Melt down

Anonymous · Post by **Anonymous** » Mon Jul 28, 08 9:47 pm

Some may of heard or seen the damage done to the Pit when the nitrous/fuel charge backfired & blew me carb to bits setting light to the bonnet & bulkhead.

Been scratchin me head thinkin how this could of happened , came to the conclusion it had to of happened due to crossfire , may it be bad/touching leads or rotor phasing , as the spark must of occured with the inlet valve still open.

Anyhow , drilled a hole between towers 6 & 5 on the MSD rotor cap (gotta get a new one now

) , set the timing light to 35* advance , bought the rpm up to 3000 (total) , then shone the light @ 6 & 5 towers , could'nt believe it when i saw the rotor arm fireing off smack between the two towers , set the light to 0* then saw the rotor arm just off the tower but still towards the centre of the two , can't believe MSD when they say all their dizzys are phased , it's Bananarama! , they should @ least phase em for some degree of advance , as no motor runs below 25* total.

I would say the motor crossfired to the next cylinder due to the phasing being incorrect , bearing in mind the huge cylinder pressures created with the nitrous/fuel charge , the spark jumped forward to the next terminal & fired off the cylinder when the valve was just closing (easiest path) , causing the backfire.

I don't believe ANY dizzy is rotor phased , may it be Mopar , MSD.............that's two manufacturers i've had to sort out , was suffering a 3000 rpm misfire on me ols mopar dizzy.

Now phased correctly , might even pull cleanly above 5500 RPM.

Bananarama!.

Rant over.

Pulled the plugs on this run , they looked real good , this was what i've been looking for all weekend , @ least the tune up was good.

Dave-R · Post by **Dave-R** » Mon Jul 28, 08 9:55 pm

Didn't know that happened Adam. Glad the damage was minimal.

Do us a step by step on the phasing thing when you get a chance eh? probably something we should all be checking.

Anonymous · Post by **Anonymous** » Mon Jul 28, 08 10:05 pm

Dave , should of run with the air filter on & minimised the damage, hindsight is a great thing , but the air filter is tight on the underside of bonnet.

Should of followed Nicks advise about the air filter (surrey muscle)

Pete · Post by **Pete** » Tue Jul 29, 08 10:38 am

Good threads, this.
I understand phasing, but I am not sure how to correct it as I thought it was depenant on the keyway in the chopper.

Can you adjust phasing on a standard Dizzy? Got a Billet MSD for the Hemi, but I would like to check Julie's motor as well. Do the top plates move at all sufficiently to permit a slight adjustment of the rotor to cap alignment.

Any info would be most welcome, thanks, as I obvioulsy want to check the MSD as well.

Adam is on an intel mission again

Pete

Anonymous · Post by **Anonymous** » Tue Jul 29, 08 11:06 am

Move the reluctor round the shaft for good ole mother Mopar dizzys , or move the pickup on the MSDs , better still install an MSD 'adapt & cap' , which places the towers further appart.

Pete · Post by **Pete** » Tue Jul 29, 08 11:29 am

You mean re-drill the slot for the roll pin? ~I can see me screwing that up

Got any pics? Before and after would be nice

Dave999 · Post by **Dave999** » Tue Jul 29, 08 3:19 pm

I can see the need for a crank trigger here?

1/8 of a degree accuracy even when fangled together with bits you found down the dump

megajolt Lite
snice
switch maps when you switch on the gas

all thats missing is the welder like spark of capacitive discharge.

Dave

Dave999 · Post by **Dave999** » Tue Jul 29, 08 3:46 pm

Under the hood

comes with nice software to fiddle with

Have a read

http://www.autosportlabs.net/Main_Page# ... s_Projects

Dave

GTXJim · Post by **GTXJim** » Tue Jul 29, 08 4:55 pm

Could you please explain phasing for me had a problem with my MSD dizzy had a wet plug on No 8 was checking a few thing and notice the dizzy was wobbing all over the place seems to have a bent shaft

as it seem alright before don't know how this could have happened so we just packed it out a bit, with some O rings seemed to calm the wobble down.But not 100% about phasing

Dave999 · Post by **Dave999** » Tue Jul 29, 08 6:00 pm

dissy should be set up to fire a spark at 1 contact in its cap and it should be the one connected to the lead for the plug that needs to fire

if it fires em off excatly inbetween then a multitude of variables dictate which contact the spark goes to and which lead/plug actually sparks.

issue gets worse the faster you go
issue gets worse if running a coil of double power with a standard size cap (check out a standard mopar cap against a stadard chevy HEI cap
issue gets worse if the air in the cap ionises (vent the cap)

issue is caused by position of towers on the cap in relation to the position of the spiky collar or trigger wheel/chopper on the shaft that triggers the ignition

spark is unleashed at the point where a spike passes the reluctor pickup

the reluctor pickup is on a movable platform that advances round the shaft of the dissy as the centrifugal advance comes in . it goes even further when the vaccumn advance comes in

now in relation to degrees of advance at the flywheel the distance moved is small. but if your dissy was made on a friday afternoon after a nice burger n beer then the bloke who made it may not have got everything spot on

i.e the drive cog on the shaft and its mesh with the drive
the position of the spiky collar on the shaft
the position of the pickup
and variances in cap
can all conspire against you to give a dissy that is right at one end of the tollerances considered good enough for a daily driver

good enough for a daily is probably considerd well-poor for a race engine

a process of correction and checking can be gone through

basically you can't alter the position of the cap on the dissy body to make sure that when a spark is triggered and the advance is at any point in its range of movement that the rotor is pointing closer to 1 contact than any other.

unless you change something else to take into account the fact that the cap needs to be x degrees clockwise or anti.

think adam might post back his findings

Dave

Philth · Post by **Philth** » Tue Jul 29, 08 7:06 pm

Let's see some pictures, Adam please please please!

Dave-R · Post by **Dave-R** » Tue Jul 29, 08 7:09 pm

Better still. If we pass the drilled dizzy cap around it would save everyone having to destroy a cap and replace.

Anonymous · Post by **Anonymous** » Tue Jul 29, 08 10:36 pm

Got no pics of the rotor cap , drill a 20 mm hole between two towers that will be easy to see when distributer cap is refitted to dizzy , crank engine until rotor arm is JUST coming round to the first tower you can see through the hole you just drilled , remove cap & slowly crank engine until reluctor lines up with pickup , refit cap to see if rotor arm is inline with the tower on cap , job done.

When the mechanical curve advances , the rotor arm will move with the reluctor , so if the phasing is spot on , the mechanical advance will be spot on too.

I moved the reluctor around on the mopar dizzy , on the MSD i redrilled the pickup as i'm not sure the adapt a cap will fit without hitting the valve cover , unless they come with a raised spacer of some sort.

Decided to change the vertor as i had to pull the engine to clean/spray the bulkhead , also gives me some space to replace/tape the burnt/scortched wireing on the bulkhead.

latil · Post by **latil** » Tue Jul 29, 08 11:01 pm

Bloody nightmare,still it could have been worse

Didn't cook those new bowl gaskets did you?