The Stovebolt Site Forums The Shop Area Driveline Side mounts for 235 in '51 3100

I'm swapping out a tired 216 in my '51 3100 with a rebuilt '58 235. I've been through several discussions on this site regarding the front mounting of the 235 in the truck's frame. As mentioned in discussions, the timing cover plate on my 235 does not have the 2 bottom mounting bolt holes, so it sounds like the typical modification is to accurately locate the position of the holes on the plate and drill for proper-sized bolts.

Since my 235 does have 3 threaded holes on each side of the block, I was wondering why I haven't seen more discussion on the possible use of aftermarket side mounts which would bolt from frame to block. I would think that side mounts would be more secure than the single front mount. I've seen some posts about miss-alignment of the front mounting causing vibrations, and I'm thinking that positioning the side mounts accurately might be difficult.

My mechanical abilities are intermediate and I have never done an engine swap so I'm relying on the expert advice from you all out there. I'm sure I'll be back with many more questions!

Thank you

The front mount works perfectly if it is installed properly. There is a section in the shop manual that covers the installation and it’s not hard at all. The two rear motor mounts on the bell housing provide more than enough stability for these engines. Why reinvent the wheel?

A template for drilling can be found on ‘Pre ‘68 Dave’s’ website. Here is a link. http://chev235guy.blogspot.com/search/label/Timing%20Plate%20Drill%20Template

Thanks for the advice. Looks like a great deal of good information I will check in to on 'Pre '68 Dave's site.

Just to satisfy my curiosity, since you have the side mount block and mounts are readily available why are you wanting to revert to the bird leg mounts?

Not to hijack the thread, but when is one of our mechanical geniuses going to design a simpler design for the original design front motor mount., or at least steal the design from another inline engine where the work has already been done?
I do not understand why a mount which has such a simple task needed to be so complex. Is it because of the inferior material of the era required such a design to work? Especially since it will eventually become soaked in oil in a very short amount of time.
Modern, oil resistant "rubber" must be available today that could be used in place of all of those metal parts, and vulnerable rubber pad.

As I mentioned in my opening post, my mechanical abilities may be amateur but I'm willing to learn through these forums and work through this swap one step at a time. One of my concerns is that I have the 235 assembled without the holes in the timing cover plate and wasn't sure whether drilling the holes, inserting bolts and mounting to frame could be accomplished without removing the gears and plate. My thought was that the installing side mounts would be an easier process, and perhaps the side mounts would be more substantial. I have not yet found a set of bolt-on side mounts. Not speaking through experience or prior knowledge, just looking for the best way I can accomplish this step in the swap.

There is a reason GM chose an effectively single front mount. Trucks have ladder-type frames that twist limited only by the resistance of the cross members. If you mount the engine in four places, the stress of the twisting frame will also stress the motor mounts, irrespective of the engine's torque reaction, which also introduces its own twist into the frame. This is particularly noticeable on long-wheelbase truck tractors. Watch one pull off from a stop sometime. When loaded the driver's side of the bumper will rise several inches. Same is true pulling a hill down in the gears.

There is significant twist between the cross member under the bell housing and the front one where the engine mounts. One the one-tons and up, the whole front sheet metal is mounted on one point at the center so the frame can twist under the fender/hood/radiator assembly without tearing it apart. On half tons this is not true and there are cross-braces ahead of the radiator where as on the bigger trucks the braces go to the mount point at the center. Since the half tons aren't supposed to be loaded so heavily the frames aren't supposed to twist so much. I don't know which way three-quarter tons are rigged.

If you're dealing with a half ton, you might get away with it but why? The factory system works well. The holes aren't hard to drill.

A modern urethane GM rear trans mount from Energy Suspension might be easily adapted.

We have our first volunteer genius!!!
Congratulations Mark.
Can't wait to read your post on how you came up with this solution. Don't forget to take lots of pics, and provide part numbers.
I see a great Tech Tip in your future.

I agree with Tommy...all engine mounts from old to modern use three points of attachment to allow for engine/frame twist. The old truck had two mounts on the bellhousing and one at the front, new setups use two on the engine and one at the rear of the transmission. If you plan on keeping the original bellhousing with it's two side mounts and then add the engine side mounts you'll have 4-points of attachment which will resist twisting until something finally tears apart. So, unless you're swapping to a modern transmission you should drill and stay with the front mount.

Mike B

2nd gen 55 to ? had 4 point mounts for the 6 and 8 cylinder engines. The 2 in the front and the 2 on the bellhousing. I suppose the common front mount crossmember and double isolated front mounts made that possible.

You are correct, but the bird leg mounts were made in such a way to allow for flexing/twisting. Their mounting stud went through the middle of all four rubber bushing on each side so they could flex up and down as needed.

Mike B