bad vibrations

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canner78

canner78
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Aug 14, 2007
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weyburn sk
we just recently did a engine swap from a slant 6 to a 340. it seemed to run nice and smooth while breaking in the cam but now that i took it out on the road for the first run it has a bad vibration a low rpm. it seems to go away at higher rpm. i checked the front vibration damperer and it is the right one with no weights on it. i checked the converter and it doesn`t have any weights.

where should i be looking next.
 
Are you sure the vibration is with the motor? Do you still notice the vibration at low rpm when the car is sitting? or only when driving? If it's only when driving, you may be looking at something else, tranny?
 
are you using the right converter to match the internal/external balance of the engine? i have a 360 and my balancer is weighted and my converter is neutral balanced. also make sure your bolts are tight to the tranny and anywere else.
 
What year is the 340? if it's a 71 or older it is internally balanced and don't need any weights on the converter. If it's newer it will need the proper weights. But by the description it sounds like it may be just running lean or missing if it just vibrates at low rpm. If you had an unbalanced problem it will usually show up at different harmonics of rpm. Such as first at 1500 rpm then at 3000 then at 4500.
 
the engine is a 1970 340. stock flywheel and converter with no weights on them.i dont know if it comes back like you said 3000 or 4500 because i just broke the engine in and i have not had it over 3000 RPM.

the vibration is the worst at idle and smooths out at about 1500 RPM. it does it at idle and while driving.
 
Sounds like you have the proper parts. Check to see if it's hitting on all 8 cylinders by carefully pulling the plug wires one at a time. You'll notice a big difference it it's firing. If nothing changes that's the cyl. not firing. A real lean carb. mixture can also cause this. Check your carb. mixture adjustments.
 
Did you use the Schumacker kit for the conversion? Are they installed correctly, broken?Alignment? did you change the Torsion bar for / to v8? Im just guessing and thinking
 
i talked to a mechanic tonight and he thinks it is just the temperature. it is around 30 degrees Fahrenheit outside. he said once it warms up out that it will go away and that the vibration would be alot worse if it was a balance problem. He said that cammed up motors like the heat and will act up in the cooler weather. this also explains it wanting to stall at intersections.

The conversion was done properly, V8 K member V8 torsion bars.
 
canner78 said:
i talked to a mechanic tonight and he thinks it is just the temperature. it is around 30 degrees Fahrenheit outside. he said once it warms up out that it will go away and that the vibration would be alot worse if it was a balance problem. He said that cammed up motors like the heat and will act up in the cooler weather. this also explains it wanting to stall at intersections.

The conversion was done properly, V8 K member V8 torsion bars.
Click to expand...

My 360 that I have cammed up pretty good runs the same in cold weather as in the summer. It gets pretty cold here in Ill to. It just takes longer to warm up. Yours, if it is tuned properly should also.

If it's dying at stop signs either the idle speed is set too low or it's running lean. After the engine is warmed up try enrichening the idle adjustments an 1/8th turn at a time and see if that helps. An engine does need more fuel in colder weather because the air charge is denser so allot of times you have to rich-en up the idle mixture when it's cold out.
 
If it does it only while driving I would check the drive shaft pinion angle. An engine swap may have changed this? I had a similar problem because of a worn-out tranny mount after an engine swap. It caused the tail-shaft of the tranny not to be at the right angle side to side and up and down. New one fixed the problem right up.
 
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