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Info Castrol 6 Hour Stories

Discussion in 'Motorcycle Racing and Track Days' started by maelstrom, Feb 21, 2020.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Added a new pic to the previous post to try to make it easier to follow.
     
  2. gregt

    gregt Well-Known Member Premium Member

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    Cunning. Possible on engines with a fine tooth gear train.I looked at the feasibilty of doing something similar with the RC30 engine I finished recently for a team here. Std lobe centers are 100 inlet and 105 exhaust. Looking at it, you just know 105/105 would be better. All the gears except the idler are integral to their shafts so no offset keys possible. And it's a coarse tooth pattern all the way through so any tweaks would be bigger than you want...
    Incidentally, using the point of max lift can be a trap. It'll work on symmetrical cams - but not all are symmetrical. Across all engines it's safer to use the geometrical center of the lift period.

    As an aside, I'd like to see you work it on a Velocette with a hunting tooth type gear drive, LOL. That'd drive you to drink.
     
  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I only use the CML value as a reference point for tuning. Some people like to use inlet closing etc. It dispenses with the issue of considering valve clearances because as you know the cam timing values are usually nominated at a certain clearance. I don't use it a cross reference across engines though. Ducati's desmodromic cams tend to be anything but symmetrical, Since there are no springs they can be opened and closed as fast as required. What do you mean by geometrical center @gregt? Never worked on a Velocette, now I will have to read up on that. Thats why I love this forum, lots of smart friendly people. :)
     
  4. gregt

    gregt Well-Known Member Premium Member

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    What I mean by geometrical center is the midpoint of the opening period.
    Example - inlet opens 30 BTDC, closes 60 ABDC - total period open is 30 plus 60 plus 180 equals 270 degrees.
    To find the center of the opening period - 270 divided by two equals 135. Less the 30 before TDC equals 105 degrees lobe center. In this case the center of the opening period is 105 degrees after TDC.
    Where - like the Duc and a lot of Suzukis - you have leading and trailing rocker arm followers, the cam is visibly assymetric to accomodate the different rocker ratios as the contact patch moves in and out. If you plotted the lift and fall curves of these setups you'd often find that the point of maximum lift isn't in the center of the opening period. I can quote a certain GSX1100 which went a lot better once the

    Doing it this way, clearance isn't important as long as you use the same distance off the seat as your reference point opening or closing. I use .040in - most jap specs are at 1.0mm lift. Most aftermarket cam grinders use .050in lift as the base.

    Using lobe centers as a base for comparison does work. Some families of engines like a particular set of lobe centers - even across cams with different duration and lift. I once read in a car tuning book - American - that a particular cam grinder was sceptical so ground up a set of cams with max lift well away from the lobe center point. The engine when dynoed still liked the known lobe centers set by the geometrical method.
     
  5. gregt

    gregt Well-Known Member Premium Member

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    Hmm, site dropped some of that post.
    GSX went better once the owner set the cam timing this way. Won at Eastern Creek, 2nd at PI.

    Velos use a geartrain with the tooth number selected to give what's called a "hunting tooth" - evens out the loads carried.
    But the timing marks only line up every 40 revolutions from memory...

    Anyway, cam dialling on proddy bikes is semi-legal. Certainly on Supersport here anyway. In the past, not so much. I've heard of cam sprockets being made from scratch once the bolt positions had been finalised.
     
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  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Okay, the geometric is what most talk about. It means you need to take a measurement at either end and you are assuming a symmetrical lobe. With your Suzuki example do you mean you moved the actual maximum lift to where the geometric value should be according to the published values? Also, just curious, did you retard or advance?
    I take two points on the degree wheel, say 0.2 mm either side of max lift then I split that. Since I am just dialing those cams it is not going to make any difference which way you do it. I just want to know where this cam is in relation to the crank and be able to move it easily. I also agree with you on the engine family point. Comparisons across different engines get interesting because now rod-stroke ratio becomes a factor.
    I don't think that the timing of maximum lift is particularly important when compared to the opening and closing events. Example being the effect of inlet valve closing and dynamic compression etc The example you gave, (sounds like something Smokey Yunick would have done), sounds perfectly logical to me.
    I checked out the Velo and I will pm you soon. :)
     
  7. gregt

    gregt Well-Known Member Premium Member

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    The point of doing it this way is that it works either with a symetrical lobe or a non-symetrical one. The opening and closing points are taken at a height which gets around any ramping done at the ends of the lift period to silence the valve train.
    Where max lift is, is irrelevant. You're only interested in the center of the opening period.

    In the Suzuki case, I'd tuned it by email. I've since built several engines for this guy and the team he works with.
    He'd set the cams to what he thought were the correct lobe centers by using the point of max lift and was disappointed
    with how it went so a mutual friend said - ask Greg. I talked him through the correct way - and told him to use 106/108 lobe centers as the bike at that time was going to be used at Wanganui. Short street circuit. That timing gives huge midrange on those engine. Mission accomplished, Wanganui Posties won handily so lets take it to Aussie....
    In that tune it won at Eastern Creek but while finishing well up it was outgunned at PI.
    Owner comes back to me and asks if he needs different cams for PI - they're aftermarket ones already, quiite big.
    The answer is - no, just retime them for PI. Went to 110/113 lobe centers. Rider reports vast difference and finishes second to a well ridden TZ750.
    That bike is now retired i think as the team he's with have bought/leased more sophisticated posties. But the experience gained with this one helped in the IOM where they got a notoriously unreliable leased bike home in one piece at very respectable speed.
     
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  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    All makes perfect sense. Swings and roundabouts when working on the same engine with standard cams. In the Ducati case that I am referring to I just want to know where the cam is in relation to the crank so I can get both cams in the position that I want them. I am not interested in the timing unless the engine is going to be modified and then it is a whole new ball game. I like the Suzuki story. I have also move the cams about the same amount for different track types.
     
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  9. gregt

    gregt Well-Known Member Premium Member

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    As far as Ducatis go, I've done my share of singles and have of course made up offset keys...

    Now, if the same trick could be worked with the belt drivers it'd save quite a bit of time.
    But from memory I don't think it can ?
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    For belt drives, just cut a series of extra keyways in the pulleys and spread them as evenly as you can. I think I use to have a total of 5 or 6. You can mark them -4 +4 etc. We use to sell them over the counter in Brisbane. The actual timing numbers in the manuals were wrong for 500 & 600 Pantahs. I contacted the factory to get the correct ones. A lot of the time they make these books and then there are changes made that don't make their way into the publications.
     
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  11. gregt

    gregt Well-Known Member Premium Member

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    Guy here used to make two-piece pulleys. Very easy to use.

    My limited experience with factory timing figures led me to ignore them. Particularly the racekit suggested figures, LOL.
    When F3 started here, a good local rider came to me with a 500 Pantah. Actually a 600 bottom end as it was stronger - with aftermarket high com forged pistons for alky. I set it up on from memory, 107/109 lobe centers. They were aftermarket cams from somewhere I didn't recognise but allegedly kit copies. I made a pipe for it too. Ported it mildly.
    Anyway, it went very well - 3rd at the local round of the nationals.
    This had been noticed by the BMS team from Wellington. They ran Robert Holden on a 600 on nitro in F2 in NZ. Fitted in well with his riding for Bob Brown in Aussie.
    I was approached and asked what was in the 500 as they'd built one and dynoed it. Not happy with it so it was abandoned.
    I told them asnd asked what timing they were using in the 600. Factory kit figures.
    I explained to them - actually Dick Hurdeman who was the engine man - what and why of the 500 and told them what I'd do to the 600 - in for a penny, LOL.
    Anyway, Holden came to see me at the next round of the Nats and said thanks - 600 cam timing changed, pipe changed, gained 8HP at the wheel. Dick never looked at factory timing figures quite the same after that.
     
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  12. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Nitro is legal?
     
  13. gregt

    gregt Well-Known Member Premium Member

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    It was legal here up to the '88-'89 season. Then when they banned it they threw out Methanol too.

    Which was a bugger as I'd become the local Methanol carb guru. I'd been running several bikes on meth based brews and had an engine customer who was running 25% nitro in an EX500 kawasaki twin. Won F3 two years running with that.

    Methanol is legal here for BEARS, Classics and Post Classics up to '89. Your period 5 I think.

    More 6 hour stories please.
     
  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Kudos man. Running methanol without burning holes in pistons is quite the achievement. To say nothing of Nitro. There are loads of talented Kiwis, seems to be in your genes, or the water. I was in NZ when NZ lost the America's cup and everyone was moaning. I was telling the locals to hell with that, you came within one race of beating the most powerful country on Earth.
     
    Last edited: Feb 25, 2020
  15. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Loving the chat fellas - now I know who to come to when I get to timing cams for different performance
     

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