351C Vibe & misfire..

'70 Ranchero that I picked up last weekend has a persistant misfire & the worst vibration I've ever experienced. Feels like the engine is trying to rip itself out of the vehicle.
So Far:
It stood for 3 years so I cleaned out the carb (2v) & threw a set of new plugs in it......
It fires right up without any problem at all.....& it will idle ok (well, ok for a misfiring SOB).
Plug leads are on in the correct firing order...

The hood is off the truck right now as the hinges had snapped at some point & I just replaced them. Don't want to put the hood back on yet as I fear the vibration will snap the new hinges & throw the hood across the front yard.

My (possibly backasswards) thinking:
I've never seen anything shake like this from a misfire.
Vibe is maybe so pronounced because it has a broken an engine mount?
Maybe a broken rocker arm?
Bent push rod?

I'm grasping at straws here cus I've never seen anything like it.

HHHHEEELLLPPP!!!!!!!

I'd pull the valve covers. If it sat for awhile, and someone tried to fire it on the old varnished gas, the gas will make the intake valves stick, and when you got to fire it again, it usually bends the pushrod and ejects the lifter.

If thats the case, it'll be easy to see. I rigged up a tool to use a lever to open the valve (rocker off) and sprayed wd40 on the valve stem though the intake port till it loosened up. What I did was bought an eye bolt from homedepot in the same thread as the rocker bolt, screwed it in as deep as possible, inserted a rod through the hole and layed a piece of plastic between the rod and valve stem to prevent scratches. Works like a charm.

Have done this on 2 diff 400's, which are the same headwise as the cleve. Had to pull the intake anyway to re-insert the ejected lifter, so it worked out well. The last one was 2 yrs ago in a motorhome, and its still runnin strong.
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okee doke, I'll give that a whirl & see what we find... soon as I get someone to look at it while I spin it over...
Insurance turned up today so I can at least get it tagged on Tuesday. [img]/phpBB/images/smiles/icon_smile.gif[/img]

If it's a prob with a pushrod or rocker, start pulling/reinstalling plug wires(one at a time) until you find one(or more) that doesn't affect the idle. If you find a dead cylinder check to ensure the plug wire is good, if OK then perform a cylinder compression check. If the comp check comes out decent then pull the VC's off and check for something amiss.

if it vibrates as bad as you say it does, I don't think that valvetrain would cause it. Kind of reminds me of a 351w I bought once, guy told me I could hear it run. Got to the guy's house, he started it up (an old van) and yeah...it ran, on 7 cylinders by the sound of it, and man did it vibrate! Turned out that one of the rods had broken and the rod & piston were just pushed up the cylinder and werent causing any problems. Also bought a '74 H2 Kawasaki 750 cc triple 2 stroke, also vibrated like hell. Figgered it was just a characteristic of the beast. Burnt a piston one day going to work, tore it down at work and guess what...the center cylinder didn't have an piston or rod in it. Guess it was burnt at one time too and they took it out alltogether. Guess that's what they call 'Arkansas engineering'

Had this same thing happen on the 289 in my 65. Intake valves were stuck open. Shook like a mo-fo and wouldn't rev. After disassembly I discovered the pistons had smacked 6 of the valves. Fortunately, none were bent. Pull the V.C.'s and spray everything with some penetrant. Let it sit for a day or two, then spray it again. Change the oil, then fire it up. If you haven't bent any valves, it should smooth out. My $0.02.


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I had a 289 do the same thing and it turned out that the distributor bushings were shot, the "vibrating" that got worse with rpm was just random, delayed spark. easy to check for, just pull the cap and rotor and move the distributor shaft side to side and back and forth.

I second the stuck/sticking valves diagnosis. Had a 351M do this, bent several pushrods and there were several valves stuck open, some stuck shut.

Shook like a wet dog in an out of balance washing machine.

Greg
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On 2004-02-07 22:36, mavman wrote:
Also bought a '74 H2 Kawasaki 750 cc triple 2 stroke, also vibrated like hell. Figgered it was just a characteristic of the beast. Burnt a piston one day going to work, tore it down at work and guess what...the center cylinder didn't have an piston or rod in it. </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Friend of mine did the same thing except the H2 he bought had a tennis ball stuck on the end of the rod instead of a piston...

&amp; thanks for the 351C replies, I'll get busy tomotrrow.

Well, I sure got busy on the Ranchero today:
Phoned the tow company &amp; had it taken to R&amp;E Racing with instructions to "fix it &amp; lemme know when it's ready".
Man, thats surely the most stress free work I've done in a while. Tow truck was just loading it up as the wife got home. She was briefly happy until informed that I hadn't sold it, was just sending it off so I could spend more money on it.... that went down well....[img]/phpBB/images/smiles/icon_bicker.gif[/img]