Ignition Advance Revisited.

CastleMGBV8 · Post by **CastleMGBV8** » Thu Oct 09, 2008 4:25 pm

Pete (Sidecar)

You may recall we had a lengthy discussion re setting up a 35DLM8 and I have only just got round to stripping the dizzy to check it over and recurve as necessary for the new engine which is 4.350l so should only need approx 32 degrees of total advance.

The dizzy is from a 93 Range Rover 3.9 so should have mechanical advance to suit a larger engine.

I think I may have made a bit of a mistake in that to gain access to the advance mechanism I attempted to remove the star wheel by removing the circlip but the star wheel was reluctant to come all the way off and didn't want to force it.

There now is a now almost a full point of the star wheel of free play in relation to the gear at the bottom of the dizzy.

Should I just remove the gear at the bottom, and if so what is the best methods of removing the pins that locate the gear and the part below it.

Presumably I will then be able to extract the whole shaft and see what I have cocked up

The new engine will be in the car next week so need to get it sorted.

Kevin.

sidecar · Post by **sidecar** » Thu Oct 09, 2008 6:02 pm

Hi Kevin,

You've not cocked up, removing the circlip is the right way to go. Then remove the washer and the rubber O ring. The star wheel can sick a bit, it could be a bit rusty. Be really careful, my mates star wheel fell to pieces when we gave is just a small amount of stick! (One of the stars points fell off, I had to build it up with weld and file it back into shape as a temporary bodge...not easy!)

All that play will be due to stretched springs.

Or it will be because the advance retard mechanism has fallen apart. This can happen it the little plastic clip at the top of the shaft that lives under the rotor arm has bust.

You don't need to remove the gear at the other end of the shaft unless you want to get the shaft out of the dizzy. If you want to do this then support the dizzy and gear on soft wood then knock out the roll pin with a drift. You MUST put the gear back on the same way that it came off otherwise its likely that you will crack it when you tap the pin back in.

I've done some more work on my dizzy recently, my 4.6 is running better now than it ever has. I also did the mods to a 3.5 and that runs better to.

Basically, I'm now running 12 degrees static 32 all in (but I might back this off a bit when I get the thing on a RR)

The main changes are that I now run one silver spring and one copper coloured spring. (Real Steel spring kit). The mechanical advance is all in at round 3K, maybe a shade less. I also don't run the vac advance at all.

This has made the pickup much smoother. I still get good BHP and MPG because the mechanical is kicking in sooner.

I bet running no vac will create a big "bun fight" on the forum!

My mates 3.5 runs the same setup but 14 static, 36 all in.

Also I've helped a chap out with a 3.9 and a twin points (spit) mallory system. The vac was kicking in about 45 degrees total advance and nearly causing the engine to spin in the opposite direction!
Anyway his mechanical was all in at 2800, he now runs 14 static 34 total and no vac and is very happy with the setup. (he's converting it to electronic soon). I've heard that the mallory vac is adjustable so he might be able to restrict it if he wants to connect it back up.

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Thu Oct 09, 2008 6:35 pm

Pete,

Thanks, thats very helpful, pleased your getting good results on your 4.6 just hope mine goes as well.

Also taken note of your spring change and will give it a try as my engine is only 200cc smaller than a 4.6 (4554cc) but 77mm. stroke which may be relevent.

Kevin.

sidecar · Post by **sidecar** » Thu Oct 09, 2008 8:00 pm

CastleMGBV8 wrote:Pete,

Thanks, thats very helpful, pleased your getting good results on your 4.6 just hope mine goes as well.

Also taken note of your spring change and will give it a try as my engine is only 200cc smaller than a 4.6 (4554cc) but 77mm. stroke which may be relevent.

Kevin.

Hi Kev,

I can't see you engine needing settings that are much different from mine.

Beaware that I don't think the motor will tolerate the mechanical advance comming in too hard if you leave the vac connected. Two silver springs was pretty marginal.

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Thu Oct 09, 2008 11:13 pm

Pete,

Glad I stripped it down, found both springs unattached and a burr on the bottom plate that was preventing vitually any advance at all.

There isn't any wear in the spindle/ bush so just a matter of cleaning, lubricating and putting it together properly with new springs as suggested.

Found the plastic cog that fits uder the trigger wheel and thats ok and fits into the wheel properly,

There is another plastic cog which dropped out when Pulled the plate above the mechanical advance out and not sure how that goes back.

Should there be a figure stamped somewhere that indicates the max mechanical advance.

Also do you know what the max advance of the vac unit is or where this can be found out.

I have been advised that the standard unit has too much advance and that it is wise to restrict it to about 5-7 degrees. I don't know if this is possible or whether there are alternative units with less advance available.

I would like to retain vacuum advance if possible to maximise economy, with my gearing my cruise RPM at just over 70 mph is 2500RPM so below max mechanical advance RPM.

Kevin.

sidecar · Post by **sidecar** » Fri Oct 10, 2008 6:59 am

CastleMGBV8 wrote:Pete,

Glad I stripped it down, found both springs unattached and a burr on the bottom plate that was preventing vitually any advance at all.

There isn't any wear in the spindle/ bush so just a matter of cleaning, lubricating and putting it together properly with new springs as suggested.

Found the plastic cog that fits uder the trigger wheel and thats ok and fits into the wheel properly,

There is another plastic cog which dropped out when Pulled the plate above the mechanical advance out and not sure how that goes back.

Should there be a figure stamped somewhere that indicates the max mechanical advance.

Also do you know what the max advance of the vac unit is or where this can be found out.

I have been advised that the standard unit has too much advance and that it is wise to restrict it to about 5-7 degrees. I don't know if this is possible or whether there are alternative units with less advance available.

I would like to retain vacuum advance if possible to maximise economy, with my gearing my cruise RPM at just over 70 mph is 2500RPM so below max mechanical advance RPM.

Kevin.

Hi Kevin,

I guess you got the star wheel off then!

Not sure what the other plastic cog is, can you post a picture up?

My vac was adding about 18 degrees I think but I'm not too sure. Nothing was stamped on it to indicate that. (I measured it and wrote it down some where!) It might have had an 8 stamped on it, i.e half of the total that it adds

At one point I modified my base plate to restrict the vac but this might not have been doing the diaphram inside the canister much good.

Some of the mechanical units have a figure stamped on one of the lugs that hit the stopper pegs. (The pegs that the springs hook onto). This is the total mechanical advance although I would not believe it, I'd measure it on the engine.

At 2500 most of the mechanical advance would be in so the MPG should not be too bad. The problem with the vac is that it kicks in too hard and too fast just as you start to open the throttle at any revs so if the mechanical is all in as well it's just too much in total.

I even made a lump of ali that had a the restrict how quickly the vacuum get to the canister, it only had a pin hole sized hole in it. The vac still came in too quick. The other problem with this is that if you can make the hole small enough the vac would not turn off very quickly which could cause issues.

You need to decide what you want to do with the vac before you fit the springs, like I said soft springs and a vac system is no good.

Anyway keep us posted!

Pete

sidecar · Post by **sidecar** » Fri Oct 10, 2008 9:07 am

Hi Kev,

Just a thought, if you can actually get to the bob weights and remove them from the shafts that they run on then this means that the plastic clip that sits just underneath the rotor arm has bust. Normally you can not remove the bob weights. If this is the case the plastic thing that you are not sure of fits between the lower plate in the dizzy and the upper plate that has the rotor arm shaft. It's an odd piece of plastic, you'll just have to try to fit it and then test the advance retard by hand. The plastic thing under the rotor arm is not mega important but not having it does mean that the mechanism is likely to fall to pieces if you ever try pulling the rotor arm off. Also the dizzy springs could get stretched at the same time.

I actually broke mine on purpose so that I could work on the mechanism, my mates was already broken. To hold the whole thing together I first made the slot in the upper shaft about 4mm longer with a dremel. (The slot that the rotor arm engages into). This allows you some room to work. I then fitted a couple of close fitting washers over the very thin "nippley" bit of the shaft at the very top. (under where the rotor arm sits) I then used some lock wire that went into the groove that was ment for the now broken plastic clip. Make the washers the right thickness so the that there is a fraction of a mm of vertical play.

(I have some lockwire pliers which helps alot, and make the lock wire do two revolutions round the shaft, not just one before you start to twist it)

pete

CastleMGBV8 · Post by **CastleMGBV8** » Fri Oct 10, 2008 12:32 pm

Pete,

Just had another look at the dizzy, the second plastic cog fits underneath
the plate which the springs are attached to and can only seat one way so will be a bit of a sod to get to fit, as will be the one that fits between the star wheel and the top of the plate to lock it in the correct position.

I am just about to order some bits from real steel so will order the spring kit as well.

I note what you say re the vacuum advance being excessive and will probably run with it disconnected but attached, otherwise the plate could rotate and vary the timing.

Kevin.

sidecar · Post by **sidecar** » Fri Oct 10, 2008 3:21 pm

CastleMGBV8 wrote:Pete,

Just had another look at the dizzy, the second plastic cog fits underneath
the plate which the springs are attached to and can only seat one way so will be a bit of a sod to get to fit, as will be the one that fits between the star wheel and the top of the plate to lock it in the correct position.

I am just about to order some bits from real steel so will order the spring kit as well.

I note what you say re the vacuum advance being excessive and will probably run with it disconnected but attached, otherwise the plate could rotate and vary the timing.

Kevin.

Kev,

Nothing was a "sod to fit" on my dizzy, something odd is going on here, can you post a piccy.

It all was a "piece of piddle" on my dizzy!

Pete

tetlow · Post by **tetlow** » Fri Oct 10, 2008 5:08 pm

Set up my 3.5 with Perry. We found that we did not need the vacuum. ( I was getting 50+ advance with the vacuum connected) and spot on with just the machanical)

Perry had the same on a previous 3.5 of his!!

Dave

CastleMGBV8 · Post by **CastleMGBV8** » Fri Oct 10, 2008 5:39 pm

Pete,

I was probably being a bit over the top regarding the reassembly, I had some really bad news re my immediate family a couple of weeks ago and everything just seems more difficult.

I'll just have to take it easy and not force anything and I'm sure it will work out fine.

If I have any problems rest assured I'll be back asking questions

Kevin

CastleMGBV8 · Post by **CastleMGBV8** » Fri Oct 10, 2008 5:42 pm

tetlow wrote:Set up my 3.5 with Perry. We found that we did not need the vacuum. ( I was getting 50+ advance with the vacuum connected) and spot on with just the machanical)

Perry had the same on a previous 3.5 of his!!

Dave

Thanks dave, nothing like a bit of confirmation.

I never got to ask you how you liked the new rear springs, you certainly had a few miles to check them out.

Kevin

tetlow · Post by **tetlow** » Fri Oct 10, 2008 7:29 pm

Rear springs are great thanks Kevin.

They settled to the horizontal position and the top of the wheel is now hidden.

It might be a coincidence but the tyre rubbing seems to have improved so they must have better latteral stiffness too.

The only problem we had was that I was told to change the drop links to the Rubber bumper version. Every time we hit a bump the links hit the floor of the boot before the axle hit the shortened rebound rubbers!!

I have fitted the shorter CB ones now so should be sorted.

Dave

CastleMGBV8 · Post by **CastleMGBV8** » Fri Oct 10, 2008 9:17 pm

Dave,

I agree about the lateral stiffness they seem to make a panhard rod totally unecesary, I'm running 195/65 x 15 with very liitle clearance but with the inner lips removed and I have no rubbing problems.

What I particularly like is the compliance and the improvement in handling and grip.

Kevin.

sidecar · Post by **sidecar** » Fri Oct 10, 2008 9:50 pm

CastleMGBV8 wrote:Pete,

I was probably being a bit over the top regarding the reassembly, I had some really bad news re my immediate family a couple of weeks ago and everything just seems more difficult.

I'll just have to take it easy and not force anything and I'm sure it will work out fine.

If I have any problems rest assured I'll be back asking questions

Kevin

Hi Kev,

Take it easy, I hope everyting works out on all fronts.

Pete.