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  1. #11
    I'm Not Jed Clampett stueeee's Avatar
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    Quote Originally Posted by Mad Mark View Post

    I understand the 50thou point on lift to get a standard, but once I have the degrees of open/close for inlet/exhaust how can I get the alignment right?
    An accurate way to time any cam is to use the point of maximum lift. This always quoted by cam manufacturers in their data sheets; unfortunately you don't have a data sheet, but that needn't stop you dialling your cam in.

    If you look at cam timing diagrams, here's one Google Image Result for http://3.7mustang.com/vb/attachments/f5/81752d1132326110-cam-timing-diagram-800-615-valvetimingillustration-002.gif the point of maximum lift on the inlet happens at something like 106-110 degrees ATDC (After Top Dead Centre) if you look at what's going on with the exhaust on cam timing diagrams, the point of maximum lift is almost always exactly the same number of degrees BTDC (before Top Dead Centre) If you've heard engine tech heads say their cam is "timed down the middle" that's what they mean -the ATDC (inlet full lift)and BTDC (exhaust full lift) figures are the same. Sometimes, usually on high performance cams, the points of maximum inlet and exhaust lift don't exactly match which is when the cam is said to be "advanced" or "retarded" but the advance or retard will only result in a ATDC/BTDC figure differing by a couple of degrees at the most; if you're running problems are due to cam timing your cam is probably out by 5 degrees or more.

    IMO it's always worth the time to dial a cam in, Gears aren't always correctly marked by the manufacturer; a motor I re-timed recently after A N Other's rebuild had markings that were way out -the timing gears were probably two odd gears rather than a pair. By dialling in the cam, you either find the markings are spot on and so have the confidence that it's dead right, or you get to fix a problem which is going to cost you BHP, fuel consumption and general aggro later on.

    I have dialled in "unknown" cams (usually in Vintage or Veteran cars where there's no data available) with the cam timing set "down the middle" as I described and they've always worked so far.

    Having said all that, I would make sure I checked every other possibility before stripping a motor to check the cam timing.
    Last edited by stueeee; 10-05-2013 at 08:51. Reason: more added to (hopefully) clarify
    Stuart.
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  3. #12
    Rods 'n' Sods Junkie
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    Did I miss something what is the engine? How do u get it to start if it wont run below 2000. If it starts then I can't imagine it's cam timing. I also don't think that spings will have any affect in the rpm range your looking at. More info and will do best to help.

  4. #13
    Official RnS Addict cptpugwash's Avatar
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    iv got a 600 holley sitting doing nothing,your welcome to try it before ripping the motor apart again

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    Quote Originally Posted by stueeee View Post

    IMO it's always worth the time to dial a cam in, Gears aren't always correctly marked by the manufacturer; a motor I re-timed recently after A N Other's rebuild had markings that were way out -the timing gears were probably two odd gears rather than a pair. By dialling in the cam, you either find the markings are spot on and so have the confidence that it's dead right, or you get to fix a problem which is going to cost you BHP, fuel consumption and general aggro later on.

    I have dialled in "unknown" cams (usually in Vintage or Veteran cars where there's no data available) with the cam timing set "down the middle" as I described and they've always worked so far.

    Having said all that, I would make sure I checked every other possibility before stripping a motor to check the cam timing.

    How true is this, as rare as it is it does happen. I have had timing gears sent over with no marks at all and years ago BMC knocked out thousands of gear sets for a truck engine with incorrect markings and kept it as an in house secret on how to time up an injector pump. So always worth a check.

    Bob

  7. #15
    TechnicalTom
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    Stueeee above has hit" the nail on the head " when in doubt time the camshaft " down the middle" I have done this countless times on just about every kind of engine both petrol and diesel , OK if you have a camshaft spec. sheet then use the figures on there .Heres how I see things, A do it right using spec sheet = very good result.B timing it "down the middle" = engine timing will be more than 95 % correct. C take a chance and use the DOTS on an engine that has a mixture of factory and aftermarket parts = a gamble.
    C moving the camshaft timing back and forward when you are not certain of the starting point= a bigger gamble !!!!!! .
    Just make sure all other things on the engine are correct , assume nothing check everything. Hope your luck changes .

  8. #16
    Full Bloody Rebel! Mad Mark's Avatar
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    Quote Originally Posted by Pistonpusher View Post
    Did I miss something what is the engine? How do u get it to start if it wont run below 2000. If it starts then I can't imagine it's cam timing. I also don't think that spings will have any affect in the rpm range your looking at. More info and will do best to help.
    Before I say owt, I must thank everyone for their input and help. I really appreciate your efforts and can't believe how steep this bloody learning curve is!

    When starting it 'builds up' to running. An odd firing, than the engine speeds up a little, then a couple more and speeds up and finally it fires and runs., but won't keep running down to idle. It stalls between 1500 and 2000rpm, sometines popping back through the carb.

    The daft thing is that these are all the same bits that worked in the engine before. Gear drive, carb, cam, dizzy, heads, block, etc. The only thing changed is the followers.....

    The cam gear has a zero offset collar on the pin, so I 'guessed' that the timing marks on the cam and crank gears needed to be aligned correctly.

    Thanks for the offer Captain, but this carb ran perfectly on the 350 just before I pulled it and had run on the 327 in the past.......... but I might just try!!

    I need to get a degree wheel and DTI so I can get the information, or if I can get it off Simon, then I'll have to take the front off the unit as I'm not going to pull it again (or at least I don't want to!!) Anyone local got these I can borrow, please??

    Tom, thanks again! I don't think 3 and 4 and possible with a SBC as it would take too long for each iteration. I think down the middle will have to be the way forward with this one.
    Last edited by Mad Mark; 11-05-2013 at 08:01.
    If I wasn't meant to go that fast, the pedal would only go half way!

  9. #17
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    I'm sure it's something silly as it usually is, the fact that it runs it can't be that far out. Good luck let us know how u get on.

  10. #18
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    I'll have to take the front off the unit as I'm not going to pull it again (or at least I don't want to!!) Anyone local got these I can borrow, please??

    [/QUOTE]

    Just for checking purposes why not dti off a pushrod and just bolt a degree wheel to the crank pulley? Rather than stripping the thing down you will know straight away if its a country mile out.

    Bob

  11. #19
    Full Bloody Rebel! Mad Mark's Avatar
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    Quote Originally Posted by robo1 View Post
    I'll have to take the front off the unit as I'm not going to pull it again (or at least I don't want to!!) Anyone local got these I can borrow, please??
    Just for checking purposes why not dti off a pushrod and just bolt a degree wheel to the crank pulley? Rather than stripping the thing down you will know straight away if its a country mile out.

    Bob[/QUOTE]

    Thanks Bob! Trust me, I'd not be stripping it down until I get the cam info. I just need the DTI and degree wheel to get it.
    If I wasn't meant to go that fast, the pedal would only go half way!

  12. #20
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    If all is back in the motor as before except the lifters,, was it running ok before you built it,, if it was and you replaced everything as it was before how can the cam timing be out,, surely if the lifters are the only thing changed then wouldn't it make more sense to start there ...have you done a cranking compression test on the motor

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