A TR7 16V

Just done the oil filter on the herald with my old chain wrench, which has lain unused in the toolbox in the back of the Sprint since God were a lad. What a horrible job! But I see there are several alternative types of tool on eBay. What do you guys use? Graham

Just done the oil filter on the herald with my old chain wrench, which has lain unused in the toolbox in the back of the Sprint since God were a lad. What a horrible job! But I see there are several alternative types of tool on eBay. What do you guys use? Graham

Yes, it's a 1216 tpm one. And so is the spare one I have. Graham

I did wonder if it was more like it over-read by 12 percent, i.e. the speedo drive was right for a ratio of 3.63:1 or so. But  then sombody went the wrong way with the speedo drive, and doubled the error rather than fixing it. And then went, "Oh sod it!". I need to find out how to determin the speedo drive ratio, prefereably without pulling the overdrive or box, and certainly without tying a pointer to the head end of he speedo cable and seeing how far it pushes for one turn. I might, jack the back up on one side and turn one wheel. But not today, it's wet. Graham

If the speedo over-reads, the gearbox is turning faster than it should for the road speed, and the ratio is too big. So if I've got a 4.11:1 ratio, the speedo would be right for about 3.3:1. What would that be off of? Graham

Thanks rustbuckit2011, I found some stuff on the head on the net. I'm not sure I really want to have a go at the cam just yet, and upping the carb size is probably just idle musing - but if the cam's already been done, despite the possible loss of torque at low rpm, there may be enough to be gained higher up. And that could be an easier way to find out than pulling the engine just for a look see at the cam. Mind you, should it not be possible to get some idea of the profile from measuring the rocker movement, i.e. how much lift, and maybe angles as well? Is there enough data on the various profiles to make that possible? But thanks all for the help identifying the head and for all the useful advice on what's likely to work. The alloy bell housing is doubtless connected to the gearbox and overdrive, if that's not stating the bleeding obvious. I wonder if they're Spitfire too. I've still got to sort out the speedo problem that's also connected - it over-reads by about 25 percent. I have the GPS speedo as a fix, and a spare speedo head to swap to - it's not likely the problem, but it's the easiest thing to swap, and if it is that, and I only found it after pulling the box, etc., I'd be pretty p155ed off. It does look like someone spent no small amount of time and effort here and there, but not on cosmetics. Seems that was done in Yorkshire somewhere. I suppose I could go through DVLA and try to trace the previous owner – see if they can tell me about the cam, etc. Off the performance mod issue, I did wonder about an alternator kit: The dynamo didn't do too well on the run through Blackpool Illuminations. The Herald didn't overheat like the Sprint did though. Outside the engine and transmission, it needs a hood – the one that's on just looks like it shrank. I've tried the adjustments that are there, but it still only fits where it touches, and that ain't everywhere it should. Took it to an auto-upholsterer nearby, who reckoned that vinyl doesn’t shrink, so it must be a wrong one. But I wasn't impressed with that, so I still don't know. It does look like it's been on twice though – many of the holes in the vinyl are duplicated, about half an inch further in. Graham

All I can read off the head is "218142", no prefix or suffix. Graham

I'm not sure about "NO gains". I understand the issues with the bigger chokes having a lower air velocity, for the same volume flowing, and thus (from Bernoulli) a smaller pressure drop, across the airflow, to lift the dashpot and draw fuel up through the jet. But that's a largely a low rpm/small throttle opening thing. And, to some extent, it's correctable by using lighter dashpot springs.   But at higher rpm, there should still be enough velocity and pressure drop to lift the dashpot, etc., especially against a lighter spring. And as the larger choke gives less restriction to the flow, the engine will get more air/fuel mix, and will thus give more torque. And if you're after more power it's important to maximize torque at high rpm, because power is just torque times rpm. I'm not sure that the gains would be worth the losses, but I'd have to try it to be sure. Graham

Well I'm reasonably happy, nay surprised, at how well the car drives – overall, not just the engine. But I wouldn't mind a little more power, if it doesn't risk reliability too much. And I know, going back to my motorcycle days, that I do like the responsiveness that two smaller choke carbs give over a single larger choke. I admit I've not driven a single carb Herald, so I don't know what the actual difference is, but I've always been happier with multi-choke setups. And if the head and cam are stock, then I might look for something, e.g., with bigger valves. I have even thought about upgrading to a set of HS4s, if the carbs were still a significant limit to the engine's breathing. I'm not quite sure how to determine that without giving it a go. But I have a spare manifold, so I might start building up a set for a simple swap later. I also wondered if anybody's used a pair of HIFs? Graham

Any pointers to where the head number should be? Graham

While I was out checking what filter I wanted (done that) I took some pics of the engine and wondered what you guys might be able to tell me about it and the mods that have been done to it. And what might be worth consideration, if it's not too much like work. The nunber on the top of the block is GE45422HE, which I see is an 8.5:1 compression 13/60 engine. The number on the BMIHT PRS certificate is GE/80220-HE, which is, presumably, a bit later in the production run. I know the wirings a bit of a snake's honeymoon, but it's working at the moment, so I'm in no rush to fix it.

Thanks guys. Ordered one. Graham

Does anybody have a recommended source for an inner drive shaft flange, part number 128136, or a good one to sell? One of my spare half shafts has been butchered, and it needs to be replaced. Graham.

How did that run inside the car? Graham

Just got  a universal GPS speedo delivered: less than £30 and 10 days from China. I've only connected it up temporarily: I couldn't find the cigarette lighter socket thingy anywhere. Had to hard wire it off the coil in the end. It does seem to work reasonably well. There's about a 2 or 3 second lag in the display, near as I can tell. It will certainly be good enough to re-calibrate the analogue speedo. Have yet to see how long the start-up process is in a morning, but it warm starts quick enough.   The instruction manual's is pretty funny though: "After long press the menu button over 5s, the unit of vehicle speed will switch to MPH" isn't too bad; but "In the instant energized, the LED of the host will be fully lit, and then give out a 'tick', the host back to sleeping mode, while the satellite icon starts blinking" isn't quite so translucent. Graham

I've had my kids whining for a while about how hard the passenger door lock button is to press and the handle hard to turn. So I greased the square pin that engages with the striker plate mounted on the B post, and it's fine now. Graham.

I've had my kids whining for a while about how hard the passenger door lock button is to press and the handle hard to turn. So I greased the square pin that engages with the striker plate mounted on the B post, and it's fine now. Graham.

I think the issue of rear discs vs. drums is more complicated than commonly understood. That's because there's a self-servo effect on the leading edge shoe(s), where the action of the drum on the shoe pulls it into the drum - in effect, a limited amount of positive feedback. I have a nasty suspision that it's also non-linear. That self-servo effect does make the calculation of the brake effort from a drum rather more complicated than the disc and calliper, so it can be hard to work out if you actually are upgrading or not. I'd probably try to guess what the rear drums are doing from the effort of the fronts and what the balance should be, where known. But if you put rear discs on, it's fairly easy to work out what the ratio is (unless there's some kind of reduction/delay device in the system; then you're on your own). But working out what the limit is, i.e. the perfect balance, is not so easy. The interesting question would be, if you did set the brake balance behind the perfect balance for the very cleanest, dryest road you're ever likely to drive on, with nicely warmed new tires, etc., would you know that was the case before you try to brake hard in that extreme case? I ask that, because for all other road surfaces the perfect balance moves backwards as the CofF is reduced. So, what's safe on a wet surface, in the sense that the fronts will always lock first, isn't necessarily safe when there's more friction. Graham

If you're just upgrading the front brakes, and only by a bit, I don't think you have anything to worry about in regard to brake balance. I think that the worry comes if you want to upgrade front and back brakes together or if you're going totally nuts with the tires and front brakes as well. My concern is that there are those who think that if you're upgrading the fronts, you should also upgrade the backs more or less equally. That does sound sort of logical, I suppose. But, as it turns out, it's actually dangerous bollocks.   It's bollocks because, as you brake harder than before, more weight is transferred forward, the front wheels are harder to lock, and the back wheels will lock more easily. It's dangerous because if the back wheels lock first you lose directional stability and probably spin. If it's a TR7, that's "you lose what little directional stability you had, and you will spin". So, if you are increasing the total brake effort, you always want to increase the front brakes more than the back ones. And if you only do the fronts, you obviously are. It's true that if you go absolutely nuts at the front, you can actually need to reduce the back ones – either that, or lower the cars CofG a fair bit. As I said, if you were to get to the point where the back wheels lift off, any back brake effort is too much. But, roughly speaking, the turnover point, where the back effort starts to need to be reduced, is about half way to where the Back wheels have no load on them at maximum braking (would be exactly half way, if the CofG didn't move, WRT the wheels, under deceleration). And I think that is a long, long way from where you start with a Vitesse or a Herald or can get to with road going tires. That is, unless you stick up a mast and heavy canvas sail, and raise the CofG way up high. But what kind of "forest clearing" is going to do a thing like that. Graham

I make the change in area to be less than 1 percent, which is probably much smaller than the effect of errors in or rounding of the measurements of the piston diameters. For example, taking the OEM ones as 54 mm diameter, for the four pot's to be exactly the same area, its pistons would want to be 38.178 mm diameter, rather than 38 mm. So, if their areas are the same, the volume of hydraulic fluid needed to move them the same distance is the same, and there should be no effect on the length of the brake pedal. There will, however, be some effect of moving the pressure centre. However, I don't know either their actual values or their relationships to the effective disc radii (if they were to be the same thing, then there's no significant improvement whatsoever – less than half a percent 112.5/111.985 = 1.0046). And without those values, the best I can give you is a range. Assuming that the largest possible value for the radius of the pressure centre for the four pots is 112.5 (and I think it must be less than that) and it only moves 8 mm from the change in radius, the minimum change in brake effort would be 7.6 percent. So I think you must get at least that much increase.   I struggle to see minimum possible values for the radii to the pressure centres. So it's a bit hard to estimate the most you could get. But if the outer edge of the pad were at the effective disc radius (111.985 mm) and the width of the pad were the square root of 3024.06 sqr mm (55 mm), the pressure centre radius would start at near enough 84.5 mm. Allowing that it moves 8 mm for the change in piston diameter and 0.5 mm for the change in effective disc radius, that gives (84.5 + 8.5)/84.5 = 93/84.5 = 1.101. So assuming those assumptions are correct, the maximum you could possibly expect is 10 percent increase in effort. There might also be some small additional effect from the edge of the four pot's piston being nearer the edge of the pad, but I'd expect that to be around 0.15 times whatever that selvage is. So a small fraction of not very much, i.e. bugger all. So, these callipers should give between 7.6 and 10 percent improvement in effort for no effect on peddle length. They will also give either a longer pad life (and be less prone to fade) or allow a higher coefficient of friction (which will give more improvement in effort) for the same life (and, perhaps, fade), because of the greater pad area. If, for a first approximation, you take 3675.58/3024.06, you get 1.21. So, if you can get a pad that gives the same life as the OEM's, you could get something like another 20 percent improvement in brake effort for no more pressure on the pedal. You may also be able to compromise, and get some improvement in effort from the pad and some increased resistance to fade. But, I have to admit, we're now well in the area of speculation as far as I'm concerned. So, if it were all down to moving the pressure centre, I'd see 8 to 10 percent as a marginal improvement. If you can also gain from the increase in pad area as well, then 25 to 30 percent sounds much more reasonable.   However, I still think I'd go for a larger four pot piston. With a four pot calliper with 40 mm diameter pistons, you get 10 percent more brake effort from that, and maybe 6 or 8 percent from moving the pressure centre. And that's clearly more than nothing. If you can also get say 25 percent from the ability to use a higher CoF pad (a four pot with 40 mm pistons should have a bigger pad area than one with 38 mm pistons), that sounds like a significant improvement to me. I suppose there's a worry that, with the improved brakes and tires, you've moved the balance of braking on a clean dry road too far back. I know that sounds the wrong way around, but it's not: if you brake harder, without the front wheels locking, more of the car's weight is transferred forward off the back wheels; and because the maximum force of friction that can be applied before a wheel locks is proportional to the downward pressure on it, which is less, they lock sooner; even if the back tires are improved as well – which means the balance, at the limit of braking, has moved backwards. That would require that you reduce the back brakes a bit, e.g. by using smaller diameter slave cylinders at the back. It is possible to work out what the effect on brake balance is. But, to do that, you need the height of the centre of gravity of the car. And that's not so easy to find. There is another effect that I can't assess, partly because I forgot to ask for data but mostly because it's outside my area of ken, and that's unsprung weight. I'm guessing that these new callipers are made from a much lighter alloy than the OEM ones. And with the same total piston area, they probably won't have a very much larger volume. In which case, they are very probably a good deal lighter, and thus reduce unsprung weight. However, I've no idea if that's an issue that bothers you at all. Graham.

I can do the effect of the upgrade from the change in area from those, but I would need the radii to the centres of pressure to get the effect of that moving outward. though I can make a rough estimate of that effect, by assuming it moves by the change in radius of the pistons. I'll post the results in a little while, as I'm currently bored to frigging tears. Graham

All I need is the piston area or piston diameter and the distance from the centre of pressure to the centre of the disk when the calliper is fitted, for both the new calliper and what you've currently got fitted. The centre of pressure should be near enough to the centroid of the pad (the point where any straight line passing through divides the pad into two equal areas). That should also be near enough the centre of the two pot piston and halfway between the two centres on one side of the four pot.   Assuming your current callipers are a standard type, maybe someone here has that data already. No, the pad area is largely irrelevant to the brake effort, though it will have an effect how quickly the brakes fade - the bigger it is, the more it will take to overheat them. Also, the bigger they are, the longer they will  tend last. But I'd like to know what their areas are, because I'm like that. Graham

Actually, they may well be a really easy way to a really good upgrade. The problem is that the ad doesn't give specs, and I don't have specs for what you've got on currently. Without those, I for one couldn't tell you if they are any better or not, and if they are, by how much. With those specs, I think it's relatively easy to work out how much additional brake effort you would get, and whether they are likely to affect the pedal, etc. The discussion John and I are indulged in is more than a bit esoteric. To you, the pad size will be what it is, and why it is won't matter. I'm just betting that, if they are a worthwhile upgrade, the pad will have at least as big and area as what you've got, and conversly, if the pad is smaller than what you got, they wouldn't be a worthwhile upgrade. But it's the two sets of specs that allow that to be worked out. Graham

I actually do think they have to be bigger in this case, but only because it applies to the situation where you're keeping the same disc while replacing the two pot calliper to increase brake effort. The size of the disc then limits how far out you can move the centre of pressure, to the extent that you can't use a four pot calliper with pistons any smaller than (I estimate) two thirds of the diameter of the two pot ones, or the brake effort must be less, not more.  This is partly because the effect of the position of the pressure centre on the brake effort is linear but that of the piston diameter goes by its square, so it very quickly becomes dominant. I admit I'm assuming in the above that you don't want to move the outer edge of the four pot pistons closer to the edge of the disc than the two pot ones were. But, because I don't think I understand all the safety implications in doing that, I'm sure I don't want to. Even if you think that distance should be in proportion to the piston diameter, you can't reduce it by more than about a third (with pistons two thirds the size). And a third of it is bound to be small in comparison to the distance between the pressure centre and the centre of the hub. I also assume that the centre of pressure for the two pot calliper is the same as the piston centreline, and for the four pot, is on a line joining the centres of the pairs and equidistant from them. I have thought about thinking about what happens if that doesn't line up with the centroid of the pad, but decided against it. Again, I think the error in that must be small compared with the distance from the hub centre, so its effect on brake effort will also be small. Since the point of the discussion is improving the brakes, you don't want to go anywhere near as small a factor as 0.66 anyway – that's where, I'd say, you are absolutely guaranteed to get no return at all on your investment. So the pads on any 4 pot calliper you would use will, I would say, necessarily be larger than those of the two pots you replace – but only in this context of keeping the same disc. For example, with pistons 0.707 times the two pot one, the area of the four pot pad, relative to that for the two pot calliper, will be roughly 0.707 * 1.414 plus 0.707 times the distance between the pairs of pistons, and as 0.707 * 1.414 already equals 1, it must be larger. But even with pistons 0.707 the size of the two pot ones, which keeps the same pedal length, I estimate you'll get at most 10 percent improvement in brake effort (it must be very much less than 30 percent, unless the diameter of the two pot piston was half that of the disc [LOL]). Actually, I think it's nearer to 5 percent, but I don't have numbers to firm that up. And while 10 percent improvement in the front brake effort is not nothing [yes it is] I don't think it's enough to justify the cost of replacing the callipers. So despite the effects on calliper weight and pedal length, if upgrading to four pots on the same disc, I'd be inclined to look for a calliper with pistons a little bigger than 0.707 times the two pot ones. At 0.8 you get 28 percent increase in brake effort from the increased pressure on the pad.  You might also get  few percent from moving the pressure centre, assuming you keep the outer piston edge the same distance from the disc edge, as I would be inclined to. And a third more front brake effort sounds much more like a reasonable return on the investment to me. Graham.

Oooh, a physics question. Sorry if this is late in the discussion, but I just can't resist these. True, but it's only a part of the truth. Another part of, in effect, spreading the piston out around the disc, is that the total area of the pistons can be much greater, even double, without their outer edge being further from the centre, which would force you to use bigger discs and wheels. And from hydraulics 101 the force on the pads is proportional to the area of the pistons (for a given hydraulic pressure), and the braking effort is proportional to the force on the pad (Amontons' first law of friction), more piston area gives more braking effort. There is the drawback, however, that a bigger piston area generally means a bit longer travel on the pedal. But if the discs are flat, and parallel, that won't be much. It generally also increases the pad area too. But, interestingly, the area of the pad has no effect on the braking effort as such (Amontons' second law of friction), though it can affect fade. What a bigger pad can mean, however, is that you can use a material with a higher coefficient of friction (CofF), pad to disc, which would normally wear more quickly, for the same pad life. It's also interesting to apply Amontons' second law to the situation of wider tires and greater grip. I've fitted the big Princess 4 pots to several TR7s as a very nearly direct replacement - same discs and wheels, etc., but you have to move one of the mounting holes on the calliper about 1/4 inch outboard, or the pads hang over the edge of the disk. They have (IIRC) about half again the piston area of the TR8 callipers, and the improvement in braking is significant. The improvement over TR7 callipers, which are the same as HA viva ones, just with a servo, is vast. There's less fade as well, but (IMO) not as much less as vented discs. The effect on lengthening the pedal on the TR7 is normally countered by fitting the 4 speed rear brake cylinders, which are a smaller diameter, and effectivly shorten the pedal back to where it was. That will also have the effect of moving the brake balance forward, but if you also put wider, stickier tires on as well as improve the front brake effort, that' also has the effect of moving the limit of brake balance forward anyway, so you have to move the actual balance forward again, just to keep up. Otherwise, if the balance is too far back, the rear wheels lock first when hard braking on a clean dry road, and... Think about it this way: If you were to increase the front brakes and CofF, tire to road, (or raise the CofG) to the point where you could reverse wheelie on a dry road, any back brake effort would be too much, as the back wheels must always lock before the fronts. Graham