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ricey
Phil Rice
Chessington Surrey
(33 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

rebuilt v8 wont start!!
Posted by: ricey
Date: December 22, 2017 12:25PM

HI all

Finally got the 3.9 engine in and all set up but having a problem with intermittent spark so cant get it to start. Running on carb with standard electronic dizzy with side module.

It cranks over no problem
I checked the TDC 3 degrees before TDC on number 1 on BOTH revolutions of the crank, and found originally I had the dizzy at No1 when both valves were just closed and starting to rock. Whereas on the other revolution both valves where shut and had no immediate movement as I passed through the TDC 3 deg.

I picked the second option of TDC.... was this right?

with the first option of TDC, I did get a loud bang out of the left right hand bank (with No8 cyl)

When it didn't start I swapped to the second set up of TDC and checked with a spark indicator fitted between the lead and the plug and on initial turn of the key I got a flash for two times on plug number 2 that I had the indicator connected to,and then that was it, no more spark.

It seems that when the ignition is turned off and then turned on again and cranked a get a spark once maybe twice and thats it.

The coil is new but the dizzy with the module bolted to the side came with the engine.

I have the white/green from the loom to the +, then the red from the module on the dizzy to the +, then the white black form the loom to the - along with the white from the module.

One other element is the new starter fitted has the white/brown and white/green jumped together onto the ignition live connection together....is this wrong?

checked for fuel, no issues there and squirted carb cleaner down 1404 but no life.

Any help greatly appreciated.


88v8
Ivor Duarte
Gloucestershire UK
(607 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: rebuilt v8 wont start!!
Posted by: 88v8
Date: December 23, 2017 04:51AM

The exhaust valve should be closing when the piston is coming up to TDC on the compression stroke, and opening when it's coming up for the exhaust stroke.

Wiring woes:

You mention 'standard'. You mean standard for this engine?
Like this? [www.ebay.co.uk]
Dunno about the wiring colours but you'll find them on a Rover V8 forum when you know which module you have,

Whilst cranking, measure the input voltage at the power module, and measure the input voltage at the coil +.

Do you have a ballast in the circuit? If so, do you have a ballast (0.8ohm) coil? Check the resistance across the LT terminals with the wiring detached. The wrong coil can give a lousy spark.

Ivor


ricey
Phil Rice
Chessington Surrey
(33 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

Re: rebuilt v8 wont start!!
Posted by: ricey
Date: December 23, 2017 12:03PM

Hi Ivor

Thanks for that, I have sussed the starter motor wiring so thats correct.

The fading spark I think is the secondhand dizzy. I am gong to test the coil tomorrow before ordering a new one. Ill let the thread know the outcome


ricey
Phil Rice
Chessington Surrey
(33 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

Re: rebuilt v8 wont start!!
Posted by: ricey
Date: December 24, 2017 07:22AM

Hi all

checked coil for spark with king lead attached to spare plug. on cranking I get 2 -3 tiny sparks then dies.

on disconnecting the - side of the coil that goes to the dizzy, and using a fly lead to touch against good earth in its place I get decent sparks, which leads me to believe the coil is good.

I tried a couple of tests on the dizzy to see if I got a on/off output on the - wire coming from the module to the coil and the + of the coil, but I just got a steady 13v dc, and when I tried to rotate the rotor arm against the advance mech of the dizzy to induce the fluctuation of the signal, the rotor wouldn't budge it just clicked like a switch about 3 degrees and then clicked back.

secondly i tried measuring for a resistance in ohms across the two outer terminals on the module and this showed an open circuit?

Does this sound like just put a new dizzy in? I have absolutely no knowledge of the one that came from the donor, it could be 150K old!

(Finally did any of you ditch the ballast wire in the loom and replace it with a permenant 12v live? I ask this as I HAVENT DONE THAT YET and I am running a 12v Lucas 198 coil,)

Any thoughts greatly recieved

Merry xmas



Edited 1 time(s). Last edit at 12/24/2017 08:20AM by ricey.


88v8
Ivor Duarte
Gloucestershire UK
(607 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: rebuilt v8 wont start!!
Posted by: 88v8
Date: December 28, 2017 02:54PM

I believe the Lucas 198 is a ballast coil, in which case it needs a ballasted feed.
Measure across the coil's LT terminals, you should find a resistance of 0.8ohm.
A coil designed for a 12V feed will have a resistance of 2-3ohm.

To run a ballast, there should be two feeds to the coil. 12V from the starter which is only active whilst cranking, and 6V or perhaps 8V via the ballast which should be present all the time the ignition is on.

With your DVM, check the voltage whilst cranking, and when not cranking. If the ballasted feed is not working, the ballast may be faulty.

Ivor


ricey
Phil Rice
Chessington Surrey
(33 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

Re: rebuilt v8 wont start!!
Posted by: ricey
Date: December 30, 2017 02:29AM

Thanks Ivor Iím away for a few days once back Iíll check this and fit the new module and pick up plate I ordered and report back hopefully with a result cheers. Phil


ricey
Phil Rice
Chessington Surrey
(33 posts)

Registered:
07/05/2017 02:19AM

Main British Car:
Mgb gt 1975 3.9 rover

Re: rebuilt v8 wont start!!
Posted by: ricey
Date: July 29, 2018 06:04AM

Guys

A final update having stripped everything down twice checked the cam and the timing and the coil. I took heads off and found that front 6 cylinders were starved of fuel and it became clear as to why when I pulled out the pistons. The new rings and pretty much welded themselves to the groves and the ring gap had closed up which resulted in hire wash and the fuel disapppesrkmg into the dump hence the fuel vapour out of the breathers.

The doing all the work and replacing the rings resulted in the engine firing up.

In conclusion the general consensus was over the past 7 months I have had prob dodgy coil which caused intermittent spark, and lack of knowledge led me to concentrate on other aspects of why it wouldnít fire, resulted in constant cranking which heated up the rings and seized them onto the pistons.

This was only discovered once I threw in the towel and shipped it to Mount Garage in Tadworth Surrey who race and compete Mgb v8s, who after many hours found the problem. One benefit is having the engine stripped and rebuilt by a pro engine builder who clearly knew more than me!!!

Now itís getting the rest of it back together !

Thanks for all your input



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