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10-07-2024, 11:19 PM | #51 | |
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Re: Rough idle and takeoff 250 inline
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10-07-2024, 11:45 PM | #52 |
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Re: Rough idle and takeoff 250 inline
If you’re setting the valves, make sure to check all the rockers are moving the same amount.
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10-08-2024, 12:28 AM | #53 |
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Re: Rough idle and takeoff 250 inline
Maybe check that the points condenser is healthy with a multimeter. I know it's new, but chaotic timing and backfires might be caused by a dying one
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10-08-2024, 08:11 AM | #54 |
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Re: Rough idle and takeoff 250 inline
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10-08-2024, 08:12 AM | #55 |
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Re: Rough idle and takeoff 250 inline
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10-08-2024, 07:45 PM | #56 |
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Re: Rough idle and takeoff 250 inline
I readjusted the valves and set them a 1/4 turn from zero lash. When I did a 1/2 turn it was still idling a little rough. I did this with the engine running. The idle is smooth now. Before I put the valve cover back on, I'm going to let it sit overnight and start it again tomorrow to see if it's still ok.
So are the 1/4, 1/2 and 3/4 turns on a valve adjustment simply recommendations and each motor is different? I originally did a 3/4 turn on each valve. |
10-08-2024, 08:45 PM | #57 |
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Re: Rough idle and takeoff 250 inline
Cut-Out Valve Cover. That's a Pro move!
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
10-08-2024, 08:46 PM | #58 |
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Re: Rough idle and takeoff 250 inline
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10-08-2024, 11:02 PM | #59 |
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Re: Rough idle and takeoff 250 inline
Especially as the little spoon clips they sell for adjusting V8 heads just wobble off L6 rocker arms. I have an old valve cover to use iike that, too.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
10-09-2024, 03:52 PM | #60 | |
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Re: Rough idle and takeoff 250 inline
Quote:
For SBC the consensus seems to be 1/2 or 3/4 turn, but for a battleworn six, I'd guess you're going to know better than anyone else where it's happiest
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1970 C10 Custom longbed 350/350 |
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10-09-2024, 04:05 PM | #61 |
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Re: Rough idle and takeoff 250 inline
When I adjusted them the first time, I tried the one full turn like the shop manual said, but the motor really didn't like, it barely kept running, so I ended up doing 3/4 turn. At the time it seemed ok. When I readjusted last night, it didn't like the 3/4 turn, so I tried a 1/2 turn and it was still idling rough. I backed it off to 1/4 turn and it idled good. Gonna go back out there this evening, start it up, let it run and see how it goes. If all seems good, the valve cover is going on and I'll take a test drive.... We'll see.
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Today, 05:38 PM | #62 |
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Re: Rough idle and takeoff 250 inline
UPDATE:
I did a compression test on the cylinders. Here are the results... #1 - 160 #2 - 165 #3 - 165 #4 - 165 #5 - 65 #6 - 160 Another thing to note. All of the valves were backed off and tightened 1/4 turn, except the fourth valve from the rear, which I believe is the exhaust valve for cylinder number 5. That one needed to be tightened almost two full turns before the lash would go away. I'm guessing something is going on right there. What does this mean and what are my next steps? |
Today, 06:53 PM | #63 |
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Re: Rough idle and takeoff 250 inline
Check the height of the rocker stud, compared to the others. It could be pulling out of the head. Try a wet compression test. If that cylinder's pressure comes up it's rings leaking by. If not, it's an exhaust valve. I'm curious if you used a vacuum gauge on it. Is, was there a lot of fluttering? IIRC, the one you indicate is the intake valve. Did you check the compression after making the lash adjustment? It would be rough at idle and at low speeds, but the rotational inertia of the engine at higher rpm can cover up the weak cylinder to some extent.
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Today, 06:55 PM | #64 |
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Re: Rough idle and takeoff 250 inline
Could be the rocker stud is pulling out of the head.
Or the cam is going flat. Did you check all the rockers are moving the same amount? |
Today, 07:56 PM | #65 |
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Re: Rough idle and takeoff 250 inline
Cam lobes can flatten if you're not cafeful to use oil with the right amount of ZDDP. Because the Zinc ruins the platinum in catalytic converters, Lube Manufactorers have steadily weaned it out of modern motor oils. Engines of Our vintage have no Cats and relied on the Zinc to minimize tappet/cam lobe wear.
I use Valvoline VR1 SAE 30 Racing Oil in my 292. It has the right amount of ZDDP. There are other ZDDP additives, including STP, but one also has to be careful not to ''overdose'' the zinc.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
Today, 08:01 PM | #66 |
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Re: Rough idle and takeoff 250 inline
[QUOTE=Steeveedee;9346511]Check the height of the rocker stud, compared to the others. It could be pulling out of the head. Try a wet compression test. If that cylinder's pressure comes up it's rings leaking by. If not, it's an exhaust valve. I'm curious if you used a vacuum gauge on it. Is, was there a lot of fluttering? IIRC, the one you indicate is the intake valve. Did you check the compression after making the lash adjustment? It would be rough at idle and at low speeds, but the rotational inertia of the engine at higher rpm can cover up the weak cylinder to some extent.[/QU
I'm assuming all the rocket studs be the same height? So I check by laying a straight edge across them all to see if that one is higher than the rest? What is meant by a "wet" compression test? How is that done? I apologize for what may seen like dumb questions, but I am new to a lot is this. Thanks! |
Today, 08:13 PM | #67 | |
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Re: Rough idle and takeoff 250 inline
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Today, 08:26 PM | #68 | |
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Re: Rough idle and takeoff 250 inline
Quote:
Real Lead was a additive with actual TetraEthylLead that really made old engines zoom again. I think it's illegal now. It disappeared from shelves 24 years ago.
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