Author Topic: 1975 Chevy 350, Cam Timing  (Read 4249 times)

Offline motorbreath777

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1975 Chevy 350, Cam Timing
« on: June 07, 2009, 06:21:03 PM »
About a week ago I picked up my first project vehicle: 1975 Silverado K10, 350/350.  The previous owner rebuilt the engine about 1,000 miles ago (stock rebuild, .030" over).  It has been fitted with an Edelbrock carb, manifold and camshaft he said, "(he) retarded two teeth to give it better low end for towing". 

I don't know the cam grind, but this doesn't seem right anyway.  I'm thinking retarding the cam robs from the low end and gives more to the upper. More over, two teeth sounds like far more degrees than would ever be advisable. Additionally, the ignition timing appears well retarded, which may be necessary in this case, but .... yeah, I'm confused.

Overall the truck feels pretty strong but I've been driving Toyotas, so maybe it's me.  It stumbles a bit off the line, and sucks fuel to the tune of about 9MPG (32" tires on stock gears).

Does it sound wise to set the cam back at zero, with slightly advanced ignition timing? 

All advice is appreciated.  Thank you.



75 Silverado K10, SWB, 350/350

Offline VileZambonie

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Re: 1975 Chevy 350, Cam Timing
« Reply #1 on: June 07, 2009, 06:45:58 PM »
If it's a stock cam grind or near to it I would install it "straight up"

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1974 GMC

Offline eventhorizon66

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Re: 1975 Chevy 350, Cam Timing
« Reply #2 on: June 07, 2009, 07:38:15 PM »
You are right, retarding a cam does not help low end.  It does just the opposite.  Many cams have about 4 degrees of advance built into them and are intended to be installed "straight up."
'85 C10 SWB 350 700R4 TKO600

Offline motorbreath777

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Re: 1975 Chevy 350, Cam Timing
« Reply #3 on: June 13, 2009, 12:24:47 PM »
Thanks again for your replies.  I got sidetracked, back at it, and now have another question or two.

When I got the timing cover off, the DOT on the cam gear lined up with the ARROW on the crank gear.  As far as the crank gear is concerned I see 3 gear markings ( rectangle?, a TRIAGNLE, and a 0 ).  From what I have read, this appears to be the system Comp Cams uses on their timing sets.  To go further, they (Comp Cams) say to use the 0 mark, and the corresponding, marked keyway to set your timing "straight up." 

I don't readily see a mark on any of the three keyways, which are located approx 120deg apart.  The keyways all appear to be 2-4 teeth away from a gear marking (rectangle, triangle, 0). 

Would any of you be able to tell me which keyway I should be using for: "straight up?"  Is it the keyway closest to "0?"

Again, thank you for your time.
75 Silverado K10, SWB, 350/350

Offline HAULIN IT

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Re: 1975 Chevy 350, Cam Timing
« Reply #4 on: June 13, 2009, 01:00:32 PM »
Yes, You want to line up the dot on the cam gear with the tooth with the circle, square or triangle on it, not the tooth at the keyway. Does the triangle stand for retarded, do you know? Invision it this way...the cam is in the same place for all Three positions (your not going to move it), either the tooth with the circle, triangle & square line up with the dot on the cam gear, so what has changed is where they put the keyway in relationship to the tooth (one tooth change is way more than the 2-4* your changing the timing. With the gear on the workbench, if you get a straightedge & line it up with the side of a keyway, then check the other ones, you will see the slight variation in this placement to the point of the tooth. Why I say to view it as "moving the crank" is because that is what you will have to do to get the sprocket on & lined up with the dot on the cam gear. You should check/set your ignition timing when your done. Understand? Any questions just ask, Lorne 

Offline VileZambonie

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Offline motorbreath777

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Re: 1975 Chevy 350, Cam Timing
« Reply #6 on: June 13, 2009, 04:13:49 PM »
I've seen the CompCams instruction posted in the thread by Zombie.  Thanks anyway. The problem is that they tell me: "Use keyway marked O and crankshaft gear tooth marked O."  My timing set has no visible keyway marks. 

HAULIN IT: the timing set was aligned with the triangle, which according to Comp, is ADVANCED (contrary to the previous owner's claims that he retarded it).
75 Silverado K10, SWB, 350/350

Offline VileZambonie

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Re: 1975 Chevy 350, Cam Timing
« Reply #7 on: June 13, 2009, 06:24:06 PM »
put the engine on tdc and align whichever keyway lines up your dot
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Offline HAULIN IT

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Re: 1975 Chevy 350, Cam Timing
« Reply #8 on: June 13, 2009, 09:01:08 PM »
Can you post a picture of the crank sprocket?
The problem is that they tell me: "Use keyway marked O and crankshaft gear tooth marked O."  My timing set has no visible keyway marks. 
I see in the instructions that Vile posed what you are referring to. Now I see why your question. That sentence doesn't make sense. You can't have Two different marks to line up. I think they were meaning camshaft sprocket 0(dot) lining up with "0" on the crank sprocket, however that isn't what it says by any means. To the best of my knowledge with the multi-key sprockets you are not trying to line up the keyway with anything...just the tooth with the circle, square or triangle with the dot on the cam gear, but to be in proper phase, the crank key needs to be in the keyway closest to the mark your using not one of the other Two. Does this make sense? I think all of the keyway wording is the confusing part
When I got the timing cover off, the DOT on the cam gear lined up with the ARROW on the crank gear.  As far as the crank gear is concerned I see 3 gear markings ( rectangle?, a TRIAGNLE, and a 0 ).  From what I have read, this appears to be the system Comp Cams uses on their timing sets.  To go further, they (Comp Cams) say to use the 0 mark, and the corresponding, marked keyway to set your timing "straight up." 

I don't readily see a mark on any of the three keyways, which are located approx 120deg apart.  The keyways all appear to be 2-4 teeth away from a gear marking (rectangle, triangle, 0). 

Would any of you be able to tell me which keyway I should be using for: "straight up?"  Is it the keyway closest to "0?"

 When you mentioned the ARROW is this the triangle maybe or something else?
Yes it sounds like the cam was in advanced, unlike what the guy told you (which also would make more sense in a truck used for towing) Lorne
 
« Last Edit: June 13, 2009, 09:03:49 PM by HAULIN IT »

Offline VileZambonie

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Re: 1975 Chevy 350, Cam Timing
« Reply #9 on: June 13, 2009, 10:15:56 PM »
There is an o and an 0 those are the two that should line up with the cam sprocket dot and keyway.
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                         /  _ _ _\_
              ⌠'   [☼===☼]
              `()_);-;()_)--o--)_)

1974 GMC

 


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