New motor runs rough ,suspect timing - need help - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-21-2006, 05:33 PM
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New motor runs rough ,suspect timing - need help

Hi All,
Fresh SBC , car still on jack stands. Engine runs like a 4cyl ( bad miss )
I adjusted the valves and set the timing. When running I disconnected one
plug wire at a time. cyl's 1-4-5-7 were good and 8 & 2 were poor and 3 & 6
made no differance at all when pulled. So I tried a second set of known to be
good wires and got the same results , then checked the ohms on the first set
and they were ok so I put them back on. Everything is new so I dont think its
a defective part. I think I screwed up the timing somewhere along the way but cant figure out where. When I was setting the valves it was at #1 TDC
0-deg on the hub and both # 1 int & exh were closed ,so I dont think I'm off
by 180 because the rotor was pointing to the # 1 plug lug on the cap. I dont
think the valve adjustment is wrong because I've checked and readjusted
them five times in the last three days. I tried to get a flash light and mirror
into the #1 hole but there isn't enough room ,all I could see was '' up '' to
the underside of the head. Is it possible for the mtr to start and run (poorly)
while being a 180 out, or will it just not start at all ?
The mtr, is carburated and has a MSD ignition 6BTM & a pt # 8570 distr,
The plugs are autolite # AR3910 , they were hard to gap but I think I have
a consistant .048 gap on them. Also # 1 or # 3 cyl makes a funny noise
when the mtr is running, kind of like a spring is actuating a air leak ?
I've adjusted the valves five times , first to lose then to tight then in between
Its possible the tentsion isn't right but I highly doubt it, more like the phasing
is wrong ?? Anybody live in the Lake forest So Cal area and want some cash
for a house call ? cause I'm lost !
Thanks, Joe

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Old 04-22-2006, 11:56 AM
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Do a compression test. If its 180 out, it won't run. You sometimes get the #2 cylinder firing on the intake stroke which makes a nice gunshot up through the carb

It sounds like either it was a bad valve job or some rings are upside down. If you have spark and it runs on 6 cylinders, look to a compression test.
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Old 04-22-2006, 11:58 AM
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Wait... did you set all of the valves at TDC #1? If so, that's your problem. You can only adjust a couple valves there. You have to rotate the crank to do all of them.
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Old 04-22-2006, 12:03 PM
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Quote:
Originally Posted by curtis73
Wait... did you set all of the valves at TDC #1? If so, that's your problem. You can only adjust a couple valves there. You have to rotate the crank to do all of them.
My thoughts exactly when I first read what he said, I was just like wait what?? You adjust the valves seperately, you may have adjusted them correctly to 0 lash on the #1 cylinder when both the valves were closed but like curtis said, you have to rotate the crank to set the other valves like the #1 cylinder valves were set where both are closed. Then repeat the process till you have all of them set correctly and try firing it again.
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Old 04-22-2006, 02:04 PM
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new motor runs rough

I used the '' Watson Guide to Happy Valves " which is #1 at TDC & do
exh, 1348 & int 1257 Then bring #6 to TDC and do exh, 2567 & int, 3468.
Now I'm going to readjust them one cyl, at a time - rotating the crank 90 deg
each time . I also changed plugs to a hotter one ,the first set were autolite
# AR3910 which it turns out is for use with compression ratios around 13-1.
I'll report after all the new plans have been tried. Thanks.
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Old 04-22-2006, 08:19 PM
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Ive been there

Upon my first engine rebuild I had the same problem where the motor ran but ran rough. I had all the valves set as close to right as i could get them and everything checked out good. That day i found out that a motor will run when it is 180 degrees out of time. It will run like **** but it will run. Before you go dicking with the valves and all sorts of other things. Try to rule out the simple things first. But the #1 Cylinder at TDC with the Dist. cap off. Mark where it is pointing then remove the dist. and turn it 180 degrees and reinstall it. I am confidant this will either sooth your thoughs of being 180 off or it will fix your problem.
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Old 04-23-2006, 09:42 AM
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Been there

I now am confident its not out 180 , got a visual of #1 piston at TDC
and the valves are closed & the dist, is pointing at #1. Now Im thinking
that there might be a vacuum leak where the intake meets the head on
the bottom floor side which could explain some of the oil on the plugs.
Thanks.
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