Original motor or not????

[mac1576]

Figured I'd leave this to the Subject Matter Experts.  Here's the situation: 
I have (what I think is a 1986 Chevrolet C-10), I say I think because everything I thought I knew about this truck during the last 24 years of me owing it may have just gone out the window.  The VIN indicates this is a 86 and should have a 262 V-6.  The truck (I'm the second owner) since I've owned it has had a 305 in it.  While talking to my mechanic about this he said the 305 looks like it is original.  I said that's impossible as the VIN said it came originally with the V-6 and that the original owner must've switched it out.  That said he showed me the sticker under the hood (in front of the radiator) that show's it should have a 5.0???  The stickers in the glove box that shows what the truck came with (and matches the VIN plate on the dash) indicates it came with the 262. 

Now the punch in the gut.  He thinks somewhere along the line before I came in possession someone may have done a switch aroo with the VIN plate and stickers.  However the paint scheme and other options matches what the glove box says the truck came with (no indication of it being repainted prior to me getting it), other than the engine. 

How can I make sure 100% what engine was supposed to come in this truck or is it possible the VIN was switched?  Is there another location the original VIN would be located besides the VIN plate on the windshield.   

[zieg85]

A picture of the engine frame mounts would/should indicate if the engine/core support with sticker was changed out.  Frames in 1985-1987 with the 4.3L had a couple of extra holes on top because the V-6 mounts were closer to the firewall.  The green arrows are the V-6 holes used and the orange are the V-8 holes used.  If your engine was changed you should see indications of the holes being used by looking underneath.

[Engineer]

Look on the little flat pad machined into the engine block behind the alternator in front of the passenger side cylinder head.

There will be at least one set of numbers on this machined pad, and possibly two. If there are two sets of numbers the smaller set of numbers should be about 7 digits long and should correspond with the final 7 digits of the original truck's VIN that the engine was installed into to begin with.

It is possible that your engine won't have this second set of numbers. I have engine blocks that are both ways, with and without. If an engine was a factory replacement, or crate engine, the VIN won't be stamped into the block for obvious reasons. If the engine came from a different truck it could have that truck's original, albeit only partial, VIN.

[Stewart G Griffin]

There is probably a vin stamped on the frame somewhere?


This is an interesting case, as most people who swap out a 4.3 go with 350 or bigger.

[blazer74]

Top of frame rail drivers side adjacent to the exhaust manifolds should be the vin stamped into the frame that matches the dash vin.
The earlier trucks are this way I assume yours is the same.

[Irish_Alley]

i think the frame vin is hit or miss, we've had people find theirs and others who havnt

[Greybeard]

There is probably a vin stamped on the frame somewhere?


This is an interesting case, as most people who swap out a 4.3 go with 350 or bigger.

Especially back in the eighties when the 305 was as scorned as a rabid skunk.

[philo_beddoe]

Right, the 305 was not exactly a screamer!! Just a basic putt around town engine.


Sent from my iPad using Tapatalk

[Stewart G Griffin]

It might be a case of a cab swap.

[Greybeard]

In the end, why worry about it? if the truck has been legal to license all these years it was apparently an above board move or done illegally but done very good. Either way, after 24 years it's not a game changer. Now, the question is- how do you know for certain it is a 305 and not a 350? The previous owner had the truck for 5 years, there was ample time to replace the engine with a different one when s/he realized the 262 just didn't move the truck fast enough. For instance, my old 78 was four years old when I bought it in 82. Totally stock engine yet it had been involved in a slow roll and had some body panels replaced before I took it over (left door, fender, etc.) about a year into owning it a cam lobe flattened, maybe due to running too long while on it's side (lack of lubrication). In my case I rebuilt the engine into something I could proudly call an engine, but this owner before you could also have had some mechanical issues with the six and put a junkyard find in. It's not unusual.

Especially back then, changing an engine was a driveway job done in a day. Three wires, four hoses (and a fuel line), some bolts around the rear of it, four or six exhaust bolts and two mounting bolts. It took longer to drain the coolant than anything else (when the trucks where still fairly new). Two guys, one cherry picker and a short length of chain. Of course if they took the radiator out it took about twenty minutes longer.

Obviously that is an exaggeration to make a point. There is a little more to removing a v-8 engine than that, but not much. It got tougher and longer each year after about 1979 to R&R an engine. By the time the 90's got here there wasn't enough room in a trucks engine bay to allow a dropped wrench to reach the ground. In the 78's and earlier, my 250lb frame could sit in the engine bay with the engine to replace the spark plugs. The biggest worry about breaking anything was a plastic vacuum 'T' or your knuckles.   

But I'm getting off topic...