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MG MGB Technical - hotter plugs
| Hello everyone. I have a slight problem. the plugs i am running are grtting fouled. they are NGK BR73S i took them out fri and they were black, the clymer shop manual showes just what My plugs look like.it says they are carbon fouled. cleaned them (sand blasted them) regaped @26 runs good,BUT the book says to try a hotter plug. any Ideas? i do have the eng mod. hot coil, elec.ing, carb air intake is bal,air to gas mix seams to be ok buy the lift pins on carbs. i do run 94 0ct w/booster. the eng is board 30 over with kent cam (road grind power band 2000 to 6000 rpm) the head is ported polished an decked fly wheel is shaved also. Thanks for any help, Don Baker |
| dab donald a baker |
| It sounds like yor car is running a little rich. Try adjusting the carbs abit leaner. Bob |
| Bob Ehstrand |
| Use NGK BP6ES! |
| Chris at Octarine Services |
| Donald. I second Chris's recommendation. I have been using the NGK BP6ES for about ten years now. Since Roger Parker recommended them to me on this BBS. Definitely the best plug I have found for these cars, including those with performance modifications. This is the starting place for any spark plug experiments. Les |
| Les Bengtson |
| Chris I have recently replaced the thermostat on my 67 Roadster (2100cc motor) and run it at around 90 degrees celsius. I am astonished at the improvement in the performance as I was obviously running it far too cool at the old 74 degrees. Which plug should I be using? Thanks Peter M |
| Peter M (Member) |
| Peter - I run a 195°F (90°C) thermostat in our MGB with NGK BP6ES plugs and they work fine. Cheers - Dave |
| David DuBois |
| Peter, The BP6ES is good for all engines / temps up to full race where I would normally fit BP5ES instead. For ally cross flow heads I use the BCP version of these plugs that has a smaller hex to allow the plug spanner to reach into the head. |
| Chris at Octarine Services |
| Many thanks Dave and Chris. Peter M |
| Peter M (Member) |
| Chris, just went out and got a set of plugs should i gap @26? thanks, Don. |
| dab donald a baker |
| Hi Chris Don't you mean BP8ES for race as they run cooler? We tend to use BP7ES for spirited driving on road engines and BP6ES when lots of town driving is the main use. The plugs are very good as they overlap each other in terms of effective heat range. Can you tell we have been fans of NGKs for 25 years and use nothing else :) Peter |
| peter burgess |
| Aha, at last someone agrees with me on plugs! My 'tuned' engine eats BP6ES when it is being used hard, fouls BP7ES when it is not. When I say 'eats' the BP6ES, I mean they get so hot that the ceramic cracks. I've tried BPE7V too. The problem with those is that they are (i) very expensive and (ii) impossible to clean when they foul. So I keep two sets, one BP7ES for driving hard and one BP6ES for driving 'soft'...! Neil |
| Neil |
| When I first recieved my supercharger kit from Moss it included Champion plugs that were 1 heat range cooler than stock. Six months later I got an email warning that they were having problems with these plugs and suggested NGK BP7ES in their place. I have been using NGK plugs for 20 years and this came as no suprise to me. I, too, tried the BPE7V but was informed that these had a tendency to run a little too hot and caused detonation. RAY |
| RAY |
| Hi Don try the gaps at 35thou and see how they work for you. We used to run tighter gaps but the current fuel blend seems to enjoy a wider gap on either points or electronic. Peter |
| peter burgess |
| Thanks, Peter. Don |
| dab donald a baker |
| When MG went from the 25D to the 45D in 1974 they increased the gaps from 25 thou to 35 thou anyway. |
| Paul Hunt |
| The only trouble is that was 35 years ago when dinosaurs roamed the Earth, the Earth was still cooling and copious chunks of lead were in the fuel too :) Every so often we get a standard race car and take the gaps from 25 to 45 thou to see what happens. Up to two years ago we got the best results with 28 thou then the 35 suddenly went better than the 28. All we do is pass on the info when we come across it, that is the nice thing about 1st hand knowledege running up loads of MGBs on the rolling road. Peter |
| peter burgess |
| Peter, Yes, sorry, I can never remember which way hotter & colder run! On the subject of gaps, I always set road cars to 25 thou, regardless of which dizzy they are using. The higher kV generated in the HT circuit by larger gaps tends to blow holes in the rubbish rotor arms sold these days. |
| Chris at Octarine Services |
| Hi Chris We haven't been able to correlate rotor arm faults with plug gaps. The rotor arms we have seen that are faulty can be any make and become conductive when hot. Oddly the same makes of rotor arms for Bosch distributors do not have the problem, the rotor arms have all been red for the other distributors, any mileage in the colours being different materials? Peter |
| peter burgess |
| Peter, Most of the cars I service are low mileage per year - some as little as 400 or 500 miles between MOTs. Cars with 35 thou plugs gaps (either set at 35 or worn to greater than 35 thou) often suffer from rotor arm failure with the plastic tracking through internally between the brass rotor and the dissy cam post or dissy cap failure with tracking across the cap or through the turrets. Resetting the plug gaps to 25 thou seems to cure the problem without affecting the running of the engine. Possibly not optimal for power but these owners are more concerned about reliability! The rotors currently available seem to be poor quality - I know of at least one person getting OE quality rotors made in the US but I think these are only 25D4 rotors. I think Bosch parts are probably still made by Bosch and I would guess the reddish brown plastic is a better quality material. |
| Chris at Octarine Services |
| >I think Bosch parts are probably still made by Bosch and I would guess the reddish brown plastic is a better quality material. Maybe completely irrelevant to the discussion, but I recently replaced the cap and rotor in my '91 Honda Accord. The rotor I took out was Bosch, as proven by the Bosch logo printed on it. The one I put in was "OEM", branded Nippon or some such. It was identical in every respect to the Bosch one (right down to the casting marks left from the mould), but for lacking the Bosch logo. So at least in _some_ applications "Bosch" isn't necessarily Bosch.... |
| Rob Edwards |
| The problem rotors I have seen are those with the rivet inside the base circle which puts it close to the dizzie shaft. The better ones either don't have a rivet at all, or it is outside the base circle. See http://www.mgb-stuff.org.uk/rotors.htm for examples of all three types. |
| Paul Hunt |
| Hi Rob I tend to agree on the materials. Doesn't make sense but seems to hold true. Chris, the problem must be KV requirements if the narrower gap seems to stop the problem, if so, simply using EV NGK plugs should stop the problem altogether as they tend to take 2-4Kv for the ionisation voltage as opposed to 4-16 for ES type NGKs. Nice pics and possible explanation Paul I will keep an eye on the failures and report back. Peter |
| peter burgess |
| HI, Don Baker here. so back to what i should gap my plugs at? i have set them to 35. they came out of the boxes at 35, but i still check them. i have also changed my dis. to elec.no points. so to everyone, is 35 good? Thanks Don. PS, my left front caliper is locking up. any ideas? Thanks Don |
| dab donald a baker |
| Don. I have run .035" for many years without any problem using both the points type and non-points type distributors. Again, NGK BP6ES plugs which show a coil build up of about 10-11Kv at idle and about 18Kv at load on my engine analyzer. As to the caliper problem, please start another thread about that one so that it will archive properly. But, there is a lot of information already in the archives with the common problem being a bad flex line going to the caliper. Test is, when locked, open the bleed nipple and see if the caliper releases. If so, some form of blockage in the line to that caliper. Les |
| Les Bengtson |
| Don Go for the larger gap that gives better burn with current fuels. Peter |
| peter burgess |
| Thank You to all. This is much more fun than looking in a book. Don |
| dab donald a baker |
| Dab What is a book? Peter |
| peter burgess |
| The things that predated the Internet. RAY |
| RAY |
| It's what RTFM refers to. |
| Paul Hunt |
This thread was discussed between 16/03/2009 and 21/03/2009
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