Re: 1966 GMC 305 V6 Service
 

Thanks Jake.
I've experimented w/ Pertronix.
It is a fine ignition that allows you to keep OEM distributor cap:)
I found no increase in mpg and couldn't detect smoother operation.
One advantage of points is you can cheaply keep a spare in glove box.
One advantage of Petronix is it maintains accuracy over 5000 rpm.
My rule of thumb is to keep points in sub 5000 rpm and sub 5000 miles per year.

Re: 1966 GMC 305 V6 Service
 

Dropped the first run oil and I'm happy.
Have to look close to see any trash on element.
I didn't find any large glitter.
Couldn't feel any metal on rare earth magnet inside pan.
Little trash inside canister unfiltered side but not bad at all .

That 1/4" dot on bottom of canister is where I punched drain hole in effort to avoid mess. Ended up making a mess anyway:)

Re: 1966 GMC 305 V6 Service
 

Driving around I noticed I don't have to hold teeth just right to avoid clutch chatter. Both driver side mounts were loose before rebuild which explains chatter. The driver side trans mount dropped bolt which would have been an easy fix had I noticed. The engine mount rubber separated from metal which isn't obvious. The passenger mount was attached but loose.

I've weened 2 cycle oil to 100:1 ratio in fuel.

Break in tip: Squirt valve train w/ oil during first few minutes; can't hurt but may help.

Re: 1966 GMC 305 V6 Service
 

This picture reminds me of your rebuild

Re: 1966 GMC 305 V6 Service
 

Wow!
Thanks for that pic.
It made my day!

Re: 1966 GMC 305 V6 Service
 

I know it's kinda early but I am really curious what kind of mileage you are getting.
Are they really as bad as they say?
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Re: 1966 GMC 305 V6 Service
 

I'm very curious about the mileage also. I log mileage every fill. I put smaller main jets in worn out 305E last year and improved hwy mileage from 10 mpg to 12 mpg. The compression was so low and oil consumption so high I was surprised it didn't foul plugs. I hope the fresh 305E will do better. My gear oil in rear and trans may be too heavy for mpg; I'm thinking of switching to lighter gear oil.
I expect initial readings to be low because not fully broken in.

Guess I should road trip to get mpg data faster:)

Re: 1966 GMC 305 V6 Service
 

thanks for the reply. What rear end gears are you running?

A friend of mine had one of these and swears he got 7mpg no matter what. He also said it was geared to low for much hwy use. After looking at their low rpm torque curve I wonder if it is necessary to gear them that low?
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Re: 1966 GMC 305 V6 Service
 

Pre 2012:
305E loves 70+ mph cruise:)
3.07 dana 44
P235/75R 15 28.9"
Stromberg WW 280 CFM 2bbl
Main jets 0.055", 0.054"
Poor compression
high oil consumption
2" single exhaust pipe
quiet muffler
mix 8-9 mpg
70mph hwy 9-10mpg

2012 changes:
Main jets 0.050", .050"
70mph hwy 11-12 mpg


2013 changes:
Main jets 0.050", .050"
305E rebuilt
Good compression
Low oil consumption
mpg to be determined

Re: 1966 GMC 305 V6 Service
 

thank you again!

There is a really clean long bed knee knocker that has been sitting for at least 5 years that I am slowly convincing the owner to sell to me. I wanna like the V6, I really do...:)
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Re: 1966 GMC 305 V6 Service
 

You don't have to like the V6; I have a place to store it:)

Re: 1966 GMC 305 V6 Service
 

here is a suggestion

Re: 1966 GMC 305 V6 Service
 

That truck used to have an "It's a Doozy" camper top that looked like that.
Functional but looks only a mother could love:)

Re: 1966 GMC 305 V6 Service
 

I just reread this whole thing(again)...

...any updates? How's the mileage doing?
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Re: 1966 GMC 305 V6 Service
 

Running great.
Only put 250 miles so far.
Only getting 9 to 12 mpg.
Has steering vib above 60 mph.
Plan to address vib next.
Then tune distributor.
Maybe AFR and vacuum gauge in future.
Maybe dual exhaust in the future.

Re: 1966 GMC 305 V6 Service
 

Thanks again for taking the time to do this write up. It has been a big factor in finally buying the truck I mentioned earlier.
http://i197.photobucket.com/albums/a...psa0bc4191.jpgIt is a 62 with a 4 speed Hydramatic auto and it's pretty heavily optioned and complete down to the hubcaps and radio... the way it was parked and the fact that I was on his land for work made it hard to get an up close look. Stay tuned for a build thread starting in the fall.

I might be in the market for engine parts soon also if you have any leftovers?
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Re: 1966 GMC 305 V6 Service
 

Your truck looks good; looks straight and solid from here.
Have spare short block but you probably don't need it.
I was tempted to hoard some ebay and Rockauto parts but didn't.
Wouldn't hurt to check hot lash, compression, plug color, head temp, etc.
I glued gasket to vc and it's still leak free even though it's been removed a few times.

Re: 1966 GMC 305 V6 Service
 

The owner before last used a barrel nut and some all thread to convert it to a modern air filter. The barrel nut rattled loose and went into one of the cylinders while it was running and I guess it made some noise before he shut it off. He thinks it was brass but couldn't remember for sure. I have no idea what damage that could've done?
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Re: 1966 GMC 305 V6 Service
 

Rufton....engine came out great

Re: 1966 GMC 305 V6 Service
 

Thanks.

Unlike modern engines, 305E head remove/install is kinda fun (for gear head). I wouldn't run it a second before pulling head or using an inspection scope camera to have a look see. If very lucky you may retrieve through plug hole; then buy lotto:)

Re: 1966 GMC 305 V6 Service
 

Rufton: I am impressed by the work you've done on your 305 V6 engine! Do you happen to have a part number for the oil filler cap? I could use a new one and yours looks just like what I need.

Re: 1966 GMC 305 V6 Service
 

Interesting, not sure I would get it right!

Re: 1966 GMC 305 V6 Service
 

Thanks. Maybe you can find a match at swap meet, ebay, etc.

Re: 1966 GMC 305 V6 Service
 

Strange road trip 305E V6 HWY milage.

1. 9.3 mpg (about 60 mph I-75)
2. 17.1 mpg (about 70 mph I-75)
3. 16.7 mpg (about 70 mph I-75 return trip)
4. 9.5 mpg (about 60 mph I-75 return trip)

Mileage calibrated against map quest.
Triple checked full tank when I got the 17.1 mpg; even saw gas in tank through filler neck.
Thought I was home free until the last 9.5 mpg reading.
I suspect the carb or distributor is misbehaving under 70 mph.
Maybe I'll advance timing a bit more than stock and verify timing advance is functioning. I'm a little suspicious of carb power valve function.

Re: 1966 GMC 305 V6 Service
 

Rufton: Thanks for the detailed images of the oil filler cap. The cap in my 305E has two thinner mounting tabs on the underside. It kind if resembles the tabs on a breather/oil filler cap. I will consider trying a cap like yours. Can't explain your spotty fuel consumption, but mine is in the shop right now getting a proper tune since it has been backfiring a little. I may have damaged the power valve in my Holley carb

Re: 1966 GMC 305 V6 Service
 

I've got a spare Stromberg. When time allows I hope to rebuild it for comparison. I hope to install an UEGO O2 AFR gauge because it takes away a lot of guess work. I'm willing to consider holley as well. Don't think Stromberg power valve is affected by back fire but it's design does look primitive. Not sure how to test power valve function; suppose one could wire open/shut to see how it affects performance.

Re: 1966 GMC 305 V6 Service
 

The Stromberg power valve actuation rod ( looks like nail ). Moves up and down w/ vacuum to stroke spring loaded power valve (looks like jet w/ wire in center). Don't know if hangs up.

The old Stromberg suffered plenty of back fires through the years but power valve still functioned on the bench.

Re: 1966 GMC 305 V6 Service
 

Distributor seems to be behaving. I wanted to dial in a couple more degrees but advance already looks good relative to some other engines. Not sure if I ever hit mechanical advance stop; didn't wan't to spin it faster cause not confident in tach accuracy (indicates low compared to car tach).

7-31-2013 66 GMC 305E V6 timing data:

Timing (vacuum advance connected, cold engine):
6* 490 RPM
24* 1000 rpm
42* 1500 rpm
45* 2000 rpm
48* 2500 rpm

Timing (vacuum advance connected, warm engine):

9* 600 rpm
16* 1000 rpm
16* 1000 rpm
42* 1500 rpm
46* 2000 rpm
49* 2500 rpm
55* 3000 rpm

Timing (vacuum advance plugged, warm engine):

9* 600 rpm
16* 1000 rpm
25* 1500 rpm
29* 2000 rpm
33* 2500 rpm
38* 3000 rpm

Dwell (warm engine):

31 dwell 620 rpm
30 to 31 dwell from 620 to 2500 rpm.

Timed vacuum port Stromberg WW:

<2” Hg 620 to 900 rpm
4” Hg 950 rpm
6.5” Hg 1000 rpm
13.5” Hg 1200 rpm
15.5” Hg 1500 rpm
18.5” Hg 2000 rpm
18.5” Hg 2500 rpm

Re: 1966 GMC 305 V6 Service
 

I have a couple spare caps. I never compared them but they appear the same. When I get home I will compare them. PM me your address and I'll send you one.
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Re: 1966 GMC 305 V6 Service
 

what's the rpm on the engine when your running 60-70 mph

Re: 1966 GMC 305 V6 Service
 

I did the math and 60mph should be about 2150rpm. 70 should be pushing 2500rpm.
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Re: 1966 GMC 305 V6 Service
 

I must have been smoking crack because my oil filler cap is just like Rufton's and likely the same as all other oil filler caps for this era GM vehicle. Sorry for the stupid posts and thanks for the offer T Duncan.

Re: 1966 GMC 305 V6 Service
 

rufton , what port do you have the vacuum on now ?? From what you are telling us it looks like it is on the ported vacuum , it should be on manifold vacuum .. all the vehicles I have had got much better milage on manifold vacuum than ported...

Re: 1966 GMC 305 V6 Service
 

Hello, Does anyone know the factory weight of the GMC 305 v-6?

Thanks in advance.

Re: 1966 GMC 305 V6 Service
 

the number I keep hearing is 800 lbs and judging by how the two I have on stands feel when I try to move them I believe it!
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Re: 1966 GMC 305 V6 Service
 

That works for me. I have been scouring the internet and can not find the weight specs. Thanks Tommy.

Re: 1966 GMC 305 V6 Service
 

I just stole this from Jolly's site:

The "GMC Replacement Engine Catalogs" lists the following dry weights:
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.
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Re: 1966 GMC 305 V6 Service
 

Great weights reference, Thank you

Re: 1966 GMC 305 V6 Service
 

Rufton, I would like to thank you for all the hard work, pictures, and detailed information you have put into this thread. I recently purchased a '66 with the 305 V6, and I have been a little worried about how to take care of it. You have saved us so much time and probably wasted effort. You are great! :truck:

Re: 1966 GMC 305 V6 Service
 

X 2. Do you have a list of
part numbers and vendors?