| Author | Message | ||
     Brian Vogel Grand Master Username: guyslp Post Number: 1044 Registered: 6-2009 |
This question has come up elsewhere and my research is coming up empty. On my two SY cars either the HT leads have labels on them or the distributor cap has (hand written) annotations on it. However, I'd think that somewhere there would either be a "complete map" showing which distributor cap slot is meant for which cylinder or showing which slot is always the A1 slot and then allowing you to figure out the rest based on firing order. Perhaps the location of the A1 slot was one of those things "every mechanic knew about" and thus it wasn't documented. I've seen the A1 firing position referred to several times without any corresponding diagram indicating which position the A1 firing position is. If the A1 firing position is the key, then where is it "always located" when the distributor cap is on (and, presuming of course, all the other bits are assembled as they should be)? If it's not, what is the search term one would use when searching the workshop manuals (including the various supplements) to find the diagrams that show which positions correspond to which cylinders for a specific car and model year? Brian | ||
| Chris Browne Prolific User Username: chrisb Post Number: 152 Registered: 2-2010 |
Hello Brian, When viewed from the drivers seat, if you imagine the distributor cap as a clock face, A1 is at one o'clock. Moving anti-clockwise, from A1 the order is B1, A4, B4, B2, A3, B3, A2 and finally back to A1. Hope this helps. Kind regards, Chris | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 1045 Registered: 6-2009 |
Chris, Thanks much. Is the A1 position always the 1 o'clock position? I ask because the firing order is different on later cars, and that's what I'm trying to help someone with, a 1988 Bentley Eight. See below the table from TSD4400 to see how the firing order changed.  Brian | ||
| Bob uk Unregistered guest Posted From: 94.197.122.84 |
SRH 17668 1974 A1 is at the front by the A bank. It doesn't matter but nice to have right as per left the factory. My leads are labelled with printed sleeves, black with white printing capital letters used. A or B. Then number. (Message approved by david_gore) | ||
| Nigel Johnson Prolific User Username: nigel_johnson Post Number: 130 Registered: 12-2008 |
On the high powered versions (Turbo R) the firing order was changed to that of a more conventional V8. The reason being the possibility of broken crankshafts. Regards, Nigel. | ||
| richard george yeaman Prolific User Username: richyrich Post Number: 201 Registered: 4-2012 |
If RR changed to a more conventional V8 firing order in 1986 why did they not do that at the very start and what noticeable difference audible or smoothness does that make does the later cars have more of a burbling sound or what??? Richard. | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 151 Registered: 10-2008 |
Brian, I cannot find the table you show,can you forward a link. The exhaust note on my 1988 Bentley 8 is much harsher than my 1983 Mulsanne, but I thought this was due to the exhaust systems being completely different. I had assumed, wrongly it appears, that all engines had the same firing order. Mark | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 1046 Registered: 6-2009 |
Mark, It's on PDF document page 18 of Chapter A of TSD4400. I have several different scanned copies of TSD4400, a couple of which are OCR-ed PDFs which allows me to search them, and that's how I found it. The PDF page I refer to above is the one that's downloadable from the RROC-A Post-War Technical Library. The version I was using to find this is available for download from: http://webstorage.rroc.org/TOL/. It's in three parts (and I have no idea why the second part has a ZIP file and the straight PDF file there). Other documents are available at that site as well. This particular document set is the oddity in that it is accessible by the public (at least for now). It's an absolute godsend to be able to use the search facility in Windows to plow through these documents to locate stuff. There are things that end up being buried in the oddest places! Brian | ||
| Jim Walters Experienced User Username: jim_walters Post Number: 25 Registered: 1-2014 |
Hi Brian, I learned 40+ years ago that to find the #1 firing plug lead turn the crank over until the timing marks (TDC) line up on the damper or front crank pulley. I was told that if the distributor rotor is pointing towards the front of the car it will indicate which is #1, or A1 as the case may be. I can't recall if this is a hard and fast rule, but you will have at least a 50/50 chance of it being the right one. (The timing marks will be a constant, but the rotor pointing towards the front may not be) SRE22493 NAC-05370 www.bristolmotors.com | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 472 Registered: 5-2012 |
I read somewhere that when you've lined up the timing marks, remove the A1 spark plug and push a snug fitting tube into the hole. You then blow into the tube. If resistance is felt you know you are on the compression stroke (the one you want) and if there is no resistance you are on the exhaust stroke, since the exhaust valve is open (180 degrees out). I have never actually tried this, but it seems a useful trick to prevent your having to remove the rocker cover and monitor the rockers/valves. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.89 |
firing order is controlled by the crossplane crankshaft and the position of the cams relative to each other. RLRLLRLR or RRLRLLRL The firing of two cylinders consecutively in one bank gives the burble and requires a dual plane inlet manifold to even out the pulses on the carbs. Multipoint injection doesn't need a dual plane manifold. one plane feeds A1 B2 B3 A4 and the other feeds B1 A2 A3 B4. Flat plane engines such as Ferrari V8 fire RLRLRLRL. Which gives even fueling and easier exhaust manifolds on performance engines. A Ferrari is two straight fours on a common crank and RR is four Vee twins end to end, offset 90 degrees to each other at the crank. The Ferrari has two pistons at tdc in one bank. RR has two cylinders at tdc split between two banks. This causes the Ferrari to be not as smooth and no burble but allows quick revving. To smooth a crossplane engine heavy counter balances are needed which slows up revving. A straight six has perfect balance and is always naturally smoother than a V8. But anything over 5 litres is either tall for a longer stroke or longer due to bore diameter. V12s are two straight sixes on a common crankshaft and the angle is 60 degrees which gives a narrower engine double prefect balance and a V12 will run smooth with out a flywheel. (Message approved by david_gore) | ||
| richard george yeaman Prolific User Username: richyrich Post Number: 203 Registered: 4-2012 |
Bob I thought you would be the person to have a go at answering my query which I am sure you have done in a round about way, Mark Aldridges post gave me a clue when he said his 1988 Bentley 8 was much harsher sounding than his 1983 Mulsanne what is the difference mechanically between these two cars ??? Just found this question mark key thanks to new glasses. Richard. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.81 |
Changing firing order of a cross plane burble V8 should make no difference to smoothness or reliability. Some individual engine and or engine installation can be a bit harsher ancillary components can cause harshness. Normally aspirated engines when on inlet stroke the load is opposite the power stroke. Turbo charging the load is the same way and the pressure is blowing the piston down,not a lot. This makes the engine smoother at speed. This blow down is often overlooked in why turbos work so well. The rocking couple from the power stroke while the other cylinder is sucking is diminished because the turbo is blowing the piston. If the engine is diffinately good then the mountings maybe worn. When mountings are changed misalignment can occur which is hard to figure out. Or it could be an illusion caused by the exhaust note and the turbos torque mountain. I had a ride in Turbo with a RR dealer driving and he put in 2nd and full throttle at 40 mph and held it to 80 mph and the grunt was --- more than adequate. The squat was bad though but on the other hand it didn't snake. And so smooth. Normally when a V8 is pressed hard it loses it's smoothness. Because the firing is doing a tango whereas a flat plane V8 is in march time which makes the engine howl at revs like Ferraris and some Nascars. Note the rev worthy ness of crossplane engines has been greatly enhanced by Audi AMG and BMW, the flatplane is falling out of favour with performance guys because of low rev vibs. Its very complicated. (Message approved by david_gore) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3082 Registered: 4-2003 |
On 17 September 2014 richard george yeaman wrote:
Try a Silver Shadow in good condition and compare it to a 1990s Crewe motor. The early car is silky smooth and super-responsive. The later cars are more like the usual crude American V8. Bumpy, gutsy-sounding but unrefined. Love them, but not exactly up to Crewe standards. It would have been n nice to retain the dignity of the earlier firing order with the 90-degree V8, but there is a nasty harmonic introduced by the early firing order when Crewe changed the crankshaft front configuration for the SZs. The bolted extension to the front of the crankshaft helped accommodate the necessary hardware but was not entirely smart as it snapped when the torsional vibration became too large. It all went pear-shaped when the torque available exceeded 400lb-ft with a turbocharger. Probably a turbocharged motor with a Shadow crankshaft would have been OK, but the radical change to the front of the SZ crankshaft left no quick option but to resign to the crude GM- and Chrysler-derived firing order. To fix it properly would have taken five years and a production stop for Turbocharged cars, so we have the cars as they were built. | ||
| richard george yeaman Prolific User Username: richyrich Post Number: 204 Registered: 4-2012 |
Excellent Richard that is exactly the kind of answer I was expecting to hear as I have only ever owned a Silver Shadow 1 SRH19529 I had no way to compare. Mark Aldrdges comment about his two cars one sounding harsher than the other was a good pointer to the difference in actual fact they are quite different. Richard | ||
| Bob uk Unregistered guest Posted From: 94.197.122.83 |
The bolted on counter balance weights on the shadow were dropped in favour of one piece cranks. Maybe RR dropped a clanger or a counter balance. A straight four fires 1243 or 1342 it makes no difference to the running. Notice that 1 is opposite 4 and 2 is opposite 3. The idea of blowing into a cylinder to see which is on compression is a new idea to me and a cracker which I shall remember for future reference. I assumed that RR kept the same firing order throughout. Why they changed I don't know but I know of a man with a in depth knowledge of all things V8 I shall ask him when he returns from Quebec, he's French and a very funny guy who plays with words. He's back on Monday. (Message approved by david_gore) | ||
| Bob uk Unregistered guest Posted From: 94.197.122.87 |
The penny dropped after reading Mr Treacy posting about vibration. In one Firing order A1 and then B1 fires. These are on the same cranking pin which winds the front of the crank up which then unwinds and overshoots. This is torsional vibration. Plus the camshaft drives gets a flutter going which upsets valve timing and ignition timing. This makes for harsh rough running if the engine is made to produce more power. In the other timing in Mr Vogals chart B2 and then B1 is fired which uses two separate crank pins. And there fore smoother if lots of torque is being made. Other makers use numbers only 1 to 8. Usually left hand bank as seen from driver's seat is no1 front of engine. Then no2 is right hand bank so r/h is 2468 and l/h 1357. Some makers have no1 on the right. And some go 1234 on one bank and 5678 on the other. So comparing makers firing order needs care otherwise it gets confusing. Twin cylinder engines are easy because the engine fires 1 2 or 2 1. For 360 degree twins it's a joke but with 180 twins, because of the uneven firing pulse the first cylinder fires then 180 degrees second cylinder then 540 degrees and the first fires making 720 degrees. I know this as lead and trail cylinders. (Message approved by david_gore) |
