So I went to check out a disused airfield nearby (in the header) with a view to doing some sort of top speed run, as legally as possible, on level ground.
And whilst it’s a great moody spot (especially in the mist) and it might work for head-to-head over an 1/8 mile or something like that, unfortunately it wasn’t really smooth enough to even be thinking about trying to get near triple digits like i’d been hoping to.
Which sucks, I was really hoping it would be suitable as santa pod is such a looong way away.
Well, dismayed I went back to check out if any other options had magically presented themselves, and in fact they had!
Last year I booked in to an event at Dakota Raceway which was then cancelled at short notice, and given they’d cancelled all events for the rest of the year after that, I thought it was game over there.
But apparently they’re back, which is awesome. and they have a RWYB event on the 16th August….so….
BOOKED!
Unfortunately it’s also only 1/8mile rather than 1/4, so we still won’t be hitting top speeds and will need to gear right down, and it’s likely to be as rough as the other airstrip, but it’s organised racing with (presumably) proper timing gear and any racing is fun so hell tf yes. Plus I bet they have an ambulance on standby which is a lot more than we’d have out in the wilderness by ourselves.
No-prep, not no prep:
So given I’ve been kinda flat out with moving the last couple of years, i’ve not really done a whole lot to the bike. I was very lucky in that I was able to just build the current engine, put it in and it *relentlessly*worked*great* for a couple of years, despite much adverse weather and circumstance. Nonetheless, I still wanted to give her an at least cursory going over to check there weren’t any glaringly obvious issues pending which might escalate when being run repeatedly down some rough concrete. I also wanted to just listen and feel and check that what I’d been observing while out riding was actually grounded in reality.
Dyno time
Whilst my dyno still doesn’t really give reliable power readings (yet!), so i can’t really say “it has x hp” with any certainty (at all), it does let me observe the bike closely while it’s under load, which is something I don’t usually get to do (e.g. when riding).
Whilst I’ve been working on the 2019/gen3 i’ve been kinda spoilt since the Tuneboss ECU works over bluetooth so I was able to keep my phone connected the whole time and either watch the map or be datalogging or whatever the whole time – it’s been rather convenient.
However, this bike is built using “prev-gen” technology so it’s all laptops and USB cables to talk to the PCV, flashing ecus (very slowly) with a spaghetti of wires and a half-hour round-trip to make a single change (and risk bricking your ECU)..arg. I’m realising how easy i’ve had it on the gen3 xD.
Since i can’t fit a laptop on the fuel tank, I also can’t usually have the PCV software hooked up when it’s in gear and under load so being able to see the AFR values and just generally how it’s doing whilst feeding it different throttle situations, is pretty useful (again, on the gen3 the AFR gauge on the dash let’s me keep an eye on that while riding).
I’m sure I’ll figure the dyno thing (not being able to get truly comparable/repeatable results) out in due course, and in fact i have thoughts on this so I’m trying to not be too annoyed that it hasn’t worked perfectly like I expected right out of the gate, but instead am trying to use the roller in ways I *can* apply and are still helpful… like being able to see what the bike does at 60mph.
Power readings or not, that’s still incredibly useful from a diagnostic perspective. Imagine being able to observe, prod and poke your bike while it’s at speed and hooked up to monitoring gear? Very handy.
I had a few modifications planned for the bike and was hoping to get them done before Dakota but actually my takeaway from today’s session is “it’s great! don’t mess with it, go race”, so I’m going to do just that and give myself a break for once.
Forced modifications, vibrational harmonization:
The modifications mentioned above are neither whimsical nor through choice.
I feel like the timing chain has stretched somewhat over the 3000miles the motor has done so far and that’s effectively retarded the valve timing (i.e the angle of the cam vs the crank, not ignition timing/delivering the spark) which has pushed the power band higher, in the process separating the optimal “vibrationally harmonious” band (i.e. the rpm range in which the engine vibrates the least and feels smoothest in terms of reciprocating weights inside it – crank, piston con-rod, balancer/counterweight etc) and the “engine” power band (i.e. where the engine makes the most power). They used to be almost perfectly lined up which meant when she hit power it also got smooth and the combination was noticeable and the rear tyre would dig in in a very pleasing way.
The separation of the two ranges seems to soften the power hit slightly (and no doubt loses a little power in the process), and is not really what I would prefer, but is perhaps still not the worst thing to happen to a potential straight-line enjoyer and at least the power-band is going in a direction we can actually still use (albeit increasingly high-risk). If the power band was dropping that would likely be a bigger issue.
I kept wanting to think the worst but apart from a radiator clogged with the beige dust we have here which covers everything (since meticulously cleaned out), and a couple of slightly stiff bolts there wasn’t really much wrong since I’ve replaced pretty much any bolt I can with stainless equivalents. Today she was happily revving to the limiter (11.5k) and I wasn’t seeing or hearing any signs of distress, which isn’t bad for a 17-year old bike which hasn’t had an easy life 😉
It felt like the power was plateauing around the limiter, like it started to feel a bit ‘floaty’ and vague which seemed to me like harmonies breaking down and maybe a good point to not go past. It’s kinda *just* within tolerances of what I want/can use, though I wasn’t really intending to go all the way up to 11.5k regularly. Before, the power band was done by about 11, which was nice, and more what I was trying to achieve.
Raising the limiter to 11.5k was more intended as 11k soft/mental limit with a little wiggle room to maybe get me into triple digits, should the situation arise, rather than a place to slam into repeatedly while chasing the last drop of power.
Apropos nothing here’s a couple of diagrams hopefully explaining what I think has happened:
Despite not making any changes before the 16th, I would still like to resolve, or at least gain some level of control over this, and I realised that I might be able to do so using an adjustable cam pulley. I did a little reading and that seemed to confirm this was possibly a valid solution. So I’ve obtained one of these, which also retains the decompression mechanism so we don’t melt our starter motor. Thanks to Tn for the link, great find!
When folks on the forums or my discord go thru the process of checking the alignment of the cam gear with the tdc/timing mark, it’s almost always out by half a tooth or so, usually due to timing chain stretch.
I suppose if it gets to more than half a tooth out it ends up being back in time on the next tooth, but the chain is still stretched and you’re likely to be 0-0.5teeth out of alignment which is in turn going to do funky things to your power band.
When reassembling the top end and threading the timing chain onto the top gear, if it’s out of alignment due to stretch, you need to decide whether to go with the earlier tooth or the later one, whereby the earlier one would shift your power-band down a little and the later would shift it up a little.
You could arguably put a fresh timing chain on. I believe it’s possible to do without taking heavy metal apart *as long as you can get the flywheel off*. If your flywheel has apparently welded itself to the crank like on my A-motor, then you’re outta luck and you better learn to work with the timing chain you have.
If you change the timing chain you’re meant to change the top and bottom gears too, but the bottom one is pressed onto the crank and needs a full bottom end disassembly to even access (so: “hell no from me dawg”). Thankfully the top one can be easily replaced and isn’t too expensive, so if you’re doing the chain, do the top gear too.
When I built the B-motor (the one that’s in the bike now) I was meticulous with the alignment of everything related to the timing chain precisely because I’d had my suspicions about this for a while. And when first assembled it was pretty much perfect, valve timing, fuel power-band and vibrational harmonious region all coincided beautifully and she’d dig right in. It was glorious.
But over time and miles even the most carefully built motor will wear and start to drift. Hopefully the adjustable top gear will allow me to correct that and bring the valve timing back to “sharp”.
I have no idea whether the *ignition* timing is optimal on the current setup. I may (or may not) have added a little to the latter part of the table, but i don’t remember whether I did or not and I’m not super inclined to have to pull the ECU out to find out.
However I think given how often I’ve ridden it up to 11+k, if the timing was off and it was knocking, it would have blown itself up by now, so once again: Seems to work, not going to mess with it. We’ll pick up that extra power once I’ve fitted the knock sensor unit I just got from Knocksense in Canada.
The Event Details:
This should be happening at:
Dakota Raceway on the 16th August for their RWYB drag and drift event.
I’m hoping I might encounter another R125 or other familiar faces there. Apparently they do small CC bikes quite seriously there so I’ll prob get repeatedly gapped by a 12-year old on a 50cc scooter burning methanol xD.
If you are going (or are thinking of going), either as a participant or spectator, please do let me know 🙂
2008 (gen1) YZF-R125 180cc on the roller, short pull
Here’s a short clip from the testing session today. There may be more from this as I work through, and begin to make sense of the footage and data.
