I just bought my 86 iroc i need help identifying the block as ive learned to trust nobody. The block is supposedly a 355 but id like to get some confirmation that it is indeed a 350.

If someone could tell me exactly what year this block is i would really appreciate it.

I searched the block for casting numbers and this is what i found.

Thanks in advance

General view of engine



Number behind alternator from what i can tell its 1099 jam. But theres a smaller number behind it that i cant see too good.




Side of block


Top of block

 

The number behind the alt is worthless; that's some rebuilder's stamp, over the top of the factory's.

A block is not a "355" block. There's no such motor. It's a 350, which after its first round of scheduled maintenance, happens to now have 355 CID. That doesn't make it "a 355". Those non-stock-ish numbers should be reserved for non-stock combinations, like the 383 for example.

The fundamental properties of a block are: bore diameter, whether it's 1-pc or 2-pc rear main seal, and whether it has the factory roller features. That information is all contained in the casting number.

Get the casting number off of it. That's the only way to tell FOR SURE what the block is.



Conveniently located out in the open, in the most accessible and readily visible place they could think of; on top of the bell housing flange, behind the driver's side head.

/sarcasm off

(Yes the block in the pic is indeed what you think it is; the casting number does not lie EVER)

Then, you need to know what heads are on it. The casting number for those can be found under the valve covers among the rocker arms. Looks somewhat like the block one except harder to see; you actually have to disassemble stuff to get at it.

 

The 1099JAM number is meaningless. Looks like a machine shop rebuild code for their own personal use.

Best guess from the numbers I can see is a 1984 305

You need to get those smaller numbers off that pad behind the alternator and get the casting number of the back of the engine like in the above picture to confirm what it might be.

 

so the person who assembled the block stamped the 1099Jam on top of those numbers?

What do the numbers originally mean behind the stamp? Is it part of a vin number?

I'll have to search behind the block again, for the actual number im trying to verify the year before i order the valve covers you suggested me getting. Since i don't like doing returns from online orders i wanted to double check.

I hope i have some luck finding the casting number, i figured one of those numbers would give me some info but i guess not.

 

why do you think its a 305? Thats one thing i want to find out..im hoping the seller was correct and it is indeed a 350..otherwise ima be dissapointed.

What gave off the year?

 

Just read the casting in the back of the block..says



GM5OLG or GM50LG

Guess i got ripped and stuck with a 305

 

The little numbers behind the alt has part of a vin.
It may be the org block if it matches your car..
Call the guy and tell him you'll be over to get the 355 he said is in your car..

 

I sent the guy an email about it, i traveled to a small town 4 hours away to pick up this car, now im pretty dissapointed..i should have known better it felt nothing like my 91.

It still feels like a healthy motor though cant complain but damn... it sucks loosing nearly 50 ci..guess i learned my lesson..

 

That "GM50LG" is not the casting #; but it's a pretty good indication that it's a 305 block.

Get the actual casting #, and you can know for sure. It'll be a 6-, 7, or 8-digit #, like the one on the block in the pic.

The factory stamping code has 2 rows: top row (closer to the head) is the engine "code", bottom row is the sequence # part of the VIN of the vehicle it was installed in at the vehicle assembly plant. If those #s match the last part of your VIN, then it's the motor from your car.

Welcome to buying used cars & parts!!

There are 2 rules for this.

Rule 1: Any word that comes out of the mouth of a used car seller is a lie, unless you can prove with your own eyes that it's true.

Rule 2: In case you can't instantly disprove on the spot that the seller is lying, see Rule #1.

YOu know how a used-car seller is lying? His lips are moving. You know how he's stabbing you in the back? He's smiling.

I've been accused on this very forum of having "trust issues". Hmmmmmmmmm...... I wonder why.

Think of it as a learning experience, a lesson in why you should ALWAYS independently verify ANYTHING and EVERYTHING about a car you are buying that matters TO YOU by means other than the seller's drivel and diarrhea of the mouth, and an opportunity to at least have a car to drive while you go about building a more .... ,,,, ..... satisfactory ..... motor.

 

Thanks for the reply sofa, gm50lg doesnt automatically rule the block as a 305?

I figured it did since when i ran a search gm50lg it said it was a 305.

If theres still a chance that its a 350 im gonna feel like an *** cuz i sent an email to the previous seller ranting.

 

Sorry
350 block has GM 5.7LG cast there

As noted above;
the SDN letters on the block pad visible under the rebuilder's stamp identify block as being from a 84 305 with carb

 

I can't state that FOR SURE, absolutely, pay money for it, take it to the bank, stake my very life on it; close maybe, but .... not.

OTOH, I CAN have that level of confidence in the casting #.

Same for whatever remnants of the stamping code might remain.

Think of this being like a criminal trial, with the outcome being the death penalty; you're on the jury; you've got to GET IT RIGHT; because there's no "going back". So, you don't want "the preponderance of the evidence"; you don't want even "beyond a reasonable doubt"; what you REALLY want is "beyond any doubt whatsoever".

Get the casting #. It's the only piece of evidence that meets that standard of ABSOLUTE TRUTH. All those other things are just "pretty good guesses", while the casting number is ABSOLUTE PROOF.

In case you can't tell, I'm a stickler for ACCURACY and TRUTH. I'd like to think it's a good mental habit to develop.

 

I will take another look today, the casting should be right below the gm50lg correct?

 

Same area , opposite side ( pass side )

 

Should be exactly where I circled it in the pic.

Where my block says "GM", yours says "GM 50 LG".

The casting # is right there.

 

That GM50LG is a set in stone guarantee of a 305. GM57LG is a set in stone guarantee of a 350. Better than any casting number.

 

I called it a 305 block because behind those new stamped number I see what looks like SDN. The only time that suffix code was used is for a 1984 305. A casting number can confirm that it's not a 4" bore block but you've already found a casting stamp saying it's a 5.0L.

The stamped number below the SDN is the last part of the original vehicles VIN #.

 

All my 1 pce RMS blocks ( with 5.0GL or 5.7GL ) inc LT1 have the casting number on other side