Indian GP Engine Build Part 8

Buzzwanglelisatering!

The woodruff key has arrived from Steve Diffey, so I now have two. Luxury. Time to switch focus to the other side of the crank.

I'd picked up a BGM stator and flywheel at a discounted price from Scooter Center, so intended to use these (anyone noticing a pattern in my sourcing (hoarding) of cheaper parts for use in projects?). I did wonder if the 2kg flywheel weight might be too heavy, being obsessed with lightened flywheels like most old scooter boys...It came up in a phone conversation with Steve Diffey and he couldn't see a problem, preferring to use a mid-weight one for touring use, which allow a lower tick-over and provide a slower drop-off in power when hitting a hill or headwind. Looking at the flywheel chart in Sticky's manual, 2kg is significantly heavier than the 1.35kg AF ones I'm used to using, but sits right in the middle of the flywheels available on today's market. She'll be right. On thing missing, possibly due to the bargain price, are fitting instructions. Well I've got detailed ones for using the stator with non-BGM flywheels...

The instructions are abvailable on the Scooter Center website, so I download them from there. Turns it you just bolt it on, strobe it and move if required. I don't have the proper BGM flywheel holding tool but a 32mm spanner does the job. It'll be a bit big to carry in a toolkit though, so one goes on the shopping list.
I do like the bigger GP exit arrangements for the stator wiring. Saves all that fiddling trying to get multiple spade connectors though a hole that's the same size as a spade connector...not that I've got any connectors on the wires yet.

Okay, time to get completely side-tracked by a new toy. I bought myself a Buzzwangle! The club also now has them available for members in most regional toolkits. I've got a couple of 200 barrels lying around for future projects, a Mugello and an AF Rapido (road version I think). I intend to use one for my next engine build and so am curious to compare port timings. First up the Mugello.

With the barrel and piston on I use a dial gauge to set the top dead centre mark. The BGM flywheel has lovely clear scribe marks for TDC and various BTDC settings. Very nice, and using these it's easy to see that my existing mark sits nicely in the centre of the TDC dwell, the gauge moving just as the scribe line reaches its outer edges on either side.

Checking port timings with the Buzzwangle is very straightforward, requiring only a thin bent feeler. I just bent an old one which I'll leave in the Buzzwangle box. There's no point me trying to explain because Sticky has provided a simple, easy to follow YouTube clip in his manual (https://www.youtube.com/watch?v=hWRTeAvhBG0). This covers the exhaust port. Just use exactly the same technique to measure the other ones.

The Mugello has the following timings:

• Inlet - 152 degrees
• Transfer - 112 degrees
• Exhaust - 173 degrees
• Blowdown - 30 (this is the difference between the exhaust opening and the transfers)

I'm not claiming any expertise, but these timings are all over the place. A standard Lambretta large block has a transfer timing of 120-124 degrees, so 112 is stuffed. At 152 the inlet is a little above what MB considers a touring tune (I know it's just one man's opinion, but it's a well written guide for an amateur like me) and at 173 the same is true for the exhaust.
Now having said that, looking down the barrel it's clear that the piston is significantly blocking the transfers at bottom dead centre. Simply fitting a packing plate under the barrel will solve this and probably bring the timing up to a usable 120 or so, especially as the kit has wide transfers and a boost port. However, that may stuff up the cylinder head squish clearance...

Mugello transfer and boost port (above the inlet)

Rapido transfer

So the Mugello is down but not out. It's just not a simple bolt-on, but are any kits truly? I should also point out that this is a very early Mugello and I understand that port timings have been significantly revised for later versions. I'll give it another go when building the next engine, whose casings may be totally different from these Indian ones...MB considers a blowdown of 30 to give a peaky difficult to set-up engine, which is certainly what I found when using the kit before.

Now to play with the Rapido.

The Rapido has the following timings:

• Inlet - 144 degrees
• Transfer - 128 degrees
• Exhaust - 182 degrees
• Blowdown - 27.5

This inlet timing is nicely in the middle of MB's recommended touring range of 140-150. Transfers at 128 is at the top end of MB's magic range of 122-128. Should work fine. The exhaust at 182 is big and the blowdown at 27.5 is on the large size. Both of which could apparently mean a loss of power on hills, etc. Taffspeed favoured large exhaust timings and MB talks about Terry always losing out on hills when riding his tunes against MB on one of his, but Terry was a large bloke! Hmm. Also this kit felt nicely torquey running a 22mil carb and BGM big-box. I'll be looking to run a 30mil and clubman type exhaust, so it might well work. Problem is it needs a rebore and new piston. Should I go to this expense?

Well, that was totally inconclusive! What is great though is that using the Buzzwangle an amateur like me can get some insight in to why a kit hasn't worked. Now it might well be a case of a little knowledge being a dangerous thing (stop sniggering down the back), but I've found it an interesting waste of time. I highly recommend a Buzzwangle! A whole new world of fettling awaits.

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