Help! Engine Vibration

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71demonz

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Clifton, TX
I recently finished rebuilding and installing a 318 block with 340 heads.
It runs fine with the exception of a noticeable vibration. At idle I can observe some wobble in the vibration damper and more so at the lower pully. The vibration will increase or decrease at different RPM's.
The engine shop honed the crank and check for true. I didn't balance the assembly during the rebuild and I'm wondering if that is the problem. Other than the heads and a 4 bbl intake the motor was rebuilt stock.
The balancer is a standard replacement 318/340 balancer.

Would I be able to fix this vibration with a better harmonic balancer? What is the difference between a internal and external balancer?

The car is a daily driver my Son and I built.
Thanks
Steve, TX
 
if it had new pistons put in, they probably weigh different than the originals did. also do you know if the engine was originally internally or externally balanced? if external, you need the appropriate balancer and torque converter/flexplate.
 
Red,
Yes the pistons were replaced as well as 2 of the rods. I don't know about the prevois balancing. I don't recall any balance plugs on the crank so I'm assuming it was stock.
The motor was previously hooked up to a 74 duster with a manual 4 speed tranny. My demon has a 904 auto with the original torque converter/ flex plate.
 
What year is the 318??..some early ones especially truck motors came with forged cranks,but most 318 have cast cranks,if its a internally or externally balanced crank,you may have the wrong flex plate on it,or the wrong damper..just a tip for ya' ALWAYS balance a motor when you have them built,it save you the headaches your having now,i;m surprised the builder did'nt highly recommend this...
 
Yea, I know that that it was a dumb A$$ rookie mistake. The block is dated 1980. I do have the cast number of the crank but I couldn't tell you if it is internal or external balanced.
The builder was me, my kid, and the help??? of my body guy, (a chevy man). So a lesson learned. Now, I'm just trying to figure out if I can smooth things out short of a rebuild.
All advise appreciated.
 
hi, the dampner is not supposed to wobble, period. did it go on crank easy or you have to pull it on with a bolt? were the two rods, same casting # as the originals? look up the weight of pistons, compare to old weights. all this can be done without tearing into motor. i suspect the balancer is not right. as for internal and external balance, 318's were internal .as far as i know, the 360 and 72-73 340 were external balanced.
 
If I remember correctly the damper was a snug fit. I still have the original damper which I'm going to reinstall tomorrow. I replaced it because the rubber material was cracked. The balancer is a replacement 318/340 made by Dorman.

Reviewing the work done by the engine shop, the crankshaft was ground 20/20. There is no notation of balancing and the rods were two used replacements, no numbers anotated. I don't have any details on the pistons either. I think I got schooled at the engine shop, (engine rebuild kit, 8xhardened seats, 1xrepair sleeve, 2xused rods, vat. block and parts,7x bore block,1xinstall repir sleeve, install cam. bearing and freeze plugs,grind shaft020/020,8x R &R pistons, 6xhone size rods,2xvalve job,8x install hardened seats, 2x surace heads) total $1012.56.

Well see how things go tomorrow.
 
71demonz said:
If I remember correctly the damper was a snug fit. I still have the original damper which I'm going to reinstall tomorrow. I replaced it because the rubber material was cracked. The balancer is a replacement 318/340 made by Dorman.

Reviewing the work done by the engine shop, the crankshaft was ground 20/20. There is no notation of balancing and the rods were two used replacements, no numbers anotated. I don't have any details on the pistons either. I think I got schooled at the engine shop, (engine rebuild kit, 8xhardened seats, 1xrepair sleeve, 2xused rods, vat. block and parts,7x bore block,1xinstall repir sleeve, install cam. bearing and freeze plugs,grind shaft020/020,8x R &R pistons, 6xhone size rods,2xvalve job,8x install hardened seats, 2x surace heads) total $1012.56.

Well see how things go tomorrow.
Click to expand...


Have you checked the torque convertor? Rotate the crank and look for weights welded to you convertor. You may have a 360 convertor.
 
That '80 engine should have a cast crank/external bal. As early 318's & 340's were steel crank/internal bal.,later were cast crank/external bal,a 318/340 replacement balancer could go either way. My guess is you have an internal bal. dampner on an external bal. engine.
 
340srule said:
What year is the 318??..some early ones especially truck motors came with forged cranks,but most 318 have cast cranks,if its a internally or externally balanced crank,you may have the wrong flex plate on it,or the wrong damper..
Click to expand...
Yep, could'nt have said it better.
 
I will pick up my rebuilt and balanced 360 engine on Sat. I ordered a new torque converter when trans was rebuilt with 360 external balance weights on it.With balanced engine and external balanced torq. conv. I would think there would be a problem. Am I right?
 
Yes you will have problems, just knock the weights off and your good.
 
balanced does not necessarily mean internal. did you get your 360 internally balanced? if not you NEED those weights on the t.c. and on the damper.
 
The torque convertor is from the '71 a 904 torqueflight. It has no weights. Perhaps that is part of the problem. Is there any site available to match the production date to the crank casting number?? The stamped number is 9462387......Thanks again for everyones input.
 
'73red-duster said:
That '80 engine should have a cast crank/external bal. As early 318's & 340's were steel crank/internal bal.,later were cast crank/external bal,a 318/340 replacement balancer could go either way. My guess is you have an internal bal. dampner on an external bal. engine.
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:read2:There is no such thing as an externally balanced 318 from the factory, irregarless of cast or forged crankshafts.
 
I have the same problem. I had my 360 rebuilt professionally. I have a slight woble on my balancer though. I had the 904 rebuilt that originally came with the motor. I put the same parts I took off the trans and put back on, with the exception of a new, factory torque converter. The only thing I could think of is when we had the motor on the cherry picker, (before the motor and trans was rebuilt) the weight of both the engine and trans was to much for the picker and the motor fell to the ground. Unfortunatley, the balancer took the brunt of the impact. I have since bought a balancer. It is a Pro-street by cyco systems, which I bought from Mancini. It is externally balanced, and will put on the motor this spring. I'm wondering what the issue could be as well.
 
Dago Red said:
:read2:There is no such thing as an externally balanced 318 from the factory, irregarless of cast or forged crankshafts.
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where do you get this info? every engine i have ever dealt with(all brands included) follow the same general rule. forged steel cranks are internally balanced and cast are externally.

are you saying that the factory internally balanced all 318's even if they were cast cranks?

please supply us with some in depth knowledge as to why you think this.
 
redfastback said:
where do you get this info? every engine i have ever dealt with(all brands included) follow the same general rule. forged steel cranks are internally balanced and cast are externally.

are you saying that the factory internally balanced all 318's even if they were cast cranks?

please supply us with some in depth knowledge as to why you think this.
Click to expand...

:read2:please provide what indepth knowlage you possess that proves me wrong. I'm sure any source quoted or referenced by me will be refuted as being incorrect. Let's help this fellow get his car fixed and then we can figure out which one of us is incorrect.
 
redfastback said:
where do you get this info? every engine i have ever dealt with(all brands included) follow the same general rule. forged steel cranks are internally balanced and cast are externally.

are you saying that the factory internally balanced all 318's even if they were cast cranks?

please supply us with some in depth knowledge as to why you think this.
Click to expand...


Maybe you should go to school about engines. Just because it is a cast crank does not automaticaly make it an external balanced motor. The 440 6 pak motor had a forged crank and had a small counterweight on the balancer....yet is was internally balanced.

The 318's came with cast and forged cranks and up thru 1991, use the same balancer. I just checked the Mopar parts book and they list one part number as a replacement. (yes there were a few variations with the timing mark in a different location, but the same neutral balance)

Now, the outer ring on the damper is neutral and even if it has slipped or is wobbling won't cause the vibration. You could take that off and throw it away and it won't vibrate... done that on many a dragster way back when to keep it from slinging off going down the track (before they made good balancers). Crankshaft pulley wobble? Show me one that doesn't from the factory.

If this thing is vibrating from an idle all the way up, it is more than likely the engine is grounding against something.... like a bad trans mount. They are notorious on Chryslers for slipping out of place, coming apart.... you guys have replaced your share so you know that is fact. If the rods that went in were factory 318 rods and the pistons that went in were cast, there wouldn't be that much of a difference in the weights to cause the thing to vibrate all the time, only at certain RPM's and it would be slight at that. I replaced 2 rods and pistons in my race motor and it has solid motor mounts.... it doesn't vibrate.

So let's look at this a little closer.... Look at the trans mount and exhaust system before ripping the motor out for no good reason. If the mount is bad, replace it. If the exhaust is touching anything.... fix it. Eliminate the simple things first.
 
I replaced the damper with the original one taken off the motor before rebuild. I compared it to the other and is similar in size, shape and weight (only slight variations). When I started the motor it initially ran smooth but has since begun to wobble lile the other damper.
The motor mounts are new, spool type and the trans. mount is new as well. The exhaust is TTI headers 2 1/2 in H-pipe, nothing touching or rubbing. Im thinking about putting balance weights on the torque convertor, or replacing flex plate with an external balance plate (I think B&M makes one). Any thoughts on those choices??????????
 
Something is wrong with the damper if it is wobbling, they are not supposed to do this. I have seen in some cases where the damper doesn't fit snuggly onto the crank snout.

Tell us how you installed the damper. These should be a very tight fit, requiring the center bolt to pull it on. I'll bet your damper fit on the crank is loose, which is causing the damper to wobble and also maybe (not 100% sure) causing the vibration problem.

If the fit is loose, I have seen some backyard mechanic fixes for this problem.

One motor I took apart had this issue apparently, someone prior to me had taken a very sharp center punch and punched the circumference of the crank snout in an even pattern over the contact area every 1/4 to 1/2 inch creating raised areas which allowed the thing to tighten up. I don't like this idea but it worked.

Another idea is to try using red loctite on the mating area of the crank. Allow the loctite to set up overnite and see what happens.

A third option would be to try one of the fluid dampers, Ive heard these fit extremely tight on regular cranks and have heard of people having to use a damper installer instead of using the bolt to push the damper on. Maybe one of these would be tight enough to do the trick. Keep in mind you may need to monkey with the pulley alignment afterwards.

4th option. remove the damper, measure the crank snout with a mic, and then have a competent machinist remove enough material on the inside of the damper to allow a sleeve to be installed and then have the sleeve turned down to the correct size for the crank.

5th option - Punt ?

Hope this is helpful and let us know what you find.
 
The damper came off and went on snug. The first damper was brand new, and the second one is original. Again, the vibration is not present at all rpm's and it isn't unbearable but still noticable throughout the car frame. I'm just concerned about the integrity of the motor.
 
i still think that the rotating assembly is not balanced correctly. even factory parts were off by a bit. the factory could have up to about 6 grams off on balancing and still be put together.

bu then again i have to go to school about engines.......................
 
I have never heard of an externally balanced 318. Even with the cast crank all 318's I've ever dealt with were internally balanced. Just my 2 cents.
 
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