my 351c vibing problem, I don't think its running right

[DarkoStoj]

Here is the original thread if anyone is interested on my problem
http://forums.stangnet.com/showthread.php?t=627148
cliffs: My 351c vibrates at 3k rpm after I've replaced almost everything and I can't figure out the vibe.



Yesterday I started playing with the timing, and I never really noticed how rough the motor actually ran. At idle the whole motor shakes a good amount, I never really paid attention because I just assumed it was a large camshaft creating the choppy idle. I've replaced the plug wires, head gaskets, intake gaskets, and spark plugs. What else is there that could cause the motor to not run correctly? I am completely stumped on this thing, and don't even know where to start now. I have a compression tester & was going to do a test on all cylinders and see what that tells me, any other ideas?

 

[ttoney]

Could be a CAM lobe problem (shhhhhhh. knock on wood). Is this a newly built motor? Rocker adj properly, a pulled stud. Hmmm, just throwing things out there. How about a fried valve or loss of cyl pressure on one cyl.

I noticed the pic of your motor apart, is this vibe a new feature or did it happen b4 you tore it apart? I bet you need to go re-adjust your valvetrain, and or replace head gaskets carefully.

 

[DarkoStoj]

Could be a CAM lobe problem (shhhhhhh. knock on wood). Is this a newly built motor? Rocker adj properly, a pulled stud. Hmmm, just throwing things out there. How about a fried valve or loss of cyl pressure on one cyl.

I noticed the pic of your motor apart, is this vibe a new feature or did it happen b4 you tore it apart? I bet you need to go re-adjust your valvetrain, and or replace head gaskets carefully.

I have had the problem since I bought the car. This is not a newly built motor, its closer to being tired.

Rockers are adjusted properly, studs are fine, head gaskets are new.

Since the motor was build who knows when, and the camshaft is a mech flat tappet, could it be possible that the lobes on the camshaft have worn down causing these problems?

also could a poorly tuned carb cause these problems?

 

[ttoney]

I doubt a carb could cause it but stranger things have happened. How did the cyl walls look?

Pull the valve covers and rotate the crank. Make sure all of the valves are opening and closing properly. You may be able to identify the problem that way.

 

[DarkoStoj]

I doubt a carb could cause it but stranger things have happened. How did the cyl walls look?

Pull the valve covers and rotate the crank. Make sure all of the valves are opening and closing properly. You may be able to identify the problem that way.

motor looked VERY clean when I took it apart, I mean there wasnt even a ridge on the cylinder walls, and zero gunk or carbon build up in the lifter valley, but I still have low oil pressure and burn oil.

 

[ttoney]

Well, check out the cam like I said. Perhaps a lobe is dead and you just need to throw a new cam in it.

 

[ttoney]

How much of a Bear was it to remove the heads with the motor in the car? That is a 65/66 right? I didn't think there was enough room for that.

 

[DarkoStoj]

How much of a Bear was it to remove the heads with the motor in the car? That is a 65/66 right? I didn't think there was enough room for that.

my shock towers are notched, lotsa room! Gotta love the ease of exaust,spark plug work Plus I'm a big guy so I just manhandled them outta there.

When I do a compression check what should I be looking out for? I don't have a leakdown, just the guage that screws into the spark plug hole and you turn the number over? I've never done one of these tests before

 

[ttoney]

Well, you want all of the cly to have about the same compression. That wont tell you anything if they are similar. If they are way diff it may indicate a stuck open valve or bad rings.

 

[68RCodeConv]

First you need to find out if it is an overall engine problem (like a vacuum leak or dirty carb) or is it specific to one cylinder. Start pulling spark plug wires one at a time to see if one cylinder is not firing.