The Stovebolt Site Forums The Shop Area Engine Shop GMC 228 - Chevy 235 swap in a '46 GMC

I'm in the process of doing a frame up restoration of a 1946 GMC 1/2 ton. The truck was originally equipped with a GMC 228. I bought it with a Chevy 235 with a Saginaw SM420 4 speed transmission. I've now torn the truck down to the frame and pulled the engine and transmission and notices that the front engine mount was moved forward about an 1" by welding a "gusset" on the front cross member. I'm sure this was done to create space for the water pump/fan blade. I'm assuming that like the 216 - 235 switch, that there is a fit problem between the fan and the radiator. Another modifcation was the removal of the bolted in frame cross member that holds the rear transmission support. It was recmoved entirely and the ransmission simply hung off the back of the engine unsupported. It have the original cross member and in trying to refit it I discovvered that there is not enough clearance for the support due to the fact that the engine was moved backwrds about an inch with the modification of the front mount. My plan is to go with the shorter water pump and return to the original front mount and then the cross member with the transmission support should fit. The puzzle for me is the rear side engine mounts. They seem to fit and the mounts look stock. If I move the engine forward an inch to its original position then I think that the side engine mounts wont align. Just to complicate things a little more, it looks like the transmission and/or bell housing is not original based on some home made brackets that are welded to the bell housing to support the brake/clutch peddle assembly. Does any one have any experience retro fitting a 235 in to a GMC? Is the frame the same as a Chevy. Are the mounts the same? My big concern at this point are the rear engine mounts. HELP! Any thoughts or idea would be appreciated.

First off, you are not doing a "restoration" if you are putting a Chevy engine in a GMC.

Second, it seems strange that the front mount was moved forward since a Chevy engine is shorter than a GMC engine. Even stranger, you say it looks like the engine was moved aft an inch. Doesn't this contradict the first statement?

Originally your pedals were mounted on a bracket that attaches to the bellhousing. Sounds like a later bell housing was used and brackets cobbed in.

The front cross member of a GMC is different from a Chevy to accommodate the longer engine.

Why not find a GMC engine with the correct bellhousing? This will simplify things considerably.

Jeff, the transmission is a Muncie not a Saginaw. The SM stands for synchro mesh.

The transmission you have is a '48 or later, and so is the bellhousing. The 'correct' transmission for your truck did not have the synchros and its not uncommon to find that someone changed both transmission and bellhousing to get the synchromesh transmission.

The original bellhousing did have some bosses to mount linkages, and the mess you're seeing now is someone's effort to adapt all that.

Some of what you describe does not make sense to me either, as Cletus said. Some of the changes seem a bit backward from what I'd expect.

On a little later truck, the Advance Design/New Design trucks, the only difference between a Chevy and a GMC frame is the front crossmember. I don't know the earlier trucks as well but would expect the crossmember to be a key difference.

If you are serious about that word 'restoration' 228's aren't really very hard to find, and 248's, 270's and 302's would all bolt up in exactly the same spot and look much closer to original than a 235.

Personally I'm not picky about restoration and would tend toward a larger GMC motor if I had your truck.

Thanks Oldsub for your very civil help. In fact, I should have said - moved the front motor mount back - not forward. I'm in the process of evaluating the engine. If it needs major work then I'll look for a 228 replacement, otherwise, I guess I'll stay with the 235, although I will not have an genuine restoration. I don't think I want to go back to a non SM transmission, so I'll have to customize some sort of bracket to supplort the brake/clutch assumbly. Hopefully someone sho has taclked this problem before could help provide me with a more professional solution than the "cobbled" solution I know have.

I have a '48 1/2 ton GMC (FC102) with a stump puller 4 speed manual...I'd like to find a Power Glide and wonder what will be involved with the swap. There are lots of Power Glides out there but I'm not sure which would "bolt" in or what's involved with the swap. I'm new to the forum...please help with a response. santagaryoldcars

Hi santagary. Please post an introduction in the Welcome Centre, if you have not already.
You should probably start a new thread in the Driveline forum with your questions about a PG swap. Not many people will see your question tacked onto a thread about an engine swap.
Powerglides were never offered in pre-1960 GMC's. Starting in 53 Hydramatics were available in GMC's, and then in 54 for Chevy trucks. I don't know if a cast iron 'Glide from a 235 Chevy car will fit a GMC or not. Good luck.

Piggybacking on a almost 10 year old thread?

santagary, Best way to add a 'modern' powerglide is to purchase an adaptor kit, check out Langdon's Stovebolt.com.