LCGB Forums

Hi All,

I've been playing around with my newly built GT186 motor which is going well apart from hitting a ceiling when it gets to 6500rpm (carb jetted as recommended, timing set to 21 btdc, TSR Evo pipe...)
It's certainly got some poke about it but I have built it using the existing Harry Barlow built crank which has a 116mm Conrod and an Li taper.... and I am running a Varitronic ignition. I'm considering changing the crank to something more robust whilst the going is good to a GP tapered crank and also then changing the ignition system to suit. I could just change the flywheel I guess but If I'm doing this I like the idea of having a full DC system and was wondering what recommendations would be on -

Crank - 58 or 60mm, does the extra stroke make much difference, and
Ignition/flywheel etc - what system would work best? Obviously the Varitronic is a complete package but if I am to move away from that, what would be a good choice of components?

Richard Taylor doesn't speak highly of systems like the Varitronic but I am assuming it is good to have advance/retard to some degree?

I'd be grateful for any opinions, preferably ones the won't break the bank! The GT cranks look great but they're not cheap, hoping to keep a bit of a lid on it..

Thanks!

I love full DC ignition. Really strong spark from tickover, super-reliable and so simple to diagnose.

Any stator is ok as you only need the lighting coils. You can use the stator mounted pickup or an external one; I prefer external.

The DC ignition and regulator that Anthony tambs sells is pretty good and works with kytronik if you choose to use it.

If you get a gp taper crank, I think a 2kg flywheel is a sensible choice for performance without being too light.

However, on my next build I'll be using the aprilia rs125 based system that richard Taylor developed as it is 3 phase, so almost ripple free on the DC side. I won't be using aprilia ignition though, probably fixed or maybe add kytronik if I want to mess about.

Personally, perhaps because I got used to really light flywheels with racing, for road use, I think the Vega/J range flywheels are a good weight, as you can set a tick over & the mass allows for better acceleration & can be far more forgiving.

(I'm one of the cynics that doesn't believe in the necessity to go 'pointless' in the name of reliability, & by all accounts with what I know of Indian set-ups, conventional contact breakers with a 12 volt system are a far better bet.....)

Anyway, you no doubt want an electronic kit, so the AFR will most probably be the lightest @ 1.38 kg. There must be thousands of these in use, so worth thinking about. You might want to run such a system as it is, then consider a retarding add-on @ a later date. In which case, if you can get a programmable CDI, then the choice of ignition curve is your's (or the Dyno operator!) Similar to the AFR, though hardly ever heard of these days, are the PX based systems, which are IMHO a far better bet than the Indian set-ups....

Which leads me to think that, @ 1.85 kg, what you already have is not that heavy. If it were me, I'd persevere with what you have as the smaller flywheel taper should cope. The GT is more of a torquey plodder, whereas a TS1, say, is very revvy by comparison, & the smaller taper might not last too long. That said, I would try & find out whether anybody has reduced even that Varitronic weight & were there any detriments in doing so.

BTW. I'm not dismissing other advice you have been given about other Manufacturers, it's just that the Varitronic shouldn't be too far away from one of the better systems, despite the ignition curve being unadjustable.

However, if you are struggling to spend all of your cash......

Could be wrong but from memory I thought the variatironic of kits should be set to 24 degrees (not 21) at tick over ..... I’ll try and find some info but I’m quite sure....

Update casatronic = 24 degrees according to RLC , variatronic 21 deg according to cam lam...

The spec' says it retards 8 degree so 24 would be a good starting point. Plug chop as you go.

Thanks for your answers, and really interesting to hear about the lighter flywheel of the Varitronic maybe being ok on the Li taper crank.... the only reason I was considering changing is because the general advice is to always use a GP tapered crank because of the extra meat on it... but physics would suggest less weight equals less stress so less strength needed possibly.... I am merely a ‘garage tinkerer’, learning all the time and have had no experience of cranks twisting or anything like that and it’s my first ‘proper’ engine build so I am led by the advice of those with more experience.

The crank was built by Harry Barlow (Pro Porting) using a decent quality 116mm conrod and quality bearings, not sure why it was built on an Li taper but I guess it is probably more robust than a standard 50 odd year old standard crank with old bearings. If changing it is not necessary with a lighter flywheel I’d rather save my money, I just don’t feel over confident in light of what I’ve read.

Regarding the power, I haven’t had it dyno’d yet but it is definitely way more pokey and rapid than my mates Stage 4 GP200, albeit it tops out at about 6500 revs in each gear, almost like its restricted and therefore probably 65 - 70mph (17/46 sprockets, Pacemaker gears, pulls fine uphill etc)

One more question, just so I’m convinced, is advancing the timing to 24btdc likely to cause any over heating issues? If it’s a safe way to go I might just leave the crank alone and save myself some money and bother.

I appreciate the advice and knowledge gained from you guys, thanks.

I've got one of the GT 60/110 cranks in mine along with SIL electronic ignition converted to DC and a 2kg flywheel, works really well. The extra stroke gives more torque and helps to pull taller gearing, mine is 4.8 with a Franspeed Race which I think it would struggle to pull with a 58 stroke crank

burnside wrote:I've got one of the GT 60/110 cranks in mine along with SIL electronic ignition converted to DC and a 2kg flywheel, works really well. The extra stroke gives more torque and helps to pull taller gearing, mine is 4.8 with a Franspeed Race which I think it would struggle to pull with a 58 stroke crank

Quick question how’d you get the 4.8 gearing.?
Cheers Shane.

shane BBoys wrote:

burnside wrote:I've got one of the GT 60/110 cranks in mine along with SIL electronic ignition converted to DC and a 2kg flywheel, works really well. The extra stroke gives more torque and helps to pull taller gearing, mine is 4.8 with a Franspeed Race which I think it would struggle to pull with a 58 stroke crank

Quick question how’d you get the 4.8 gearing.?
Cheers Shane.

Sorry that should be 4.89, Li150 16/46

burnside wrote:

shane BBoys wrote:

burnside wrote:I've got one of the GT 60/110 cranks in mine along with SIL electronic ignition converted to DC and a 2kg flywheel, works really well. The extra stroke gives more torque and helps to pull taller gearing, mine is 4.8 with a Franspeed Race which I think it would struggle to pull with a 58 stroke crank

Quick question how’d you get the 4.8 gearing.?
Cheers Shane.

Sorry that should be 4.89, Li150 16/46

I was thinking along them lines for my read valve 186 Muggy with the same GT 60/110.
Cheers Shane

Standard Sx/TV gearing is 4.8 15/46 or GP200 box on 19/46

Or pacemaker 18/47