Register or Log In To remove these advertisements. |
|
|
|
Thread Tools | Display Modes |
10-07-2024, 11:19 PM | #51 | |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
Re: Rough idle and takeoff 250 inline
Quote:
|
|
10-07-2024, 11:45 PM | #52 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,669
|
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.
|
10-08-2024, 12:28 AM | #53 |
Senior Member
Join Date: Jun 2022
Location: San Ramon,CA
Posts: 547
|
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
__________________
1970 C10 Custom longbed 350/350 |
10-08-2024, 08:11 AM | #54 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
Re: Rough idle and takeoff 250 inline
|
10-08-2024, 08:12 AM | #55 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
Re: Rough idle and takeoff 250 inline
|
10-08-2024, 07:45 PM | #56 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
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 |
Senior Member
Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,368
|
Re: Rough idle and takeoff 250 inline
Cut-Out Valve Cover. That's a Pro move!
__________________
Every 25 years I like to rebuild that 292, whether it needs it or not. |
10-08-2024, 08:46 PM | #58 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
Re: Rough idle and takeoff 250 inline
|
10-08-2024, 11:02 PM | #59 |
Senior Member
Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,368
|
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.
__________________
Every 25 years I like to rebuild that 292, whether it needs it or not. |
10-09-2024, 03:52 PM | #60 | |
Senior Member
Join Date: Jun 2022
Location: San Ramon,CA
Posts: 547
|
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
__________________
1970 C10 Custom longbed 350/350 |
|
10-09-2024, 04:05 PM | #61 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
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.
|
Today, 05:38 PM | #62 |
Registered User
Join Date: Jun 2017
Location: Painesville, OH
Posts: 167
|
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 |
Who Changed This?
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,544
|
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.
__________________
~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
Today, 06:55 PM | #64 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,669
|
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? |
Bookmarks |
|
|