Home Forums Gear Hunting Trucks and Four-Wheel Drives 305 question

I recently inherited my grandfather's truck, 84 gmc sierra classic 305 2wd 264,000 miles with zero engine work before now.

I've been having some carb issues out of it, but now I have a more serious problem.

Driving on the interstate the other day I lost power. Got off the road and popped the hood to find a belt broke.

Towed it home and changed out all the belts. Now at idle I have a horrible knock, also it is idling higher than it should. When you try to drive it, it has no power. At idle I have oil on the dipstick, but after turning it off and letting it sit, no oil is present on the dipstick. At idle I have between 30-40psi oil pressure and slightly higher under acceleration. In neutral it will accelerate up but will not in drive or reverse.


Any clues or directions to go in I'd love to hear. I'm afraid it may have thrown a rod.

Sorry to hear about your problems. I would try to find an independent garage and get an evaluation of your situation. If there is a community college near you that has an auto tech program there is a good chance that they take in outside work and it would be the cheapest route outside of doing the work yourself.If the engine is toast ,a donor is probably the best option. Good luck.

Sounds like the oil returns are gummed stopped up!!!!!!!!When it is running the oil on the dip stick is being thrown up there from the crank.....take the valve pans off....... I bet the top end is full of oil....It may have already damaged the crank bearings!!!!!!

I would dump a bottle of seafoam in the crank case and let it idle for a bit. If there is any sludge in there that should loosen it up. Change the oil to get the gunk out and use a good filter.

Hopefully you don't need a new engine. For what they charge, it is hard to beat a GM crate engine these days.

I bet you have water in your crankcase due to a blown head gasket. Take off the oil pan drain plug (after truck has sat overnight) and see if water or oil, or oil/water comes out. One thing is for sure, if it's knocking badly, your engine is shot. The knocking is likely a rod, which also (when it's knocking) destroys the crankshaft. THEN, if you do have water in the oil, and have run it a long time, the main bearings will be scored and the block could also have "spun mains", which means the block is junk. Well, it could be fixed, but it's cheaper to start a rebuild with an undamaged block, as it is cheaper that way. Good luck.

lets start simple. low oil can cause a lot of lifter noise. top it off with oil.

did the engine overheat?

was it working 100% before the belt popped? assuming so....
I would look at my electrical connections under hood. a coil wire barely touching can cause the same symptoms. any chance the belt moved the distributor enough to alter timing? I actually suspect this could be it as the raise in rpm is typical with a vacuum leak. I would go over my electrical and vacuum connections with a fine tooth comb.

the knock can be an effect of timing, low oil, low to no oil pressure (although you have enough to satisfy most engines at 40psi)or mechanical issues that will need to crack the valve covers off as a minimum.

to ease your fears, unless you ran it out of oil, it is dang near impossible to hold 40psi at idle with wasted rod or main bearings.....but overheating it can bring a can of worms from every angle.

I did add three quarts of oil and still nothing on the dipstick unlEss the eNgine is running. However when running that oil looks fine no sign of water.

Thinking about draining what oil is in the pan, inspecting it, then as long as No sign of water in in refilling with oil and some seafoam tI do a flush if you will draining again then changing filter and putting 5 good qUarts in and seeing what I have. Then moving on to vacuum lines and electrical.

3 quarts is a bunch in a 305....it only holds 5. I would save the mechanic in a can and find the problem.

Edit: My suggestion below is based on a problem with a 30 year old SBC with 264,000 miles, it's not worth agonizing over.

It depends on what you want to do with it, being your grandfathers I bet you want to hang on to it. But 305 was and always will be a turd, I owned several in cars and trucks.

Quick and easy is to grab a 350 long block and get back on the road in a weekend, new carb, distributor and wires while you are getting dirty.

A nice upgrade would be a 350 TBI out of a later model Chevy, 88-92 and get better drivability but not necessarily better fuel mileage and a tad more power.

Growing up with SBC's, I would jump right over them all and find a complete LS 5.3/4L60E, ECM, harness and pedal and make an engine swap worthwhile.

I always appreciate Dave's input on rifles and cartridges, he knows his chit. It appears he has a definitive knowledge of these older chevy's as well. Great suggestions there Dave. However, here's how I'd roll:

Chit can the 305. They are crap. Plain and simple...

Find a long block as Dave suggested and make sure it's a 350 (5.7 litre). I've had (and rebuilt) plenty SBC's myself and currently have a vortec 5.7 litre in my wife's 99 suburban and a 5.3 LS1 in my 04 GMC sierra 4x4. The VORTEC 350 gets better fuel mileage, even though the suburban is much heavier. The 5.3 is snappy as hell, but I like the low grunt of the vortec 350 better. I would also not suggest going to a 4l60E unless you know how to build them right. They are weak and very vulnerable to failure with weak clutch packs and bad reaction sun shells. Trust me, I've been into mine and replaced such parts. Both 4L60E's have been torn apart. The 04 GMC 4l60E had to be completely gone thru at 111,000 miles.

Back to the venerable SBC 350: There's nothing out there that is as easy to build and parts are dirt cheap. The sky is the limit when it comes to all the performance mods you can get for these. This is how I'd roll:

1. Long block 350
2. New weiand 8004 (if I remember correctly) or edelbrock dual plane intake manifold
3. Edelbrock 1406 (600 CFM) 4 barrel carburetor.
4. Upgraded HEI distributor.


Stay away from the quadrapuke carb. They are great if you know how to work on them.....

Another way to roll:

1. Locate a computer from a 96 or newer Chevy and do a Vortec transplant into grand dad's pu. You'll have the best of both worlds: Good mileage, great power, dependability. You'll appreciate it in the cold weather when the carbed engine will want to warm up first before operating.... Hope this helps Matt and hope things are going well for you buddy...

Update for any that were/are interested. When the belt on the secondary air compressor/charger thing broke the engine jumped time. Found multiple vacuum leaks, once timing was set and vacuum leaks fixed truck still had very bad bottom end knock. Ended up being a couple of rod bearings.

Got a sweet deal on a Goodwrench longblock 350, put it in along with new water pump radiator and muffler. Reused everything else from the stock setup. This spring when I have a little money saved up I plan on upgrading the cam, getting vortech heads and intake, new carb and headers.

Truck is running great with the new engine, i'm just about at the 500 mile mark of the break in process. I have some suspension and brake areas that need some attention, but over all the old girl is doing great.

Sounds like you did good Matt. Nice to see you posting here again. How have you been???

Be aware of one thing with these rebuilt engines - many rebuilders won't honor the warranty unless it's installed by a professional mechanic.

Got a 3yr warranty on it and had it installed by a shop, just been too busy to do it my self.

BSA, it's good to be back! The last year has been rough but things are really good now and the futures looking bright. Not sure how much time I'll have in the woods this fall, but coworker and I are starting to plan an elk hunt for 2016 and I'm looking for a local club to join for next season.

When I bought my new 350 it came with a 100k warrenty no matter what I put it in...sell a lot to hot rodeos and such...the good wrench is a good choice

When I was raising holy hell as a youth in Oregon I had a chevy truck and my buddies were into the whole dirt track scene (they still are) they told me how to build a good sbc as long as you wanted to put the money in it. It all started with a 4 bolt main sbc 350. then I would pop the heads off a 305 onto it. Always made for one hell of a motor. then my bud offered me a deal on a BBC 454 holy [bleep] talk about a lot of ass.. I said this before I think I was getting maybe 8 MPG but man was that truck fun.

Good to hear Matt, and even better you are driving your grandpa's truck!

My '81 was totaled around 1992, by that time the '88+ was growing on me and I bought a shortbed 4x2 Texas Oklahoma package with a 4.3 V6.

Nowadays, I have no interest in the old slab sides but darn sure would not mind another square body!

Thanks , I got her all cleaned up this evening.

Nice looking truck, I love those old Chevy trucks.