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Old 08-15-2018, 11:48 AM   #1
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Location: Denver, CO
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Engine Replacement

I read the forum fairly regularly, and have gained some good information. I guess it is time to give back, maybe providing other readers with some helpful information. A couple of years ago I purchased a 1996 GMC K1500 short bed manual transmission 305 engine, base model SL with cruse control. It had every thing I wanted, and paid 2800 dollars (probably over paid a little). The truck had a lot of problems but was rust free. It leaked oil everywhere, including pan gasket, main seal, cam shaft cover etc. Clutch was really messed up, you could not put any throttle when releasing the clutch or the truck would shake violently. I decided to replace the engine. It has 247000 miles and to put that much work into the engine just to have it fail in a few years made my decision easy. I wanted to put in a new engine, not a rebuild or remanufactured engine. I thought the 305 was a good engine, but discovered that GM stopped making that engine a few years ago. I bought the 350 and installed it in the truck. I replaced a lot of other parts as well, including water pump, thermostat, radiator, radiator hoses, distributer, clutch, flywheel, engine mounts, injectors, intake, headers, plug wires etc. Some of the things that I discovered is that the engine was not the original engine. Not sure if it was junk yard engine or rebuilt. The radiator was very new but it was the wrong radiator and the hold down brackets were missing. The radiator was a good 10 inches in width less than stock, so the brackets that I got would not attach to the radiator. There was nothing holding the radiator in the truck except the upper and lower hoses. If I had taken the truck off road the radiator would probably have fallen into the fan. The bottom radiator shroud was broken from trying to support the radiator. Both the engine mounts were broken as well as the transmission mount. The flywheel was scored bad, probably because of main seal leak fowling the flywheel. The clutch disk was only about half worn out. When I got the truck I was surprised how much force it took to push in the clutch, but thought that was just the way it was. After the engine and clutch rebuild it takes about 60 percent less force to push in the clutch. I am not sure why that occurred? The tough parts of the rebuild were getting the engine back in. I spent hours and hours with different angles and heights and then it dropped in. On first startup it leaked antifreeze from the intake. I was using the felpro steel gaskets. I took it all apart a second time and noticed that there was a fair amount of pitting that I did not notice when cleaning the old intake. I cleaned it again and checked to see if the intake surfaces were flat, they were. I put it back together a second time and it still leaked. The third time I tried rtv on the pitted areas and put it back together. It still leaked. I should have thrown in the towel sooner, but sometimes you have to hit me with a 2x4 to wake up. I ordered a new AC delco intake manifold and new felpro gasket and installed it back together a fourth time. This time it did not leak from the intake and engine seam but was dumping antifreeze out the front of the engine. I had not installed the gasket correctly on the thermostat, so that was an easy fix. The truck was not running very well and I figured that the cam retard was off, it was throwing a code. I took it to a garage and had the cam retard set, it was at 22 degrees. The truck now runs well. I have read a lot of information on many forums that said the conversion would not work and some said it worked fine. Some said that you had to have a 350 computer, or have a tuning done on it. I have a 350 engine, with 305 computer and 305 single exhaust. I am still breaking in the engine so I have not done full throttle, but it runs very good. The fuel filter was really dirty, I am surprised that it would run. Would it run better with a tune? Maybe, but even a stock engine and correct computer might run better as well. Hope this helps someone out, if they are thinking about a 305 to 350 conversion.
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Old 08-15-2018, 02:31 PM   #2
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Re: Engine Replacement

It kinda sounds like your 305 replaced a 4.3/ 262 V6. V8 SBC parts like the radiator shroud are pretty common. When you installed the 350 the engine was a multi-point fuel injection setup (?). I think in 1996 the engines were closer to OBDII specs than OBDI. On my '89 going from a 305 to a 350 didn't cause me a lot of trouble. At the time it was the best thing I could've done. The main things different on my swap were the PROM change and a 350 TBI unit in place of the 305 TBI unit. Your swap sounded a bit more complicated.
1989 K1500 Chev. EC
Original owner; some of the aftermarket parts I've installed are Borla headers, Hypertech chip, Edelbrock water pump, and a Stillen rear disc brake conversion kit.
2009 Hummer H3T 3.7L 5M.
1997 K2500 Chev. EC 7.4L/ 4L80E
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Old 08-15-2018, 03:01 PM   #3
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Location: Denver, CO
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Re: Engine Replacement

According to the RPO codes my truck came with the 305. I think someone installed the wrong radiator and removed the brackets because they did not work with the wrong radiator. Out of all the parts that I purchased all of them were the same for the 305 and 350 except the knock sensor. The 305 had the old style popit type injectors. These were all replaced with the new injector system from AC Delco. It was a lot of work, but it would have been a lot easier if I just bought a new intake from the beginning. I spent a lot of time cleaning the intake with oven cleaner and engine cleaner only to scrap it. I just did not know how much pitting was too much for the intake to seal.
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Old 08-15-2018, 03:13 PM   #4
95 S_Trucker
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Location: Lancaster, PA
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Re: Engine Replacement

I have filled in the pits with epoxy and sanded them smooth. I've haven't had one leak.

There are 2 radiators listed for the 5.0, 28" core and 34" core. And 2 listed for the 5.7. They are both have 34" cores, but one is thicker.(there are other differences with trans/oil coolers, but they are physically the same size)

28" radiator fan shrouds and mounts will not work on 34" radiators.

I will assume your truck came from the factory with a 28" core, and a 34" was installed later on.
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