Frame/crossmember question

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howiess2000

Active member
Joined
May 31, 2009
Messages
34
Location
Wauconda, IL
I’m building a 29 model a. For the frame I used 2x4 rectangular tubing 3/16 thick w/ fishplates at the joints, it is quite stout.

The engine mounts are welded directly to the frame rails with equally thick universal mounts and gussets. Until now ive never questioned the strength of the frame, but looking at other builds I see guys using engine mounts welded to the frame, like mine but they have a crossmember under the engine, or a crossmember with the mounts attached to the CM.

Is a crossmember under the engine necessary? Will the crossmember for the tranny and one near the back suffice?

As far as engine, I have a stock 2bbl 351w and a c4 trans, not exactly a powerhouse. I’m about to pull the engine (hopefully for the last time). If I need to make a CM, I will, but what the people who have done it before think?

Thanks in advance
 
When we were young, my brother and I put a couple of big torquey motors in a '56 Ford pick-up. There was a crossmember at the front and one at the back of the transmission. We welded the motor mounts to each side frame rail. With sudden acceleration the torque of the motor twisting clockwise, twisted each frame rail counter-clockwise, significantly. That was un-boxed ordinary '56 Ford truck frame. You should be quite a bit better off with square tubing, especially if you have a cross-member under the bellhousing.
 
I believe firmly in overkill. I also believe an engine block should not serve as a "stressed member", which could be the case, depending on the distance between crossmembers as you have it now.


I always say, "It's better to have it and not need it... than need it and not have it." ;)

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You know, you guys are all right. I’m just going to do it, no screwing around. Thanks. I’ll try to post a before and after just for fun.
 
Seriously guys?? It's 2x4 3/16 wall! :eek:

I guess I'm gonna be the fly in the ointment here - They're completely unnecessary in a proper chassis, and ESPECIALLY in one built like you described. Thousands of cars built without them - no issues.

Plus they're just ugly. [;)
 
The difference between the 2x3x3/16 that I used and the 2x4x3/16 mentioned may be enough to keep the twist out.
The engine in my '33 was dead nuts level side to side and after driving it for 4 years the engine had a list to it (rolled a little)
This could be from the long stand off mounts I had to use and in this case had I used a cross member it would still have set level.
I would have made the motor mount stand offs welded to the cross member and bolted it into tabs on the frame.

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On the other hand the '37 GMC has really short motor mount stands, less leverage and doesn't need the cross member.

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Brookville Roadster builds hundreds of hot rod chassis every year. Every single one of them that leaves equipped with motor mounts are stand alone type (no crossmember) - zero issues. That's just one company.
 
Seriously guys?? It's 2x4 3/16 wall! :eek:

I guess I'm gonna be the fly in the ointment here - They're completely unnecessary in a proper chassis, and ESPECIALLY in one built like you described. Thousands of cars built without them - no issues.

Plus they're just ugly. [;)


I agree 100%. Now, if you had a stock model a frame, that is a different story, but a 2 x 4 x 3/16 frame is VERY stout ( that is what my frame is made of and I have no crossmember under the engine.

My one son's 30 rpu has a heavy 468 Olds with no engine crossmember, and my other son's T bucket has no engine crossmember, and they are both fine.

Now, I do have one under the engine in my 27, but that is because I am running a model a frame, it may be boxed, but it is nowhere as heavy as 3/16 steel.

The downside to an under engine crossmember is that it does not allow you to easily drop the pan or work on the bottom of the motor. When I need to do that in my 27 the engine has to be pulled out.
 
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After a couple of months of hmm-hawing around, I finally got around to building the crossmember. I think it turned out "Dead Sexy
 

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I’ve done it both ways depending on the type of frame. On a leaf spring car I put the mounts on a crossmember since the frame doesn’t have a crossmember close to the mounts. On an independent suspension car I usually just weld the mounts to the frame since there is a stout crossmember near the mounts to keep the frame from twisting.
 

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