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finally got around to dry fitting engine, wheels etc to my flat track project - like a kid with a new toy or a dog with 2. ... bones (1980 T6 frame, 1970 T120 engine)
so exciting to see a project starting to look like the real thing
the dry fit is to identify what bits are missing (this project started with a bare frame, no swingarm) - there are lots of things missing
not so sure about the xr750 seat now, but we'll see as i progress
engine has a boyer ignition fitted but no coils - am tossing up whether i should remove the boyer trigger and go with a whole pazon system including dual coil unit under the tank, just like my 76 T140
rory
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Hi Rory,

engine has a boyer ignition fitted but no coils - am tossing up whether i should remove the boyer trigger and go with a whole pazon system including dual coil unit
o_O This is confusing. Boyer-Bransden and Pazon e.i. are apparently so similar that boxes and trigger units are interchangeable (Andy and his wife used to work for Bransden).

So, by "engine has a boyer ignition fitted but no coils", do you mean the engine has the trigger unit but, as well as not having any coils, you don't have the B-B 'box'? If so, then possibly replacement with new Pazon 'box' and trigger unit might be wise, especially as Pazon is closer to you than Bransden if anything goes wrong.

Then what do you mean by "dual coil"? All the e.i. from both Bransden and Pazon are capable of working a dual-HT-lead coil, it just has to be the correct primary resistance for the 'box' - 3-4 Ohms for B-B MicroMk.4 and MicroDigital, Pazon SureFire and Altair; low-resistance (0.5 Ohm?) for B-B MicroPower and Pazon SmartFire.

My only concern with dual-HT-lead coils is practical - you have to work out a mounting for it. Otoh, if the frame has the 'oles for standard coils, why wouldn't you use 'em? :unsure: Grommets to fit are available, as are coils to fit in the grommets; another thing ticked off the to-do list, another step closer to a rideable bike? (y) What advantage would any of the dual-HT-lead coils offer over two bog-standard single-HT-lead coils?

just like my 76 T140
Ime, having the same e.i. on two different bikes does have an attraction - both my T160's have the same Rita bits one 'em; trying to diagnose a running fault, when testing ignition components, it's handy having a source of alternative components for substitution testing. However, if you have both Boyer-Bransden 'box' and trigger unit and the system's the equivalent of the Pazon on your other bike, aiui you have your source of alternative components for substitution testing. (y)

Hth,

Regards,
 

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thanks as usual Stuart - you've made me rethink the throwaway thought about the ignition
the trigger unit is fitted to the engine see photo, but the box that came with the engine isnt - yet
the box is a micro mk III unit, but the cardboard box it came in says micro mkIV - not sure where the box sits in the history of this engine. i assume the engine builder (USA apparently) fitted the trigger unit
my t140 has a pazon surefire box and pazon trigger as well as a dual ht lead coil mounted on the frame under the tank (nippondenso) - doesn't look like the one on the pazon site
first i've heard about interchangeability between the 2 brands
my reading on the boyer site suggested that i needed to use 2x6v coils with the MKIII unit - but i'd be happier with a dual lead coil mounted under the tank - i prefer it to the bulky 6v coils under the seat - and i dont have the tray to mount them in - more bits required. i was also thinking that the same system on both bikes had the benefit you mentioned. maybe i should consult the guys at pazon or boyer about my bits
something else i noticed while getting these pics is that someone seems to have used 5mm screws to mount the points cover on the T120 engine - the ones that screw into the threaded posts - and the screws only go in a few turns before the start to bind - any idea what size and thread these screws should be - the ones on the t140 seem to be 3/16 32tpi
again many thanks for your insights
rory


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Hi Rory,

trigger unit is fitted to the engine
box that came with the engine isnt
box is a micro mk III unit, but the cardboard box it came in says micro mkIV - not sure where the box sits in the history of this engine. i assume the engine builder (USA apparently) fitted the trigger unit
B-B Mk.4 superseded the Mk.3 (iirc in the early naughties?); they're basically the same analogue electronics, just Mk.4's don't have the Mk.3's variations in where individual units start to throw wobblies if the Volts fall below 12V. The trigger units are the same/interchangeable.

I'll speculate the reason for the Mk.3 Transistor Box in the Mk.4 cardboard box is your engine's seller kept the Mk.4 bits and gave you the Mk.3 ones? That your pictures show the red-insulated bodgers terminals fitted (they're normally just loose in the box when it's first opened, to be squashed on the wires by whoever fits the ignition) also suggests the unit's been used?

my t140 has a pazon surefire box and pazon trigger as well as a dual ht lead coil mounted on the frame under the tank

my reading on the boyer site suggested that i needed to use 2x6v coils with the MKIII
Uh-uh. If your Mk.4 cardboard box came without destructions, they're these on Bransden's website; note not only they say they apply to both Mk.3 and Mk.4 (not strictly true but I'll bore you with the details only if you decide to use your Mk.3) but also:-

General Data

4) For ... high compression engines two 6 volt coils (2 Ohm resistance) in series, or one 12 volt 3.5 ohm or more primary winding resistance dual output coil will give the best results.
... so "2x6v coils" are only one option specifically for a twin-cylinder engine, irrespective of whether the e.i. is B-B or Pazon (or Sparx, Wassell/Vape, Tri-Spark "Classic Twin").

Longer explanation
All e.i. for our heaps (except specifically Tri-Spark and Sachse for triples) hark back to the original Lucas Rita and Boyer-Bransden of the late 1960's/early 1970's. When they were first marketed, it made commercial sense to make the (then-expensive) electronics suitable for as few and as many separate coils as possible; the minimum is a single coil so the electronics 'box' has a single switched output (Black wire on pretty-much all of 'em except Rita or Tri-Spark); a '12V' coil designed to be switched by points (all these e.i. basically just replace points and auto-advance unit) has a primary resistance between 3 and 4 Ohms.

Coils intended to be switched by points, the 'Volts' are actually an indication of the primary resistance. The primary design criterion of all such coils is they draw between 3 and 4 Amps when the rated Volts are applied across them. So Ohm's Law (E=IR, Volts = Amps x Ohms) says a '12V' coil must have the aforementioned primary resistance between 4 and 3 Ohms respectively, a '6V' coil must have the primary resistance between 2 and 1.5 Ohms respectively, a '4V' coil must have the primary resistance between 1.3 and 1 Ohm respectively, etc.

Multiple coils must be connected 'in series' to the Black wire - the wire is connected to only one coil's "-" terminal, that coil's "+" terminal is connected to another coil's "-" terminal; on a twin, only that second coil's "+" terminal is connected back to the battery +ve terminal.

When individual resistances (in this case each coil's primary resistance) are connected 'in series', they're cumulative - each '6V' coil's primary resistance is between 2 and 1.5 Ohms so two add up to between 4 and 3 Ohms, same as one '12V' coil. The dual HT lead coil connected to the Pazon SureFire has a primary resistance between 4 and 3 Ohms; were you to connect it to the B-B, it'd work exactly the same.

someone seems to have used 5mm screws to mount the points cover on the T120 engine - the ones that screw into the threaded posts - and the screws only go in a few turns before the start to bind - any idea what size and thread these screws should be - the ones on the t140 seem to be 3/16 32tpi
;) Close but no cigar - they're specifically 2BA.

Of the four similar-looking :whistle: - 2BA, 3/16", No.10 UNF (aka 10-32) and M5 - 2BA has the smallest major diameter - 0.185" - while M5 has the largest - 0.197". 2BA is actually 31.4 tpi while M5 is 31.8 (and 3/16" Cycle or BSF are also 32). Some will fit together - M5 female thread on a 2BA male thread, but not the other way 'round.

first i've heard about interchangeability between the 2 brands
Pops up every now-and-then on BritBike?

Hth.

Regards,
 

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i have had a 22 year relationship with a MK3. Just one breakdown when the black box just died suddenly and was absolutely dead. replaced the box only and that is still running now. Does what it should and only problem is a very low battery will make starting difficult. Just keep the battery in good shape.
 

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Took a ride out to view some bush fire ravaged areas close to my home today. We’ve had some rain since and these eucalyptus trees are reshooting already. Won’t know there’s been a fire in a month. You might spot green grass reviving in a creek photo. Nice warm day out at around 34C RR.
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Geat pic! Sad about the fires. Glad to see you're okay and out and about with the 72! All the Best from Canada (too much snow on the roads to ride right now).
 

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Interesting to see how quickly the landscape recovers - all the leaf litter cleared away and room for new seeds to sprout. Keep us posted on the re-growth?
 

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Geat pic! Sad about the fires. Glad to see you're okay and out and about with the 72! All the Best from Canada (too much snow on the roads to ride right now).
Ditto on this Rambo......
 

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Geat pic! Sad about the fires. Glad to see you're okay and out and about with the 72! All the Best from Canada (too much snow on the roads to ride right now).
Yeah the fires are settling a bit. Sad that 3 US firefighters were killed when their Hercules crashed. We get these bad fire plagues every decade or so. Some 187 people charged with arson can you believe ( the bastards). Old ‘72 just keeps rolling along. 😁. Yeah big bad winter storms reported up your way and snow so high I could only gasp!!
 

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Some EI trivia for ya all. Old ‘72 stalled on idle today, a rare occurrence. Just earlier, Old ‘72 kicked back on the start, another rare occurrence. Old ‘72’s surley conduct was all about the battery delivering low volts to the Pazon unit which must then advance the timing causing the kick back behaviour. No break down of any sort, but a new battery may be order. RR. 😀
 
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