Harmonic Balancer? Motor combo?
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Freshman User
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Harmonic Balancer? Motor combo?
Ok i am about done building my 400. Got a quick question for you guys since it would take me forever to find it on the search engine on this site.
Would the balancer be the same for the 351m as the 400. I am pretty sure it is but figured i would ask you guys first. Plus figured i would see what you guys thought of my combo i am putting together. It is a 79 bronco that weights right around 5100lbs. Putting this 400 in that has badger pistons, a weird reverse split crane cam. I cant remember the exact specs but advertised duration is around 256 intake and 268 exhaust. Also the heads have been milled (9.8to1), smoothed intake runners,ported and polished exhaust runners,oil restrictor kit, edelbroch intake, and 500cfm 2 barrel maybe a 600cfm double pumper. Has you start moving back i am putting fenderwell headers (not sure of size yet) with 3" flowmasters. Then i got a 2000 stall converter for it and putting 4.56's in it. Mostly all this is at the same time. I know this is a long post but thanks for the replys in advance.
Would the balancer be the same for the 351m as the 400. I am pretty sure it is but figured i would ask you guys first. Plus figured i would see what you guys thought of my combo i am putting together. It is a 79 bronco that weights right around 5100lbs. Putting this 400 in that has badger pistons, a weird reverse split crane cam. I cant remember the exact specs but advertised duration is around 256 intake and 268 exhaust. Also the heads have been milled (9.8to1), smoothed intake runners,ported and polished exhaust runners,oil restrictor kit, edelbroch intake, and 500cfm 2 barrel maybe a 600cfm double pumper. Has you start moving back i am putting fenderwell headers (not sure of size yet) with 3" flowmasters. Then i got a 2000 stall converter for it and putting 4.56's in it. Mostly all this is at the same time. I know this is a long post but thanks for the replys in advance.
Lead Driver
Joined: Nov 2000
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From: Albuquerque
I have heard some say the balancers have the same part number but I don't see how that could be correct as I understand the engines are externally balanced. How could the same balancer work on two different stroke cranks?
Elder User
Joined: Jan 2004
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From: Eastern Pa
This is one of those questions that never seems to get ansered. Ford list's a different number but many parts houses do not. Most yards will probably tell you they are the same. If you go to some of the after market companies they are the same. I got one of the ones rated for a higher rpm. I'm thinking it was a patriot but not sure. Any way I would put a better than stock one in there. Sounds like you have a build that's going to go past 5k so you want to get a balancer that rated for your rpm. You can google it or just look at some of the aftermarket suppliers and they will list them for all different performance apps.
Senior User
Joined: Mar 2005
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From: Blacksburg, VA
I asked TMI this same question when I ordered my parts from him, and he seemed to think there was no difference (at least not from the company he orders his 351M/400 balancers from).
Why would a harmonic balancer have any impact on the external balancing of differently stroked cranks? I thought the purpose of the balancer, which should really be called a dampener, is to do just that - dampen vibrations associated with the rotating assembly, not provide some sort of moment arm. (I'm thinking out loud here, not saying I know this for sure)
Why would a harmonic balancer have any impact on the external balancing of differently stroked cranks? I thought the purpose of the balancer, which should really be called a dampener, is to do just that - dampen vibrations associated with the rotating assembly, not provide some sort of moment arm. (I'm thinking out loud here, not saying I know this for sure)
Lead Driver
Joined: Nov 2000
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From: Albuquerque
On an externally balanced motor a lot of the crank balance is in the balancer. The cranks have different strokes and different weight.
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Posting Guru
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From: PacNW
OK, let's clear up a few misconceptions here. Regardless of whether the engine is internally or externally balanced the majority of the balance weight is still in the crankshaft counterweights. Harmonic balancers are not custom designed for each specific engine, IOW a 351M balancer will fit any 351M engine, it doesn't need to be custom balanced for your specific engine. If you take your engine to be balanced at a machine shop then first of all you need to take the entire rotating assembly including the balancer and flexplate/flywheel. The machinist will add/subtract weight from the crank counterweights as necessary not the balancer or flexplate.
There's no reason that FoMoCo couldn't cast the 351M crank to require the same external weight amount and position as a 400 crank which is obviously what they did.
There's no reason that FoMoCo couldn't cast the 351M crank to require the same external weight amount and position as a 400 crank which is obviously what they did.
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Senior User
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From: Blacksburg, VA
Also, remember that there a variety of different pulleys that get bolted onto the dampener. If its purpose was to "balance" the engine in any way, that would be completely screwed by the different size/weight of pulleys that can be attached to the engine (w/ AC, w/o AC, etc).
Lead Driver
Joined: Nov 2000
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From: Albuquerque
Well I'm not quite an expert but,,,, If you look at the balancer it definetly has an off set weight cast into it. A pulley on the other hand should be balanced to start with. As Bill says Ford could have made the 351m crank in such a way as to equal a 400 in balance. Also many of the aftermarket balancers have a moveable weight medium that will find it's on balance as the assemble turns.
Laughing Gas
Joined: Jul 2002
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From: USA
In my 1977 Ford Truck Shop Manual, the first 2 paragraphs on page 21-22-1 titled "Description, Engine", it states:
"The 351M and 400 CID V-8 engines have the same basic design and structure. The cylinder block is thin wall, special high grade cast iron. The crankshaft has five main bearings and is precision cast nodular iron. The pistons are autothermic aluminum alloy, tim plated. Valve rocker arms are pedestal mounted and the lifters are hydraulic.
With the exception of the crankshaft dampner the differences between the two engines are internal. The 351M has a shorter stroke utilizing a revised crankshaft and a piston with an increased compression height. The camshaft is revised to provide proper valve timing. Refer to the chart at the end of this part for complete specifications."
I believe that the dampeners are indeed different between the engines.
"The 351M and 400 CID V-8 engines have the same basic design and structure. The cylinder block is thin wall, special high grade cast iron. The crankshaft has five main bearings and is precision cast nodular iron. The pistons are autothermic aluminum alloy, tim plated. Valve rocker arms are pedestal mounted and the lifters are hydraulic.
With the exception of the crankshaft dampner the differences between the two engines are internal. The 351M has a shorter stroke utilizing a revised crankshaft and a piston with an increased compression height. The camshaft is revised to provide proper valve timing. Refer to the chart at the end of this part for complete specifications."
I believe that the dampeners are indeed different between the engines.
Posting Guru
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Most research suggests they are different. That doesn't mean they balance differently or cannot interchange, it just means that the outer dampening ring has more thickness because Ford felt the additional tortional stresses in the crank from the longer stroke needed more mass to compensate.
The same practice was used on 351CJ, Boss and HO vs the std 351C because of the additional crank stress in a higher revving engine. Ideally, I'd prefer to have a 400 balancer over the 351M or 351C. Look for the dampening ring that is more than 1" thick.
The same practice was used on 351CJ, Boss and HO vs the std 351C because of the additional crank stress in a higher revving engine. Ideally, I'd prefer to have a 400 balancer over the 351M or 351C. Look for the dampening ring that is more than 1" thick.
Posting Guru
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From: PacNW
I think Brian's right on the money on this. Originally there were different dampers not only for the 351M and 400 but also there were truck specific dampers for each engine. Regardless the 351M and 400 cranks all have the same 28 oz. imbalance so the dampers are interchangeable.
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