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  1. #526
    Fellow Frogger! R8philSA's Avatar
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    Hi Fans.
    Yes, it definitely looks like vapor spraying on the plug electrodes so that would have been that piece of aluminum alloy from the spark chamber.
    I have always found that Gordini head design unusual. The designer was trying to create the duel flame front for quicker and more thorough combustion process similar to the duel aircraft systems on piston engines. Aircraft piston engines were primarily fitted with two plugs per cylinder for safety reasons, if you lose a plug in flight the other will get you home. It is also a bonus to have two flame fronts per cylinder for better combustion.
    Cheers
    Phil

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  2. #527
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    Quote Originally Posted by R8philSA View Post
    Hi Fans.
    Yes, it definitely looks like vapor spraying on the plug electrodes so that would have been that piece of aluminum alloy from the spark chamber.
    I have always found that Gordini head design unusual. The designer was trying to create the duel flame front for quicker and more thorough combustion process similar to the duel aircraft systems on piston engines. Aircraft piston engines were primarily fitted with two plugs per cylinder for safety reasons, if you lose a plug in flight the other will get you home. It is also a bonus to have two flame fronts per cylinder for better combustion.
    Cheers
    Phil
    I like the 'unusual'... I'd sort of thought it was his only way of getting a flame front (in this case two) near the centre of the hemisphere having already filled it up with valve heads!! So recessing the plug gave him some meat to screw it into and at the same time allowed bigger valves or fixed the "oh bugger" problem he'd already created. Chicken and egg situation.... I wonder is it written up in France somewhere?
    JohnW

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  3. #528
    1000+ Posts bowie's Avatar
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    I hadn't realised these heads had two flame ports as it where. How far is the electrode tip away from those ports.

    Also neat! And also bugger.

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  4. #529
    1000+ Posts Frans's Avatar
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    Rubalpine......Thanks for the concern but it should be easy. (famous last words?)

    R8PhilSA.....I think that is the brilliance of the G head design although it might give you some other unforeseen issues. I think this is the sole reason why the max HP is developed at 6800 or thereabouts. Other engine's are running out of breath at that rpms.

    Bowie......The electrode is at the point where those 2 flame shoots meet. If you can imagine 2 drill bits shoved into the holes, the spark starts there. A true twin spark with one spark plug.

    A bit useless info on that and only my worth. Imagine a Chev V8 with a 101 mm bore. The plug at the side starts ignition and the flame travels 101 mm across to the other side and ignition needs say 10ms to complete combustion. If they made a Hemi head with the plug in the center, the flame only needs to travel the radius, 50 mm to complete combustion. If they copied Gordini with the flame shoots the one flame only needs to ignite half of the radius and the other the other half of the radius. The result is that at 5000rpm the first design will complete combustion only when the piston is almost rock bottom, 180 degrees, and at that stage the crank angle is of such that there isn't much force to transfer to the fly wheel. The Hemi design, same rpm, will complete combustion much quicker and the crank angle will be maybe 120 degrees from TDC which transfers a lot more power to the fly wheel. The G design, same rpm, might complete the combustion when the crank is at 90 degrees from TDC and max power will be transfered to the flywheel.
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  5. #530
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    Hi Frans ,

    Greetings from SA .

    Two new racecars in NZ-head-pic.jpg

    In this pic of the head which featured in my Gordini 50 article which you shared here , one can see the effects of the repair . If I recall all four combustion chambers were cracked across the flame holes between the valves , so to be safe I had all four repaired . From what the head specialist told me they removed the valve seats , cut out the offending portion , insert a screwed plug from the spark plug side ( not sure what they used that didn't stick with the welding ) , welded it up , recut the valve insert space, bored out the spark chamber from the top , and then used a jig to bore the interconnecting flame holes from the combustion chamber side . Not trivial , but possible . This was first pioneered by Frank Shearsby here in the 1970's with Gordini heads and Lotus Cortina heads at the time . This head is also interesting from two other aspects in that larger inlet valves have been fitted , and the head has been built up to the original specified 73mm thickness using the aluminium metal spraying technique to bring the compression ratio back down to a comfortable road going figure given that this engine featured 77mm domed pistons from Salv Sacco ( 1340cc) ,


    All the best for the New Year , and good luck with the repair ,

    Carvel
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  6. #531
    1000+ Posts geckoeng's Avatar
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    HI Carvel,
    What would a re-weld and rebuild cost ???

    Ray
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  7. #532
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    Hi Ray - and greetings ,

    At this point I don't know - this job was done for me about 10 years ago , and only this year got to the top of the pile after re-retiring myself ! I will enquire in January when the guys get back , and see what I can find out . The chap who was doing the metal spraying has also retired and passed on the business - I have another job lined up for his successor after which I can give you a Q/A report . As per our other messages , the 1420cc test run yesterday is looking very good with carbs sorted and tappet clearance reset hot - I LIKE that engine - keep well,

    Carvel

  8. #533
    1000+ Posts geckoeng's Avatar
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    Hi Carvel,
    Always so satisfactory to start a new motor and have it run well ........ !!!!

    No matter how well you build a motor, turning the key is always a thrill.

    Ray
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  9. #534
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    Hi Ray - indeed !

    The only heart stopper was the oil pressure which was indicating low . However a check with a mechanical gauge showed all was well, and it turned out to be a faulty sender unit ! If interested in the 'blueprint' for this motor , I can briefly describe it here , but not sure what level of detail is appropriate for this forum

    Regards,

    Carvel
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  10. #535
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    Quote Originally Posted by CarvelSA View Post
    Hi Ray - indeed !

    The only heart stopper was the oil pressure which was indicating low . However a check with a mechanical gauge showed all was well, and it turned out to be a faulty sender unit ! If interested in the 'blueprint' for this motor , I can briefly describe it here , but not sure what level of detail is appropriate for this forum

    Regards,

    Carvel
    Hi Carvel

    The greater the detail the better
    Regards Col

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  11. #536
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    Hi Carvel
    Plenty of detail is OK for me. Stop at a couple of pages though Pics too. Like Frans does, we all enjoy his pain and joy .
    cheers Jaahn

  12. #537
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    Quote Originally Posted by CarvelSA View Post
    but not sure what level of detail is appropriate for this forum
    A good start would perhaps be reproducing the articles you posted on Katriina's Renault pages many years ago. They contained plenty of detail!
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  13. #538
    1000+ Posts Frans's Avatar
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    Hi All,

    Carvel, I posted a photo of a built up head on page 1 of this thread some 9 or even more years ago. It could even be your head that on there. The guy that did it those days where Izak Janse van Rensburg of Advanced Metal Spray & Welding Technology. I did contact him recently (4 years ago) and he told me that he sold the business. I have lost the detail of the new owner, so if you do have it please post it.

    Just to put you in the picture, I started this thread in 2005 I think and then after a huge amount of detail of the build of my race car the Internet service provider had some issues and we lost about 4 years of threads and info right across the AF Forum. That is the reason for the big jump in dates when you read my thread from P1.

    Thanks for the tips re the repair. I will have a closer look at it now. Does anybody here know that if the cracks are repaired, do they return after some time of use or is it a permanent solution?

    This incident made me think of another possible modification. As mentioned earlier, during the 2nd race with a new plug the times where back to normal. Now, what if the 2 flame shoots remain and a 3rd is drilled in the center? It might cause other issues but I was just thinking. (Rather forget that)

    Regards, Frans
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  14. #539
    1000+ Posts Kim Luck's Avatar
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    Quote Originally Posted by Frans View Post
    ..................................This incident made me think of another possible modification. As mentioned earlier, during the 2nd race with a new plug the times where back to normal. Now, what if the 2 flame shoots remain and a 3rd is drilled in the center? It might cause other issues but I was just thinking. (Rather forget that)

    Regards, Frans
    I think you just hit the nail on the head (with a mallet!) That modification sounds so easy you wonder why the factory didn't come up with it?
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    It's another lovely day! Again!

  15. #540
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    Frans and friends ,

    Firstly all the best for 2018 . Izak has retired and passed on his equipment and hopefully knowhow to a chap in Springs . His name is Nic , and I have a phone number , but have yet to visit him , with another head under my arm ! Will share more info as I get it . The repair that was done on my head(s) involved removing the valve seats and completely welding up the offending section and re-cutting/boring/drilling it , so no reason to suspect it would re-crack ( and hasn't so far ) unless of course it is again overheated which seems to be the cause of the problem in the first place . . . . Personally I would be concerned that drilling a 3rd hole would weaken an already fragile section too much ?
    Simon - I have elaborated on some of the material I wrote on Katriina's pages in bygone years ( you have a good memory! ) , and it should be on the CCA website , but I can certainly share it here if appropriate .

    Enjoy the day everyone ,

    Carvel
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  16. #541
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    Ah, Midrand. Must try and see you in September...

    Fascinating stuff - we were lucky with Katriina's pages back then.
    JohnW

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    Two new racecars in NZ-20180101_185616.jpgTwo new racecars in NZ-20180101_185908.jpg

    John and friends ,

    Any visits always welcome

    Here's a New Years tip ( literally) that may help . Getting the wheels back onto our 3 stud hubs can sometimes be a challenge , particularly in poor light . A small trick that helps is to put a blob of white Tippex ( typist correction fluid) on the end of each stud which makes 'sighting' them through the stud holes in the rim a lot easier . . .


    Keep well,

    Carvel
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  18. #543
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    Brilliant! Next time the wheels are off..... Now, why didn't I think of that!

    Thank you! Until September then...

    Cheers
    JohnW

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    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Peugeot 306 XT 1995 (daughter's)
    CitroŽn CX Pallas 1980

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  19. #544
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    Quote Originally Posted by CarvelSA View Post
    Click image for larger version. 

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    John and friends ,

    Any visits always welcome

    Here's a New Years tip ( literally) that may help . Getting the wheels back onto our 3 stud hubs can sometimes be a challenge , particularly in poor light . A small trick that helps is to put a blob of white Tippex ( typist correction fluid) on the end of each stud which makes 'sighting' them through the stud holes in the rim a lot easier . . .


    Keep well,

    Carvel
    Quote Originally Posted by JohnW View Post
    Brilliant! Next time the wheels are off..... Now, why didn't I think of that!

    Thank you! Until September then...

    Cheers
    Because you are probably like me John and just keep trying until the wheel studs line up.

    I usually spin the hub around until one of the studs are at 12 o'clock, but I do like the white high light idea.
    JohnW likes this.
    Regards Col

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  20. #545
    1000+ Posts schlitzaugen's Avatar
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    I always wondered why the design of the head was so complicated and if this made it more fragile (which it seems it did). Granted the heads are now ageing and have held up pretty well, and have been pushed a fair bit perhaps beyond their intended purpose. But I always thought about the alloy and how it changes when welded. I don't know much about it, but I think it is important to know if the new bridge has a modified metallurgy. This might lower the melting temperature (locally) but it may make the alloy less prone to cracking (more prone to melting). I don't think spikes on combustion matter much if they are short enough. Long term steady-state temperature however might be a problem if above a certain threshold - don't know what this value would be. It would make for a very interesting study to look at the modified alloy and build a temperature curve for it.
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  21. #546
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    CHT (Cylinder head temperature) and EGT (Exhaust gas temperature) are critical in aviation engines and are monitored during all phases of flight. You can't just pull up on the side of the sky and rebuild a cylinder head....
    It's another lovely day! Again!

  22. #547
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    Given the design we are talking about, I think the temperatures important here are at the bridge. Ambient head temperature is of course important but only as a background (though important for the steady-state temperature). The question is whether or not fluctuations around this ambient temperature impact on the bridge and by how much (I mean are these enough to weaken/soften the bridge and eventually crack it ?).

    Pressures are of course another factor to be considered and I have no doubt they impact seriously (even if indirectly) on the bridge longevity.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

  23. #548
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    Quote Originally Posted by CarvelSA View Post
    Hi Frans ,

    Greetings from SA .

    Click image for larger version. 

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    In this pic of the head which featured in my Gordini 50 article which you shared here , one can see the effects of the repair . If I recall all four combustion chambers were cracked across the flame holes between the valves , so to be safe I had all four repaired . From what the head specialist told me they removed the valve seats , cut out the offending portion , insert a screwed plug from the spark plug side ( not sure what they used that didn't stick with the welding ) , welded it up , recut the valve insert space, bored out the spark chamber from the top , and then used a jig to bore the interconnecting flame holes from the combustion chamber side . Not trivial , but possible . This was first pioneered by Frank Shearsby here in the 1970's with Gordini heads and Lotus Cortina heads at the time . This head is also interesting from two other aspects in that larger inlet valves have been fitted , and the head has been built up to the original specified 73mm thickness using the aluminium metal spraying technique to bring the compression ratio back down to a comfortable road going figure given that this engine featured 77mm domed pistons from Salv Sacco ( 1340cc) ,


    All the best for the New Year , and good luck with the repair ,

    Carvel
    What an extraordinarily interesting post; thank you.

  24. #549
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    Hi there Carvel.
    I was just looking at your photo of the rusty disc as I have 4 on my R8 restoration (BARNIE). Did you clean up the rust on your disc or are we forced to by new discs just because they rust??

    My rusty disc looks similar to yours.

    Cheers
    Phil

    Two new racecars in NZ-dscn1225.jpg


    Quote Originally Posted by CarvelSA View Post
    Click image for larger version. 

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    John and friends ,

    Any visits always welcome

    Here's a New Years tip ( literally) that may help . Getting the wheels back onto our 3 stud hubs can sometimes be a challenge , particularly in poor light . A small trick that helps is to put a blob of white Tippex ( typist correction fluid) on the end of each stud which makes 'sighting' them through the stud holes in the rim a lot easier . . .


    Keep well,

    Carvel

  25. #550
    1000+ Posts Kim Luck's Avatar
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    Quote Originally Posted by R8philSA View Post
    Hi there Carvel.
    I was just looking at your photo of the rusty disc as I have 4 on my R8 restoration (BARNIE). Did you clean up the rust on your disc or are we forced to by new discs just because they rust??

    My rusty disc looks similar to yours.

    Cheers
    Phil

    Click image for larger version. 

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    Applying a set of old pads at speed would give you an instant readout of their usefulness. Modern car discs become rusted in a few days left out in the "weather".
    It's another lovely day! Again!

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