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Old 12-14-2003, 05:57 AM
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New Engine build, is cam gear one tooth off?

I just started for the first time a new build 350 SBC. Cam is roller with 280 duration, 1.5 rockers, MSD distributer, Blaster 2 coil, Edelbrock carb. The engine starts and runs with no pops or backfires and is very throttle responsive. I initially set the timing for best idle with no timing light. Later when I hooked up the timing light the timing was very high, at least 25 degrees initial with vacuum blocked. Engine will die when I back it off to 12 degrees. My question for you guys is it possible the cam gear is off one tooth to cause this problem? Will the engine even run if it's one tooth off at the cam? I can't drive it yet because the body is off the frame, just engine/tranny, frame & wheels at this point. Thanks for any help you can offer.

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Old 12-14-2003, 08:08 AM
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If the motor runs and starts good, has good throttle response and idles, sounds like you have the wrong timing tab and harmonic balancer combo or the outer ring in the balancer has slipped. Both very common problems on sbc builds.
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Old 12-14-2003, 09:08 AM
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I agree, my chevy does that too. Bigger cams like more timing, thats probably part of it. I gave up on timing a while ago. I just set it till it runs the best for me (kinda check and run check and run thing) then mark it and leave it. Numbers are pointless anyway.
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Old 12-14-2003, 11:32 AM
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It will not run one tooth off. Set it by ear and drive it. I haven't used my timing light on my own stuff in years.

Troy

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Old 12-14-2003, 02:04 PM
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Follow up, and a thanks

Thanks to those that posted a reply, here's some follow-up info. Today instead of using my timing light with the inductor clamp, I got out my 25 yr old timing light that clamps on an inline spring between the plug wire an the spark plug, got another battery for an isolated 12 volt source, the timing results were the same. The damper is new and so is the timing cover and tab, could be the wrong tab. The timing indicates 23 deg without vacuum, but the engine starts good, idles about as expected with this cam, runs smooth at 3000 RPM (no load) and awsome throttle response. I have never built an engine with the cam gear off and I double checked this one before bolting on the timing cover, but since Im not as perfect as I was when I was 18; D , mistakes do happen. Several months before I get the body back on the frame and get this puppy driveable, think I'll leave it like it is and fine tune the timing after driving it. Many thanks
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Old 12-14-2003, 03:47 PM
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The valve timing isn't off. You problem lies in the carb/distributor tuning. Always use a timing light. Your car could still seem to run okay, and it could be advanced enough to blow a head gasket.
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Old 12-14-2003, 04:05 PM
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What problem?he says it starts and runs fine,like everyone said above dont worry about what timing light says set it where it runs best.When you use new timing cover and damper you have to make the true timing marks on them if you it to correspond to the timing mark on the damper and cover.
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Old 12-14-2003, 04:56 PM
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How would you blow a head gasket? When it kicks back on the starter, it's to fast.

Troy

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Old 12-14-2003, 05:17 PM
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agree that it may have the wrong timing pointer. I've built a motor that had the balancer that was to be timed at "12 o clock"
and I was timing it at 2 oclock like normal. this set the timing very retarded and it wouldn't run.
What I did was fake the timing mark on the uppermost bolt on the timing cover toward the drivers side of the motor. i just use that as a 0 reference and use an advance light
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Old 12-14-2003, 09:47 PM
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Sure it may idle great but if you have the timing set at 25 or so and the distributor is set up to only run 10 degrees initial advance there will be too much total advance. Good bye head gaskets or youll end up with tuliped intake valves from detonation then blow a head gasket to boot.

I would check that piston is really at TDC when timing mark is on zero.

I would use a timing light too. Once you have the timing adjusted correctly start tuning on the carb.
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Old 12-14-2003, 10:09 PM
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The carb idle and initial timing work together,if you had your initial timing 'really' that high you would be backing the idle and mixture screws way down to get the idle down to around 800rpm and that would be a sign of too much advance not to mention the pinging and the hard starting.
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Old 12-14-2003, 10:31 PM
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Quote:
Originally posted by troy-curt
How would you blow a head gasket? When it kicks back on the starter, it's to fast.

Troy

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It was a early 70's 302 with low compression. I didn't have a timing light and I had to remove my distributor. When I reinstalled it I timed it by ear. It started, sounded and drove fine so I deceided it was probably okay. I was almost home and it started running rough. It ended up being way too andvanced and had blown the head gasket between two cylinders.
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Old 12-14-2003, 11:32 PM
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Something else caused the head gasket to blow. Advanced timing didn't do it.

If it dosn't kick back or ping. it isn't to fast. A lot of engines run that much advance. After you wear out a few timing lights you get the ear for it.

Why fix something, when there is nothing wrong?

Troy

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Old 12-15-2003, 12:30 PM
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Timing

The best and most accurate way to find TDC on an engine that is already assembled is to use a piston plug and a cheap easy to make timing wheel. This is how we time aircraft within half a degree. Find compression, insert a plug into the spark plug hole, turn engine till piston touches plug (gently) mark timing wheel, turn opposite direction until piston touches plug (gently) mark timing wheel, and divide the two marks mathematically down the middle, remove plug and turn to derived mark. Presto TDC compression of number one. Then look at your timing mark on the flyweel and see how far off it is. Generally the deeper the plug you can thread in the spark plug hole, the more accurate the results.
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Old 12-15-2003, 12:37 PM
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I would say that is a good way to distroy an engine.
And there isn't any timing marks on the flywheel.

Troy

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