[FrankenChevy]

I'm not sure what is wrong so I can't figure out what to correct. Here's the situation:
I've got a '67 aftermarket subframe (Wayne Due C4 Corvette based) set-up for a big-block mounted with solid motor mounts. The motor (a P-AYR big-block mock-up) does not fit into the subframe. It is about 3/8" off from centerline to centerline on the bolts that fasten the block to the integral perches on the subframe (the CL to CL dimension on the subframe is 16 5/8 whereas the CL to CL measurement of the motor mounts on the solid motor mounts is about 16 1/4). There are three things that could be wrong.

1) The aftermarket subframe could be wrong. So far the subframe has fit everything else perfectly so I doubt it is off but I will ask this question....does anyone know the correct CL to CL distance for the motor mount bolts? Is it 16 5/8 or 16 1/4?
2) The mock-up engine could be wrong. How accurate are these mock-up motors? Is it safe to assume that it is accurate? I would hate to modify the frame or motor mounts to find out that the actual engine block will not fit later on in the build. Maybe someone has some experience with these blocks.
3) Are the solid motor mounts wrong? I really don't know what brand they are because I pulled them off an engine that I've had for about 20 years. If the other two are correct then these must be wrong but I'm not sure how to check them. FYI, they didn't really bolt cleanly to the mock-up block (is the block off or the motor mount?).

Any thoughts appreciated.

 

[68z28sd]

i have heard that the plastic motor are not exact. saw a hemi that was way off.

 

[FrankenChevy]

You would think that since their primary purpose of the mock-up block is to aid in making sure everything fits then they would be within 1/8" (or closer).... 3/8" off is not even in the ballpark. Hopefully someone is at a stage in their build so that they can take a quick measurement CL to CL of their motor perches so that I can see if the subframe is off before I adjust the wrong component. I can't seem to find that dimension in the Chassis Manual or Assembly Manual.

 

[prostreet69camaro]

Well I guess I am totally screwed up because I have a factory frame with after market big block frame perches. I have mocked up a 502 motor in the car with these frame mounts and poly motor mounts. They lined up fine. I went and measured CL to CL where the motor mount bolts are and it is 17 3/16". This is not a lot of help.

 

[FrankenChevy]

If I assume that the mock-up block is correct (a scary assumption) then I may be able to use the Moroso #62530 motor mount to get it to fit. They look like they will probably fit the subframe properly. Since it's a custom subframe it is hard to determine how it was set-up... the instructions call for a NAPA part number that I can't seem to find (plus it is probably a stock type mount). The mounts that I used seem to be rather short from the mounting hole to the mounting surface.... the Moroso part would increase this distance and possibly help alleviate the 3/8 or so mismatch.

 

[pro70z28]

I used a foam mock up BBC to build my tube chassis (70 camaro). I have just recently switched to a windowed block & heads because the foam block couldn't "solidly" hold the headers in place. I'm using a motor plate/mid plate set-up so I didn't use the motor mount bosses, but the cast iron counterparts bolted right in the same bolt holes.

 

[Larger Dave]

Read Dave Pozzi's research on the motor mount issue. There are four different motor mount dimensions depending upon the year ('67-'68 or '69 up), and the motor installed (327 & 350, or the Z/28 302, 396). To use an example that I have checked on if you buy a motor mount from NAPA you will get a 1969 BBC mount as that is all they stock; even though there are three different dimensions on the other mounts, the counterman will read his book and tell you that they are all interchangeable (they are not).


Larger Dave

 

[FrankenChevy]

Thanks for all the info. I did check out Pozzi's site and that prompted me to look more closely at the motor mount bracket that I was currently using. Fortunately, the Moroso site provided some basic dimensions so that I could determine what I presently had and what I most likely will need. Dimensional information always seems to be hard to come by on most vendor sites (a hint to vendors reading this post) but this site had exactly what I needed. I'll post an update once I get the new mounts and then if it fits then the next task is to shoe-horn the headers in the car....which seems to be a topic that has been discussed at length on this board.