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BT-H Mag

Holmil

New Website User
Non-VOC Member
I have a BT-H mag on my Rapide which is about 5 years old and has covered 6 or 7 thousand miles.

Last night after about 10 miles I stopped for petrol after which the bike refused to start. On checking the plugs, which were new a month ago the spark seemed weak. The journey to the petrol station was ok, the bike started from cold second kick, the only sign of trouble ahead was a miss fire when pulling away from a roundabout a low revs.

I suspected an ignition problem, and after an hour or so of letting things cool down the bike started again. I pulled out of the petrol station and headed for home. After two or three hundred yards the bike dropped on to one cylinder and then stopped about another hundred yards later. I had to be carted home in the back of a van.

This morning I checked the timing which is exactly as it was set up. There is a spark but doesn't seem very strong. There is fuel getting to the cylinder but the engine will not fire.

On the final ride of last year the bike refused to start when warm, but I was at a friends house and after cleaning plugs we got it going and it got me home. I've been out three times previous to last night's outing this year but none involved stopping.

Has anyone experienced a similar problem with a BT-H or am I barking up the wrong tree? The bike is displaying the same characteristics as when the original Lucas mag was on its way out.

Thanks

Donald.
 

zundapp66

New Website User
VOC Member
Hi My bike has a BTH and it died in the rain yesterday, taking a look at the ignition system i found the rubber sheaf that holds the Ht leads into the ignition coils had perished and cracked allowing water into the coil and the lead to come off the metal contact spike in the coil. The Ht lead copper wires sticking out were also covered in green oxide which would greatly increase electrical resistance (caused by previous water entry) I dried it as best i could and wrapped the whole lot in insulating tape and the old bike got me to the east midalnds rally and back no problem.
Danny
 

peter holmes

Well Known and Active Website User
VOC Member
I also experienced this problem whilst on the Isle of Man at the rally in 2007, and it very nearly ruined my entire rally, it turned out to be faulty coils and apparently at that time, which would correspond to your five years of ownership this was a known fault. Whilst I was fiddeling with my non running Rapide outside a Douglas hotel a kind Vincent owner from the west country (Bernard) walked by, identified the fault and lent me his two spare coils that he always carried with him since his BT-H mag failed with the same problem, thanks Bernard, you saved my rally. In fact I rode home with the coils and then posted them back to Bernard. I then discussed the problem with the chap that makes the mags, his name escapes me, and he sent out replacements FOC, problem solved
 

Vincent Brake

Well Known and Active Website User
VOC Member
Well here's some story: yust coming home from a drive Adam-Luxembourg and a planned drive there with the aermacchi club.
It (I dont dare name this apparatus any more) broke down on me, not due to wet or any other wireing reason, It was only 2000 odd
km old (12 months) spitting back like a turbine engine, no good. (not off timeing)
The unit before this also broke down on me, (leaving me in Italy)
I dont mention the broken coils, no harm done, but 2x times the CDI unit?????

I am trowing them in the bin and am going for 12 v electronic system with a spare near my B---ks, yust in case.
either Pazon or Dutch mr. Beck.
Now its up to Alton, Lucas?? (OK I will stick a spare (charged) battery as well.

sorry Tony, to have mentioned this, but something is realy wrong with them.

Vincent (brake) Speed
 

Bill Thomas

Well Known and Active Website User
VOC Member
Hello Vincent, Have you thought about going for a D distributor, I went Electronic on one of my bikes, Not the same as you but if it goes wrong, Lots of trouble!!.My other twin has D type with a big 12v coil, I have had trouble with small coils, All you need for spares is a coil, points,and a condensor. All The Best Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
I agree with Bill on this. For a road bike the 'D' distributor, in good condition, has everything going for it and nearly all parts are small enough that a spare can be carried, (e.g. points, condenser, coil). If all else fails you can service it by the side of the road. And recon. units are available through MPH although I have no personal experience of these.
 

peterg

Well Known and Active Website User
Non-VOC Member
Howdy Chaps,

BTH's - The mounting strap for the coils places them with plug wires forward and primary wires projecting rearward in very close proximity to the engine cases. Between engine vibration, flex in this mounting arm and a tendency (especially if less flexible thick copper core plug wires are substituted) for the cowl to push the whole plot rearward, you run the risk of rubbing the wires through and experiencing a short. I try to bend the pins outward slightly to provide running clearance for the wires away from the case.
 

Alan J

Well Known and Active Website User
VOC Member
I'll stick with my old Lucas mag., for all it's faults-and I can always get J.B. to fix it for me!!-The other problem with proper coil ignition is that you need a good, reliable charging system!!-and they are "thin on the ground"!-I've probably opened the "floodgates" on this one!!
 

Bill Thomas

Well Known and Active Website User
VOC Member
hello Alan,I think you are right but good rebuilt Mags are thin on the ground as well. With the D set up you can go a long way on a full battery," Timetraveller " does a very nice kit for charging. I have an old mini alternator on my special and a very clever one from USA on my old racer. If my mag packs up on the Comet I have a Timetraveller kit and will go over to coil, Like the D. All The Best Bill.
 

Holmil

New Website User
Non-VOC Member
I have now fitted two new coils and plug leads sent to me by Tony at BT-H.

The bike starts if the carbs (monoblocks) are flooded and then cuts out almost inediately. Is this blocked jets or advance & retard problem? I have new plugs but have also tried older ones. I have taped the plug leads on to the casings minus their caps and the spark will arc between the two. I have cleaned out the carbs and blasted them through with compressed air. I have checked the tappet clearances.

The fact that the same problem persists on both cylinders makes me think the problem is with a single source, however I will try what ever sugestions are made.

Thanks again,

Holmil
 

vin998

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Hi Homil,

I have just had a BTH mag fail on my Vin. It was fitted early 2007 and has done approx 9000 miles. Last year it was no problem, but I did notice on occasion I had to kick the bike 4+ times to get it started which is not like my bike.
This year after a winter hibernation it was really difficult to start. I went through all the timing, connection etc and finally assumed it was the 4 months old petrol. Gradually the starting (especially cold) got worst and at the Severn rally I got it to start after 10 minutes kicking. At the east midlands rally a week later it would not start at all. Re-checked everything inc timing and also swapped the coils for a spare pair I carry and still no joy. There is a spark at the plugs, but I think the electronic timing is not working correctly so there is no spark at the right time even though the static timing is correct.

The final test was to after been relayed home was to take the BTH off and put the old points coil system back on. It started first kick!!! and ran fine, so the conclusion is the BTH is faulty. Haven't talked to Tony at BTH yet as his web site stated he is on holiday / working on prototypes until early July.

Cheers Simon.
 

Howard

Well Known and Active Website User
VOC Member
I have now fitted two new coils and plug leads sent to me by Tony at BT-H.

The bike starts if the carbs (monoblocks) are flooded and then cuts out almost inediately. Is this blocked jets or advance & retard problem? I have new plugs but have also tried older ones. I have taped the plug leads on to the casings minus their caps and the spark will arc between the two. I have cleaned out the carbs and blasted them through with compressed air. I have checked the tappet clearances.

The fact that the same problem persists on both cylinders makes me think the problem is with a single source, however I will try what ever sugestions are made.

Thanks again,

Holmil


Hi Holmil

This sounds very simillar to my recent post. Mine turned out to be ignition too far advanced. I hadn't run it before on unleaded, but that doesn't seem to be the case with your problem. I don't know if there's anything on that post that may help.

Good Luck.

H
 

Len Matthews

Well Known and Active Website User
VOC Member
Hi Holmil

This sounds very simillar to my recent post. Mine turned out to be ignition too far advanced. I hadn't run it before on unleaded, but that doesn't seem to be the case with your problem. I don't know if there's anything on that post that may help.

Good Luck.

H
I heartily agree with previous comments about Series D distributors; so easy to trace faults and put them right. During the Dutch Rally several years ago Jack Barker said "You've got a D distributor on your bike haven't you?" "Yes Jack". "Well, here's a spare set of points. I don't need them 'cos I'm using Lucas Rita now." On the last leg of the journey back to the Hook of Holland the engine suddenly cut out on the motorway near Rotterdam. Seemed like ignition failure so off with the distributor cap and lo! The tip of the moving contact had snapped off but thanks to Jack's gesture we were on the move again in less than fifteen minutes and still caught the ferry.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Hello Donald, It does sound like it's the BTH, But you say it starts when you flood it ? I think it's a case of it tries to start when it feels like it, Just like the old mags on a bad day !. If you are sure you have the best petrol in it and the carb float needles are not sticking, put some soft plugs in it = B5ES with small gaps= 22thou,( If you think the plugs too soft you can change them when it's sorted ) And make sure the plug leads are on the right cyl'. If that is no good, any chance of borrowing a known good mag'. Good luck , Bill.
 

Albervin

Well Known and Active Website User
VOC Member
It has all gone quiet on BT-H disasters. Has the problem been fixed? Has everyone given up on them? I noticed when attacking my oil filter that both rubber boots protecting the wires entering (exiting?) the coils
were perished & split. Are replacements available or is it conforming tape & silicone time?
 

vin998

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Hi Albervin,

Still got to send mine back. Spoke to BTH and they think its the coils, but I carry a spare set which I tried with no sucess. Bike is running great on the old points coil ignition system. Got to admit, reliability and the ability to trouble shoot and repair on the roadside is a always in the back of my mind, so even if the BTH is repaired, I think I am going to stick with the points coil system as its easy to repair and carry spares for this system. Even if the charging fails, the battery I have has a range of 250 miles.

The rubber boots on mine had also split so I used self amalgamating tape. I think for the cost of these units, better quality boots could have been supplied.

As for others, I have heard that two people who attended the Greek rally were having problems with BTH mags. One misfiring at revs and another difficult to start just like mine!!!!!
 

bengunnhrd

Active Website User
VOC Member
I have BTH mags on two bikes and have been very satisfied with them, the advantages being much easier starting and smoother running at lower speeds.
I had a problem with one fitted to a Rapide, the bike which had not been started for a few weeks only kicked up on one cylinder. Thinking it was a fuel problem i fiddled with this and fiddled with that and it cut in on the other cylinder, ran the engine for a few minutes all seemed fine. Intending to go for a spin i got the bike out a week later and had the same problem, after taking the carb off more times than the barmaids k------ i realized i had got a mag problem. It turned out that one of the ht leads had been touching a cylinder fin and melted through to the core which had caused a fault in the mag. Sent it back to BTH, and was returned quickly at minimal cost. I have since replaced the ht leads with cloth weave outer covering.
 

Albervin

Well Known and Active Website User
VOC Member
Why did I tempt fate & restart this thread??? Today was a beautiful sunny winter's day so off for a ride on the Rapide. At the top of the pass that takes you from
the coast to the rest of the world the bike suddenly went onto one pot. A quick U turn & it was nearly all down hill to home. Number one pot (rear) was cold so
out came the plug; it was black but quite dry so I checked (the very hot) front plug, very dry & ominously whitish. A quick trace of the plug leads led to a loose connection
out of the coil. As mentioned earlier both rubber boots are perished so I need to replace them but why after 4 years did a lead decide to come loose? I replaced the front plug
with a colder one & will monitor. I have recently fitted K & N air filters which one would have thought might richen the mixture... It may have been partly due to the extra load
of the front cylinder hauling the bike but do I raise the needle first or increase the main jet size first if it continues to run lean ?
 
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