73-87chevytrucks.com
General Site Info => General Discussion => Topic started by: Joe-NC on November 23, 2010, 03:43:53 pm
-
I know this question probably gets asked all the time, but I've used the search tool and read plenty of posts on other sites and still don't have an answer. Other than the casting numbers on the rear flange of the block (which are hardly visible with the engine in the truck, and are probably covered with gunk anyway) ...is there another way to tell a 305 from a 350?
-
It's never a sure indicator because you just never know what's been swapped, but typically a 305 has the timing tab up top at the 12 o'clock position, and a 350 is usually off to the side closer to 3 o'clock. If it runs like it's timed right and the mark on the balancer lines up with the timing tab that will give it away.
-
Pull a valve cover and check the casting numbers on the heads and look them up and see what they came on. But you also can run into the issue where someone has 305 heads on a 350 like how my truck is right now.
-
I've run across small blocks where 305 was stamped on the side of the block behind the power steering pump. I've also pulled a sweet running small block from a 79 K20 thinking it was a 350 4 bolt only to find out it was a 305.
Like grim82 mentioned, you never know what has been swapped around in these things.
-
Heads can be identified from the design on the front of the head.
-
It's easily visible in these trucks if you get in the engine compartment with a flashlight. If it's grimey get a can of brake clean, a screwdriver and a brush. In 5 minutes you'll have your casting number.
-
I have no clue what my '77 has either, the vin# says it came with a 305, but the previous owner(who really knew nothing about engines) told me the motor was swapped to another 305 before he owned it. The plate behind the power steering pump has nothing on it and I can't see the rear one. I only have a few bolt-on goodies on it and it really moves, and feels like a 350. I guess I'm gonna pull off a valve cover and see what that says...
-
If it's grimey get a can of brake clean, a screwdriver and a brush. In 5 minutes you'll have your casting number.
^this
If you pop the cover to see what heads you have you still won't know for certain if it's a 350 or not.
-
Am I gonna have to pull a head off to find out???
-
No, you just need to find the casting number on the back of the block, and then reference it with mortec.com. But like Vile said you might have to get dirty to get to it, and you might need an inspection mirror to see it.
-
remove your air filter housing to see better. then look down behind the drivers side head, right in front of where the transmission bolts up, scrape that grease off with a screw driver, wipe it with a rag and spray some brake cleaner and repeat until you can see the number. push whatever wires or vacuum lines may be in your way out of the way. the number is there, I have read them in the truck so it can be done, you'll have to climb under the hood and stand on the frame next to the engine.
-
Thanks for the tips! I'm gonna give it a shot this weekend.
-
...you'll have to climb under the hood and stand on the frame next to the engine.
That's what I thought. I was hoping there was an easier way. Not to mention that my neighbors probably aren't used to seeing people standing in the engine compartment to work on a vehicle. ;D
I just bought this truck and was told it had a 350, but it feels like a 305. Before I decide where to start tweaking, I want to find out what I'm working with.
-
How do you feel the difrence between a 305 or 350? a 305 "can" be made to run very strong. Like was said though some brake clean and some cleaning and you will find your answer.
-
btw; you'll want to use a flash light to help you see also.
-
Give me 5 mins with a 350 and I can make it feel like a 4 cyl. ;D
-
Found the casting numbers on the back of the motor, turns out I do have a 305, from an '80-'84 is what was listed. The numbers were not too hard to see, a little bit of grime but not bad.
-
I'm pretty disgusted right now and that's putting it politely. I've been in the engine compartment 4 times, felt all over with my hands, got grease on them that won't come off for days, and I still can't find the casting numbers.
But the real kick in the butt is finding a number I didn't want to see ...GM5.0LG. This is on the flange of the block on the drivers side. The timing tab is also at 12 o'clock just like Grim said it would be on a 305. The guy I bought it from told me he replaced the original 305 with a 350. I can deal with a 305, but I don't like being lied to. Guess its my own fault for believing him and not checking it myself.
Problem #2:
It needs a rear main seal. I spoke to a mechanic who worked on the carb before I bought it. My flywheel has a weight on it and he says its NOT supposed to and the seal is leaking because of the vibration. I thought if that were the case it would shake my teeth out. Am I wrong? It runs down the interstate at 80 mph just as smooth as can be. He says it has a little vibration at idle, but I don't feel much at all. Since I don't know what kind of engine I have, I don't know whether it takes a weighted flywheel or not.
P.S. It also sounds awful while its cranking and this mechanic says the weighted flywheel is the cause.
Question:
I like to drive faster than most people, be the first one off the line at a stop light, etc (I'm not a butt hole, I just like speed). So if I replace the flywheel, should I go with a smaller/lighter one? If I do go with a smaller one, how would that affect my ability to pull a small utility trailer?
-
the casing number is there. keep looking.
I dont know what the weight is for, but I do know that 400s were externally balanced. 400 flexplate?
-
As near as I know, any 305 should be internally balanced (no weights) and would also have a neutral balance dampener on it. As far as the rear main seal, if it's a 2-piece seal I'm pretty sure they are all the same regardless of displacement, 283 up through 400.
A smaller flywheel will spin up faster (less mass to get moving), but a bigger one will be easier to keep spinning if you are pulling anything (objects in motion...).
I think you will probably still have to find that casting number, go to a parts house and get the one specified for your motor, and compare it with what you have. Lots of things can cause a vibration, but if you can run 80 mph I doubt that that's your problem.
Here's where the casting number is on my 400.
-
I've got someone looking at it right now. This is what he's telling me: The flexplate is definitely not supposed to have the weight. I never noticed, but it was shaking my rearview mirrors. He says the casting number on this engine will be at the front near the water pump and that it probably came out of a car. The carb doesn't have the electric sensors that the original truck had, and whoever installed the engine didn't bother putting in a kickdown cable. I'll wait on that because according to him, the reason I've been having trouble with reverse is that the transmission needs a rebuild. The roaring I hear when decelerating is the rear end, so I need that replaced too. All the smog connections coming out of the manifold have been cut off and crimped with pliers.
Just stamp "NOOB" on my forehead. I've got plenty to do on my project.
-
Disregard what I said about flywheel sizes, I was under the impression that you had a manual transmission.
Unless it's a 400 it should have a neutral balanced flexplate.
If you're not required to have all of the smog business hooked up and functioning I would ditch those manifolds. Did he give you a diagnosis that's more specific than "the rear end needs replacing"? It could be as simple as a u-joint or bearing.