Just wondering if anyone has had any experience with driving a 671 Detroit? One of our farm trucks has this engine with a 7 speed Spicer transmission. Its a 86' GMC Brigadier with a dump bed. I hate driving the truck compared to our other trucks. It doesn't seem to have much power, even with a load that isn't that heavy. Once you start lugging on a hill, you can downshift, but its still lugging...downshift again and it could still be lugging. It loads easily and shifting gears is worse...even worse than a regular semi truck and we all sometimes think a semi truck seems to have a mind of its own with shifting gears. This one is very picky about the gears and the rpm's used and when it grinds, its loud. I've drove several semi's on the farm, most being a 379 Peterbilt with a Cat engine that shifts nicely. Anyways, just wanted to see what everyone's experience was with driving a 671 Detroit, and I'm curious if there is something wrong with ours or if this is just normal for these motors because sometimes I think the governor is messed up. Anyone here drove a 671?
mndriver
curmudgeon extraordinare
It's a two-stroke diesel. In a dump truck environment, great for twisting driveshafts.
They work best wound up. Tight. It's where the power band is on this beast. On the high end. That's the two stroke.
They eat oil.
And you'll likely want to learn how to replace quill shafts on the blower.
We had a 671 in an old Ford dump running gravel. They kept 3 drive shafts for it. One in repair, one on the service truck and one in use.
The 671 is also the engine in the m113 chassis armored personnel carrier in the army. Only spent 14 years working on/with them
They work best wound up. Tight. It's where the power band is on this beast. On the high end. That's the two stroke.
They eat oil.
And you'll likely want to learn how to replace quill shafts on the blower.
We had a 671 in an old Ford dump running gravel. They kept 3 drive shafts for it. One in repair, one on the service truck and one in use.
The 671 is also the engine in the m113 chassis armored personnel carrier in the army. Only spent 14 years working on/with them
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Pops65
Well-Known Member
Best thing to do is before you get in the truck slam the door on your thumb. Then get in it and drive like you just stole it keep your foot to floor and shifter fast. Its the only way to drive one and they like the 2500 to 2600 RPM range or you'll get no power out of them.
Southern Fried
Well-Known Member
Right you are. The old "Double Breasted Yamahas" (V-71's, 6-71's 4-71's) were designed to deliver power at the top end of their rpm's (17 to 2100). They never were a "lug it down" engine like the Cat.
13 OD was a very popular tranny because you only dropped 250 rpm between shifts. Many of the 671 series were mated to "twin-stick" trans and/or 4 series rearends to keep those rpm's up there.
They don't burn oil as much as they leak it. They never did have good gaskets. Used to be a standard joke that if you steamed off a Detroit, they wouldn't pull worth damn.
Good point about the quill shafts though. They were designed to break before you managed to blow up the blower gears and/or lobes in the supercharger. Do it once on a winter roadside and you'll learn to shift better though.
BTW, the 71 in the designation was cubic inches of 1 cylinder (92 in later engines), multiply by the number of cylinders to get the cu in of the engine. The common term (290, 318,350,435) referenced the horsepower rating.
13 OD was a very popular tranny because you only dropped 250 rpm between shifts. Many of the 671 series were mated to "twin-stick" trans and/or 4 series rearends to keep those rpm's up there.
They don't burn oil as much as they leak it. They never did have good gaskets. Used to be a standard joke that if you steamed off a Detroit, they wouldn't pull worth damn.
Good point about the quill shafts though. They were designed to break before you managed to blow up the blower gears and/or lobes in the supercharger. Do it once on a winter roadside and you'll learn to shift better though.
BTW, the 71 in the designation was cubic inches of 1 cylinder (92 in later engines), multiply by the number of cylinders to get the cu in of the engine. The common term (290, 318,350,435) referenced the horsepower rating.
Thanks for the replies, its been interesting hearing all of this...sounds like we are definitely talking about the same engine. We had driveshaft trouble 1 time since we've had it, a U joint went out. We've had it for about 15 years but mainly use it in the fall during harvest. It has always leaked oil like you guys said. I still think something may be wrong with the governor because I realize these engines don't have lugging power but we have had so much trouble with it. For example, one time, I was riding with my dad in it and we go around a blind curve and there's a school bus in the road at the top of the hill with traffic slowed down. We couldn't recover by downshifting (we were loaded). Even if you go from 7th down to 5th and keep your speed up, it stalls. I was embarassed, we had to stop and put it in 1st gear and start from scratch, there were cars behind us 
Pops65
Well-Known Member
Ya know California tried years back to outlaw those old jimmy's because of the oil leaks. Never a favorite of mine.
Pops65
Well-Known Member
Like my 6nz C15, and have big cam 400 in our 78 pete dump.
Coronado Kid
Cactus Patch
we got a big pete dump truck 2 axle 1992 with a detriot
Pops65
Well-Known Member
The truck was overhauled right after we got it. Dad said it actually had LESS power after the overhaul. The mechanic had dad come drive it and see what it was like compared to before the overhaul and dad told him it had less power. The mechanic adjusted the governor and got it "better" but not as good as it was before he had it overhauled....and yeah I love the 3406B Cat's. That's what my 93' 379 Pete has in it, my 98' Pete 379 has the 3406 E which I really like too. I think the 671 Detroit is crap, especially compared to the 3406's...that's why I wanted to hear you guy's opinions on the 671. Any other 671 stories are still welcomed.
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Yeah I only knew that the mechanic had tinkered with the governor... but wasn't sure about if he had set the rack. My father in law is a diesel mechanic and I'm thinking about having him come look at it. I will ask him about setting the rack. Just haven't asked him yet because he works on trucks all week so I try not to bug him much on Saturdays.
AlexG
Well-Known Member
Never drove a 3406a but I had a 1988 3406B. And it has been my favorite engine, you can do what ever you want to it and turning the AFRC screw in a good distance will get you a 6 mpg with a foot looking at the pyro
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