- Bob
8RT Timing or...?
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Parts Nerd Extraordinaire
Joined: Sep 2010
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From: Western NY
8RT Timing or...?
Tried waking Big Red for the season and she just ain't happy. Engine is running rough.
*Started with the Holly 94 carb - removed, cleaned, rebuilt, including power valve. Could not get it to run better.
*Replaced rotor, points, condenser since I had the parts on hand. No change.
*Replaced spark plugs - again, had them on hand, why not. Old ones didn't show any concern. No change.
Then I got to thinking - I recently removed and rebuilt the water pumps and had the radiator re-cored. I wonder if with all that if I inadvertently bumped the distributor and threw off the timing a smidge.
I've never timed a flatty before and I am unsure of the process. I presume I connect the timing light to the battery and plug 1 and pull the trigger, but am unsure of what I should aim at or look for. Also, do I need to disconnect the vacuum advance?
Of course, maybe timing isn't the issue at all... Possibly a stuck valve? I plan on borrowing a compression tester to check. Or do you guys have any other suggestions?
And I gotta say it - I'm running stock systems and am not looking for "upgrade to pentronix electric ignition or chevy dizzys" type advise.
*Started with the Holly 94 carb - removed, cleaned, rebuilt, including power valve. Could not get it to run better.
*Replaced rotor, points, condenser since I had the parts on hand. No change.
*Replaced spark plugs - again, had them on hand, why not. Old ones didn't show any concern. No change.
Then I got to thinking - I recently removed and rebuilt the water pumps and had the radiator re-cored. I wonder if with all that if I inadvertently bumped the distributor and threw off the timing a smidge.
I've never timed a flatty before and I am unsure of the process. I presume I connect the timing light to the battery and plug 1 and pull the trigger, but am unsure of what I should aim at or look for. Also, do I need to disconnect the vacuum advance?
Of course, maybe timing isn't the issue at all... Possibly a stuck valve? I plan on borrowing a compression tester to check. Or do you guys have any other suggestions?
And I gotta say it - I'm running stock systems and am not looking for "upgrade to pentronix electric ignition or chevy dizzys" type advise.
Fleet Owner
Joined: Jul 2004
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From: NM
It's real easy. There is a pointer on the timing cover, and a "bump" on the crank sheave. Disconnect and plug the vacuum advance line, use your timing light to set the pointer at the bump at normal idle.
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Parts Nerd Extraordinaire
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From: Western NY
Got a few minutes this evening to poke around... I have attached a sound recording of the engine looking for some assistance.
Also going to see if I can't get the compression test done tonight...
EDIT: Compression test shows equal pressure on all cylinders - about 55-60 psi (I'm guessing gauge is out of spec)
Also going to see if I can't get the compression test done tonight...
EDIT: Compression test shows equal pressure on all cylinders - about 55-60 psi (I'm guessing gauge is out of spec)
Last edited by bmoran4; May 15, 2017 at 06:25 PM. Reason: Compression Test Update
Cargo Master
Joined: Aug 2010
Posts: 2,927
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From: Houston
I prefer to static time an 8BA style flathead. With the engine off turn the crank until the pointer and bump are lined up. Loosen the distributor hold down bolt and remove the distributor cap. Turn the ignition back on. Turn the distributor clockwise a good bit, then slowly turn it back counter-clockwise. Watch for the points to spark. As soon as the points spark quit turning the distributor and tighten the hold down bolt. I usually get to do the clockwise / counter-clockwise part two or three times until I am sure I have the distributor just when the points spark (when they open). Put the distributor cap back on. Congrats, your distributor is now timed.
Fleet Owner
Joined: Jul 2004
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From: NM
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Posting Guru
Joined: May 2010
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From: Moyie, BC Canada
What I do is run my motor at idle and loosen off the distributor hold down. Then just turn it ever so slightly one way or the other and adjust and adjust until it gets really smooth then add back the vacuum ports that I blocked and adjust the carburetor see what that does and so on. Then I start thinking as I'm heading over to my tools,... why am I not using that fancy timing light I acquired sometime ago. Actually many years. ago. Funny things happen to you when your old.
Your compression is fairly even, and I don't think you have to worry about mechanical issues. I'm thinking Ross has your answer.
Your compression is fairly even, and I don't think you have to worry about mechanical issues. I'm thinking Ross has your answer.
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Fleet Owner
Joined: Jul 2004
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From: NM
55-60 is dismal compression, but at least it's even on all of them. Did you have all the plugs out while cranking, and the throttle blocked open? Good battery? A gauge that's off could explain things, too. You should be around 100, I'd say 90 - 110 is the usual range.
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Parts Nerd Extraordinaire
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From: Western NY
I was expecting 90-110 compression as well. I had all plugs removed. I didn't do anything with the throttle - why should I do with it? Compression gauge is older than me, so I think it's accuracy is suspect. I was happy to have even readings across the cylinders.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Boy, I dunno, a good old school gauge is probably built better than anything today. Could have been dropped hard maybe somewhere along the line, but they are so simple not much to go wrong. Without throttle and choke blocked open during the test it will be starved for air and skew results.
Try running 4oz. of Marvel's per 10 gallons of fuel along with 1 quart in the crankcase. A mechanic's vacuum gauge connected to manifold is one of the most useful tuning tools available, they can diagnose a whole bunch of things.
Try running 4oz. of Marvel's per 10 gallons of fuel along with 1 quart in the crankcase. A mechanic's vacuum gauge connected to manifold is one of the most useful tuning tools available, they can diagnose a whole bunch of things.
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Parts Nerd Extraordinaire
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From: Western NY
I got another gauge and did another compression test. Came back about 3 psi lower then the previous test. I saw some comments on opening the throttle, so I weighted down the gas pedal - no change in readings. Now I'm concerned about the low readings and not sure what to do. Disgusted, I worked on another project this afternoon.
Fleet Owner
Joined: Jul 2004
Posts: 27,298
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From: NM
Can you give us the short story on the engine? Rebuilt? Run regularly? low miles due to fire service? (Hours may be more pertinent)
With only 50 - 60 psi, I'd suspect stuck valves or valves that aren't seating completely, maybe due to deposits on the seats. I would think you could still get it to start, and a good long run at full temperature may be what it needs most.
With only 50 - 60 psi, I'd suspect stuck valves or valves that aren't seating completely, maybe due to deposits on the seats. I would think you could still get it to start, and a good long run at full temperature may be what it needs most.