SBC to LSx conversion - engine mount geometry problem

[Brucebe]

Hello all,

Surprisingly, I seem to have a fundamental problem fitting an LS3 into a Can-Am, and it is related to the engine mounts. Even with a slotted passenger-side mount, the driver side engine mount will *not* line-up with the receiving stand on the chassis.

The car came to me with a SBC installed, utilizing a solid Moroso mount on the driver side (non-slotted), and a slotted standard mount on the passenger side. I have tried replacing the solid mount with a standard rubber SBC mount (e.g. 1971 Camaro), but the spacing is identical. I am using an LSx engine mount adapter kit from Trans-Dapt. Each plate is approximately 8mm thick. It almost seems as if the thickness of the plate is causing the problem, but we all know that the plate is necessary to adapt the bolt pattern of the LSx engine mount to the SBC chassis mount.

Any help would be greatly appreciated!

-Bruce

[Steve_D]

It may just be that the adaptor you have does not have the range of adjustment of other makes. It can be done so I would start with contacting the Factory and try their kit.

Steve

[ezakimak]

isnt there 2 diferent mounting standards for the SBC. and 1 of them is slightly further apart.

crafty found this out if i remember correctly. might be worth going through his old posts, back a couple of years.

either that or it was "Builder"

[Brucebe]

Indeed, there is a mount with a 2 1/2" opening, and one with a 2 3/8" opening. The wider mount is also a taller mount (2 1/2" vs. 1 11/16").

I have the shorter, narrower mount of the two, and these were the mounts that came with the car (installed with the SBC). Does anyone know the nominal thickness of the Ultima-provided adapter plate? The Trans-Dapt plate is 5/16" (~8mm).

-Bruce

[spatz]

the factory kit comes with two spacers of which I used only one, so it seems that there is some individuality considering the welding......

[crafty]

I used the thinner mounts.

I remember there was still some fettling.

In the end, I put the bolt in one one side. The other side was about 1/2 the bolt diameter out.

I got a spare bolt, sharpened one end and cut the head off it.

I put the pointy end of the spare bolt into the 1/2 hole that was visible, put the engine bolt against the other end of it and drove it through with a hammer.

The pointy one (without the head) comes out the other side, leaving the proper bolt in place.

[Brucebe]

Thanks for the replies. Crafty's experience is consistent with what I'm finding with this install. The Ultima factory plates are better, since they are only 3mm thick (the 90-degree flange at the top helps strengthen the plate and resists bending forces).

It seems that all of the LSx->SBC conversion kits simply place the motor-mount at the same point on the block. Simply offsetting the bolt-holes downward by an amount equal to the plate thickness will restore all of the critical dimensions. That's what happens with the slotted motor mount holes anyway - the slots are just not long enough.

Since I've already invested in the plates from TransDapt, I've ordered the "composite" mounts (polyurethane - Energy Suspension). Both driver and pass sides have slotted holes for adjustment, and these mounts have an interlocking design. They look strikingly similar to the composite mounts offered by Ultima. And hey, if I wasn't way out in one of the colonies, ordering the factory parts would be the easy way to go.

-Bruce

[Brucebe]

Just thought it worth noting that the Energy Suspension engine mounts worked perfectly with the Trans-Dapt LS conversion plate. Both motor mount bolts installed without much difficulty, though the alignment is on the absolute bottom of the slot on each mount. If the adapter plate was thicker (> 5/16"), it would require persuasion of the Crafty variety. For those contemplating this setup during a conversion, be sure *not* install the "preload" plates that come with the mounts. They are not necessary when installing against a flush surface (e.g. adapter plate), and provided the necessary reduction in overall mount height, to install without difficulty.

Thanks again for the input and advice.

-Bruce