KR head: race cams : pocketing std pistons : some useful info, maybe....

Discussion in '16-valve' started by Jon Olds, Nov 16, 2014.

  1. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Its one of my least favourite jobs, but I have some pockets to
    deepen in some std 9A pistons.

    I have built a minimal short motor, MLS gasket and KR head with only 2 inlet valves, no springs/caps.

    With the crank zeroed at TDC on a 360 degree protector, and a DTI in line with an inlet valve, I have 4.6mm up/down movement on the valve.

    At 5 degrees before TDC this clearance increases to 4.9mm

    At 10 degrees this is 5.7mm

    At 15 degrees = 6.95mm

    At 20 degrees = 8.36mm

    At 25 degrees = 10.14mm

    When I find my proper full size degree wheel I will fill some gaps in the data

    So, if I know the lift at TDC with the inlet cam timed to default I know how much extra clearance I need.

    If I record the cam changes in lift - degrees around the nose similarly, I should be able to relate both sets of reading in one spreadsheet and establish the tightest point for clearance.

    Anybody done this? I am trying to take as much guessing out of the job as possible, and trying to minimise the pocket size to maintain CR

    Jon
     
  2. fasteddie

    fasteddie Banned

    Joined:
    Oct 22, 2003
    Likes Received:
    672
    Modify Pockets as per safe lift spec's of cams, measure cylinder/bore Chamber Volume at a set height before and after
    then skim head by the amount you have removed from pockets to regain or a achieve the cr you want to run.
    Make sure you use the right valve springs to suit the lift of your hi lift cams as spring bind will eat them [xx(]
     
    Last edited: Nov 18, 2014
  3. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Going to report back on how I get on. I must have tried lots of different ways of doing this, and have yet to do the job the same way twice.
    Last one I did was great, its in the mk1 and collects pots on a fairly regular basis.
    For this one I would like to just understand more and make best use of the kit I have and principles available to a backstreet merchant.
    Jon
     
  4. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

    Joined:
    Jul 26, 2006
    Likes Received:
    3,320
    Location:
    Creating Pfredstarke
    Keep us posted and thanks for bringing up this topic :thumbup:
     
  5. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Still measuring, quite a spread on the clearances, cylinder to cylinder. Either measuring inaccuracy (possible) or the installed valve height differ, valve to valve
    Jon
     
  6. HPR

    HPR Administrator Admin

    Joined:
    Aug 11, 2009
    Likes Received:
    1,819
  7. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    thanks, a bit of Pythagoras. I have the data now for valve to piston and cam profile, just need to get my head around what goes where / the sums in the spreadsheet
    Jon
     
  8. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Trying to tie up reality of timing up the cams with the theory, so one will validate the other.

    Surprising results, so far, at least from the reality side.
    Cams are quoted as 0.444" (11.28mm) lift at 295 duration. Lash is 0.010". Was quoted a lift of 0.100" at 108 degrees, my target default installed setting.

    The cams measure up at 11.4, so correct. The installed lift at the nominal 108 degrees is 2.25mm exh and 1.4mm inlet, so nearish. Will double check readings.

    What's surprising me is that the engine turns over with the standard unmodified pockets. I know it may have from post 1, but I'm still surprised. Only 1 inlet valve fitted, so far.

    Plasterine/play doh time next to see how much leeway I have.

    It would be excellent to not have to pocket, but will have to check all 8 inlets. My last similar build was a full race ABF that had to have large cutaways. I am questioning now why.

    Jon
     
  9. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Another thought, this could an advantage of the 9A over the ABF. With a shorter rod (144) the piston doesn't hang around as long at TDC, making the potential valve - piston clash less of an issue.
    This would explain why my race ABF needed pockets, and this one doesn't. Both sets of cams are similar. Think I like 9A's more and more now
    Jon

    2.8mm clear cutting the play doh in half on valve 1
     
  10. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Ive been told anecdotally, the tightest spot is not TDC. For my own piece of mind I would like to know definatively

    Also, ive had a 'bad experience(s)' (ie costly....) with 16V piston-valve contact. Not easily forgotten, as it really hurts your wallet
    Jon
     
  11. HPR

    HPR Administrator Admin

    Joined:
    Aug 11, 2009
    Likes Received:
    1,819
    In the first degrees the piston moves slower away from TDC as a fast opening valve, but dont worry as its only 0.2- 0.3 mm or so...
    lets take above as example: at 5 degree your piston is 0,3 mm down while your valve can open lets say 0.5 mm in that period
    but at 10 degree piston is 1.1 mm down and valve only 1.0 mm and from there on the piston will be faster down than the valves open.
    Valve opening is 0.100`` or 2.5 mm at TDC so there is plenty space with 4.6mm, so dont worry as long you have at all times ca 1.0 mm clearance.... Its only a worry with very narrow valve to piston clearance and when using extreme cams..

    Are you sure the 2.25 mm exhaust and 1.4 mm inlet are correct and its not switched > 2.25 mm inlet / 1.4 exhaust ?
     
    Last edited: Nov 20, 2014
    Toyotec and jamesa like this.
  12. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    My race ABF wouldn't turn when time up correctly and I had to modify the pistons accordingly. This is covered in another earlier thread.
    The rod length ((ABF) 159 against 144 (9a) ) will make some difference, but I am still surprised (pleasantly) by the results I have measured and backed up with play doh confirmation.
    I have learnt something doing what I have done and shared so, so its been a worthwhile exercise.
    The dummy stage build is complete, so its now in a thousand pieces again, ready for the final build.
    I will redo the inlet / exhaust timing adjustments and measure the overlap lifts and report back. I am told the grind is symmetrical, so they should be the same...
    Not quite sure what Hotgolf is on about though. (could be me...) The checks I have done are on No.1 cyl on its exhaust transition stroke , not the compression stroke is where the clearance issues are (ie exhaust shuts, inlet opens).
    There is loads of exhaust valve clearance so retarding the timing shouldn't be an issue, should it?
    Next up is the build.
    PS: Is it me, or have the price of consumable engine parts gone up? Long gone are the days when you could rebuild a motor for a couple of hundred quid. Even Jizer is 18.50 a gallon!
    PPS: Oven cleaner is great on carbonised oil on pistons, makes your hands sting though
     
    Sirguydo and jamesa like this.
  13. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Total thread tangent: I have persuaded my mate to let me fit one mech follower and lash cap to his mk2 hydraulic driver. Why? Because I don't believe what I've been told about hyd cams not being useable with mech followers. If it blows up I'll be sure to pass this info on.....
    LOL
    Jon
     
  14. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Back on thread, this may be familiar to some.
    1/2 motor built.
    Head built , new solid lifters/lashcaps, strong springs, big cams.
    The top end is tight to turn, am struggling at the moment. Any tips?
    Jon
     
  15. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Massive progress round and round and round;
    Firstly, its tight because the valve springs (and nearly the valve stem oil seals also!) are becoming coilbound. What everybody should learn from this is before you buy your cams be sure you want to deal with the issues I will set out below...
    Note: these are my measurements, not guaranteed values
    Standard 8 and 16V valve springs go coil bound at about 18.6mm (spread on this , over a set of 16) is +0.2 to -0.8
    Uprated KC151612 go coilbound at 20.6mm
    Schrick HF2080's go coilbound at 19.3mm
    ABF springs go coilbound at 20.2mm
    Stroke of valve until retainer hits top of valve stem oil seal (std length valves/std retainers) : inlet 11.2, exhaust 11.8mm (this needs increasing...)
    Have identified some springs that will work at standard spring seat retainer height.
    OR I could knock the guides out and mill down the standard spring base, then shorten and refit the guides.
    All in all I have now rebuilt the entire top end 5 * in 2 days, trying the above.
    Happiness
    Jon
    PS : questions: anybody run without the tin washer type lower spring platform things? Will the ninner / outer springs jump around or wear into the ali head? These add 1mm height to the outers and 3mm to the inners.
    Longer valves would be a good help, even recessing them down into the head would help. This would mean the lash cap could be shorter and the upper retainer woud sit higher and give more potential stroke before coilbind
     
  16. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Little surprised no one has commented on the above, however, further thoughts (if anybodies interested);

    Aftermarket valve springs are subtly different sizes to OE ones and this causes two potential problems;
    1. Bottom of the spring. The 1mm pressed steel seat cannot be modified and only suits the OE sized springs.
    2. The top cap is not ideally sized, for either spring.

    Obvious answer is to throw cash at this and buy the upper/lower seats.

    Anybody taken a harder path, and made their own lower seat, possibly 2 piece? I'm think of shim steel 16mm ID 30mm OD with a separate turned inner spring platform, or better still an off the shelf inner

    Jon
     
  17. Sirguydo

    Sirguydo Fastest milkman in the West Paid Member

    Joined:
    Nov 7, 2012
    Likes Received:
    1,203
    Location:
    Bolton
    John your stuff is very race spec stuff and most of us find it hard work [:s] but very interesting :thumbup:
    I wouldn't like to comment as it's way past my experience (yet hope to improve that's why I'm a member lol) but appreciate your sharing and therefore teaching :thumbup:
    There's not many that can do what you're doing or know how to nowadays :clap:
    Most just buy an ABF,VR6 or go turbo lol

    You seen my bore pics :cry:

    Keep up the good work
     
  18. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Got a couple of them too. (GTIR with big turbo and steel, ported, cammed 18T, KO4 Ibiza)
    Jon
     
  19. jamez Forum Member

    Joined:
    Oct 22, 2003
    Likes Received:
    21
    Location:
    Netherlands
    I just replied to your post on a thread i started then saw this , so what did you do with the valve retainer cap not fitting with the springs?? i also have 11.2mm lift on the 296 cams but stopped on assembly when i saw the poor valve cap fit but with initial measurements i don't think the springs will coil bound. When i had my piston valve pockets done i got so bogged in the numbers trying to compensate for excessive valve float in an over rev condition ( shift to 3rd instead of 5 @ 7.5k (done that) ) that in the end i went 1mm down as that is a safe limit . Now my compression measures at 225 psi across all 4 cilinders. As for the bottom seats as the original spring fits snugly into it and the uprated springs od is smaller, in any event there is going to be lateral movement on the bottom of the spring at high rpm and running without them surely would be madness with the extra load from the springs...Im in exactly the same position at the moment with the springs and have options.

    make custom bottom spring retainers to hold the bottom of the springs tight
    Modify the original spring cap retainers to match the outer springs ids
    Replace only the inner spring and use the oe outer with the oe retainers, at least it can help with spring rotation at high rpm as the inner is counter wound and fits well in the retainer
    Remove over engineered NA engine and fit a boring 20vt with mods :thumbd:



    On a side note when i was checking my engine with plasticne it occured to me that while measurements made to a static engine may be good, there is a possibility that at high rpm and abf dwell time at tdc higher that a 9a there may be some conrod stretch . A quick calculation gives, with a 95.5mm crank and engine at 7.5krpm,piston at bdc accelerating to 43 kph and back to tdc in 0.008 seconds. calculations made on the exhaust stroke without compression holding the piston down, the loading being different on the compression stroke. Using the piston weight , wrist pin and rod weight,you colud calculate the g load on the rod. and hence the stretch given the material rod data....it was just a tought after all
     
    Last edited: Nov 28, 2014
    Jon Olds, Toyotec and jamesa like this.
  20. Jon Olds Forum Junkie

    Joined:
    Jan 28, 2004
    Likes Received:
    535
    Location:
    United Kingdom
    Holy camoly. (as batman said)
    Its nice to chew fat.
    I wasn't going to say any more on this. (limited audience)
    Today I have completed the 'dry build' of my valve spring subassembly. Now have 16 off of the little monkeys
    'Right old' mish mash of parts;
    Top 16v retainer, modified. (a fair amount of carbide tools burnt out)
    Lower outer spring contained in a mild steel cupped washer, from a lotus twincam. (QED motorsport)
    Inner spring : made a simple platform with an inner step from mild steel. Nominal 2.6mm preload
    Springs VS39 kent
    This collection of parts shows a measured coil bound (delta) of 12.8 to 13.3mm, not including the installed height preload. Crude vice open / closed check.
    Springs are quoted on data sheet at delta 14mm, according to the Kent
    So, the build is still on-going.
    Next is another dry build.
    Going to face the top of the guides down and shorten (butcher?) the seal by 1mm.
    Everything I have done to date is for the right engineering reasons, whether I get the right engineering result is anybodies guess...
    Your troubles and thoughts may massively help my current project, so keep em coming
    Jon
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice