, which seems to be about 1¼”. So far not much success bleeding the system – but I think I know why. I’ve been using a vacuum pump which of course is drawing the slave piston AWAY from the operating rod – I need to use a pressure system which forces the slave piston onto the operating rod. As the rod stroke is only going to be 5/8” this is quite critical!
Watch this space.
23 Feb
After some more concerted bleeding – the clutch may be working – although the engagement seems a long way down the pedal travel. Hard to tell until the engine’s running again and I can try and get it in gear. Think I’d like the brakes functional too, first ….
Made a collapsible hub, with the intention of satisfying the IVA requirements, but as it actually looks quite good I think I’ll retain it. 

The solid boss obtained from Scarborough Racing Developments is machined right back to leave only the spline adapter and flange; this is drilled with four 6.5mm holes to suit the PCD of the rear face of the collapsible hub unit I got from Europa Spares. At the business end I machined an adapter flange from aluminium plate which mates with the collapsible hub and the steering wheel.

I’ve trial fitted one of the seats from the MX-5, which seems to give an acceptable vertical height from the seatbelt anchor point. It may be best fitted via an adapter frame to make best use of hole drillings. I’ll set some time aside for this just before the IVA test, now I know it’s a goer.

24 Feb
Got to grips with the front suspension. I’m replacing the ‘pattern’ wishbone arms with refurbished OE items; the pattern parts haven’t got the inner pivot bush welded on squarely, which doesn’t look good and while it may or may not affect the suspension performance with rubber bushes it would preclude any later fitting of poly bushes.
The front ride height’s always seemed an inch or so too high; I thought this might be due to wind up in the rubber bushes, but also could be due to incorrect springs. I carefully measured the spring when removed, and calculated the length under load. Due mainly to being too long (10.3” free length, rather than 9.9” for the pre-’72 roadster OE item), the length under load comes out at between 0.4 and 0.5” longer than the OE spring (AHH6451). Factored up taking into account the intermediate position of the spring along the wishbone, this accounts for 1” of additional ride height. I now have a pair of AHH6451 springs on order and hope this sorts the problem.
26 Feb
OE springs delivered amazingly quickly from Sussex Classics, offside spring fitted. Springs are approximately 0.5” shorter than those from MGBHive and have a smaller wire diameter (0.5” not 0.515”). This should cure the ride height issue.

For anyone interested in the spring / ride height calculation - here it is:
MGBHive spring AHH6451 spring (pre-72 roadster)
Outside diameter of coils in OD 3.8 3.8
Wire dia in d 0.515 0.5
Mean diameter of coils D=OD-d in D 3.285 3.3
Torsional modulus of steel lb/in2 G 1.13E+07 1.13E+07
Number of active coils N 7.25 7
Free length in L 10.3 9.825
Rate = Gd4/(8.N.D3) lb/in R 385 349
Spring load lbs P 1030 1030
Compression = P/R in C 2.68 2.95
Compressed length = L-C in CL 7.62 6.88
Difference in compressed length in 0.75
Difference in ride height:
Dimension from inner pivot to spring centreline in A 5.1
Dimension from inner pivot to kingpin trunnion in B 11.8
Ratio ride height / spring compression = B/A 2.31
Difference in ride height = difference in compressed length x ratio B/A in 1.73

Reflectors relocated to where the upper over-rider support’s going to be. They now face squarely rearward.
28 Feb
Finished the front suspension, pleased to say that fitting the OE springs has completely cured the ride height issue, lowering the front by about 1.75” and leaving the indicators just above the minimum required height for the IVA test (350mm).
Also fitted N/S pads and bled the brakes, front and rear. I think they need bleeding some more to improve the pedal feel, but was able to test the pressure switch and brake lights.

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