My '89 9670 build


For you lovers of the Class 8's and bigger.

Golden Jubilee
Golden Jubilee

Posts: 5989

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Thu Oct 19, 2017 2:17 am

Re: My '89 9670 build

Do you like the PT Cummins system?
I would rather have tools I do not need than to need tools I do not have

Golden Jubilee
Golden Jubilee

Posts: 3047

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Oct 19, 2017 7:55 am

Re: My '89 9670 build

nikkinutshop wrote:Do you like the PT Cummins system?

The only thing simpler is the unit injector Detroit used. The PT is reliable and easy to work on. The Bosch type injection pump that Cat uses has much more control of the timing as engine speed increases.
Each has its advantage and drawback. I think the PT is a good middle ground between Detroit and Bosch/Cat type.
On a Detroit, there are a lot of mechanical adjustment to make the whole engine work as one unit, no cyl working harder or less hard than the rest. On the PT system the injectors are flowed and set on a test stand and should hold that adjustment though out the injectors life. The only adjustment on the engine is the rocker lash.
The Bosch system is very complex but very reliable, the problem comes after a million or two miles it is very expensive to overhaul.
I've found this helpful
https://www.youtube.com/watch?v=KzuwdxEJfQA

Golden Jubilee
Golden Jubilee

Posts: 5989

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Fri Oct 20, 2017 6:00 pm

Re: My '89 9670 build

I have had experience with Detroit Unit injectors and even some time rebuilding the older DD mechanical governor systems. I was present for one rebuild on a Cummins PT and I was the guy handing the tools to the real mechanic who did the work. One of the sound good engines was the Cummins 903 V8. the company had about a dozen of these monsters. I remember the 903 having problems but I don't remember very much about that, either. I have been retired for nearly 14 years.
I would rather have tools I do not need than to need tools I do not have

Golden Jubilee
Golden Jubilee

Posts: 3047

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Fri Oct 20, 2017 6:11 pm

Re: My '89 9670 build

The Nine o nothing had a much better rep down under and marine than it did in N/A trucks. I am in inline guy and never liked V engines of any kind.
The Detroit injectors are very simple and goes a long way to explain why the 2 strokes had such a good reputation. As long as you have rail-pressure at least some of the cyl will fire, regardless of the rest. The engine may not run on all 6,8, 12 etc, but will get you home.
The PT system is a little more complex, and inter-dependent, but still is simple enough for someone like me to work on in my yard.

Golden Jubilee
Golden Jubilee

Posts: 5989

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Fri Oct 20, 2017 7:21 pm

Re: My '89 9670 build

The introduction of DDEC to GM Diesels made a big difference in performance and improved economy. Diagnostics was better, but, that sneaky DDEC like to cover for a failing cylinder and sometime it was difficult to tell there was a problem with the old hands-on diagnostics. That is, unless a person noticed that the header was cooler on one cylinder. I bought a RAYTECH laser temperature gun. A quick exhaust manifold scan, at the ports, could often direct any more diagnostics. I like the RAYTECH for air conditioning diagnostics. Now, my wife uses the Raytech to check the roasted turkey and the temperature of the jam she is making.
I just checked my self to see if there is any life left and I am at 97F or 36.5C. I AM ALIVE! I AM ALIVE!
I would rather have tools I do not need than to need tools I do not have

Golden Jubilee
Golden Jubilee

Posts: 3047

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Tue Nov 28, 2017 10:24 am

Re: My '89 9670 build

Got the last two spoke hubs rebuilt and on. For some unknown reason they torched the drums bolts off and none of the hubs had axles studs. Lots of time spent with a tap and die and double nutting everything, I was able to pull 10 studs and get them in the hubs. A little blue locktite and they should be good. Why not red you ask (bearing and stud mount locktite)? The threads on the studs are already a tighter fit then std bolts, and the studs are hard, so if one breaks I want a chance of getting it out. I'll take the off chance that I'll back a stud out when I next pull the axle.
On another topic, I have a plan to get the Marmon done also. Several years ago I bought a very good looking Hendrickson beam on leaf "cut-off". It looks almost brand new but has suffered a little being knocked around in the junk-yard. Two of the S cam brackets got a little bent, but nothing a press can't fix.
The problem with the Walking Beam suspension and also one of its strengths, is there is very little "adjustment" that can be made once it is installed. This means anyone doing the frame splice must get it dead-on from the get go. It makes me nervous farming the job out, but there is one guy on JOT who has a good rep, and may do it. He is in Tx about 800 miles from me, so that was one problem we have to over come, another option is a shop closer but if they do it wrong the truck isn't worth much.
The '89 cabover has a lot of small things that need correction, small but not nesserarly cheap. It also needs a set of tires and that is never cheap. I don't know when I'll plate it, I will keep picking away at the small stuff as I have time and money. At least today, if the little bunk had a catastrophic failure, I could put it on the road with a weeks down time, It wouldn't be done, the A/C system needs to be rebuilt, and there are plenty of other little things to work on, but it would get me back makeing money, something it couldn't do for the past 10 years.
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