Replacement 305 for a 1961

[Jmclendon]

Hello all,
If I was on the market for a replacement engine, would y'all happen to know how flexible I can be in terms of the year?

I'm not looking to get rid of what I've already got..... I'm just hoping to kill two birds with one stone. My current engine has a knock until it gets warmed up. So, I'd like to pull it so that I can see what's going on and fix the problem (and hopefully learn along the way). But in the meantime I don't want the old man to sit around doing nothing. So I figure if I can get a decent rebuilt replacement put in, then I get the best of both worlds. But, I want to stick with the 305 V6.

I've got a 305D under the hood at the moment. He's a 1961 1500.

While I'm on the subject, if anyone has a suitable pre-loved engine just lying around. Well now, I might be able to take it off your hands LOL

[TJ's GMC]

That's gonna be some heavy freight there. I'll leave it to the experts that know the exact details, but I THINK any 305A-E should be pretty much a direct replacement.

[David R Leifheit]

That's gonna be some heavy freight there. I'll leave it to the experts that know the exact details, but I THINK any 305A-E should be pretty much a direct replacement.

Correct on both counts.
It -will- be a heavy freight..
and
Any 305A - E will (or should) bolt right up.
So will any 351 v6

[TJ's GMC]

Hey if you're not in a big hurry there is a guy on youtube Rebuilding a 305. It has been bored .060 over to. He's perrty dang smart, and the motor will be for sale when completed. 3 parts so far...stay tuned to see the rest.

Part 1: https://www.youtube.com/watch?v=FXPKRjzxRTo

Part 2: https://www.youtube.com/watch?v=oWesd1oXpFo

Part 3: https://www.youtube.com/watch?v=DtMB13ochL4

[Funky61]

Thanks for those links TJ!

[Jmclendon]

Thanks for the links! Definitely one to watch later tonight.

When y'all say any 305 or 351 would work, does that mean I should be fine with anything from 1960-66? Or is there some practical benefit in trying to stick with one from the same year?

[TJ's GMC]

Thanks for the links! Definitely one to watch later tonight.

When y'all say any 305 or 351 would work, does that mean I should be fine with anything from 1960-66? Or is there some practical benefit in trying to stick with one from the same year?

You should be fine with any 305 from 60-74. Personally I'd look for a 67-74 305E as they had a little more power. If I remember right....a whole 10 HP. :teehee:

[Jmclendon]

You should be fine with any 305 from 60-74. Personally I'd look for a 67-74 305E as they had a little more power. If I remember right....a whole 10 HP. :teehee:

LOL I'm quite happy not worrying too much about the HP. The truck and I just don't have the souls of a hot-rod I'm afraid.

Thanks for the tip. That expands my options a bit....

Y'all are right about freight being an issue. But, I'm banking on a quality rebuild shipped on a container being cheaper (and less of a hassle) overall. Maybe... Hopefully.

[bobdylan]

I would think that a knock that went away after it warmed up, could not be to serious. If it was a rod bearing I think it would get worse. How is your oil pressure? You will see a drop in pressure if you have a bad bearing. Have you checked compression? I would not pull to investigate until I knew what was going on.

[David R Leifheit]

LOL I'm quite happy not worrying too much about the HP. The truck and I just don't have the souls of a hot-rod I'm afraid.

Thanks for the tip. That expands my options a bit....

Y'all are right about freight being an issue. But, I'm banking on a quality rebuild shipped on a container being cheaper (and less of a hassle) overall. Maybe... Hopefully.

You are talking an engine that has been known to kill an engine stand or two. :)

I'd say estimate 1000 pounds for engine and crate.
Weight of the engine/motor alone, according to Jolly's data:
305A = 738 lbs.
305B = 771 lbs.
305C = 840 lbs.
305E = 795 lbs.
351 = 860 lbs.
401 = 880 lbs.
478 = 925 lbs.
702 = 1485 lbs.
637 = 1219 lbs.
Then add crating. :)

As pointed out, 1960-1974 305 & 351
But also since you already have one in your vehicle, and thus the physical mounts aren't a concern (the metal mountings, not the rubber part although those are always a concern) you can also look for one out of any truck size. The 305 was available up through at least the 5500 series, and as far as I know the same holds true for the 351s as well. The mounting in the bigger trucks is typically at the front of the engine and the mounts on the bell housing, as opposed to the pickups where the mounts are on the sides of the engine and the bell housing.

[David R Leifheit]

I would think that a knock that went away after it warmed up, could not be to serious. If it was a rod bearing I think it would get worse. How is your oil pressure? You will see a drop in pressure if you have a bad bearing. Have you checked compression? I would not pull to investigate until I knew what was going on.

I wouldn't take the chance (now).
I had a small knock. Didn't sound too bad so I let it go. Besides, I had been told the engine had been "rebuilt" fairly recently. The knock got a little louder over time, but never had a power issue and didn't seem to affect the vehicle at all. One day, at 55mph, the knock quit. So did the engine. The rod cap had finally fallen off and the connecting rod no longer was "U" shaped where it went around the crankshaft, it was almost a "T" shape. And the valves/inside of the head was embossed on the top of the piston. Never did get that one out of the engine before scrapping it (wish I hadn't, the block was still good).
A small tapping can be -anything- so if you have the opportunity to go through the engine to find it, do so. Even if that noise is the sole "excuse" for getting another one and learning about these engines.

[Jmclendon]

I would think that a knock that went away after it warmed up, could not be to serious. If it was a rod bearing I think it would get worse. How is your oil pressure? You will see a drop in pressure if you have a bad bearing. Have you checked compression? I would not pull to investigate until I knew what was going on.

Once it warms up the only thing you hear is the valves happily tapping away. Oil pressure looks fine. It holds nice and steady.

I haven't done a compression test on it yet. I guess in part because other than the pre-warm up knocking it runs great. Over Christmas I was hauling about 1000 lbs (if you include my wife and the fat driver LOL) down the highway with no dramas at all. I did have to drop down to second once (I'm running a 3 spd manual), but that was on a rather steep incline off a scenic route.

I guess it's just one of those things where I know the sound can't be good news. So, I figure if I can find a quality replacement engine then the old man gets to stay on the road while I work out what's going on. If I can't find one, then I'll likely have to take it to someone for a rebuild, simply because I don't want him to sit around for ages while I learn what I'm doing and track down parts etc....

I really want to learn as much as I can, but I don't want to let the old boy fo fallow while I'm doing it. I'm greedy I guess LOL

[6066gmcguy]

As for a bolt in swap, any year 305, 351 or 401 would drop in place of the 305.
Finding one downunder mite be a bite harder then here in the states.

[Jmclendon]

My reason for concern.... Might have to turn the sound up. Sorry about the file size.

https://vimeo.com/198595814

Sent from my E6653 using Tapatalk

[turbobill]

Maybe the "knock" is a valve a bit looser than the rest. Once the engine warms up, the clearance is reduced enough that it clatters no louder than any of the others.

[bobdylan]

Take a long rod , hold it to your ear, and against the engine in different places., see if it is the upper end or lower end.

[TJ's GMC]

Take a long rod , hold it to your ear, and against the engine in different places., see if it is the upper end or lower end.

x2 to that notion

[snazzypig]

I agree that it could be a loose valve. The erratic tapping seems to point to something in the valve train.
Hopefully your stethoscope stick will find the source!

[bluestreak1854]

I have a 305e v6 that i would sell-- it would probably need work-- I completely rebuilt it several years ago -bored new 4 ring pistons- cam lifters etc. but it has been a few miles since then-- I took it out because it just quit one day and I haven't taken it apart to see what happened-- suspect timing chain or blown head gasket although it never got hot-- i also have a 478M out of an 8500 coe truck that has a allison automatic behind it -- it is a good running engine and tranny with only 8696 miles on it-- i have the radiator,shifter , and mounting if you are interested