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Discussion Starter #1
Background:
1980 El Camino. I rebuilt the 305 V8 with flat top pistons, Edelbrock 2102 hydraulic cam and lifters, roller rocker arms, Edelbrock 2101 Performer manifold, new HEI distributor/wires/plugs, and Holley 80570 570 cfm carb. I bought the carb used and cleaned it, replaced the gaskets, and verified it has the correct jets. The engine had ZDDP added to the oil during the break-in cycle, then changed and more ZDDP added to the new oil. Filter was also changed.

It starts and idles at 1500-1800 RPM until the choke warms up and then drops to 1000 RPM. Manifold vacuum is steady at 15 psi (exactly what Edelbrock says it should be at 1000 RPM). The distributor uses ported vacuum from the carb. Fuel pressure is 8-9 psi with a new stock fuel pump. Oil pressure is 40-60 psi. Temperature remains below 210 degrees.

I can set timing at about 12 degrees advanced but, if I advance it a LOT more, it continues to increase the idle speed and runs somewhat better. Either way it sounds like a slight miss (not the cam loping).

When I drive it, it runs OK at low throttle, but when I try to accelerate, it bucks and jumps and won’t speed up. Messing with the timing has no positive effect. I pulled the plugs and they’re all white (lean). The accelerator pump on the carb squirts gas when I manually open the throttle. The float levels are set correctly. In Neutral I can rev or goose the engine with no problem. It revs, but not as rapidly as I’d expect.

I then decided to verify the valve lash. I pulled all the spark plugs, set the engine at TDC on the compression stroke, loosened all the rocker arms, and primed the oil pump for a couple minutes to make sure the lifters were all pumped up. Then I adjusted the valve lash per the instructions from Edelbrock. Next, I turned the engine over until it was at TDC on the #6 plug’s compression stroke and adjusted the other valves. This didn’t help any either.

Today I pulled the plugs and did a compression test on all 8 cylinders, with the throttle fully open. They were all 115 psi except #1 and #8 which were 90 psi. I used a "borrowed" gauge from O'Reilly so I have no idea how accurate it is. I was expecting somewhat higher readings, but it may be due to the cam.

Thinking maybe I had adjusted #1 and #8 valves wrong, I loosed the #1 rockers all the way and turned the engine over a few times to pump up the lifters. Then I set it back to TDC for #1 and adjusted #1's valves. Reran the compression check and still got 90 psi.

Then I put it all back together, started the engine, and let it idle awhile. It was still missing at idle and also when I revved it. When I revved it to 3000-4000 RPM I heard a noise in one cylinder (I think) that sounded similar to a piston slap.

What should I do short of pulling the heads?

I’m also going to try a new distributor and another carb (Holley 600 cfm), just for grins. I can try to see if the missing is ignition or carb. I have no idea what else to do.

Jack
 

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1966 El Camino
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Those compression readings seem awful low to me, especially 1&8, A motor in good condition I think should show something around 150, 90 is very low for any small block unless there is a ton of overlap in cam.

The 2102 cam at 204/214 @ .50 sure doesnt seem like such a cam, you dont get much more pooch than that.
 

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Discussion Starter #3
Those compression readings seem awful low to me, especially 1&8, A motor in good condition I think should show something around 150, 90 is very low for any small block unless there is a ton of overlap in cam.

The 2102 cam at 204/214 @ .50 sure doesnt seem like such a cam, you dont get much more pooch than that.
I totally agree. That's one of the things that's baffling me.

Bad cam? Broken piston?
 

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the rings may not have seated yet but the compression should be higher than that.could you have missed a tooth on the timing chain.that will throw your compression off.but they should still be even especially on a new engine. start pulling plug wires to isolate which cylender is making the noise. if it is one of the low cylenders pull the engine and pull that piston. you didnt mention if it was bored or new pistons in a old bore. if it is the later it will sometimes make a piston slap until the piston comes up to temp and will be louder with forged pistons. if it was bored with cast pistons i should be quiet. did you check to see how much the dist was advanceing. if it was bored and new pistons i would pull it and tear it down to see what is going on before it does any damage not already done. you also didnt say which heads you are useing. the 305 heads are 58 cc anything bigger really drops your compression. pull the valve covers and spray carb cleaner down the push rod holes while idleing to check for a lower intake leak. also double check your plug wires to be sure you havent crossed one.could always be a bad cam or miss boxed maybe a cyl. swap cam
 

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the rings may not have seated yet but the compression should be higher than that.could you have missed a tooth on the timing chain.that will throw your compression off.but they should still be even especially on a new engine. start pulling plug wires to isolate which cylender is making the noise. if it is one of the low cylenders pull the engine and pull that piston. you didnt mention if it was bored or new pistons in a old bore. if it is the later it will sometimes make a piston slap until the piston comes up to temp and will be louder with forged pistons. if it was bored with cast pistons i should be quiet. did you check to see how much the dist was advanceing. if it was bored and new pistons i would pull it and tear it down to see what is going on before it does any damage not already done. you also didnt say which heads you are useing. the 305 heads are 58 cc anything bigger really drops your compression. pull the valve covers and spray carb cleaner down the push rod holes while idleing to check for a lower intake leak. also double check your plug wires to be sure you havent crossed one.could always be a bad cam or miss boxed maybe a cyl. swap cam
Carl, I don't know what I'm gonna hafta do with you!! That was MY suggestion, and ya dun beet me to it!! Well, that just proves great minds think alike!!

Jack, I agree with Carl about the compression rings for #'s 1/8. They just MAY not have seated properly yet. It's been known to happen that all the rings won't seat properly for 1-1 1/2k miles.
 

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Discussion Starter #10
the rings may not have seated yet but the compression should be higher than that.could you have missed a tooth on the timing chain.that will throw your compression off.but they should still be even especially on a new engine. start pulling plug wires to isolate which cylender is making the noise. if it is one of the low cylenders pull the engine and pull that piston. you didnt mention if it was bored or new pistons in a old bore. if it is the later it will sometimes make a piston slap until the piston comes up to temp and will be louder with forged pistons. if it was bored with cast pistons i should be quiet. did you check to see how much the dist was advanceing. if it was bored and new pistons i would pull it and tear it down to see what is going on before it does any damage not already done. you also didnt say which heads you are useing. the 305 heads are 58 cc anything bigger really drops your compression. pull the valve covers and spray carb cleaner down the push rod holes while idleing to check for a lower intake leak. also double check your plug wires to be sure you havent crossed one.could always be a bad cam or miss boxed maybe a cyl. swap cam
It's a rebore with new cast pistons and rings. The heads are the 416 with 58 cc. I have about 30 miles on the engine now. Plug wires are correct.
 

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Jack its nice to see that you get lots of use out of ,the web site .has your truck ever ran ? seams broken down or something all the time leave it alone and drive it ! stop the tweaking ! :poke:
 

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Discussion Starter #13
Jack its nice to see that you get lots of use out of ,the web site .has your truck ever ran ? seams broken down or something all the time leave it alone and drive it ! stop the tweaking ! :poke:
It's not broken down all the time. It's never been built. It's my 5-year project and this is only the 2nd year. It WAS going to the paint shop tomorrow but it won't run well enough to get it there.
 

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If you have access to a dial indicator, try measuring the lift of each valve of the cylinders in question, and compare it to the others. It sounds like a collapsed lifter or failing cam lobe.
 

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You've got 30 miles on it and you're hearing noises coming from inside the engine?

Remove the oil filter and cut it open. If there is any sign of metal in the filter, pull the motor. If not, continue on with your testing. You don't want to cause more damage if there is something wrong inside the engine.
 

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You've got 30 miles on it and you're hearing noises coming from inside the engine?

Remove the oil filter and cut it open. If there is any sign of metal in the filter, pull the motor. If not, continue on with your testing. You don't want to cause more damage if there is something wrong inside the engine.
X2 Check for metal/debris in the oil 1st thing.
 

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1 and 8 are together in the firing order,,with them low on compression,,i could see that as maybe the slight miss..

you cant start with the correct jets,, fatten it up some,, then work it down..

sounds like some late cam timing
when you degreed the cam did you have to add a lot of bushing,, or how far off was it??

what is the total timing?? leave the vacuum hose off and go drive it..

dont forget about that distributer cap..

it aint the overlap..
 

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Discussion Starter #19
Update:
This morning I replaced the distributor with an Accel. That seems to have fixed the miss but I still have the noise when I rev it up.

Now, with the air cleaner off, when I rev it to about 4000 RPM it sounds like gun shots in the carburetor. About the slow speed of an AK47, not as fast as an AR15, if that helps.

I guess it's time to change (something) in the carb? Any ideas? Remember it's a Holley 4150 series.

Jack
 

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OK, so you're getting a regular light backfire? To me that sounds like maybe you have a valve hanging up on every rotation. That would explain your low compression, too.
 
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