305C-305E Difference?

[tinman64]

I am a new owner of a 64 1000 with a 305E,I am looking for a spare engine to keep for parts,I have a chance to buy a 305C but I am not sure of the differences between the 2 engines,does anyone know what the difference is between the 2 engines?Thanks

[Jeannie]

305C = 840 lbs dry weight 250 ft pounds of torque, takes 8 qts of oil
305E = 795 lbs dry weight 260 ft pounds of torque, takes 5 qts of oil

That is the main difference I have in my notes on the two. The club's information page for engines is here:

http://6066gmcguy.org/EngineData.htm

[bigblockv6]

The biggest difference between the 305C vs 305E engine is the 305C has 4 ring pistons rather than 3 ring pistons, it will have the higher mount water pump/ timing cover housing for medium duty applications and valve rotators (which were also equipped in the optional HD305E)other than that it's really the same engine and will be good for parts. Pete Chronis Northern Cal.

[bigblockv6]

Also forgot to mention the extra oil capacity of the 305C was due to a larger oil pan and canniter style filter, still not a problem to transfer the 305E oil pan and filter assembly. Pete Chronis Northern Cal.

[tinman64]

Thanks for the quick response,I saw the weight difference and TQ,hp numbers but didn't know why.Valve rotators?what are they?I guess the early v6 had 4 ring pistons,wonder why they switched to a 3 ring

[bigblockv6]

Valve rotators were used to keep valve seats clean, they're mounted on the bottom of each valve spring. Used in bigger truck applications, though in later years an HD305E was offered with this feature. 4 ring pistons were used on all 305C engines from 1960-74, again this was a big truck feature that had one extra compression ring, it also phased out the 3 ring pistons in 305E engines for replacement for the purpose of standardization around 1970-71. Pete Chronis Northern Cal.

[jbgroby]

my 305 A had 3 compression and 1 oiler ring, most people are surprised when I show them an old pistion.

[bigblockv6]

All 305A,D and E engines all came with 3 ring pistons, while 305B & C came with 4 ring pistons

[tinman64]

Thanks guys,I'm trying to get familiar with these engines,up until 2 weeks ago I had never seen or heard of them.

[824slugger]

How do you determine the "abc's" of the engines?

[6066gmcguy]

Engine number stamped on the block, check this page of My site for more info; Engine Data Page (http://www.6066gmcguy.org/EngineData.htm).

[LEWISMATKIN]

The 305C engine was the heavy duty version of the 305 line. It was mostly found in the 3000-4000 series 60-66, then in 4500-6500series through '74. The main differences with the E series engines is all sodium filled valves on the Exhaust (called stellite), rotators under the valve springs, and 4-ring pistions. The E series was the light duty or Economy (pick up) version and lacked the things that the C engine had and also was equipped with 3-ring pistons (the only engine in the V6 line to come that way factory).

[bigblockv6]

My understanding is all GMC V6 engines 351 through 478 came equipped with Sodium cooled valves, all 305 engines did not and my factory GMC manual confirms this, stellite is a hard alloy used on the valve faces that come in contact with the valve seat. There was an HD305E V6 that was available in pickups, my 68 was equipped as such and this engine used valve rotators.

[LEWISMATKIN]

Thanks Pete, for reminding me about the valves, in that regaurd you are right. However only the "E" series ever came with 3-ring pistons, which as you have said before have been replaced with the 4-ring pistons of the A-B-C-D engines. I hope you have had a blessed day today. BTW, how is that 478LD of your running??

[bigblockv6]

Lewis, the 478M finally got fired up on this last President's day, after getting things dialed in like the valve lash and timing the engine sounds great, it's good to hear it running after some 16 years and the 478 does sound somewhat different from the 305. I have yet to finish the power steering conversion before I get the truck on the road, working 6 days a week is making things difficult at this time but hopefully next month will be better. As far as the 4 ring piston issue, what I was talking about was in the early seventies GMC issued a service bulletin that stated 3 ring 305 pistons were discontinued as a replacement part. From that point the 4 ring 305C pistons were to be used in prior 305A,D and E engines for replacement and the purpose was for standardization. This all made sense at the time since only 305C engines were in production. Of course aftermarket suppliers more than likely offered the 3 ring piston.