1967 GMC V6 - 351E on a Camper Cruiser

[Blue Sage]

Originally Posted by Bob B.

My 4 speed 351E with a 4:10 rear axle and LT245/75R16E tires gets 8-10 m.p.g. unloaded. I did replace the Stromberg WWC carburetor with a 500 c.f.m. Holley 2bbl.. That was a common swap back in the day and usually resulted in better performance with slightly better fuel economy.

As for the 351, pistons and head gaskets are particularly tough to find, but they do show up on Ebay from time to time.

Thanks Bob - SO! A first! It is possible to get 10 mpg. Hallellujia. Thx.

[Blue Sage]

Mike 16 - How weird they'd create fix it's for the engine over that span of time rather than redesign it. Thx.

[factorystock]

Originally Posted by mike16

valve train was never very durable at sustained highway speeds. there were new fix it solutions to the valve train every six months for almost the entire life of the engines. The did al right as water well pump motors.

Best way to ruin a large V6 or a large diesel is run it at high rpms. These engines were designed to put out maximum torque at low rpms, unlike most V8's that are designed to put out maximum horsepower at high rpms. High rpms are great for a race car, but lousy for a working truck. V6 valves were mechanical that required periodic adjustment during scheduled maintenance. Why v6's weren't designed with hydraulic valves ( which Chevy v8's had during this period) continues to be a mystery to me.

[Blue Sage]

Interesting; I guess the Camper Cruiser, put out in '67 was meant to be driven under 60 mph as the transaxle gears are so high. The lower gears would have allowed for driving into steep camp sites and such at slow speeds with all that torque.

I just noticed, in my project to put the engine back together, that one of the push rods for the valves is bent - a lot - the max in it's sleeve, as the elbow of the bend is roughed up. this probably means the bolt in the cylinder hit a valve - and the aluminum rod bent - which is good! Probably means the valve is undamaged - I don't see any damage. but now Have to find or make another push rod.

[Blue Sage]

To whom may be interested; I found a site with downloadable old manuals and found one for the GMC 351 / 305 ; https://www.manualslib.com/download/...c-305c-V6.html

[factorystock]

Might find this interesting. Discussing the new line up for '69, Don't know why its loading side ways, photo are upright in my files.

[Blue Sage]

Well, that is hopeful. The original transaxle was extremely high geared. You could feel it whine at 50. I realized too that the tires on there are way smaller than the wells so that it would take much larger tires = better milage. I hunted down a lower geared transaxle and had it welded on and never did get to test that for milage as I screwed things up putting on a different carb . . . so - I may have good looking numbers waiting for me! Thanks!

[MJN]

Originally Posted by Blue Sage

Well, that is hopeful. The original transaxle was extremely high geared. You could feel it whine at 50. I realized too that the tires on there are way smaller than the wells so that it would take much larger tires = better milage. I hunted down a lower geared transaxle and had it welded on and never did get to test that for milage as I screwed things up putting on a different carb . . . so - I may have good looking numbers waiting for me! Thanks!

Just to clarify by "high geared" you're referring to numerically high ratio (4.10:1 or 4.56:1)? Just saying high geared typically means it has highway gears like 3.08:1. Also, they rear axle was welded in? Can you clarify this? Any pictures of the truck?

[Blue Sage]

Yeah, I wasn't too clear on that high low thing. So - if a transaxle or a tranny is low geared it means the wheels go faster at low RPM's and vice versa. right?

I can't get my phone to send to my email to post some pics of the truck. By welded I meant that the axles were just swapped but the drive shaft difference required shortening the drive shaft - hence - the welding - on the shaft. I think it's a ford transaxle I ended up with.

[Blue Sage]

Trying to post a photo of my truck on this site. I click the icon for uploading a photo which asks for a URL for the photo - but the photo is just on my desk top. Any hints? thx

[Steeveedee]

Make a reply and scroll down to view the "manage attachments" button. Click and a box will appear where you can select up to 5 pics. Click "Choose file", and you then go to your computer and find the file. Click and then upload. This puts a pic in the post. It has to be a file, not a pic you click on your desk top (I think that is true). If you are looking to make an avatar, go to your user CP and edit the avatar. Pretty much the same process to get the avatar pic, but there are some size restrictions.

[Bob B.]

Originally Posted by factorystock

Best way to ruin a large V6 or a large diesel is run it at high rpms. These engines were designed to put out maximum torque at low rpms, unlike most V8's that are designed to put out maximum horsepower at high rpms. High rpms are great for a race car, but lousy for a working truck. V6 valves were mechanical that required periodic adjustment during scheduled maintenance. Why v6's weren't designed with hydraulic valves ( which Chevy v8's had during this period) continues to be a mystery to me.

Funny thing, the GMC V-6 had hydraulic lifters in some industrial applications. Very rare. I was told they actually used hydraulic lifters out of a later Chevy 235! The rocker arm shaft pedestals on the V-6 were made out of a special aluminum alloy that was supposed to help maintain constant valve lash whether the engine was hot or cold.

I never heard of valve train trouble on these engines, just that they gave poor fuel economy and were very expensive to manufacture. The V-6 was good for 200-250,000 miles in highway service when other truck engines were lucky to see 100,000.

[Blue Sage]

Yes I picked up that they had great reliability and endurance from an old add someone posted to me; "Our first V6 went 246,000 miles before it's first service". That's sure attractive - but for the milage thing. With the right carb, largest wheels possible and a different differential perhaps 12-14 mpg possible. It's an impressive engine. I wonder as the literature repeats over and over that the 305 and the 351 are almost identical - does that mean the 305 has the density of steel the 351 has?

[factorystock]

The 351 was essentially a larger bore version on the 305. There was a heavy duty option on the 305E, not sure about the heavy duty option on the 351E. Maybe Bob B. is familiar with this option and how to detect if a engine has this option.

[Blue Sage]

Interesting. I wonder just what 'severe service' means? Very heavy loads, and continuous use probably. So - the 351 was the same block? as the 305? Since the score on the one damaged cylinder is so slight, I wonder if I could just put the rings back in and just run it without even honing? The rings would adjust the slight difference of surface?

[Bob B.]

Originally Posted by factorystock

The 351 was essentially a larger bore version on the 305. There was a heavy duty option on the 305E, not sure about the heavy duty option on the 351E. Maybe Bob B. is familiar with this option and how to detect if a engine has this option.

That question has been debated over on the 6066gmcguy website forum. First off, there was no 'HD' option for the 351E, they all had valve rotaters and the upgraded valves and seats (they are really 351 Magnum HD engines modified to fit in pickups). The 305E did have had a 'HD' option. It does show up in sales literature and the data books, and many '67 and newer 305's in pickups have the HD features. What is a bit confusing is when the 'E' version of the 305 came out (for pickups), GMC supposedly went to 3 ring pistons on it. Earlier 305's had 4 ring pistons, as did all 351's (E's included). I think some people assumed the HD option on the 305E included 4 ring pistons as well, which it appeared not to. FWIW, that's my guess.

I think the easiest way to tell if a 305 has the HD option would be to pull the valve covers and look for the rotaters under the valve springs.

[mike16]

sustained hiway speeds does not mean over reving the motor. just hiway speeds, ordinary to you and me but hard on long stretches for that v6, even at 65 mph would wear it out pretty quick.

valve train repairs, on a steady basis was one solution but you will note that streight six and sbc v8's became available options as well.

[Blue Sage]

Thanks for the input but most of what you say is way over my head! But perhaps you could help me with something? I'm considering putting a 305 in in place of the 351E - on Craigslist they mention 305 "small block" as different from what? a 305 big block I assume. What's the diff and would the small block fit the bell housing of my Camper Cruiser? I think probably not - it would have to be a big block? Thx.

[Steeveedee]

305 small block is probably a V-8 Chevy. Did the ad say GMC? I could see the SBC 305 in a GMC Sprint. for example. I don't remember if the Sprints were still available by the time the 305 SBC came around, though.

[factorystock]

Originally Posted by mike16

but hard on long stretches for that v6, even at 65 mph would wear it out pretty quick.

Really depends on the gearing. 1/2 ton V6 GMC's came standard with 3.07's. Incorrect gearing was the problem with V6 3/4 and 1 tons GMC's. With 320lb torque @ 1600 rpm's, most should have been equipped with 3.54 ( came too late ) or 3.73's ( not offered by GM at the time ), not the 4.10's or 4.56's commonly found.

[Blue Sage]

Thanks. I'll try and put the puzzle together.

[Blue Sage]

I'll have to crawl under there and see what I've got. Thx.

[67GMC351E]

Hello fellas I am new to this i bought a1967 2500 with a 351E and 400th trans was missing two side gas tanks would like to get them, if anyone has a link or knows of a place to acquire them i would appreciate thanks W.K Thunder bay Ontario Canada tried finding them but no luck thanks again

[factorystock]

Originally Posted by 67GMC351E

missing two side gas tanks would like to get them, if anyone has a link or knows of a place to acquire them

Use to be common aftermarket pieces back in the day, several different manufactures. Doubt if anybody makes them new anymore, especially after the squarebody lawsuits. I would check out Craigslist regularly '67-'72's trucks being parted out.

[MARKDTN]

Originally Posted by factorystock

Use to be common aftermarket pieces back in the day, several different manufactures. Doubt if anybody makes them new anymore, especially after the squarebody lawsuits. I would check out Craigslist regularly '67-'72's trucks being parted out.

Or if you had dimensions you could have Boyd Welding in Ocala, FL make you some. They will build aluminum tanks to your specs/prints.