2 CUCV blazers, one purrs one rattle monster, ideas?

[ke6rwj]

I've been working on cucvs for awhile. Mine and lots of others. I'm very confident in fixing them diagnosing etc... but one thing has always puzzled me... why do the cucvs with "factory" military IP, purr like a kitten, quiet and smooth... hell they sound like a gas burner!! While anything that's gotten a rebuild pump sounds like it's coming apart. The ignition noise (diesel rattle) is insane..

I have 2 cucv blazer.. one is smooth as silk the other raspy and rattle. I understand that too much fuel will cause that, and I've adjusted the ip timing and it's quieter, but still not as quiet.

I've assumed that these pumps are set too "rich" for the 6.2 and need to be "leaned" out a bit.

Is it possible to get this rattle monster to be as quiet as the other?

Thoughts?

-- chris

 

[Skinny]

I had the OEM pump and a reman'd unit back to back. No difference in sound or feel. I wouldn't go as far to say it is smooth as a gas burner. The 6.2 normally sounds like a monkey stuck in the block and is hammering his way out.

If anything the stock pump is under fueled. No such thing as rich or lean really like a gas engine. But under wide open throttle it never would blow smoke. Turning the fuel screw in really wakes it up. If you can get it to puff a slight amount at full tilt you have achieved zen. Well as much zen as a pig can give you

Is the cold start advance coming off correctly during warm up? Maybe it's sticking on and giving you a bunch of noise for no reason.

 

[LT67]

If my 85 M1008 didn't rattle like a metal trash can full of rocks, I'd think something was wrong... it also runs very well for a 6.2 diesel.

A 6.2 is going to rattle a lil bit. If it's not something ain't right

 

[Barrman]

Timing and pre combustion chamber throat size.

The more advanced the timing is the louder the tin can full of rocks sound. Look at the lines scratched into the IP and timing cover at the front top of the engine. Are they aligned or is the IP a good bit toward the drivers side of the timing cover line? Common wisdom is that you shouldn't exceed 1/16" advanced to the drivers side without some way of actually checking the timing numbers.

I think there were 8 different 6.2 or 6.5 pre combustion chambers made. The chamber itself was basically the same size. The difference was the hole between the pre cup and the cylinder. That hole is called the throat. Once the fuel is ignited inside the pre cup the fire travels out the throat to push the piston down. The bigger the throat, the more efficient it is at getting the flame front to put pressure on the piston.

The 6.2 was designed from the start as a fuel mpg saver. It was supposed to fit anywhere a gasser V8 lived and deliver the same horse power as a standard 2 barrel 305. With, twice the mpg. It did that almost to perfection. The pre cups on those first engines have very small throats and got great mpg but power was well, low. They kept changing the design bit by bit until the 6.5 Turbo had pre cups with huge throats. Each one in the bigger progression changes the sound of the engine. I have the huge Diamond marked pre cups in my GEP 6500 with a Banks turbo in my Cowdog truck. It is the loudest 6.2/6.5 I own by far at idle. It also has the most power. Steady driving with about 2 pounds of boost at highway speeds and around 2200 rpm has it making this very addictive to hear growling noise. But, I give up mpg to get that power and nice sound.

Here is a thread that list out all the different pre cups:

Pre combustion chambers - G503 Military Vehicle Message Forums

forums.g503.com

 

[LT67]

Timing and pre combustion chamber throat size.

The more advanced the timing is the louder the tin can full of rocks sound. Look at the lines scratched into the IP and timing cover at the front top of the engine. Are they aligned or is the IP a good bit toward the drivers side of the timing cover line? Common wisdom is that you shouldn't exceed 1/16" advanced to the drivers side without some way of actually checking the timing numbers.

I think there were 8 different 6.2 or 6.5 pre combustion chambers made. The chamber itself was basically the same size. The difference was the hole between the pre cup and the cylinder. That hole is called the throat. Once the fuel is ignited inside the pre cup the fire travels out the throat to push the piston down. The bigger the throat, the more efficient it is at getting the flame front to put pressure on the piston.

The 6.2 was designed from the start as a fuel mpg saver. It was supposed to fit anywhere a gasser V8 lived and deliver the same horse power as a standard 2 barrel 305. With, twice the mpg. It did that almost to perfection. The pre cups on those first engines have very small throats and got great mpg but power was well, low. They kept changing the design bit by bit until the 6.5 Turbo had pre cups with huge throats. Each one in the bigger progression changes the sound of the engine. I have the huge Diamond marked pre cups in my GEP 6500 with a Banks turbo in my Cowdog truck. It is the loudest 6.2/6.5 I own by far at idle. It also has the most power. Steady driving with about 2 pounds of boost at highway speeds and around 2200 rpm has it making this very addictive to hear growling noise. But, I give up mpg to get that power and nice sound.

Here is a thread that list out all the different pre cups:

Pre combustion chambers - G503 Military Vehicle Message Forums

forums.g503.com

So on a n/a 6.2 or 6.5, if the timing is advanced a little and the fuel is turned up, it equates to more power?

 

[Mullaney]

So on a n/a 6.2 or 6.5, if the timing is advanced a little and the fuel is turned up, it equates to more power?

.
Also smokes (melts) pistons too.
If you decide to turn up the fuel it might be worth installing a device to measure exhaust gas temperature (Pyrometer). At least that way you can see it going bad before it happens. Generally on a turbo model, that is really important. Normally aspirated not as much... Thing is, turning up the fuel when compared to stock isn't going to make a race truck out of yours..
.

 

[LT67]

.
Also smokes (melts) pistons too.
If you decide to turn up the fuel it might be worth installing a device to measure exhaust gas temperature (Pyrometer). At least that way you can see it going bad before it happens. Generally on a turbo model, that is really important. Normally aspirated not as much... Thing is, turning up the fuel when compared to stock isn't going to make a race truck out of yours..
.

Just as long as I can out run a moped...

 

[Skinny]

I had a noticeable difference in power cranking the fuel screw in. Granted I have no idea where it was before I owned it. Who knows what happened in almost 30 years. My M1031 took two 1/8 turns so maybe it was way under fueled to begin with.

Either way I wouldn't go back to what it was. I prefer my turds polished.

 

[LT67]

I had a noticeable difference in power cranking the fuel screw in. Granted I have no idea where it was before I owned it. Who knows what happened in almost 30 years. My M1031 took two 1/8 turns so maybe it was way under fueled to begin with.

Either way I wouldn't go back to what it was. I prefer my turds polished.

Same with my 85 M1008. I have no idea what it was set at prior to me owning it. And I've never touched it. I just know that after changing fuel filters and running Hot Shot cleaner every time I refueled, the engine came to life and rattled all of the time. I can be running 55mph and I can still hear a lil bit of ratting from the engine lol.

 

[Skinny]

I will say going from my 84 Burn with an 8.1 to the M1031 you question why you don't wear hearing protection. The Burb is practically whisper quiet compared to the M1031 and they both are giant bricks...

 

[83k30]

I will add my 2 cents here...I've replaced my injection pump with no noticable change in the sound from the motor. However replacing the harmonic balancer did smoothen the sound and feel of the ol 6.2 detroit quite a bit. Just a thought.

 

[ezgn]

Same with my 85 M1008. I have no idea what it was set at prior to me owning it. And I've never touched it. I just know that after changing fuel filters and running Hot Shot cleaner every time I refueled, the engine came to life and rattled all of the time. I can be running 55mph and I can still hear a lil bit of ratting from the engine lol.

I run with the standyne diesel fuel additive and it is noticeably smoother and more quite. Maybe excess noise might be from timing being advanced slightly.

 

[Mullaney]

I will add my 2 cents here...I've replaced my injection pump with no noticable change in the sound from the motor. However replacing the harmonic balancer did smoothen the sound and feel of the ol 6.2 detroit quite a bit. Just a thought.

.
A new harmonic balancer would be an incredibly good investment. Old rubber dampening material, riding in a hot engine compartment for 35 years is just asking for trouble. When it goes bad, it goes really bad suddenly too!

 

[LT67]

I will add my 2 cents here...I've replaced my injection pump with no noticable change in the sound from the motor. However replacing the harmonic balancer did smoothen the sound and feel of the ol 6.2 detroit quite a bit. Just a thought.

Same here when I put a new balancer on my 85 M1008. It picked up a little more power as well.

 

[dougco1]

Same here when I put a new balancer on my 85 M1008. It picked up a little more power as well.

I'm not sure if my balancer replacement gave me more power but when I washed it, the truck did go faster.