| Author | Message | ||
     KC Unregistered guest Posted From: 168.209.98.66 |
Which NGK spark plugs are the most suitable for an Mk VI 4.25L engine, and what should the gap be? I use NGK BP5 ES on my Shadow, with gap setting 0.6mm. Would the same apply to the 4.25 engine in my newly acquired Mk VI? Regards KC | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 260 Registered: 4-2003 |
I would not use an NGK BP5ES in your motor, but would choose an NGK BR5ES with a gap of 0.65mm - 0.7mm. The original Champion N8 is directly equivalent to an NGK B6ES. You could use a B5ES if you go for this non-resistor type plug and they foul. The gaps were specified at 0.025" - 0.028" or 0.635 mm - 0.7 mm. However, it was common practice to use Champion RN8, which is equivalent to an NGK BR5ES. For both Champion and NGK, the R denotes a resistor type plug. For NGK, the P denotes a projected electrode. I would not use projected electrodes in these F-Head motors, so I would not use a BP5ES plug in your car. The OHV V8s are a different matter. | ||
| Bill Vatter Unregistered guest Posted From: 68.215.166.134 |
Richard, I am curious what is your reasoning to not use the projected electrode. Extra words added to make it long enough. (What a silly requirement!) | ||
| Ashley James Unregistered guest Posted From: 62.255.0.5 |
I use B6ES, they did not have projected noses when the cars were new and NGKs have such a wide heat range (unlike Champion) that a harder plug will give no problems. I've also used R's and P's and noticed no difference. KLG and Lodge too, were excellent plugs but Champions always a nightmare. We had trouble on everything from Healey 3000s to Gold Star BSAs with them. Holing pistons and electrodes disappearing mostly. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 261 Registered: 4-2003 |
Bill, A very good question. I cannot answer this one, but maybe someone else can. Years ago I asked several professionals many times, at least one a R-R technical representative, whether protruding insulator plugs would benefit my R-Type. They all told me very strongly not to try. Protruding insulators have no benefit with compression ratios below 8.5:1 I was told, and that the combustion chamber shape of the F-head 6 cylinder cars was unsuitable for those plugs anyhow. I was warned of piston burning and other damage. I have no real understanding why not to use the protruding type plugs like a Champion N12Y = BP5ES in these cars. However, I have never tempted fate. Nor have I ever had a problem with the plugs. The car has travelled over 700,000 km, so why experiment ? When asked, I simply advise my good experiences with N8 or equivalent, and will not suggest that anyone experiment on my behalf. NGK and the like produce non-protruding type plugs for a reason. I would gladly switch to protruding-type plugs if convinced there is no risk. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 262 Registered: 4-2003 |
I have just seen Ashley's post. I don't want to bad-name brands, but the only plugs which have ever given me trouble are Champions, although not in my Crewe cars. The Japanese seem to be the best, especially NGK. Having said that, I have only ever used Champion plugs in my R-Type and T-Series, and have never had a problem. However, in normal use these cars are not very demanding (although that in itself can produce plug problems). I would definitely follow Ashley's good experiences with the B6ES plugs. | ||
| Bill Vatter Unregistered guest Posted From: 68.215.166.134 |
Richard and others, In the combustion chamber the spark plug is located directly over the exhaust valve, and It is entirely possible that someone had concern that the exhaust valve might hit a protruding electrode, hence a recommendation to stay away from this configuration. I also know that gas flow around the exhaust valve is a critical point, and that milling a bit off the head to increase compression does not improve the power but instead results in a rougher running engine. This performance is caused by exhaust gas being restricted by the narrowing of the space over the exhaust valve which restricts gas flow. This is historically documented by RR. They initially tried to increase power with higher compression after decent fuel became available, but they did not have good results, so instead they increased power by making the engine larger at 4.5 L. Later, they came out with a higher compression cylinder head for the continental, with which they apparently had discovered and addressed the exhaust gas restriction problem. Perhaps Norman Geeson, who knows the complete story will see this, and give us the detailed facts on that the development of the cylinder head design. So what am I getting at with this discussion about exhaust gas flow? It is that a protrusion of the spark plug into this space may provide restriction to the gas flow. Hmmmmm. Perhaps I should get some NGK B5ES plugs and see if the engine runs any smoother than with the BP5ES I am currently using. Ralph Curzon, a RR factory trained mechanic and shop owner in Canada has recommended NGK BP5ES plugs. I personally use this plug in my car and there is no problem. This plug has a protruding tip, but possibly not as long a reach into the combustion chamber as some other plugs. I have also used Champion N9YC which also has a protruding tip, no problem. The camshaft profile in my engine is the standard profile for circa 1950, not the high lift profile that was used on very early Mk VI cars but not Silver Wraiths or Dawns. It is also possible the high lift camshaft would be a problematic combination with the extended tip plug. Certainly the clearance would be less. However, that camshaft was discontinued long ago because there was a wear problem, and I doubt anyone still has it, or if they do, the lobes are probably worn off enough to make no real difference. Champion N8 plugs are no longer made, and if you can find NOS N8s they will be pricy. There is no readily available Champion plug that is a good match for the N8. Most Champion plugs come with the protruding tip (Y or YC suffex). Personal opinion, the N8 is too cold anyway. The Champion heat ranges are larger numbers = hotter. NGK plugs have the opposite convention, lower numbers = hotter. If an engine is burning oil, an NGK BP4ES or B4ES might be a good choice, as they will be less likely to become oil fouled. Years ago, Champion plugs were the only thing to get. Today, their reputation is not so good, and many stores do not carry Champions. When you ask sometimes you get "why would you want that junk for your car?" for an answer. Probably they are just as good as they always were, but some of the newcomers are better. Anyway, I personally do not think the EPW six is very sensitive to the type spark plug used. Rather than fiddle with different plugs to get it running well, I would look for other things to improve in the ignition system. For example, I would work to remove resistance in the secondary circuit at the wires, connections (particularly the spike where the wire fits on the distributor car can be corroded), and distributor rotor. A non-resistor rotor is available, and that helps the engine idle more smoothly. | ||
| Ashley James Unregistered guest Posted From: 62.255.0.5 |
For electronic ignition have a look at www.classicheads.com it is simple to fit, all inside the distributor and works better than points because my rear set allways had oil and grease on them. I have no trouble with B6ES and they stand higher temperatures which might be an advantage over there. Also if you fit a projected nose plug, it would be wise to go to 6 rather than 5. | ||
| Dave Baron New User Username: redbaron Post Number: 4 Registered: 3-2004 |
I've just done a general top-end tune-up on my 4.25l Mk VI B386CF including inlet valve clearances, new non-projected-tip BR5ES plugs, balance and mixture on carbs. B5ES no longer available here (Canada). I'd had fairly rough idle and fouling of the plugs that came on the car, NGK BP6ES. It's now purring like a kitten, which may be because of the new plugs but could equally be because of more even valve clearances, balance and mixture, of course. I'll have to see if the fouling disappears when I get stuck in heavy traffic again (maybe in the line-up for the ever-popular annual husky sexing competition on September 31st). | ||
| Jim Bettison Unregistered guest Posted From: 203.166.107.243 |
As part of a rebuild a year ago of our MkVI (B20JO) we did an evaluation of spark plugs. Criteria were: a (subjective) comparison of the "feel" and performance, both in level cruising and up some 7% grades: observation of the plugs as to colour after several hundred miles: engine efficiency as measured by our fuel/air meter. We had replaced the original coil(s) with a Bosch GT40 (ballasted primary: the advance/retard of the distributor was checked and adjusted (in the process we found a broken spring attached to one of the centrifugal weights - another story). We found that the best performance was from NGK BP6EY. This plug has a Y -shaped end on the centre electrode. However, I must say that I think performance overall was influenced as much as anything by the fuel. Locally available fuels were then 92RON unleaded (ULP), 96RON lead replacement (LERP) and 98RON premium unleaded. We found that the ULP performed as well as any. However, I suspect that quality control ex local refinery (Adelaide, S Aust)(now closed - we buy from Singapore) was questionable. Certainly, the product had a "shelf life" of around 6 weeks. So I suspect that what we discovered was true for one or two batches of fuel from a particular refinery, and shouldn't be taken as universally applicable. Or am I being too cynical? Jim Bettison. | ||
| Martin Cutler Prolific User Username: martin Post Number: 89 Registered: 10-2004 |
Just about to nip up the road and buy some spark plugs - just to summerize the above: BR5ES, B5ES, BP5ES all used with no problems, B6ES used in sunny England with no problem (colder plug), but BP6ES gave problems in Canada. 4's used on oil burners (hotter plug). Think I will go for B5ES for my 4.5 litre, 116,000 miles, non oil burner. Will report back on any troubles. Cheers Marty |
