Project 1974 MGB GT - The Mustard (Mit) Mobility Scooter - 6yrs ownership & the end is potentially nigh!

[SiC]

 

 

Also, I wonder why they even bothered to use the 25D casting on this particular distributor. Since neither the vac advance can or the micrometric screw are actually connected to anything, it seems like it would have been better to use a 45D casting.

 

I think they use the 25D casing to keep the engine bay looking original. The vacuum advance on this is connected to a sensor, so the electronics can emulate it. The screw is pretty much still there to hold in the (now) fake vacuum advance diaphragm.

[SiC]

I still think I'm going to use this though. It's got good reviews, so can't be all that bad. Might duck tape the tag onto the reader though.

[PhilA]

As much as you say it's lowly, that's about the spec of the ignition controller in my Renault.

 

It's not got to do much, a simple compare and adjust.

 

Did they state how fine the steps of ignition timing are? On mine it's steps of one degree, which seems to be adequate enough.

 

Phil

[1970mgb]

I think they use the 25D casing to keep the engine bay looking original. The vacuum advance on this is connected to a sensor, so the electronics can emulate it. The screw is pretty much still there to hold in the (now) fake vacuum advance diaphragm.

 

MGBs used both 25Ds and 45Ds depending on the year(as well as Lucas electronic distributors built around the 45D body). Honestly, when I look at an engine bay, seeing a big bundle of wires coming out the side of the distributor raises my eyebrows more so than seeing a 25D or 45D.

 

The 25D does indeed have the micro screw attached to the vacuum can-my point is that you don't need it at all with a 45D casting.

 

Not that it matters, since all the Lucas reproduction castings I've seen have been pretty poor...

[SiC]

As much as you say it's lowly, that's about the spec of the ignition controller in my Renault.

 

It's not got to do much, a simple compare and adjust.

 

Did they state how fine the steps of ignition timing are? On mine it's steps of one degree, which seems to be adequate enough.

 

Phil

It's the white line in this graph (number 9). Pretty much identical to what the stock dizzy does.

 

I don't mind it's a lowly PIC, in fact it's commendable they didn't use an over powered micro. Or even worse ... An ATMEL328 with code written using Arduino. *Shudders*

 

I just take issue with the dead-bugged components bodged on to provide the immobiliser functionality. They could have easily spun a new board to do that. Especially when asking for a good £170 price lift over a standard unit.

[SiC]

Y u not sold this yet and purchased a Dolomite?

 

Can you not reposition the coil so it is in normal place and not upside down?

I'll give it a go to see if I can swap the coil around. I guess it depends on the king lead and low tension connection wire lengths. It's something I keep meaning to try.

 

Still really want a Dolly Sprint. But if I sell this MGB, the money will end up being swallowed moving house. Then I won't have either a Dolly or a MGB!

[captain_70s]

I think most of these after market parts are aimed at giffers who can't be arsed setting the points to drive to the shops twice a year and have already spent £7k restoring the car anyway.

Even if they opened it up they'd have no clue what they were looking at anyway.

 

I'd like to put the Dolly back on a decent quality points set up at some point (ha) but I'll wait until the current unit dies...

[PhilA]

That's a fairly sane curve. I presume the vacuum does the same as the original for cruise?

 

Phil

[Rusty_Rocket]

None of this is necessary and that flakey circuitry won't last exposed to the vibration, heat and oil fumes from on A/B Series.

 

There's nothing wrong with points and condensers if you use decent (distributor doctor) parts and fit them correctly. You can also change them at the side of the road with a screwdriver!

[1970mgb]

36º total advance is a crap ton of advance for an MGB in any configuration. Most of the MG mechanics I know will say 32º all in(no vac) regardless of how the distributor is curved.

 

Looking at that advance curve, if you do set it to 32º maximum you're going to be at 6º at idle-a value which will make for a TERRIBLE idle. Granted the vacuum will pull you up some(if you replicate a Lucas 5-13-10 can in software and connect it to a manifold source, though, you will be idling at 26º which is way too high-best connect it to a ported source so you might get something more reasonable like 3-5º at the dizzy or 6-10º at the crank at idle).

 

Aside from 6º giving terrible idle, it's going to be an absolute DOG accelerating off the line-as in dangerous unless you rev the engine and pop the clutch slow. Bear in mind too that as you approach WOT, you're not getting any vac advance. When I time an MGB, I let idle advance fall where it may to get 32º max, but a typical value is anywhere from 12-20º. I can feel the off the line throttle response dropping if my car is below ~15º, and mine actually does idle around 17º.

 

In any case, my engine is not quite stock. It is higher than normal compression(9.5:1), but the head has also had some work to get rid of the ridges and hotspots that can induce both detonation and dieseling. With top tier 93 AKI gas(R+M/2) it still will ping and knock like crazy uphill if I run 36º total mechanical advance. I can get away with 34º(and an occasional ping) but that's pretty much a hard limit.

 

Also, bear in mind that if you're replicating at 5-13-10 can, or something similar to it, you're going to be near 60º cruising. Bump that up to 70º if it replicates a 5-15-15. That's US emission-choked advance specs, and the car will run like crap on it.

 

I'm surprised that Moss would even sell a distributor that-to my eyes-looks to be so poorly curved for an MGB.

[SiC]

36º total advance is a crap ton of advance for an MGB in any configuration. Most of the MG mechanics I know will say 32º all in(no vac) regardless of how the distributor is curved.

 

Looking at that advance curve, if you do set it to 32º maximum you're going to be at 6º at idle-a value which will make for a TERRIBLE idle. Granted the vacuum will pull you up some(if you replicate a Lucas 5-13-10 can in software and connect it to a manifold source, though, you will be idling at 26º which is way too high-best connect it to a ported source so you might get something more reasonable like 3-5º at the dizzy or 6-10º at the crank at idle).

 

In any case, my engine is not quite stock. It is higher than normal compression(9.5:1), but the head has also had some work to get rid of the ridges and hotspots that can induce both detonation and dieseling. With top tier 93 AKI gas(R+M/2) it still will ping and knock like crazy uphill if I run 36º total mechanical advance. I can get away with 34º(and an occasional ping) but that's pretty much a hard limit.

 

Also, bear in mind that if you're replicating at 5-13-10 can, or something similar to it, you're going to be near 60º cruising. Bump that up to 70º if it replicates a 5-15-15. That's US emission-choked advance specs, and the car will run like crap on it.

 

I'm surprised that Moss would even sell a distributor that-to my eyes-looks to be so poorly curved for an MGB.

I think those graphs include the static timing in there too. Rather than a centrifuge graph that you add the static onto.

 

This is the stock Lucas dizzy graph for my engine: (Static given as 6degrees)

Full tables: http://www.mgb-stuff.org.uk/41234l.htm

 

CSI graph for ease of reference:

 

According to the notes at the top of this page:

http://www.mgb-stuff.org.uk/curvestext.htm

 

Note 4: In theory the centrifugal figures show only the additional advance at the given rpm, whereas the strobe figure is the sum of the static and the centrifugal advance at the given rpm, and this can be seen to be true with some distributors e.g. the 40897 and 40916 for the 18G, GA, GB etc engines (4 degrees centrifugal @ 600 rpm plus 10 degrees static = 14 degrees strobe @ 600). However the 41693 seems to include the static figure in the centrifugal curve i.e. extrapolating the curve we get 10 degrees @ 1500 rpm which is the same as the strobe figure whereas it should be 7 degrees less. Then again, there is an 'advance check' figure quoted for this distributor of 19 degrees @ 2000 rpm, which is mid-way between the two, as are some of the other distributors in the list! All I can say is that I have used the figures given in my Haynes and Leyland Workshop Manuals as given, warts'n'all.

 

Unless I'm missing something reading the graphs (I'm still learning about this), they look close similar to me.

[plasticvandan]

It's a bit daft really,a set of new points on this mgb would last until the last barrel of oil is pumped out of the ground.

[1970mgb]

Yes, I was assuming that CSI was including the base timing-the numbers wouldn't make sense otherwise.

 

Stock 18V curves shouldn't be used as any kind of reference for what will give "good" performance, but the stock curve still has more advance at idle than the CSI, and any reasonable person working on it wouldn't let it get to 36º at full advance.

 

I'm commenting on this as someone who has spent a lot of time playing with timing on MGBs, both stock low compression(8.0), stock high compression(8.8:1), and the common "street performance compression" of 9.5:1. Specifically, I'm giving timing values that I know work and give good performance on these cars.

 

When dealing with anything 18V related when it comes to both induction and timing, duplicating "stock" isn't necessarily a smart thing to do.

 

It's also worth mentioning that the 40897 is something of the "gold standard" in the MGB world, and if I'm sending Jeff a distributor for a stock engine it's what I ask him for regardless of the casting number on the side. That's true whether it's going on an 18Gx engine(always HC in NA) or 18V(always LC in NA). If it's going on higher than stock compression, there's a good chance it either has or is going to get a performance camshaft(Delta D9 or APT VP-12, which are close enough in profile that it's not worth splitting hairs over)-in that case I ask Jeff for the "Dick Moritz Street Performance curve." I actually don't know what black magic goes into the latter, I just know that I'm following Dick's formula and he specifically told me to ask Jeff for that curve to match that engine.

 

As a side note, if possible always find a way to run ported advance, and use a 5-13-10 can.

[SiC]

Yes, I was assuming that CSI was including the base timing-the numbers wouldn't make sense otherwise.

 

Stock 18V curves shouldn't be used as any kind of reference for what will give "good" performance, but the stock curve still has more advance at idle than the CSI, and any reasonable person working on it wouldn't let it get to 36º at full advance.

 

I'm commenting on this as someone who has spent a lot of time playing with timing on MGBs, both stock low compression(8.0), stock high compression(8.8:1), and the common "street performance compression" of 9.5:1. Specifically, I'm giving timing values that I know work and give good performance on these cars.

 

When dealing with anything 18V related when it comes to both induction and timing, duplicating "stock" isn't necessarily a smart thing to do.

 

It's also worth mentioning that the 40897 is something of the "gold standard" in the MGB world, and if I'm sending Jeff a distributor for a stock engine it's what I ask him for regardless of the casting number on the side. That's true whether it's going on an 18Gx engine(always HC in NA) or 18V(always LC in NA). If it's going on higher than stock compression, there's a good chance it either has or is going to get a performance camshaft(Delta D9 or APT VP-12, which are close enough in profile that it's not worth splitting hairs over)-in that case I ask Jeff for the "Dick Moritz Street Performance curve." I actually don't know what black magic goes into the latter, I just know that I'm following Dick's formula and he specifically told me to ask Jeff for that curve to match that engine.

 

As a side note, if possible always find a way to run ported advance, and use a 5-13-10 can.

I totally respect your points - you're far more knowledgeable about these cars and engines than I'll ever likely be. I'm just trying to figure out what is the best settings to give this unit a go on based on what MG said at the time and you (and others) are saying.

 

These are the selectable ignition maps it offers:

 

So would you suggest I'd be better off using something like curve number 6 or 7 to start with? It's currently filled up with Super Unleaded @ 98RON - I think that's equivalent to your 93? I'll always be using Super and not Premium (95RON). Once I actually properly get using it again, I may fill up with some leaded 4-star I can get locally too and see how that goes. But for now it'll be 98RON.

 

One thing I can't find any reference to in the manual of this unit is how much vacuum advance it puts on. Nor how it does it. I guess I would expect it to not exceed the max advance given on those graphs?

[1970mgb]

6 or 7 would probably be my first choice-I was actually going to say 6 before I scrolled down and read that it's what you had used. I like the "step" at mid-range RPMs on 7, and I SUSPECT it would play nicely with the power band of the engine, but you might also have to use your butt dyno to tell you which works better.

 

Also, you can play with it and MAYBE use 11 or 12º with either of those curves as your base timing figure-just proceed cautiously and if you ping you can back it off. Setting base at 10º and maxing at 32º with curve 6 or 7 should make most any reasonably close to stock MGB run decently, though.

 

If I were playing with it, I might even be tempted to try curve 1 or 2 and go to 17º at idle, but that's me and not something I'd necessarily suggest others try. With that said, a lot of stock MGBs were surprisingly gentle, and it's not uncommon to find a weight rated anywhere from 7 to 12º inside a stock distributor. Curves 1-4 are the same as having a 7.5º weight in the distributor.

 

I would not use one of the curves that goes higher than 32º max advance-you can still change the base timing the conventional way with those(by turning the distributor), but IMO they're all too aggressive and would leave you with way too little advance at idle/off the line.

 

It would be really nice if they published the vacuum advance values, as that's kind of important to know too. It would also be nice to be able to change it. I've been tossing out numbers on the Lucas units, but they're really pretty easy to decipher when given as a series of 3 numbers. The first number is the amount of vacuum(in inches of mercury) at which the can will start to activate, the second number is the amount of vacuum(again, inches of mercury) at which the can is at max advance, and the third number is the amount of advance at the distributor that the can applies at its maximum(remember, we measure/care about crank advance, and distributor advance is half the value of crank advance). A typical reasonably healthy MGB engine will pull ~15" Hg at idle measured off the center of the manifold and around 20" Hg at a 55mph cruise in 4th gear.  When you're dealing with ported advance, which tends to be better behaved on engines the size of the one in the MGB, the vacuum at port is significantly lower than this at idle(probably around 5" Hg, although I've never actually hooked a gauge up to it) but starts to be roughly equal anywhere from partial throttle(SWAG would be 15%ish, but again haven't tested it) to WOT. Thus, with a 5-13-10 can on port, you're probably getting a couple of degrees at idle, full advance(20º at the crank) at steady cruise, and significantly less as load is added(with no vac advance-whether ported or manifold at WOT and decent load).

 

In any case, when looking at a conventional distributor advance curve, vac advance is over and above what the curve gives-which is strictly mechanical advance. Unless told otherwise, I'd assume that the given curves are strictly "mechanical" advance(or rather the electronics duplication of mechanical advance). It's still important to know, though. Of course, with the engine running it's not a big deal to map out the vac advance using a MightyVac and dialback light-I've done it plenty of times just to see if a can is actually behaving as it claims to.

[SiC]

Thanks. That is really, really useful info.

 

One quick question, is it normal or usual to expect that points may need adjusting after setting them up then had a run? I thought they'd be opening up a bit from wear and being pushed around, rather than them closing up after a run?

[PhilA]

Not tightened down right if they're opening up. Check the mounting plate for burrs or dirt.

 

Phil

[1970mgb]

It is normal for the gap to close up as the point wear.

 

Spend some time playing with them and you'll see why-the cam(center post) pushes on the rubbing block and pushes the outer contact of the points away from the inner contact as it passes each lobe. The points then close back again as rubbing block goes back on to the high point of the cam. As the rubbing block wears, the contacts don't get pushed as far apart. 

 

Typically, a new set of points will need to be regapped at about 200 miles and then again at about 1000 miles. After 1000 miles, the rubbing block should have established a nice wear pattern with the cam, and it will then hold that gap for another 10,000+ miles.

 

When I'm fitting new points, I usually set the gap a bit on the wide side-maybe 18 thousands or so. An MG with a 25D will usually start stumbling/misfiring when the gap closes up to 12 or 13 thou in my experience. You will also see high RPM misfires past 20 thou or so(if you were to put a dwell meter on it, you'd see that dwell is way out of spec and also as a direct consequence the coil isn't getting saturated). I don't set 15 thou until I've passed 1000 miles.

 

Also, if you don't know this, the screw that holds the points in place SHOULD have a #2 Posi-Drive head, not a Phillips head. I suggest using a proper Posi driver in this location to make sure you're actually getting the points tight and not mangling the screw heads.

[PhilA]

I misread. WHS ^

[Tickman]

OH YES. I hope the Minor looks stock, ideally with ropey ancient paint.

 

Soz for thread drift. Very interested in how the leccy dizzy goes...I wonder if they do one for a Vauxhall slant four 2300...

The minor is a 4 door with suitably shabby paint that gets to look shiny with the application of an oily rag.

[somewhatfoolish]

That dizzy pcb is a sack o' shite; y u no encapsulate/resin coat electrickery? No wonder things go pop when exposed to the hot and vibratory environment under the bonnet.

[SiC]

I'm not a fan of stuff being potted. Heat doesn't dissipate brilliantly through a lot of potting compound. Plus means you can't easily fix it. Surface mount components are less likely to fall off from vibration than through hole too. Except those bodged on components won't be done any favours. Conformance coating is essential though. I don't remember seeing or feeling any on it.

[1970mgb]

The Lucas Opus ignition, which was factory fitted '75-79 or so, was potted and had no end of problems-some of which I suspect were caused by it being potted. Basically, it would overheat and kill the car, only to allow it to restart ~5 minutes later. I've heard of folks fixing it by digging into the potting and working on a couple of the solder joints.

 

Fortunately, Lucas CEI, which the factory started fitting in late '79 or so and retrofitting to Opus cars that came in for service, was a superb system that is virtually bullet proof. The secret to its success is that it's actually the GM HEI system . In the US, if the board goes(which is rare, but does happen) you can walk into just about any auto parts store in the country and by one over the counter. A parts store branded one runs about $10, while an AC Delco branded one might set you back a whole $30...

[SiC]

It is normal for the gap to close up as the point wear.

 

Spend some time playing with them and you'll see why-the cam(center post) pushes on the rubbing block and pushes the outer contact of the points away from the inner contact as it passes each lobe. The points then close back again as rubbing block goes back on to the high point of the cam. As the rubbing block wears, the contacts don't get pushed as far apart.

 

Typically, a new set of points will need to be regapped at about 200 miles and then again at about 1000 miles. After 1000 miles, the rubbing block should have established a nice wear pattern with the cam, and it will then hold that gap for another 10,000+ miles.

 

When I'm fitting new points, I usually set the gap a bit on the wide side-maybe 18 thousands or so. An MG with a 25D will usually start stumbling/misfiring when the gap closes up to 12 or 13 thou in my experience. You will also see high RPM misfires past 20 thou or so(if you were to put a dwell meter on it, you'd see that dwell is way out of spec and also as a direct consequence the coil isn't getting saturated). I don't set 15 thou until I've passed 1000 miles.

 

Also, if you don't know this, the screw that holds the points in place SHOULD have a #2 Posi-Drive head, not a Phillips head. I suggest using a proper Posi driver in this location to make sure you're actually getting the points tight and not mangling the screw heads.

I had 20 minutes this evening to nip up to the garage and check the gap. 15 thou pushed the contacts apart, 12 thou was tight and 10 thou slipped in and out pretty easily. So almost certainly, like you've said, the gap that has caused the rough running. Didn't start the engine up as I didn't have time for a drive and didn't want to start, run then shutdown shortly after. But I'll try and make some time soon to give it a run out.

[SiC]

One thing I don't get. What you said about wear makes complete sense and it's what I've seen. However when reading up about setting points, I've never seen it mentioned anywhere that you'll need to reset them after a number of miles.

 

Is it so well known that books just assume you know that you need to reset them? Obvious when I know, but not being told means that it's not something I ever thought about. Especially as I've not grown up with points.

 

What happened when you got your car serviced at a garage? Would someone go back to have them reset, or would you just be expected to do it yourself?

[SiC]

In other news, as its payday today, I might get it booked in for an MOT shortly. Seeing it after not for a good months or two has reminded me how much better condition it is than my 1100. In fact it's in bloody good condition really. No show winner but certainly wouldn't embarse herself.

[Guest Hooli]

One thing I don't get. What you said about wear makes complete sense and it's what I've seen. However when reading up about setting points, I've never seen it mentioned anywhere that you'll need to reset them after a number of miles.

 

Is it so well known that books just assume you know that you need to reset them? Obvious when I know, but not being told means that it's not something I ever thought about. Especially as I've not grown up with points.

 

What happened when you got your car serviced at a garage? Would someone go back to have them reset, or would you just be expected to do it yourself?

 

Points were better made then. I've noticed over the years that the heel of the cam that runs on the dizzy shaft seems to wear in a lot more these days than it ever used to.

[SiC]

The points currently in there appear to be plastic rather than fibre/bakelight/whatever they used to use based. Couldn't find any 45D points that weren't.

[busmansholiday]

Spot of grease on the cam and oil on the shaft were the old trick. Back then, servicing was every few thousand miles, not when some light came on the dash and it chucked it's self into limp mode.

Back then also, most people knew how to check a set of points.

 

Technology, how it's fucked up people's lives......

[coalnotdole]

What happened when you got your car serviced at a garage? Would someone go back to have them reset, or would you just be expected to do it yourself?

 

 

A good quality set of points would have lasted without adjustment between service intervals and would be checked and adjusted as part of the rounine servicing. Service intervals were very short though... 3000 miles was common on many 60's and 70's cars. Which is probably why many owners chose to do the job themselves.

 

I ran my Scimitar for years on a motorcraft set of points and condensor and never had a roadside FTP due to points or condensor problem. I only stopped using them when the supply of new old stock parts became an issue. I subsequently ran it on lumentition electronic igniton which was fault free and still alows you to time the engine statically.

 

Will be interested to see how you get on with the all electric CSI!

 

Joe