Identification of SB vs BB K-Member for 73/74

[73RedRunner]

Ok, so I have searched and read much, but have not been able to find the answer to this question: how can you identify a SB vs. a BB k-member for a 73/74? I am sure there are measurements I can take that will separate one from the other. The k-member is not in a car.

 

[Seax440Dodge]

SB and BB k members are the same, it's V8 vs /6

and the way you tell is the width of the motor mount perches, /6 is a little smaller than 3 inches, v8 is almost 4

 

[73RedRunner]

Thanks for chiming in Seax440Dodge. I guess I can point out what I do know.............

I know its a V8 k-member, using the info you just pointed out. And I know it is for a 73+ from pics posted on this site showing the difference in the engine mounts. Now I am trying to determine if it is for a SB or BB. I have noted several folks point out to "find a BB k-member" if doing a conversion from SB to BB. So, there must be a reason for that suggestion. So, what's the difference? And how can I determine that difference when the k-member is out of the car, the car is gone so there is no fender tag to go inspect.

 

[Ralph Cali]

So big block & small block k frames are different, I am doing a small block to big block k frame change on my 73 RR hopefully this winter.

The perches are located in a slightly different position which I believe you can measure off the steering box, that's why Schumacher makes conversion motor mounts if you choose to go that way. I wanted to detail my front end so in the process I am swapping it out.

If you need additional information Schumacher engine mounts are a good source to call to understand and Dick from Firm Feel is a great source as well.

Hope this helps, Schumacher may have a diagram on their website under k frames / motor mounts helping you.

Ralph

 

[Bruzilla]

The part number for the SB crossmember is 3642747. The number for the big block crossmember is 3642749. And the number for the /6 is 3642745. That being said, I've swapped two 440s into SB cars and haven't had to change the crossmember. The height of the engine is a little different, but you don't need the Schumacher kit unless you want the original height, and since the engine isn't original, why pay for those style points?

 

[YY1]

Bru- is your engine level?

Did you have to shim one side?

Schumacher says to cut down one side for oil pump clearance.

Was that an issue for you?

 

[Bruzilla]

Engine was level and I didn't have clearance issues, but the other issue I've found is our cars have been reworked and modified so many times over close to 50 years that anything is possible.

 

[YY1]

Thanks.

Mine's 99% virgin.

(or it was before I got hold of it)

 

[73RedRunner]

The part number for the SB crossmember is 3642747. The number for the big block crossmember is 3642749. And the number for the /6 is 3642745. That being said, I've swapped two 440s into SB cars and haven't had to change the crossmember. The height of the engine is a little different, but you don't need the Schumacher kit unless you want the original height, and since the engine isn't original, why pay for those style points?

Nicely put regarding the "style points" you referred to. Spoke to Stephens Performance (a MOPAR used parts dealer in Bama) regarding a BB k-member for my 73 RR, and they quoted me $400 for a bare k-member, plus I would have to pay an unknown shipping cost to get it from another used parts yard to my front door since they didn't have one. Pricey style points there for sure. That cost certainly puts the Schumacher mounts in the lead.

One concern driving all of this for me is cooling, the engine is sitting up high and I have a smaller fan than stock fit into he shroud due to interference problems at the top of the shroud. Even with an electric pusher fan, I have cooling issues when going from red light to red light, no cooling issues when moving steadily. That leads me to believe a bigger fan to move more air though the radiator when stopped would help. Here in Bama in the summer, we see temps reach over 90 degrees often. Its hot out there in the traffic during the summer. Getting the engine down to stock height will allow me to use stock fan and shroud combo, which I hope will correct the cooling issues.

 

[Nacho-RT74]

as far I know its the passenger side mount what changes location and is not about the level, like the offset further forward I think on SBs Couple of inches I think

You can see that difference one engine mount adaptors pic by shummacher.

It can get some missalignment issues, although still fit

 

[runnin74]

The biggest difference between the small block and big block K-frames is the position of the drivers side engine mount. It is about 2 inches further forward on the the small block k-frame. There may also be a small positional difference on the passenger side (small block side just slightly further forward) and the bracing is different around the right side mount between the small block and big block k-frame as well. This is why there is an angular difference in the small block vs big block drive train when a straight swap is made without adapter mounts. See attached pic.

 

[Bruzilla]

Nicely put regarding the "style points" you referred to. Spoke to Stephens Performance (a MOPAR used parts dealer in Bama) regarding a BB k-member for my 73 RR, and they quoted me $400 for a bare k-member, plus I would have to pay an unknown shipping cost to get it from another used parts yard to my front door since they didn't have one. Pricey style points there for sure. That cost certainly puts the Schumacher mounts in the lead.

One concern driving all of this for me is cooling, the engine is sitting up high and I have a smaller fan than stock fit into he shroud due to interference problems at the top of the shroud. Even with an electric pusher fan, I have cooling issues when going from red light to red light, no cooling issues when moving steadily. That leads me to believe a bigger fan to move more air though the radiator when stopped would help. Here in Bama in the summer, we see temps reach over 90 degrees often. Its hot out there in the traffic during the summer. Getting the engine down to stock height will allow me to use stock fan and shroud combo, which I hope will correct the cooling issues.

I had a problem with cooling with my first swap because I swapped the SB radiator for a BB radiator but foolishly left the shroud off. Had lots of heating issues until a wiser individual pointed out my error. But I didn't have any issues with the fan hitting the shroud.

 

[73RedRunner]

The biggest difference between the small block and big block K-frames is the position of the drivers side engine mount. It is about 2 inches further forward on the the small block k-frame. There may also be a small positional difference on the passenger side (small block side just slightly further forward) and the bracing is different around the right side mount between the small block and big block k-frame as well. This is why there is an angular difference in the small block vs big block drive train when a straight swap is made without adapter mounts. See attached pic.
View attachment 210883

Thank you runnin 74, that is very helpful info! Those pics show the differences very clearly.

 

[Nacho-RT74]

Corrected then... its driver side not passenger like I told initially! I didn't remember.

however I can see some offset on passenger side too as mentioned!

 

[moparmarks]

Just for giggles here is a real early 73B SB frame. Notice the motor mounts.

 

[Nacho-RT74]

ok, first time I see that!!!

 

[acme rat killer]

On the spool type motor mounts Im new. But the old ones Ive done a bunch of sb to bb and even sb to rb and everyone fit 72 318 Charger to 440 72 sat. 318 to 400 69 sat 318 to 383 to 440 and two 70 challangers 318 to 383 now that beeing said if the motor mounts are forward or back and the trans mount is in the same place why did mine fit because the only thing i had to change was the driveshaft but all had 904 with the 318s

 

[moparmarks]

62-72 was a V-8 K-frame. 73-up there was a SB and a BB K-frame.

 

[Vince kf]

yes man you are 100% right , i have 2 73 Chargers one is a SB 318 and one a 400 BB car , i took the 400 with the A833 and swapped it into the 318 SB car on the SB k-member , it did fit 100% , the only probelm am having is vibration at 45mph + , turned out that the driveshaft is too short ! now am extending a bit more , i always ask this question if SB and BB K-member are diffrent how the hell did my transmission fit so perfect , although i do believe that the SB engine bracket sits a bit further forward than the BB one , my 400 oil pan is barley far from the K-member , THE QUESTION IS : IF THEY ARE DIFFRENT HOW DID THE TRANSMSSION MOUNT ON THE SAME CROSS MEMBER OF THE 904 ?

 

[QuickBpBp]

yes man you are 100% right , i have 2 73 Chargers one is a SB 318 and one a 400 BB car , i took the 400 with the A833 and swapped it into the 318 SB car on the SB k-member , it did fit 100% , the only probelm am having is vibration at 45mph + , turned out that the driveshaft is too short ! now am extending a bit more , i always ask this question if SB and BB K-member are diffrent how the hell did my transmission fit so perfect , although i do believe that the SB engine bracket sits a bit further forward than the BB one , my 400 oil pan is barley far from the K-member , THE QUESTION IS : IF THEY ARE DIFFRENT HOW DID THE TRANSMSSION MOUNT ON THE SAME CROSS MEMBER OF THE 904 ?

The engine is angled sideways when a big block is bolted to a SB K-Member when using factory Motor mounts. Been there done that with Mine..