The next Manta project

Jo and I have been trying to work out what to do with the next Manta project.

The original plan with the Mantas over here was to turn the orange car into a narrow body 400 replica (silver, of course) and the new bodyshell into a LHD Starmist Black Exclusive, but without a rear spoiler. This worked well for us, since we both like both of those styles and it gives us something a little more modern (1989-style instead of 1979) to drive on a daily basis.

The revised plan came about because of Louis. Rather than have so many cars, we would cut the orange Manta shell into spare parts and build the bodyshell into a Manta, giving us one Manta over here rather than two. Nice idea, but what should we make now? Will it be the 400 replica or the Exclusive or something entirely different? And what colour?

So there's the problem... What do we make? Here are the candidates so far:

1) A clone of my silver Manta in the UK. I love the look (not surprisingly) and Jo loves it too. For both of us it's probably our favourite look. We have a nice 400 interior here, with new door panels and other bits, so rather than the blue interior we have in the UK car we'd use the 400 interior.

2) A Starmist Black Exclusive without rear spoiler. Yup, one possibility from our original list. We know we like the colour and the look of the car, but I think I'm getting a little "greyed out" and again, we'd probably end up using the 400 interior since it's so nice. The only problem here is that it's a black car with a dark interior. I'd need to find some way of turbocharging the A/C for use in California!

3) An Exclusive, possibly in a different colour. Jo suggested this one and the colour she thought of was a darker metallic grey, more blue-ish than yellow, much like the BMW in this picture. Interior colour TBD. Not bad, and at least it's not straight silver or black (it's a bit inbetween...). I'm just not sure I can handle a car that isn't black or silver. Of course, the other possibility is an Exclusive in the same colour as my silver Manta, maybe the best of both worlds.

4) A silver narrow body 400 (don't have a pic so the white one will have to do...). The other possibility from our original list and the one I'm happy to dismiss. Everyone and his brother has done a 400 clone (even spawning the "400R" fake model type) and I really don't want to do one unless I can make a totally convincing clone, complete with 400 engine, correct rear axle and 5-stud hubs. Just looking at what's involved to do that "properly" is putting me off and I think I'll just enjoy everyone else's copies rather than making another one myself.

So there we go. Other things we've decided:
- Neither of us particularly likes chrome bumpers, so we're not likely to start looking for them
- No 400 spoiler
- No matt black bonnet (Andy)
- No orange

Other than that, we're still thinking about it. Not sure on the engine either - I've got an XE here that I could use and of course it has a 2.4 at the moment. I'm not going to put a 6-cylinder in it as it would never pass smog (even the most stupid testers can count to 6), even though that would probably be ideal for the type of car we want.

Ideas / votes on email to the usual address... :-)

Quick, the Manta's on fire!

Five words you never want to hear (well, if you're a Manta owner, that is)...

Jo yelled this as she got home last night and I was straight downstairs with a fire extinguisher in my hand. I got to the car, expecting flames but I didn't see anything. Initially Jo pointed to the vents and said she'd seen and smelled smoke, so I thought it must be either the A/C blower resistor or the fan that was overheating, but lifting the bonnet it looked fine. The only minor issue was the blower motor cooling hose had come off (must use a tie wrap to hold it on) and the fan was warm but nothing really out of the ordinary.

I turned the heater blower up full and sniffed the vent and couldn't smell anything so I was reasonably satisfied that all was OK.

No, says Jo, it seemed to be coming from the heater CONTROL, not the vents. Well, all seemed OK now so I told her to park it near the house as normal and I'd pull the lower part of the dash and the instrument cover off and have a look.

Off came the lower part of the dash underneath the instruments. If there was any wiring problem then it was likely to be there as that's where the bulk of the wiring terminates (that's where the fuse box is), but again everything looked OK.

The instrument cover came off fairly easily (I've done it loads of times in the 30 years I've had a Manta...) and nothing looked out of the ordinary either. One thing I did notice was that, there seemed to be a slight melted area around the lighting switch. I pulled the lighting switch out for a better look and it really did look like there was a problem. In fact, you could smell a little of the burning smell on the back of the switch, so it might be the culprit.

I reconnected the switch and noticed that as the sidelights went on the engine note changed, suggesting a large current draw. Hmmm, that should only be a few amps, certainly not enough to drop the engine speed by a large amount. Turning round to the headlamps was more surprising - the headlamps didn't come on. That was really weird, because Jo had arrived home with the headlamps on so the switch worked a few minutes ago.

I went and got a spare headlamp switch and tried it in the car, and the headlamps worked OK, so the switch had burnt out. But that wasn't the problem because I could smell the burning smell again...

At this point I finally worked out where the smell was coming from - the fusebox around the number 1 fuse was looking slightly melted! A quick finger on the fuse (and a burnt finger) and I knew I hadn't fixed the issue yet. I pulled the (hot) fuse and realized why it was hot - it was 25A rather than the 5A it should be...

The number 1 fuse on a Manta is part of the sidelamps circuit, and also powers the dash lights and the horn. This could be a big issue to diagnose as the wires for this go all over the car. At least the wires going from the fuse weren't melted (testament to over-engineering).

So first things first, let's work out what's affected by the number 1 fuse. I put the number 2 fuse back in the box and turned on the sidelights. The dash lights stayed off but the left front and rear sidelamps came on. So the number 1 fuse had to operate the right side sidelamps and the dash lights. That at least cut the culprits down to just a few possibles.

I decided to start at the back. Jo uses the right side of the boot a lot for her rucksack and gym bag, so if she'd disturbed one of the rear lamps we might have an issue back there. I looked in the boot on the right hand side and almost immediately found the culprit - the sidemarkers.

In the US you need to have sidelamps visible from the side of the car and, since the Manta didn't have them as standard, they were (badly) put on by the person who originally brought the car into the country. To wire them up they used scotchloks to connect to the main wiring harness and then just ran a pair of wires over to the sidemarker lamps. of course, in an unlined boot like the Manta's, those wires can easily be pulled from the sidemarker lamp unit and just end up dangling in the boot.

In a fit of uncharacteristic tidiness, Jo had obviously pushed them behind a piece of insulation and that had been fine, right up to the point where the live wire touched a rusty spot. The rust had conducted just enough electricity to avoid the fuse blowing, allowing the circuit to overload and overheat with the large current it was drawing. The 25A fuse had meant the circuit didn't blow as it should have done.

Jo had stopped at the drug store on the way home and had luckily only had the headlamps (and therefore sidelights) on for a mile or so, otherwise it may have been a lot worse than it was...

So everything's OK now. I checked each fuse and put in the correct one (most were wrong) and I've also reconnected the sidemarker lamp wires. I must make a better solution for the wiring for the sidemarkers when I have time, but at least Jo knows what can happen if the wires hit bare metal!

...and nothing to show for it

It's funny how things go when you're working on a car. I spent a full day on the Monza yesterday (Saturday was magazine day) and I've got very little visible progress to show for it. It was a lot of little things that needed doing, but I guess that's how it goes sometimes.

In the end I got this lot done:

• Reconnected the propshaft and crossmember link (the crossmember that is just behind the front seats with a connector that bridges across the transmission tunnel)

• Torqued up the bolts for the transmission, connected the speedo cable and reversing lamps

• Fitted the shifter gaiters

• Connected the heater hoses at the firewall and block, dum-dum'ed them up.

• Cleaned off the alternator and engine earth straps (boy were they dirty), clearcoated and then fitted them.

• Torqued up the alternator brackets, fitted the alternator.

• Cleaned up the wiring behind the front panel, refitted the grille

• Fitted new filler strips below the headlamps

• Connected up the headlamp washer jets

• Rebuilt the front bumper and refitted it (mostly - need to pull off the right side arch liner to be able to fit one of the sliders)

• Adjusted the clutch so it actually disengages when you put your foot to the floor

• Fitted the starter motor, cleaned the starter cable

• Fitted the crank sensor for the Motronic

That's about it. The only real visible difference is that the front of the car looks complete now. I got the bumper cover back last week from the bodyshop and noticed when I got it home that they had not painted it as they said they would, so the whole lot's got to come off again when it goes back for its final touch up.

I seem to have lost practially all the bumper fixings (God knows where they went) so I've got to order some more before I can truly finish the bumper off. The fog lamps are the only real problem - they are missing 3 fixing screws so I woudn't want to drive it like this (some hope).

I was hoping to get all the wiring connected up at the starter this weekend (I'm using the starter M8 bolt as a wiring junction for red (constant +ve) wires), but I found I had practically no M8 ring terminals, so I've had to order a bunch from the UK today and that's going to take a week or so to get here. Another delay.

Speaking volumes

We’ve all heard of CC’ing an engine to get the compression ratio exactly right, but how many of us have done it? I’m just going through it myself for the first time.

First of all, why? It’s a fairly slow and not inexpensive process, so why bother? In my case I had two goals:

• I have to pass California emissions (smog) and it’s not easy with a European car that was never designed for sale here. The big problem I have is oxides of Nitrogen (NOx) and that’s caused by the temperature of combustion inside the engine. Within reason, the higher the compression ratio, the higher the combustion temperatures you’re going to see (more squeezing of the air and fuel generates more heat…) so I need to keep the CR under control. The standard engine is 9.4:1 and I want to keep around that figure so that I have a chance of passing the emissions test.
  
• I want a nice smooth engine. All straight-6 engines inherently run smoothly as they are well balanced by design, but having a big stroke engine (going up from 69.8mm to 85mm) will work against that and I might end up with a shaker, which will be a real disappointment. I’ve been very careful to balance all the engine components as close as I can (within 0.4g), but the other big factor is the sizing of the combustion chamber. If the chambers are all of varying sizes I’m going to get varying amounts of charge in them and that will create uneven running. Equalling out the chambers will give me a nice smooth engine.

So what do you need to do? First things first, you need to measure some volumes. The two that can’t be calculated are the size of the combustion chamber in the head (it’s a very uneven shape so there’s no hope of an accurate calculation without just measuring it), and likewise you need to measure the volume of the piston crown – typically you have valve reliefs cut into the piston and it may be dished too. Dan Amaral, the very skilled chap who does the machining work on the engines for me, measured these volumes while working on the bottom end as he has a burette and I don’t!

The volumes I got were these:

Head volume: 51.00cc

Piston crown volume: 12.50cc

Now for an accurate number (why calculate if it’s not accurate?) we need to think about the other spaces in the combustion chamber that will affect the volume. Here are the ones we used:

Gasket volume – The volume of the compressed head gasket

Top ring volume – Pistons aren’t the same size as the bore, so there’s a gap around the edge of the piston, between the top ring and the top of the piston that you need to take into account

Deck height volume – The distance from the top of the piston to the top of the block. In some cases (like mine) the piston may actually protrude out of the top of the block and so the deck height volume will be a negative number as it actually reduces the size of the combustion chamber.

Swept volume – This is the big one. It’s the volume that the piston actually sweeps and is the volume that’s usually quoted for the engine.

First some measured numbers that we’ll use to calculate the volumes:

Bore: 95.00mm

Stroke: 85.00mm

Gasket compressed size: 0.75mm (an average of the numbers I’d read about for this)

Gasket diameter: 97.00mm (measure the gasket and you’ll be surprised!)

Piston crown diameter: 94.20mm

Piston crown to top ring depth: 6.00mm

Deck height: 0.05mm above block

And now the maths (ever wonder what maths was useful for?).

First the basic one: volume of cylinder

       Volume = PI x radius squared x height

So for the swept volume that’s:

       PI x 4.75 x 4.75 x 8.50 = 602.50cc

(notice I converted the mm measurements into cm because we wanted the answer in cubic centimetres, not cubic millimeters)

The other volumes are all calculated the same. The only interesting one is the top ring volume as that’s the difference between two volumes. The actual space we’re interested is the cylinder volume between the top ring and the top of the block MINUS the volume of the piston in that area.

Here are my calculated volumes:

Volume of top ring area: 42.53cc

Volume of piston in top ring area: 41.82cc

Top ring volume = 42.53 – 41.82 = 0.71cc

Gasket volume = 5.54cc

Deck height volume = -0.35cc (negative because the piston is above the top of the block)

So now we can calculate the volume of the effective combustion chamber:

Combustion chamber volume = Piston crown volume 12.50cc

+ Top ring volume 0.71cc

+ Head volume 51.00cc

+ Gasket volume 5.54cc

- Deck volume -0.35cc

             = 69.40cc

Now for the compression ratios. Compression ratio is the ratio between the volumes with the piston at the top of the bore and the bottom of the bore (the difference in volume being the swept volume, right?). So, if we use ccv for “combustion chamber volume” and sv for “swept volume”, it’s:

       (ccv + sv) / ccv

or

      (69.40 + 602.50) / 69.40 = 9.68 : 1

If I didn’t have emissions issues I’d be happy with that. I’d need to run on a fairly high octane fuel but it’d give me good power. Unfortunately, I’m looking for 9.4:1 (the standard compression ratio of the 3 litre engine I started with) so we need to drop the compression ratio, and the way to do it is to increase the combustion chamber volume. We have a lot of components that make up the combustion chamber, so we can change quite a few things to do it.

The variables we can play with are:

• - Gasket thickness (you can get varying thicknesses of gasket for some engines)
• - Piston crown volume (grind metal from the piston crown)
• - Head volume (enlarge the combustion chamber in the head)

The usual way to do it is to enlarge the combustion chamber in the head, but if you need to take a lot of metal out, you might need to look at the piston too. Anyway, the obvious next question is, how much metal do I need to remove? Back to our compression ratio calculation…

       cr = (ccv + sv) / ccv

If we rearrange it slightly we get:

       ccv = sv / (cr – 1)

Which means we can now calculate our ideal combustion chamber volume…

       ccv = 602.5 / (9.4 – 1) = 71.73cc

Our calculated current volume is 69.40 so we need to enlarge it by 71.73 – 69.40 = 2.33cc

That’s quite a lot, but in reality anything between 1.75 (gives us 9.47:1) and 2.33 (a perfect 9.4:1) would be fine in my book.

Dan’s now got a head gasket and some die grinders and he’s going to try to take the metal out of the combustion chamber in the head. We’ve put larger valves in the head (45mm inlet, 40mm exhaust vs the standard 42/37 size) so the first order of business is to remove metal around the valve openings to allow air to flow past the valves as efficiently as possible.

More on the head later…

Nick vs the Engine, Part 1

Got all the bits back for the 3.6 bottom end from Dan the engine man yesterday and I was eager to get going on it. Since it's a 6 cylinder, I'm really keen to get the engine as close to perfect balance as possible, so I've had it balanced to 0.5g (much more than that is a waste of money, according to Dan, as the oil on the rotating assembly is random and may vary by up to 0.5g). I was still determined to do better, though!

The balancer had brought everything into balance individually (matched the lightest of each) so nothing was marked for a particular cylinder. I figured that if I chose each component carefully I could get an overall balance better than the tolerance of each piece. See what I mean? If one piece was 1g heavier than I needed and another was 1g lighter, the average would be spot on. It might (probably) wouldn't make a difference in practice, but I'd feel better having done the best job I could, and that's really all that matters, isn't it?

Jo got me a set of scales last Christmas with an accuracy of +/- 0.1g, max 2000g, just for this sort of work, so I could do the final component selection at home. It's bloody cold here for California, so I brought the scales and parts indoors and let them warm up for 12 hours or so before trying to measure them. I needed a solid and flat surface to work on, so I chose one of the kitchen worksurfaces as we have granite tile and that's perfect for the job.

If you ever want to do this, here's how to go about it...

Weigh everything individually and set them out so that you have the weight of the part written next to it and therefore you can easily pick up a part and know it's weight. You're going to get inaccuracies because of the accuracy of the scales you're using, but it will give you a start. I used sheets of shop towel laid on the worksurface and wrote the weight next to the part as I measured it. I piled parts of the same weight together and ordered the weights from left to right so I could pick the parts later without searching.

Use Excel to make a table of all the parts and weights. I had columns of piston, pin, clips, top ring, middle ring, oil control ring and expander, and rows of cylinder 1, 2, 3, 4, 5, 6. Sum up all the weights on each row so you get a total mass for an assembled piston. Add the lot together and divide by the number of cylinders and that will give you an average mass for an assembled piston, this is your target weight. Enter the weights in order, with the lowest weight at the top of the table and the highest weight at the bottom.

The table with all the weights. The "Set" column is purely arbitrary at this point, it doesn't refer to a cylinder number

If you've set up the table the way I did above, you'll now have a column that has the total mass of cylinders 1..6, with cylinder 1 being the lightest and 6 being the heaviest.

To get me started, I paired the piston and pin that came assembled together by moving the pin weights between rows to match the piston weight and pin. That mixed things up a little, but the total mass column recalculated itself so I could see my weight spread from the lowest to the heaviest. In my case, this was 2.0g.

Now comes the fun. "Swap" weights of bits around on the table to try to get the total masses column with the lowest difference. In my case I got it down to 0.5g after matching the light weight rings with the heavy pistons.

Once you've got it sorted on paper, make up sets of parts, based on the table you've been working on, and then weigh them. If you've got a nice set of scales, all your weights will match your calculations. If you've got a set of scales like me, the inaccuracies will add up and the measured weights won't match the calculations too much. My spread was at least down to 0.6g, but it wasn't as good as the 0.2g I had calcuated!

The next step is to use the table to work out which individual parts to swap between your sets to try to get the weights closer. I didn't have much I could do, but I did get it down to 0.5g.

Top left - swapping parts to get the closest measured weights. Below left - pairing cylinders to get the closest pairs, gives us cylinder allocations for the sets (middle upper column). Right column - adding rods into the equation and lower right is the final pairings for full rod + piston sets

We're on the home stretch. My next reasoning was that on a 6 cylinder (or a 4, come to that) pairs of cylinders move at the same time, so you want to match the weights of those pairs as close as possible to keep things in balance. Your target weight for this is 2x your calculated average weight per cylinder, of course. This is where things started getting better for me. When I paired cylinders up I got my calculated difference down to 0.2g (calculated by adding pairs of measured weights) and my measured differences (I weighed those pairs of sets of parts) down to a mere 0.1g.

The rods had to enter the equation at some point. They had all been balanced with the bit and little ends balanced separately and I had no reliable way to measure each end. I tried using a dial gauge stand to hold one end of the rod while I weighed the other, but when I added both ends together I didn't get the total rod weight, so I wasn't going to do anything reasonable there.

What I decided to do in the end was to weigh the whole rod and then match the rod up with the pistons to again get the closest spread possible. This was pretty easy as my first choice was the best - I matched the lightest rod with the heaviest piston set, then the next lightest rod with the next heaviest piston set and so on. The spread was a mere 0.4g, and that's with a total rod + piston set weight of 1255,0 - 1255,4g. Not bad. And even better was the pairing of cylinders - that was only 0.3g (1+6 was 2510.2g,2+5 was 2510.5g, 3+4 was 2510.3g).

That's as far as I'm going to go. I've bagged all the sets up together now to keep them together and I'll get on with measuring the crank clearances.

Playing the Sardines Game

Did I mention that space is getting tight on this Monza?

Case in point are the headlamps. Sure, it came with a nice four-lamp system, but these days you can get HID headlamps and they give much better light (which is great since I'm not getting any younger and I need all the light I can get at night!). We put HID lamps on the Manta a few years ago and that gave the "fishbowls" a new lease of life. With the Monza I thought I'd go one better and give it HID low and high beams, so I need to find a home for two HID kits.

On the driver's side it should be pretty easy as there's a reasonable amount of space available. On the passenger (right) side it's a different story, with the injection airbox and air conditioning pipes crowding in on the available space. Add to that, I'm trying to mount an electrical item that generates some 23,000V so I need to be careful not to get it directly in the flow of water when it rains (yes, I know the ballasts are waterproof, but would you trust it?).

I did a little measuring on the passenger side this evening and found a solution that I think will work. It's not very pretty, but it does miss existing components and I think meets the "not underwater" requirements. What do you think?

View from the side. The small box on the floor of the inner wing is the main beam lamp ballast and the larger one hiding behind the airbox is the dipped/main beam lamp ballast

View from the top. You almost can't see the dipped/main ballast and the main-only ballast looks reasonably neat

Tomorrow I'll think about the driver's side and then it's back to the endless wiring while I try to make this look like a factory installation!

Even the Arches Are Full

This Monza rebuild makes me realise how simple a Manta is. Think about it, I've spent the weekend putting wheelarch liners in the front arches, but to do that I had to first mount the oil cooler in the right hand wheel well and the charcoal cannister in the left wheel well, and while I was there I re-clipped the brake hoses to ensure both the brake hoses and the ABS sensor cable missed all the rotating bits at both locks. Anyway, enough whining, here's the progress.

First order of the day was to trim the right side wheelarch liner that I put in yesterday. The liner fitted well enough, but it got a little close to the top of the strut and the oil cooler piping. It also hung a little lower than I liked in the front, so that it would have stuck down into the airflow instead of being shielded by the airdam. I thought about that one a little before I started to cut the liner back. The liner actually bent forwards into the airflow, so there's an argument that it might have been designed that way to scoop air up and over the inside of the liner to ensure airflow through the wheelarch. Try as I may, I can't believe they would have thought about that!

Upper part of the liner showing the trimming near the spring (left)

Front of the liner trimmed, just missing the lower oil cooler pipe

With the wheel reinstalled, you can see the tyre misses by a country mile

OK, so with the liner trimmed on the right side, it was off to the driver's side to repeat the job, but first I had to site the charcoal cannister. For those of you in Europe, charcoal cannisters have been required fitments on cars since (I think) 1966 to prevent hydrocarbon emissions from fuel tanks. The one in the Manta is clipped to the inner wing on the left side behind the headlamp and the one in the Monza was mounted to a modified washer bottle bracket, holding the tank between the washer bottle and the engine. Of course, that was all well and good right up to the point where I fitted ABS and had to swap the washer bottle for one that missed the ABS pump.

Luckily there were two solutions I found; first was for a Gulf countries Senator A / Monza and the other was for an Omega A / Senator B. Interestingly, both put the tank in the left side wheelarch as far as I could tell, so that seemed like the obvious place to put it on my cars, especially with the engine bay being so full. Ah, but there was a twist - I was using wheelarch liners, so I had to fit the tank between the front part of the liner and the back part of the fog lamp, there really isn't much space left in this car for any other accessory I want to add!

So it all went smoothly enough, right up to the point I thought about how I was going to secure the tank to the frame rail. Opel say to use two of the nut inserts that they use on fuel pump assemblies, but to do that I'd need to punch a hole a bit like an Opel Blitz and 14.5mm in diameter. I actually have a 14.5mm punch from RS Components so I thought this was going to be a simple punch followed by a little Dremel work to open out the "wings" of the Blitz and I'd be done. Yes, but how on earth do I get the bloody punch in place when I can't get my hand to the back of the area where the hole needs to go? Yup, there was the problem. I'm sure it's possible to punch the holes if you've got a chassis rail on the bench, but by the time it's in the car you can kiss that idea goodbye.

In the end I managed to get the thing to fit, but Andy and any other self-respecting engineer out there is going to cringe... The lower (front) mounting hole I could actually just get to with my long 13mm spanner, so a bit of masking tape on the end of it to prevent the M8 nut falling off the spanner and I could just thread it on and tighten it right up. The upper (rearmost) mounting hole was a lot more difficult because, try as I may, I couldn't get the spanner trick to work. I thought about it for a little bit longer and realised that I had another solution. The hole in the bracket was just big enough to take an M10 screw and I could easily open up the 9mm hole to a 10mm tapped hole with an M10 tap. It was into sheet metal, but more importantly it was into 2 layers of sheet metal, giving me enough thread to hold the screw in with.

And that's how we ended up. The front mounting screw is M8 with a screw and nut. The rear screw is M10 and screws into the tapped chassis rail. Since the tank's so light and held closely to the chassis rail, I think that's going to work for us.

Charcoal cannister finally mounted in the inner wing

The rest of the liner install was the same as the other side, with the only gotcha being that one of the mounting screws hit the brake servo (it's a real tight fit on later Monzas) so I had to cut the screw down to miss it. What would I do without a Dremel tool?