Friday, February 17, 2012

The silence of the bangs

I never cared much about the exhaust note of my bike, when I initially rode it around. But the stock silencer was an enormously long one and looked totally weird. My mechanic at that time (Jaf from Chennai) swapped it for a shorter one.

I'd never given it much thought after that, but one day as I was ripping down a flyover, the silencer fell right off! Apparently the mounting bracket had cracked, and the secondary bracket bolt loosened due to vibration. I never noticed that and when I rode full speed over a rut in the road, it just fell off. It looked pretty bad, vehicles swerving around avoiding hitting that thick piece of metal on the road. Fortunately there was a traffic cop who held the traffic off as I scrambled to fetch it.

I rigged it back temporarily and then the following day, I went over to Nandan's to find out where to get it fixed. For some reason I couldn't get it done that day and Nandan lent me a silencer to use until I could get mine fixed. It was almost exactly the same as the older one. A few months later, this one broke its bracket too, and this time I went back to Nandan, to retrieve my old one and get it fixed. We could not find that anywhere amongst the huge piles of spare parts, so Nandan said "Hey, I have an experimental glass wool thing, try that out, keep it if you like."

Once I'd hooked that up, I was totally hooked - It had a nice bassy roar and lovely idle beat. It boosted performance enough to notice. But it was a little noisy and since it had been made by chopping and welding, the finish was not quite up to spec and despite my grinding and epoxy filling and painting, it was not possible to make it look aesthetic.

So I decided to build one of my own, and promptly chopped the older silencer I had into two halves, and figured out a way to bolt the two halves together as follows.

The lower half

Upper half

The stuff that was inside, which I knocked out.

The "blueprint"
Two studs made of a copper rod to enable bolting it together
A spacer I cut from a rubberized dumbbell

Close up of the assembly

At this point it was just a hollow bottle shape, and when I put it on, just for kicks, it sounded like a tin can.
Now I had not much idea about how silencers work, all I knew was a certain length would resonate nearby certain RPMs, thus boosting scavenge. I was under the incorrect impression that a certain back pressure was necessary for proper running. Thus I thought I'd need to put in something there that would be slightly restrictive, but yet allow the gas to flow in a more or less straight path.

My first experiment involved getting a number of aluminum tubes of 3/8" diameter and packing them across the length of the silencer. I thought "OK that wont be as restrictive as a baffle, but there will be some smooth restriction of flow, due to  the thin tubes".
I put it on, and it still sounded like a tin can, so that was the end of that! But I believed the tinny noise was due to gas entering the wide part of the silencer body. I bought a thick aluminum tube that fitted snugly across the length of it.

Then I remember reading somewhere on some blog about the Brough Superior or some such ancient legendary motorcycle having a spiral baffle and blowing smoke rings. I had no idea what a spiral baffle looks like, but I thought "Aha! I'll put a spiral strip in a tube and the gas will spin around slowing a bit and I shall have a glorious and unique design."
I spent the better part of a day hacksawing a 1.75" strip of thick stainless steel from a sheet I had. Then I decided I'd twist it into a strip that would fit in the aluminum tube. It was an exercise in frustration - That piece of Al was completely stubborn and all the kings men and wild horses could not have twisted it into the tight, even spiral that I wanted. I tried hammer and vise, and vise-grip and bare hands, and gloved hands and I finally gave up after some bruised knuckles and bleeding heart. So the whole spiral idea spun away into oblivion.

Then I thought "OK, while I'm at it, maybe I'll go back to my initial idea, but this time I'll put the thin tubes in the thick tube, and no gas will leak into the main silencer body - It will be like a long, straight through pipe, except for appearance."

Instead of putting long tubes through and through, i inserted small (3") pieces of 3/8" tube on either end of the bigger Al tube, wedging in enough of them to pack tightly. Some I hammered into a slightly flat shape so that I'd get a denser packing. This should work!!
But this was again not to be... Same old leaky tin-can noise... Arrrrrgh!

Then I decided I'll go ahead and use the tried and trusted design, use a perforated tube and pack the gap between with glass wool. After much study on the intertubes, I realized that the ideal silencer was no silencer, and all the stuff was there to muffle the sound (obviously! it's called a muffler/silencer, not a "gas flow constrictor"). I also learned that the tinny sound was not so much due to the gas flowing incorrectly, but simply the effect of a loud bang happening within a hollow pipe.

So I started drilling holes in the tube, and got tired after about 40.
Then I thought I ought to try with something more easy to prototype, before committing to this design. Suddenly, I remembered I had this old rolled up aluminum sheet with holes (that I had originally made for this very purpose many many months ago, and relegated to a junk box while I dallied with all the unworkable ideas.

The shiny thing in the corner is the down tube using which I rolled this aluminum sheet into a tube.
Glass wool, however, from what I had heard of it, was a nasty substance, just ready to get into your skin and lungs and eyes, I wanted no part of it. I looked on the net and some people were using wire meshes and stuff for silencer packing with good results, so I decided I'll use steel wool - the maximum danger seems to be tetanus, and that's avoidable, as opposed to silicosis or some such horrible ailment you may get from inhaling microscopic glass.

Trying to buy a small amount of steel wool was a challenge. I ended up buying 5 KG, which is a lot of it! Finally, today, I stuffed about a kilo and a half in the gap, with the reverence of a Christmas ritual, and rammed it in tight. I fitted the silencer with bated breath and fired the beast up, and SILENCE! Finally it was doing what it was meant to! A silent silencer, with nothing that is obstructing the gas flow. So silent, that now the valve train noise is unbearable! Something quite charming about a muted thump that's barely heard at idle, yet without the whiny sound associated with the stock Enfield silencers.

So this week I'll drill the remaining 360 odd holes in my thick gauge tube, and replace the thin rolled sheet tube with this.

My calculations seem to point to a resonance frequency of about 3300 RPM - They say a glass pack is like a very long collector pipe, and I have about 67 inches from exhaust valve till the end of the silencer.
So that would put the ideal scavenging RPM range somewhere close to peak torque ate about 3000-3500 revs. This would be very good, as the major portion of my riding is done at between 2800 and 4000 revs, and a boost there would make it more relaxed. 
I might go a bit easy with the steel wool now, maybe I like a little more of ze what you call - "Ze thump"

Remains to be seen if the hard rubber spacer thingummy withstands the heat. If it starts burning, I'll have to make that piece with metal somehow.

Altogether cost me about the equivalent of 25 US$, including the value of the silencer that I cut up. This is what you can do with an Enfield!

Monday, February 13, 2012

Throttle wide open at Kari race track

Racing bikes...

On the one hand, the sheer excitement of being able to actually ride on a race track, and be trained by experts, all at a very affordable price!
On the other hand, the awareness of one's own meager riding experience and skills, and the fear of possible failure, injury to flesh and steel, and humiliation.

But the former won the day, and I rode down to Coimbatore, to attend the indiMotard T.W.O. track school event.
On the ride down, my ride buddies found it quaint that I'd wanted to bring a Bullet of all the things - One expressed surprise that I'd often out braked him at the speed breakers on the highway. 

Somewhere along the way the bike suddenly dies and I coast to a halt... I forget the cardinal rule with my bike - "If it stops without any reason, it's a fuel problem, it's probably in reserve".

I cranked it like a donkey, checked the spark plug, tapped the carb to free the float if stuck, but nothing. Then i checked the fuel flow and saw it was in reserve - As far as I can remember, the only time my bike ever gave out mid-journey was due to either lack of fuel or a stuck carb float... And each time I'd done all crazy things trying to start it (including once pushing it uphill on a steep flyover in Chennai to try to get a rolling start, thinking the battery was dead) except the most simple thing - to check the petrol!

So much for the famed unreliability of Bullets.

We climbed to Ooty, all of 36 hairpin bends, lovely road, lovely weather, but nowhere near as scary or difficult as the Himalayas. On the downhill section, at some point I suddenly found my front brakes going spongy. I quickly stopped, using the very inadequate and worn out rear, and looked for any damage, lost brake fluid etc. All seemed fine, then i touched the brake caliper unit and it was burning hot. Seemed like the brake fluid had boiled due to aggressive use over the entire descent. After a 15 minute break waiting for it to cool, we set off and my buddies graciously agreed to ride slowly for a while, just to be on the safe side. We soon hit the plains and the brakes worked just fine. Then a lot of traffic, all the way into Coimbatore city.

In the morning, I taped the headlight and indicators, and took off the main stand for safety reasons, as advised. Then we set out for the track about 15-20 KM away.

I had no idea what to expect there, but no sooner than I saw the instructors however, that I knew things were gonna be great - you can just see it - there are people who have things and do things and there are people who be things - These guys were not the guys who "have bikes" and "do racing" - they "were racers".
There were lots of R15s and P220s, hordes of CBR 250s, some Ninjas, the odd R6 and Duke 795 monster.
We started off with a classroom and much of it was familiar to me as theory - Apex points, no rear brakes, throttle modulation, slow entry, fast exit - but I'd never given it much thought, since I never ever expected to ever apply that theory on a track.

Then we got on the first track drill, by following the instructors on the track for a couple of laps, slowly, first on the outer line, then the inner, then the middle, to get a feel for the track and identify any markers. Then came the single gear drill... We were supposed to ride the track in one gear without any brakes. It wasn't that hard for me, because I decided beforehand(wisely), that I would concentrate less on going fast and more on doing what had been told. Besides my 3rd gear is good for anywhere between 20 and 90 kph, so that was that. I was disappointed by the fact that many of the guys were not following the no-brakes rule, coming too fast into corners and correcting with the brake. Even more scarier was the sight of seeing the brake lights glowing mid corner.

After a couple of drills, at some point they said, OK just ride around the track now, any which way - and then everyone went nuts, and even so did I foolishly, rather than trying to apply what had been taught in the drill, everyone, including me started just gunning like crazy and taking totally incorrect lines - I was stupidly chasing down the bike ahead of me, rather than concentrate on the track. That's when I saw the first guy deck his bike - it was a blue R6 and it went down at the "bowl" - a relentlessly long sweeping curve, which I personally felt was the most difficult part of the track to drive fast.

Then we were given more "track-gyaan" in the classroom, and did drills for entry and exit of each curve - there were little blue X marks on the track at the good entry and exit points and we were supposed to ride as close to them as possible... One drill for entries, one drill for exits, and each time to attempt getting the apexes correct. It wasn't at all going well for me... I touched my crash guard down and got a bit jittery, so I started taking more lazy and invalid lines. The instructors were eagle eyed and they hailed us down to talk to us and correct our mistakes - I loved the fact that they had great patience, and very objectively encouraged us to get it right - not at all a "school" kind of sternness or reprimanding. Once in a while they led us around the track, pointing and signalling at us as to, where the markers were, when to open the throttle and so on.

There was Anand, really experienced, who raced extensively in club events in the US, and Joshua who led my drills (who's also a pilot), and Daniel 'Dodo' - who I'd met in 2004, at the Madras Bulls group, and 'Schumi' from Overdrive, and of course, Prashanth who had done all kinds of crazy things on the track with Bullets and Yezdis, back in the day. 
They seemed to know every kind of bike on a first name basis...

Obviously my noisy old beast of a clunker attracted some attention, and enough good natured ribbing about the only three tools ever needed to fix a Royal Enfield...
A small hammer, a bigger hammer, and a matchbox to set it on fire. They forgot about the 4th tool, the nice guy who usually rides on one!
Dodo especially, hid his pain as Bullets were joked about, since he himself owns and rides several, but then again all the indiMotard guys own an Enfield in some form or other, and ride them, so LOL!

During the drills when we were allowed to use all gears, and brakes, people were falling left and right, every which way. I was once in a while gouging my crash guard into the ground and it wasn't doing much for my confidence.I was glad I didn't fully lose it though. My (biased?) opinion was that the drills were actually quite simple, and there was absolutely no reason to fall if you followed instructions and didn't act too gung-ho. This was later vindicated when I took a joy ride with Anand on day 2 at a blistering pace on a Ninja - at times the horizon seemed almost vertical from my view, I had the tank in a white knuckled death grip, and as he snapped the bike to and fro across the chicanes, the G forces made me feel like my liver and pancreas were doing a little dance inside. I daresay he could have easily maxed out the capabilities of the lil' green Ninja 250 if he'd wanted to. All our level 1 guys speeds were nothing compared to this.

At the speeds at which all of us Level 1 guys were riding, the only reason to fall during the drills, would have been rider ineptness or panic reactions. There was no way anyone could have been approaching the traction limits of the bikes, if they rode on the right lines as instructed. 
I took the policy of easing off if I took the wrong line, and trying to do better the next time around, rather than try to gun it when it's clearly going way outside the proper path. I was very wary of falling, for fear of damaging the bike, which may have been either a good or bad thing - good because I didn't get shaken up and lose my nerve, bad because perhaps at points I didn't push my limits, especially on Day 1.

After lunch we had the brake drills, where we had to start off from about 10 meters away and brake smoothly to stop exactly at a given line. I did the first drill and heard some "chak chak" noise from the rear - braked a little too much and stopped short. Second time round I noticed while waiting for my turn that some of my rear sprocket teeth were broken off... I was like "Oh hell! Of all the times!". I did the second drill anyway, managed to stop on the line, and then took a break to inspect the damage...

Prashanth of "Let-me-tell-you-about-the-time-when-we-completely-destroyed-RD350s-on-the-track-with-our-bullets" fame, tells me "If less than 7 teeth in a row are broken, just tighten the chain and keep going! It will work just fine".

Inspection showed however that about 12 or 13 consecutive teeth had been sheared of, and a couple of them right at the roots. It seemed that the chain had been quite loose and the hard ride down had caused the damage. Prashanth told me where to go get it fixed, and I had to skip the rest of day , since it was about 4:30 PM and a Saturday, and I needed to get it done before the garage folks closed.

I tightened the chain by several notches, and set off to the city again - Even with the busted sprocket, I could not tell there was anything wrong now! Such is the nature of the beast.

I spent the rest of the evening getting the parts, and holding a torch for the mechanic guy when the power failed. Very decent chap, he had gotten word from the track guys that my bike needed a sprocket job, and he worked fast and hard, in the poor light to get it done for me.

Got back to the hotel, had dinner, and then joined a friend and hung out with the instructors for a while... Everyone called it a night and then it was just me and Shriram, a young chappie who'd just joined indiMotard and we got along really famously, and kept blabbering on till almost 2:30 AM.

The next day dawned, and I was feeling a bit nervous, since I'd not ridden to the level I'd be satisfied with, the previous day.
We did a couple of sessions and though I did better on the chicanes, I was completely inconsistent and totally off on the first corner and the bowl curve. We were supposed to do the whole combination - everything we did in all drills combined - brake smoothly, enter on the blue X, apex it, exit on the blue X, throttle wide open...

I consulted with Schumi, about the right line for my troublesome areas, and tried to make sense of the shape of the track. He emphasized that the point was to get the line properly, and that speed was the side effect of correct riding, not vice versa.

Anand advised to concentrate on just one of the troublesome points per lap, rather than stress out, trying to ride the whole thing perfectly, and to relax.

After lunch, I walked down to C1 and did a sighting from several points, as to where the X marks were (each time before when I rode, I'd been hunting for the second X and found it way too late)

Then it was time for the final session of the day, and somehow things just started to fall into place for me. I did these things...
  • I braked slowly and smoothly, way way before the bend, so I'd not use an aggressive downshift to control speed.
  • I realized I needed to swing the bike deliberately at the S and Z bends - Earlier, I had been leaning it in fast, but letting it straighten on its own, which made it take too long to lean in the other direction.
  • I turned in a little later consciously - this helped me judge the right apex point
  • I looked far far ahead on the track.
  • I taped over the rev counter as advised (speedos had been taped over on drill 1 itself)
  • I sang (in a very ad hoc nursery rhyme like tune) to myself, telling me what to do - something like "Now take the first X, cross the oil patch, take the second X, look at the ape-X... Swing it right and, hit the apex, gun the throttle, swing it left now.... when its the 100, press the brake-ed, when its 50, you down-shifty...."
After a couple of laps, I was feeling really good, I managed in many places to up shift before I even hit the second X, coming out of the apexes. I still did have to take a slightly easier line at the curve where my crash guard would bottom, but at least I got some consistent line there. Next time I'll get a higher one!

Each time around, I eased off on the main straight, relaxed a bit - I was totally unconcerned about lap times - straight line top speeds were hardly the point of the whole exercise - as one of the instructors said, even a monkey can top out any bike on a straight line!

It was a glorious 10 laps or so, I think, until the red flags waved, and in the last one, I managed to actually keep throttle fully wide open coming out of the bowl. I was really grinning when i got back to the pit. I probably made a horrible lap time, even discounting the straights, but I was happy because I had learned something.

After that there was some open session time, and Dodo took my bike out (while I rode pillion with Anand on a Ninja)  - Dodo was able to ride the hell out of it, leaning motocross style, avoiding the crash guard scraping, putting the toe out under it to gauge when it would touch. He managed to outdo many of the nimbler bikes on the track, with my ponderous lumbering beast.

There was one particular guy, with a Splendor... He was doing an amazing job, of course the bike was not quite up to ripping down the straights, but on the curves, he had a perfect consistent line, and was a treat to watch. Then there was this souped up screaming Shaolin that would hold a CBR all around the track, lose on the straight, and then catch up again in a couple of bends.

All this convinces me that it takes a huge amount of skill to get the maximum out of a bike. I was told (and I am convinced), that I should try a more nimbler bike, so that I could learn faster with less effort. I will probably do that, but I will definitely stick to my Enfield primarily until such time that my skill reaches a much higher level - of course, by then, I'll do a Fireball conversion, so it will once again be way beyond my skill to max it out.

I hung around till the end, hobnobbing with all the chaps, and we went back to the hotel. Spent a couple of hours with the indiMotard guys and Karthik from TopGear India. Had dinner and went to bed, deciding on a relaxed start the next day for the ride back home.

Next morning me and Karthik rode back together to Bangalore, we started at 11:30 or so, and he maintained a perfect consistent pace on his CBR, just at the cruising speed of my bike, and we maintained approximately 115 to 120 kph for about two hours non-stop on the nice Salem - Krishnagiri route. Bike was roaring beautifully, a very relaxed and non-tiring ride, we hardly knew by the time we were in Bangalore city, and despite the slow progress through the messy traffic at Coimbatore and Bangalore city limits, we'd reached the forum mall by around 4:15 PM.

Altogther a really wonderful experience, I'm certainly going to try to make it for the Level 2 course next month, and I am bringing my black, noisy, hunk of cast iron too!