Motor Swap (LA360/408), Now Vibration

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Lik

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Hello All -

Looking for some advice / assistance with a new issue after engine swap.

I purchased a used Blueprint 408 engine from a local seller as a temporary swap while building my 340.

Since the blueprint Engine contains a cast crank, they require a 360 LA externally balanced flywheel, and since the seller was Auto trans, I had to purchase one from Brewers. While I was at it, I also purchased a new McLeod clutch, and all new mounting HW. I finally got the install completed yesterday, but sitting in neutral and revving the engine introduces a "Engine RPM Related' vibration.
1747401106941.png


- I re-used motor mounts from 340, but they appear to be in good shape. Motor is not twisting / jerking around. I cannot feel the vibration from the engine when revving it from under the hood.
- A833 Trans mount is relatively new, and appears to be in good shape.

Any other places you would recommend I look? Is there an easy way to ensure this is an externally balanced flywheel from looking at it? It does have a harmonic balancer on it also, so externally balanced at the front.
- Seller had a balanced flexplate like this:
1747401018379.png


Any assistance would be greatly appreciated. Finally got it back on the road after sitting for many years, and now a new gremlin.....

Thanks,
 
Get in touch with @Johnny Mac and see if he can give you correct information regarding how your engine was balanced. He works for blueprint and is a member here, and extremely helpful to his customers.
The only other thing I can recommend is to make sure your flywheel has the appropriate weight bolted to it, as some of them come with two weights, one for magnum balance and one for LA balance. They are different. Which flywheel did you buy? Got a link?
 
I'm aware of the balanced flywheel requirement; I purchased A balanced flywheel from Brewers:
1747411669357.png
 
If your flywheel has the three holes and it still vibrates you may need a neutral balance. We just had a 360 here that was neutral balanced with the 360 damper still used on the front.
 
Thank you - I have contacted blueprint already, and have an open ticket with them. If I do not get a response from them soon, I'll go through @Johnny Mac.
 
Lik said:
Thank you - I have contacted blueprint already, and have an open ticket with them. If I do not get a response from them soon, I'll go through @Johnny Mac.
Click to expand...
I'd agree it looks like the correct flywheel for an LA360- balanced engine. Depending which engine this was from us, the balancer may, or may not have been installed here, or came from here. The common balancer used is this one. Harmonic Balancer - Chrysler Compatible - 273, 318, 340, 360 and 408

it ships with the magnum balance weight installed (thats what we use on the nose, despite the LA rear)

Can you post a serial #? and/or PN? happy to help.
 
Johnny Mac said:
I'd agree it looks like the correct flywheel for an LA360- balanced engine. Depending which engine this was from us, the balancer may, or may not have been installed here, or came from here. The common balancer used is this one. Harmonic Balancer - Chrysler Compatible - 273, 318, 340, 360 and 408

it ships with the magnum balance weight installed (thats what we use on the nose, despite the LA rear)

Can you post a serial #? and/or PN? happy to help.
Click to expand...
PN: BPC4083CT
Serial: 327687
 
Also - Here is the balancer on the motor: I cannot make out the stamping on it to designate what it is exactly.... Maybe you/someone here may be able to pinpoint from looking at it?

1747417878936.png

1747417908441.png


EDIT: Looks Like 83184-106 4 for a PN on the balancer. This balancer came installed on the engine which came from a running car.
 
Last edited:
Lik said:
PN: BPC4083CT
Serial: 327687
Click to expand...
That was fast!

Thats about 8 years old per the serial number.
Was ordered as just a longblock. no balancer installed. no intake, dist, carb, etc.
looking at the damper, it looks like a factory style to me. Magnums had serpentine pulleys...so best guess is it's an LA damper? or at least an LA intended damper? unless you can see a weight bolted on the back? but those look like factory ish balancing holes.

Also... this a dent maybe...? (RED BELOW)
1747418308827.png

i'm happy to sell you a damper at cost. best case, it fixes it, worst case...you have a new damper at a pretty good price, and the damper is scratched off the list of problems? could also use on the 340 with weight change (comes with them all)

But before you throw any parts at it, are you absolutely positive the exhaust isn't resting on a body seam, or headers touching the frame rail, or something coming in contact with something else?

have you ran it w/o the belt on it? (possibly an accessory with a bad bearing?) or crank pulley wobble?

We had a guy recently chasing a vibration, and when he put the car in gear, the engine flexed enough for the header collector to touch the starter motor (non mopar) would rattle the mirror out of focus.
 
It might be an optical illusion but in one of your pics it looks like the ring of the balancer is no longer bonded to the hub. Just an fyi
 
Johnny Mac said:
That was fast!

Thats about 8 years old per the serial number.
Was ordered as just a longblock. no balancer installed. no intake, dist, carb, etc.
looking at the damper, it looks like a factory style to me. Magnums had serpentine pulleys...so best guess is it's an LA damper? or at least an LA intended damper? unless you can see a weight bolted on the back? but those look like factory ish balancing holes.

Also... this a dent maybe...? (RED BELOW)
View attachment 1716406075
i'm happy to sell you a damper at cost. best case, it fixes it, worst case...you have a new damper at a pretty good price, and the damper is scratched off the list of problems? could also use on the 340 with weight change (comes with them all)

But before you throw any parts at it, are you absolutely positive the exhaust isn't resting on a body seam, or headers touching the frame rail, or something coming in contact with something else?

have you ran it w/o the belt on it? (possibly an accessory with a bad bearing?) or crank pulley wobble?

We had a guy recently chasing a vibration, and when he put the car in gear, the engine flexed enough for the header collector to touch the starter motor (non mopar) would rattle the mirror out of focus.
Click to expand...
I definitely like the idea of scratching the harmonic balancer off the list - That is the only thing not new attached to this motor. Maybe this worked for the previous owner in a automatic application where it does not work for me in a manual application.

These MOPAR's and their balancing.... man. I thought it was tough enough knowing I had the ONE YEAR of 340 External Balance... Add this one to the list now too.

Unfortunately I cannot really see the back of the balancer - I'll pull it off and get more photos.

I will also inspect the exhaust. I DID have to remove the passenger side pipe in order to install a O2 bung for the Sniper 2 I am running... MAYBE, just MAYBE it is interfering somewhere. Other than that, the drivers side, both manifolds (I know I know, should let this motor breath with headers - eventually) are what came off the 340 - which did not vibrate like this.

I'll remove the accessory drive belts, remove the dual v pully from the balancer (alternator/PS), and fire it up to see if the problem persists prior to removing the Harmonic balancer.

Thanks for the tips - I want to drive this thing!
 
Lik said:
I definitely like the idea of scratching the harmonic balancer off the list - That is the only thing not new attached to this motor. Maybe this worked for the previous owner in a automatic application where it does not work for me in a manual application.

These MOPAR's and their balancing.... man. I thought it was tough enough knowing I had the ONE YEAR of 340 External Balance... Add this one to the list now too.

Unfortunately I cannot really see the back of the balancer - I'll pull it off and get more photos.

I will also inspect the exhaust. I DID have to remove the passenger side pipe in order to install a O2 bung for the Sniper 2 I am running... MAYBE, just MAYBE it is interfering somewhere. Other than that, the drivers side, both manifolds (I know I know, should let this motor breath with headers - eventually) are what came off the 340 - which did not vibrate like this.

I'll remove the accessory drive belts, remove the dual v pully from the balancer (alternator/PS), and fire it up to see if the problem persists prior to removing the Harmonic balancer.

Thanks for the tips - I want to drive this thing!
Click to expand...
Sounds good. Also thats old enough to still have a flat tappet in it...don't forget the zinc oil, even if it's not ours lol.
BluePrint Engines 10w30 Engine Oil - 1 Quart

just PM me your email and address and Phone when you're ready for the damper, and I'll have one of my sales guys do an invoice.

you'll have to oblong one of the crank pulley bolt holes possibly...pending what year the pulley is from. pre 1970 have an offset hole. post 1970 are symmetrical.
 
Johnny Mac said:
Sounds good. Also thats old enough to still have a flat tappet in it...don't forget the zinc oil, even if it's not ours lol.
BluePrint Engines 10w30 Engine Oil - 1 Quart

just PM me your email and address and Phone when you're ready for the damper, and I'll have one of my sales guys do an invoice.

you'll have to oblong one of the crank pulley bolt holes possibly...pending what year the pulley is from. pre 1970 have an offset hole. post 1970 are symmetrical.
Click to expand...
Oh, I am very familiar with flat tappet - lol. Vr1 - quick and easy to get. almost bought yours, but did not.

Update:

Removed accessory drive pully - still vibration.

Removed Harmonic Balancer - found a PN............. 3614369 - which according to Mr. Google, this is an internally balanced 318/340 Harmonic balancer...... wonderful.
1747426859181.png

1747426882973.png



I am in need of that balancer now - I will PM you.

Pulley is from a 73 340 - so should be good.

Thanks
 
Last edited:
Lik said:
Oh, I am very familiar with flat tappet - lol. Vr1 - quick and easy to get. almost bought yours, but did not.

Update:

Removed accessory drive pully - still vibration.

Removed Harmonic Balancer - found a PN............. 3614369 - which according to Mr. Google, this is an internally balanced 318/340 Harmonic balancer...... wonderful.
View attachment 1716406118
View attachment 1716406119


I am in need of that balancer now - I will PM you.

Pulley is from a 73 340 - so should be good.

Thanks
Click to expand...
BOOM! Smoking gun right there. Easy fix.
 
Thank goodness there is a guy on here that can check it and tell precisely what it was !
Excellent work Johnny !

As soon as I saw the pic,,,I didn’t believe that was your balancer .

Tommy
 
Lik said:
Oh, I am very familiar with flat tappet - lol. Vr1 - quick and easy to get. almost bought yours, but did not.

Update:

Removed accessory drive pully - still vibration.

Removed Harmonic Balancer - found a PN............. 3614369 - which according to Mr. Google, this is an internally balanced 318/340 Harmonic balancer...... wonderful.
View attachment 1716406118
View attachment 1716406119


I am in need of that balancer now - I will PM you.

Pulley is from a 73 340 - so should be good.

Thanks
Click to expand...
Well that's a good day when we find such a simple solution as the wrong damper! Will get ya one out Monday. Returning your PM now.
 
Vibration Gone!

I cannot thank this forum enough for the quick responses and assistance.

Special thanks to @Johnny Mac for his superb customer service and support!

and TT5.9mag for tagging him in the first place.

​

 

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