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13 May 2010


Twisty, originally uploaded by pjvenda.

08 May 2010

Hydraulic vs bucket+shim valve adjusters

Been researching the various valvetrain designs out of a philosophical discussion on hydraulic adjusters not commonly employed in motorcycles (H-D engines are the notable exception). Fascinating!

I found out how hydraulic adjusters are currently used in various car engines and how elegantly they solve the problem of keeping valve clearances. I also read a bit about pneumatic actuated valves with cams/followers or with electro-hydraulic actuators and no cams. Clever!

Being uninformed about hydraulic valve adjusters, I did the right thing and researched a bit. I'll share a summary for those that, like me, would like to know.

Hydraulic valve adjusters are a clever solution meant to solve the problem of keeping correct valve tolerances at any engine/oil temperature. Incidentally the design led to having permanent contact between cam, lifter, pushrod, rocker arm and valve stem, making it quieter.

[I now realise that the more common cam followers+shims+buckets should equally have (more or less) permanent contact between all the parts. This happens because followers to shim clearances are filled by oil pressure that builds up underneath the buckets as the engine runs: makes sense and came from a very reliable source.]

This is an open loop feedback system in which pushrod operating travel changes by action of hydraulic lifters which, in turn, are influenced by engine pressure and/or temperature. Ingenious!

"Our" design is more on the style of "getting it right for the typical range of engine temperatures".

Two typical engineering approaches to the problem, both with their pros and cons. While it's easier to see the cons in the non-hydraulic shim+bucket style system, the hydraulic type is not without them:

Being an open loop system, it relies on correct information coming in from oil (density+type+dirt+volume=different pressure vs temperature curves) as well as integrity of the lifter itself (spring load). But even if everything else is kept, oil changes with wear and that affects operation of the lifters. Self adjusting valves gradually come out of adjustment at all engine temperatures. Then of course this is a more complex system and probably more expensive to manufacture. Hydraulic lifters are precision parts with very tight tolerances. It is hard to tell if the time it takes to get a valve significantly out of tolerance is so long that it becomes non-serviceable... I really don't know. Some people say yay other say nay.

Me, I would go for the hydraulic type, but I'm an engineer, not a business man. On that note, how about the desmodronic valve actuator system currently used in Ducati engines? Funky, eh?

Thanks for reading. Feel free to poke holes at it.

References were:

03 May 2010

The long way home

One wonderful thing about bikes is that much more often than in a car, you go out for a ride with no purpose, sometimes with no defined direction or destination.

I work in an office in Thame, roughly 15 miles away from home. Commuting by motorcycle is good and fun: not too long, very little traffic, twisty but safe (good visibility throughout, no sudden tight bends, etc). It's a good mix of city, dual carriageway (A40) and A-road (A418).

As the weather improves, the sun now shines past 7.30pm (sunrise, sunset, dawn and dusk times), it's time for some road exploration / wandering on my Triumph (I really should have blogged about my new speedmaster by now...)!

I prepared a route based on something I tried before and set off from the office after work with a memorised list of road names and a few visual cues taken from google street view. Although I didn't follow the plan entirely, the result was the route below:

"The long way home" is the name I gave to the 50 mile route (above) out of Thame around the south of Oxfordshire and back into Oxford via the Donnigton bridge / Iffley road.

  • B4009 from the A4074 turnoff to Goring-on-Thames: Superb scenic twisty road with a few villages here and there but without breaking the rhythm too much;
  • A417 from Goring-on-Thames to Blewbury: Another very scenic twisty road with a number of hills and less villages than the B4009 (IIRC);

Great bits of road, but not quite highlights:
  • B4009 from Thame to Benson;
  • B4016 from Blewbury to Didcot: very twisty, most bends are blind. not too many chances to overtake;

Ideas, alternatives, improvements:
  • Avoid Didcot ring road by following the A417 a bit further and then turning off to the A4130 at Rowstock;
  • Try the B4009 further than Goring-on-Thames, perhaps even all the way to Newbury;
  • Keep on the A417 until Wantage, then A338 up to Wootton or join the A420 and back to Oxford;

I managed to discover/execute this alternative route home which included some of the best bits of road I've ridden so far (mind you my experience is limited). This was a fantastic ride that I look forward to do again soon.

(feel free to share if you know any great roads around Oxfordshire)

Until next time,