Cam timing questions

Discussion in 'Engine Topic' started by ULTM8Z, Oct 9, 2021.

  1. jeff swisher

    jeff swisher Veteran Member

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    I have a timing chain set that 4° + or - is actually 6°
     
  2. ULTM8Z

    ULTM8Z Veteran Member

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    Looks like I have a decision to make here... looking for input.

    So I forgot that 4° on the crank equals 2° on the cam. The timing chain I ordered is only going to get me an additional 2° on the cam, so I'd end up at 108 rather than 110.

    I ended up lookiing for one that would get me the 4° at the cam, but damn... what a PITA trying to find info on what fits on a late model Vortec block. Info on the double rollers seem to all indicate that you end up with an interference between the cam sprocket and this area of the block above the front cam bearing. Some people say to grind the area down a bit, but I'm not about to start grinding on an engine that's under warranty that I haven't even started up yet.

    None of the single rollers that I see will give me the 4° at the cam. So I appear to be stuck...

    The question then is, if I install this cam 2° retarded, am I going to notice a significant reduction in idle quality? Intuitively I wouldn't think so for a cam this size (213° @.050) in a 383 with a 114° LSA. The Crower guys are saying I shouldn't really notice any detriment to what I'm after with this cam.

    Figured I'd pick your guys' brains too...

    Unless anyone knows of a single roller that gives 4° at the cam? Either that or I go with the cam offset bushings...
     
  3. sandlapper

    sandlapper Veteran Member

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    Between some offset crank keys and a set of cam sprocket bushings, you should be able to fine tune & reach its G-spot ... they both rely upon you knowing where it is!
     
  4. ULTM8Z

    ULTM8Z Veteran Member

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    Crower has the bushings that I would buy... they'd get me the 4° I need at the cam and have a shoulder to capture them after install so the don't fall out. I'd have to get a machine shop to machine a c'bore in the back of the sprocket so the bushing sits flush. Maybe when I take my heads in, I'll take the sprocket and a set of these bushings and have them make the modification.

    But I'd still rather do the adjustable timing chain route if there is one out there...

    upload_2021-10-15_17-16-28.png
     
  5. Romney Mawhorter

    Romney Mawhorter 70½ Z/28 RS, M21, 4.10, 65k/71 Restomod SS396

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    Seems you may have figured this out. And I'm no cam expert but it sounds like if a cam has a "4° advance built in" to me means you have to RETARD the cam 4° to measure the 110 thing. Anyway, my 2 cents.
     
  6. ULTM8Z

    ULTM8Z Veteran Member

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    I'm still kinda scratching my head that the factory timing chain setup retards the cam by 4° though... I can't totally shake the feeling that I'm doing something wrong...
     
  7. jeff swisher

    jeff swisher Veteran Member

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    Ford began retarded cam timing in the early to mid 70's and the earlier timing chain sets would add some advance to these low power smog engines.
     
  8. ULTM8Z

    ULTM8Z Veteran Member

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    I had ordered a Cloyes single roller a while ago and was going to send it back when I saw I'd only get 2 deg at the cam, but something told me to try it out first.

    Just put the crank gear to full retard on the adjustable Cloyes timing set and the Comp Cam very nearly came in to spec.

    110 ICL exactly per the cam card.

    22 deg intake valve open at .006 tappet lift exactly per the cam card.

    66 deg intake close point .006 tappet lift vs 62 deg on the cam card. A little off. If I put the degree wheel at 62 deg, I get .008 tappet lift. So I guess the closing ramp is pretty sensitive to measurement error... 4 deg for .002 lift...

    But if I can get everything this close on the Crower, I'll probably call it day on that.

    I'll reinstall the Crower later today and see what I get... the Crower and hte Comp were off by the same amount, so hopefully this is a good sign.
     
  9. ULTM8Z

    ULTM8Z Veteran Member

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    Ok, finally got this damn thing figured out I think... I ended up opening that Cloyes timing chain I bought that I thought wouldn't work..

    Put the Comp Cam back in...

    With the crank gear full 4 deg retard, the Comp Cam mostly came in to spec

    110 ICL per the cam card.

    22 deg intake valve open at .006 tappet lift per the cam card.

    66 deg intake close point .006 tappet lift vs 62 deg on the cam card. A little off. If I put the degree wheel at 62 deg, I get .008 tappet lift. So I guess the closing ramp is pretty sensitive to measurement error... 4 deg for .002 lift...

    Also measured the exhaust centerline and then calculated out the LSA to 112.5 where the cam card says 112.

    So FINALLY I got a baseline install that tells me my degreeing process is good.

    Put the Crower Cam in and had to put the crank gear at full advance but I got the following...

    108.5 intake centerline when it should be 110. If I go to factory setting I get 112, so I'm kinda in an in-between scenario. I'm going to err on the 108.5. Figure with the 114 LSA, this thing is going to idle really smooth, so I can err on the side of slightly more top end power with 1.5 deg retard.

    Also measured the exhaust centerline, then calculated the LSA to be 114.5, pretty much right on the money.

    The intake valve closing event is also pretty much right on the money... should be 36.5 deg ABDC @ .050 tappet lift and I get etiher 35 or 38 depending on the crank gear registration. That's really close IMO.

    The intake valve event is still kinda puzzling me though... they say it should be 3.5 deg BTDC, but at full advance I'm only getting 2.5 ATDC... essentially 6 deg off. Maybe it's not a big deal... I'll probably still call Crower next week, but absent anything earth shattering, I think I'm finally done with this cam install.

    There must be something funky with that GM L31 Vortec crank gear that came with the engine. What constitutes the "factory setting" on that gear is pretty different than what is the "factory setting" on the Cloyes. Which is what was probably throwing me for a loop earlier...
     
  10. ULTM8Z

    ULTM8Z Veteran Member

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    interesting comparison between the L31 gear and the Cloyes "factory" setting...

    The Cloyes is the installed one and the L31 is out by itself...

    There's a ~5-6 deg relative retarding on the L31 relative to the factory setting on the Cloyes. Which probably explains how the L31 resulted in a 106, and the Cloyes 4 deg advance resulted in a 108.

    [​IMG]

    [​IMG]
     

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