The Stovebolt Site Forums The Shop Area Engine Shop Question's on Rebuilt Motor

Once again, I have a couple questions on a 305 SBC I recently rebuilt. First of all, is a newly rebuild motor supposed to shake, and also shake the truck a little more than usual, until it has bean broke in? To try to fix this I have timed the engine to its specs, except I raised the ideling RPM's from 500 to 700-725, because it would almost die when being put into gear. Even at 700+ RPM's it seems a little hard on the tiny motor, but it does stay running. There is a new Carburetor, and spark plugs on the engine. And I tightened the vavles enough so they weren't real loose, is this ok? I have no idea how to adjust valves. And also, the cap and wires were never replaced, is this possibly the problem for the engine shaking as if it was having trouble running? Thanks guys in advance for your help, please help me out because this truck is going on the road very soon for the first time since 1999. Thanks!

- Shane

First, install new spark plugs, wires, distributor cap, and rotor, and make absolutely sure the firing order is right. It should be 1 8 4 3 6 5 7 2, with the distributor turning clockwise from the top. The cylinders are numbered 1,3,5, and 7 down the driver's side, with #1 in the front, and 2,4,6, and 8 down the passenger's side. Get hold of a service manual, and adjust the valves correctly. It's absolutely important to smooth running, and you could do major damage to valves and/or pistons with a too-tight valve adjustment. I've outlined the procedure several times in the forum, so a search for "valve adjustment" might bring up the right thread. It's best if you do it with the engine stopped, as I've never gotten a really good adjustment on a running engine. With the right firing order, good plugs and wires, and correctly adjusted valves, there shouldn't be any shake! Good luck!
Jerry

New carbs must be fine tuned to the engine. Uneven idling in neutral or in gear usually means problems with idle mixture, choke adjustment, idle speed, float level, etc. Ignition timing has a big effect on manifold vacuum. Set ignition properly, then adjust carb.

Very good sugestions there. Also check for
vacuum leaks. Remove the pcv valve with the
engine running & check for vacuum in the
ventilation tube or valve cover openings.
This would indicate a bad intake manifold
gasket. :confused:

Thanks for the suggestions so far guys, tomorow I will check the firing order, and make sure the wires are in their correct place. I already put new spark plugs in, and the new carb was barely used when i got it, and I also adjusted the mixture and got it to quit popping out the tail pop. I do remember when I had the bad carb on there, gas got all over the intake manifold on the passenger side, and soaked the gasket, I hope this didnt mess anything up with the gasket :confused: . Other than that I cant get new wires or cap cause I am broke, so I will have to do with the ones I have. I will also search for the vavle adjustment thread. When I adjusted the valves, I just tightened them up enough so they wouldnt rattle, that shouldnt be too much, right? Thanks for the help!

- Shane

Well, today my Dad told me how to adjust valves, and I couldnt believe how simple it was. All you do is Loosen the vavle until it starts clacking, then tighten till it quits, and tighten it another 1/4 turn. And just do that to all the vavles. Tomorow we are going to the parts store to get a new cap and rotor to see if that will also help the truck run smoother, we pulled the cap today and there was corrosion on the points. Other than that the engine seems a little better after we did the vavles, and messed with the carb again. We wont know for sure though until we take it out on the road for a real drive.

- Shane

Well today we got the brakes fixed, and replaced the cap and rotor which didnt fix the rough running engine. So, we went through each wire and discovered that when you take the wire off cylinder #6 and #8 it barely made a difference. So we are going to replace those 2 wires and hopefully the motor will run smooth like it should. Thanks for the help guys, but it looks that its the wires that are causing the problem, if not I will update you. Thanks,

- Shane

Check the vacuum outlet on the intake manifold
behind the carb. It effects #8 cyl. Feeds the
trans. modulator if equipt. Gas leaking on the
manifold gaskets won,t hurt them

I will check that after this dang rain stops, but I am pretty sure that the vacuum line is still hooked up to the tranny, unless it popped off, in that case I will put some clamps on it. Thanks for the help!

- Shane

Well, we bought new wires today, and that made no difference. Finally we discovered that 2 of the spark plugs were bad, then I accidently broke one which makes 3 bad plugs. We went to the parts store and got the plugs, put them in, and the engine runs so much better and isnt gutless. Thanks for the help guys, and that vaccum line that goes to the tranny was ok. Thanks -

- Shane

better replace them all