4.3 swap or flop

[magnum59]

1985 c10 4.3 autoamtic trans 2wd
   My sons truck.
we just replaced the 4.3 ( cracked block) with a used but less miles on it 4.3.
   I didnt do the work we had a mechanic do it at a  local shop, but after the motor was put back in we now have a sever shake in the motor at idle and thru out all driving range.
  the mechanic claims this will go away, but i am not sure.
there is no miss and all cylinders check out and all fire correctly, it truly seems to me that something is off balance
so I was wondering if anyone hear could maybe have an idea as to what may be the problem.
thtis is my first post here  

[123 pugsy]

Interesting mechanic.  I wish all my truck problems would "go away" after driving for some time.
Anyway ,I had a fan blade break off once and it caused the whole truck to shake.  

[VileZambonie]

Your mechanic is a tool! Did he put the correct flexplate on it? Did your old one have a one piece or two piece rear main seal? What about the new one? Did he leave an engine mount loose? Is the correct damper on it?  

[magnum59]

Hey thanks for the reply, but the fan checks out fine.
this truck has been in the shop for almost 2 months and noone can figure it out, so i really dont want them working on it any more.the ransom demand goes up allmost every time they open the hood  
 thanks again for the reply.
 Steve

[magnum59]

engine mounts are tight ,as for the flex plate or the damper I cant really say as i was not present when they actually did the work. Is there anyway to check this other then taking it to another shop.

[magnum59]

Just a thuoght now would the flex plate have anything to do with low power in drive.

[VileZambonie]

No.

Start with the basics here, do a compression test

Check your distributor timing and your ignition timing.

check the firing order

[DnStClr]

Makes ya wonder what was wrong with the replacement motor- why was it removed from it's original vehic.

Don St.Clair
Culleoka Tn

[xtreme80]

To be honest, you don't seem too mechanically inclined, (no offence at all to you) so doubt many of these things mentioned are going to be things you can look for.  Your best bet would be to take it to a different shop and have them run some diagnostic tests on the engine to find the cause of the problem.  Shops have the tools required to run these tests and can do so rather easily.