This is my externally balanced 360 magnum. Neutrally balanced converter. The vibration comes in from around 1600 rpm and builds around 1800 to 2400 rpm. It comes in for a few seconds and then goes away for a few seconds continuously like clockwork. (Maybe harmonics) It comes through the steering wheel and up through the seat.
I tried the usual 1st easy things like balancing wheels, straightening rims, balancing tail shafts.
It was after then I realised it was happening even when stopped in park. I had my harmonic balancer reconditioned but no good. I then changed my torque converter and it was a bit better but not completely gone. I then brought another complete transmission and converter. Again it got better but not completely gone.
I had no more ideas so I sent the complete motor in with the flexplate into the machine shop and had it balanced. It came back with a smallish hole drilled into the weight on the flexplate but they said it was not out enough to make a vibration. I reinstalled the motor but still vibrating. I still felt it was in the converter/transmission area so I ordered a 4 speed auto and a stall converter from the usa. It came a few weeks ago and I have now installed it. Still vibrating.
I took it to a local performance shop this week and he had a look. He said that my exhaust mounts were too ridged and the sump was slightly touching my rack and pinion cross member and to try them. Today I spaced the engine mounts up to clear the rack and took off the exhaust mounts. Still vibrating.
There is not much left to try now. I can’t start it with the trans off as the teeth are on the converter. I thought of changing the factory flex plate but the engine balancing should have picked that up if that was it. The converter bolts are quite small and the flexplate holes are large but the nose of the converter fit into the rear crank fine so it should not be that.
Not sure where to from here!
any suggestions?

 

I looked back and couldn't see what ignition/distributor you have. I,m wondering because the RPM range is where centrifugal advance should occur. If it is or isn't or fluctuating could lead to a studder or vibration. What do you think?

 

Your post is kinda confusing. This is what you said at first.

This is my externally balanced 360 magnum. Neutrally balanced converter.

You can't run externally balanced with neutral balance. Do you now have the manual tranny in? I hope your not running solid motor mounts or the polylock ones from Schumacher Creative. You will have motor to body vibration issues.

 

Yes post is confusing, but doing a small bit of digging around for an answer, I found This . Not for sure with out more engine details, machining etc... Let us know a little more details on your engine build...

 

I think this is indeed external to the engine.

You say you had the rotating assembly balanced and "it did not need" much to balance it, and..........

you have tried a different trans/ converter I ASSUME has the same balance characteristics as the original converter, IE if you are running a neutral balance converter, you have stayed with that?

(You should be running a flex plate which matches your engine balance situation)

"Barely touching the rack" is all a problem like this needs, as is things like improperly hung exhaust. The fact that you can feel it in the steering wheel might just be a huge clue.

Go CAREFULLY through the engine bay looking for ANY place that the engine may be touching the body/ chassis

HAVE YOU tried running the engine briefly with no fan belts?

What did you do about the exhaust? I would pull the exhaust and run it long enough to decide if that is causing the problem. Should not have to run it more than a minute or two if noise is a concern

I agree with Brem, take a GOOD suspicious look at your engine mounts. And don't forget the trans mount -- could be touching back there, too.

 

Yeah, pull the belts. My money is on the alternator. Good luck, bud.

 

You are running serp belt correct? Pull it and fire it up.

Neutral converter is correct if you weighted the flex. So rotating assembly is fine if shop is good.

We need more info.

Does it vibrate in neutral? In gear only? Same RPM no matter what gear or is it load specific?

Do you have a back up distributor to throw in there and rule out advance?

You are leaning towards drive train. Your shaft have weights? They still there? Any dents in it?

 

Does it ever go away? or does it quit @ the aforementioned 2400 rpm?

If you checked the link i had posted it has a couple different variables. After hunting around for more info on YOUR build, you did say it is a Magnum engine and not the LA which ARE different. I am guessing the machine shop balanced the flex-plate for zero balance, but if i understand right the flex and the tq converter have to be indexed properly to each other. You stated the bolts are small but the holes in plate are large. Get the proper bolts for starters... I always thought an external balanced engine, needed @ least the proper (externally weighted) flex plate and possibly a weighted tq converter.

JMO tho...

 

Thanks for all the info guys, Sorry if my post is confusing. My converter is neutral balance because there are weights on my flexplate. The flexplate is a factory one. When the shop balanced the motor they took the flexplate too.
Last night I pulled the serp belt but the vibration was still there. Tonight i pulled the exhausts off at the heads and ran it but the vibration was still there. The vibration does happen in neutral so that counts out the tailshaft.
I have upgraded my dizzy to an electronic dizzy but it did it with both of them. I spaced up the engine mounts last night to get more clearance but it still vibrated. I will take it back to the balancing shop as I am out of ideas. As the revs build it makes the vibration hold longer each time.

 

You use any poly urethane mounts or bushings on motor or trans?
You needed rear main recently and frequently correct? Did you check crank shaft end play when you installed crank? And what were your bearing clearances? And crank run out?

 

Copy and pasted from another forum:

To clear all of this up:
1) the 360 magnum is externally balanced
2) it is different from the "old style" 360
3) the 318 magnum is internally balanced
4) Mopar performance has a flywheel available, last time I priced it out it was $499Canadian.
5) The magnum engine book does not tell you how to rebalance a standard flywheel to work on the magnum engine. So don't waste your money on this book, I already wasted mine. I bought the book for that reason!
6) If you have a copy of the mopar chassis manual, it explains how to put the proper imbalance into a flywheel for a number of engines (but not the 360 magnum). The location or angle for the holes is shown in the book (use the regular 360) but the weight removed will be different. You will need to remove 2.28 oz of metal at a radius of 5.625".

I successfully rebalanced the flywheel for to work on the 360 magnum in my stock car. It sees lots of 6000rpm jaunts (twice per lap) and no vibrations.


Wasnt really looking for any more info on subject, but ran across it. If the whole thread is needed I can post a link later... The flywheel he mentions is for a manual trans and not an auto... FYI.And this is for trying to use what he has on hand vs what to buy... but this maybe some insight into your problem...

Also put a post up on the topic asking about the problem your having being you are running an automatic.

 

Thanks for posting that MrOldFart2U
Yes that is my understanding of the magnum balance. Weighted flexplate and balancer with a neutral converter.

Hey PK1
I dont have any poly urethane mounts or bushings on motor or trans. Just the stock rubber ones. I ran the motor tonight and layed under the car to try to see anything touching the body. I can feel the vibration with my hand on the sump. I think it must be a balance problem in the motor or converter area. I had the motor put together at the shop so i didnt see the bearing clearances and crank run out.

I am going to the shop that balanced the motor this week to give them a look.
cheers greg

 

Not suire if this is going to help but heres the info I have --externally balanced engine, had the engine run/tunned by kilpatrick, he said he could feel a slight vibration in the motor on the engine stand, he said any motor he builds is internally balanced, but I bought my motor from a private party so I wasnt sure if it was internally balanced or not, he told me to buy the flexplate from b&m that has the big cut out huge difference compared to the internal balance plates(take a look at them on summit-almost a quarter of the plate is missing, and then I bought a nuetral balance converter. But heres another suggestion, is it possible your engine is internally balanced by the builder(like I said my engine builder said he always internally ballances the 360) and your running the stock externally balanced flexplate? This would cause vibration? Also maybe check around to have the engine balanced again but by a different shop-probably not much help just trying to give the info I have Good Luck

 

Bingo

 

Try an internally balanced flex plate and see if that corrects your problem.

 

I agree, sense all the "normal" magnum balanced styled flexplates/tq converter combos have failed to clear the vibration I would try the internally balanced style flex. I mean ya can only bang yer head on the same wall so many times, its time for a different wall.

 

I'm going to remember that line.....!

 

Hi all
Took the car today to Russell jones who did the balancing. (father and son team)
There 1st thought was the motor/trans was touching somewhere as they said they could feel it at idle through the whole chassis.
After playing around for 20 min the son Darren said he thinks it’s a tuning problem. He said he wants to put it on the dyno and check its fuel/air mix and tuning etc. We sat in the car with the brakes hard on and the motor in gear. When revving the motor it started to vibrate as usual but when the motor revs past the 2800 rpm stall converter under heavy load the vibration goes away and the motor sounded smooth. He said if the motor was out of balance it would not get better but get worse under load. Because i have a high stall converter in general driving on the road it is not under enough load to get rid of the vibration.
After the heavy revving and loading up the engine there was a load whistle (maybe airleak) that none of us could find. I have had 2 different carbys on this motor and it vibrated with both of them.
What are some thoughts on the vibration going away under heavy load? Does sound logical.

 

Maca,

Thought 1:

Are you running the stock valve train or did you switch to guide plates and stud conversion? If you tighten the guide-plates without a shim between the head and plate they will rotate big time because the are chevy plates. Then they gall like crazy.
Could that noise or whistle be galling?

Thought 2:

Next, I would go to the boneyard and purchase a used motor from a van, ram, or durango long block. I hate throwing money at problems but this will save money over replacing parts one at a time. Take the converter and flex plate with you. If you compression test this it wil give you a decent short block if you still believe rotating assembly is an issue. You will have this in your shop should you want to swap the SB in it.

Swap the flex and TC from the used motor on yours and run. You have the 46RH so they will bolt up. Use the used motors dampener too. All mag 360 are external balance.

Thought 3

You need to once and for all isolated the motor from the drive train. So the dyno will at least give you that. Tell them that rear main has been off a couple times. I still think you may be out of round or have excessive clearance there. If it comes out for dyno, flip it and check those items for run out , clearance and end play.

Thought 4

LA pan and mag block correct? Did you clay the oil pump pickup to bottom of the pan for clearance. Is it touching? Cavitatiing? Under load is it starving?

Clues are a whistle or noise and a vibration you could feel in the pan correct. I can assume you determined no vacuum leak are rear on intake manifold.

Good Luck!

 

Unless its missing I wouldnt think the tune would cause a vibration.

Quote:

He said he wants to put it on the dyno and check its fuel/air mix and tuning etc. We sat in the car with the brakes hard on and the motor in gear. When revving the motor it started to vibrate as usual but when the motor revs past the 2800 rpm stall converter under heavy load the vibration goes away and the motor sounded smooth.

Well now isnt that a revelation.What stall IS the converter? And I know you may not want to pull it apart again, but one way to eliminate PARTS of the equation, I would remove the trans, TQ, and flywheel, bolt on a manual trans fly wheel with the correct balance and test run. If Vibration isnt present then its either the flex plate, or you need a weighted TQ. ( reason I am saying this I had a mustang that was a manual trans car, got a flywheel, clutch,pp ect from a friend, un known to me he had redrilled the flywheel for the 'big' clutch and related parts. It had a vibration @ idle up to about 3k rpms but it would go away. Anyways when i replaced the pp,disc with the 'small' parts it went away) I know thats not your case but you really need to eliminate the possibilities before tossing more bucks in the pot. The TQ converter could be the problem. You did say it was neutral balanced have you tried a externally balanced one @ any point?

Quote:

He said if the motor was out of balance it would not get better but get worse under load.

Normally that is the case, and also worse higher in the rpm bands.

Quote:

Because i have a high stall converter in general driving on the road it is not under enough load to get rid of the vibration.

Possibly.


A loud whistle as in vacuum leak? I would check for obvious of course, power break booster hose, maybe the vacuum hose for trans modulator (if it has one) etc. Maybe the rear end seal from intake as was suggested. The problem going away under heavy load tho sounds more like a converter issue to me, but I am wrong more than I am right also...
I did run across a bit of info on the actual difference between the LA 360 and Magnum 360 balance issue, (its a copy and paste affair):The non-Magnum engines required 19.79 in.oz. and the Magnums need 14.65 in.oz. in order to be properly balanced.

 

Thanks for the advice guys,
Unfortunately the magnum motors were never released in Australia so they are very uncommon. I have never seen them at the wreakers. Pretty much any parts or gaskets i have to order from the USA.
My valve train is standard apart from the retainers and springs that i replaced. I think there may be a clue for me tonight. I just did a compression test and it looks like a couple of plugs are not firing properly or they are starving for fuel. I will look more into this as a misfiring cylinder will defiantly vibrate.
cheers greg

 

Maca,

Hopefully you can get the bugs worked out of the ignition.

Here is some info I found helpful when dealing with the mag motors and their ignition. I know you are using a carby but you may find this info helpful in chasing a "misfire" or intermittent "misfire".

I use Autolite 5224 conventional metal tip (Resistor 5,400 ohms) plugs or go one heat range colder. If you run a 180tstat go the colder range.

When I use the platinum, iridium, ngk brand or bosch I encountered problems. The closed combusiton design of the mag heads are very efficient. I think the plugs on these motors was more of an after thought than a design element.

Many of the TSBs I see about the v6, v8 and even the viper motor all state that spark plug wiring, routing and plug range and even plug manufacturer are very important in diagnosing off idle stumbles and stutters. Champion and Autolite are preffered as replacement in recommendations.

Keep in mind this is for FUEL INJECTED motor but the principles are the same.

However with a proper ignition and fuel sync zero'd I get noticeable misfiring in varying banks. NOT all banks. The biggest offender is cylinder 1 and 2 or 1 and 4. The IAC masks the stumble but a trained ear can hear it in the pipe. The system will not code to OB2. However it can be seen with a basic Snap On 2500 or equivalent. And it is blatant, 100s of misfires or "weak fires" in a short time. The tool reads differential between upstream and down stream narrow band o2 sensors. So actual no spark and weak spark cant be isolated completely.

The 5224 plug, a decent cap and rotor, and a 8mm wire (msd super conductors are my choice but pricey). And no misfires are reported to the snap on and hesitations are gone.

I also use a AFR meter in the collector and have added bungs to individual header pipes to see what each cylinder is running. You can add as many bungs as you want and plug them until needed. Then rotate one wide band to the location you need. Something you may want to consider to help with diagnostics. I use zetronix because you can add numerous temp fluid sensors and o2s and piggy back to one gauge.

Good Luck!!

 

Thanks for the info PK1
Today i put new plugs in and put on another carby i have. I blocked all the vacuum hoses and started it. Still vibrating.
Its time for me to pull the motor out and take it to the balancing shop as they have an engine dyno there.
Will let you know how i go.
cheers all

 

Well sometimes its better to start from ground zero than to try and fly low. Hate that you are having to go to such extremes but like i said once before, time for another wall is what is needed...

Keep us posted/updated on whats found, for future information of course.

 

Hi all
Just an update on my motor.
The engine shop has a v8 supercar motor on the dyno and its taking longer than they expected. Mine is sitting there ready to go on next. They said they will let me know asap.
Cheers Maca

 

Keep us updated. I'm sure curious.

 

i think you still need a tq converter that has the weights on it

 

That or as was mentioned way up, use the internally balanced flex.(318) He still needs to change walls, he has tried all other options, and still no different results...

 

Hi all
Today i got a call from the engine shop as they had run my motor yesterday. They said the manifold was very uneven in different banks. They machined some metal out of the divider as it is a duel plane manifold. They said it ran better but it was still far from being any good and they said it was not making good horsepower. I will go and chat to them in the morning. Here is my manifold.
http://www.professional-products.com...oductmopar.php
I have a feeling they will want to change it. Maybe to a single plane?
Anyone had any experience with this manifold. Good or bad?

I was given this link on getting HP out of a magnum motor.
http://www.hotrod.com/techarticles/e...e/viewall.html
They say they swapped the duel plane manifild for a (Mopar Performance M1 single-plane intake) on a magnum motor. I have googled this manifold and cant find it. I can only find 1 to suit a LA motor. Does anyone know where i can purchase one?
cheers greg

 

hey guys,
I spoke to the engine guys today and I am still trying to process the information. They showed me the dyno results. My motor was only making about 260 hp which is far from where I thought it was and very low torque. They took out a bit of the manifold divider under the carby as it is a duel plane. They also hooked up a MSd ignition and ran it again. It then showed a max of 290 HP and at 5500rpm died very quickly. They said with my set up it should be pushing out much better HP than that.
The reason this dyno reading surprised me was I ran this motor in my charger with stock diff and 2-9 highway gears and pulled 13-9 second ¼ mile run. I have since then upgraded the cam and springs and I can really feel the power increase. When I told them this ¼ mile time on the old cam they were in disbelief that this motor could have done that.
I had a hard time understanding all the info but the biggest item they were concerned about was the intake as they said the delivery of air/fuel to each bank was so far out it was terrible. Hence the reason they milled out a bit under the carby. They said after running a while some cylinders were hot and some cold.
They have recommended some head work with new roller lifters and roller rockers. But the main thing they want to do is use a single plain intake manifold as they feel this will make the biggest difference. They said I may lose a little down low power but the fuel delivery will be alot more even.

Oh yeh, They said there was no vibration on the dyno and my dizzy seized too.
Any comments on the duel/single plain manifolds?
cheers