8V71 & "Advanced Cam Timing"

[OneLapper]

I have the entire weekend.
I have the engine.
I have the gaskets.
I have the new N65 injectors.
I have the cam gears off.

I have the engine manuals.
I have the maintenance manuals.

Neither of the the manuals cover how to advance the cam timing! The manuals only reference standard or advanced timing as they are set up at the factory.

Does anyone on this board have advice for me?  I'm curious to know if advancing the cam timing consists of more than just advancing the cam by one tooth.

Thanks for any feedback, guys!

Mark

[bevans6]

Well there are two cams, so you have to do it twice...  But fundamentally advancing the cam timing is as simple as setting the gears per the book for advanced timing, and then completely re-running the rack.  resetting everything in the injector and governor to accommodate the change, and doing the valve lash as well.  In my engine manual, timing is covered in chapter 1.7.1.



Brian

[OneLapper]

Wednesday was not a good day.  My friend with the wife that works at the closest DD dealer to me, who hooked me up with great pricing and the ability to talk and visit with the parts manager, service manager, and the old timer mechanic mentioned later in this post, had a stroke.  His second in 7 years.  He's lost most of his vision in both eyes. Very sad, he's a huge car nut and diesel fanatic. He will not be able to drive.  Too young, he's in his 60s.

Friday was a good day, relative to Wednesday, that is.  I went to the DD dealer to pick up my parts.  They shorted me a gasket, so he picked up the phone and called someone.  That guy had the gasket in stock! And he's only 7 miles from my office!  More on him later...
The parts manager looked at some photos of the block I took.  He thought it was a V92 block, and asked the service manager to look at the photos. We all agreed it's a V71 block because of the heads installed, but while talking to them, someone mentioned it was too bad I wasn't looking for a 8V92 coach engine!  Well, I am! For Divine Rights Trip's Prevost, that is!  So there it is , wrapped in plastic, in the corner of the shop for the last 9 months, looking for a home.  The service manager said it was a running take out, a bit tired.  The engine came out of an early 90s Prevost and the owner provided a really whipped 8V92 for the core and planned on keeping this engine for spares if he needed them. In short, the shop kept the engine and gave him a credit on the bill.  They are pulling the pan to inspect the crank and bottom end.  I'll find out Tuesday if it's good to go!

Now on Injectors and Timing:

I finally found an "old timer" that has been repairing, rebuilding and modifying 2 stroke DDs for 35 years.  All he does is 2 strokes.  Nothing else.  I visited him yesterday and spent the afternoon picking his brain.  Amazing!  He does mostly marine work now and, in the middle of his shop, had the engine (8V71 Turbo) from one of the four boats used in the film "Jaws" that's being restored.  I got his input on the N60 vs N65 injector debate.  Now, hold that thought....

Some time ago, I had a very good friend of mine who is literally a "rocket scientist" (builds atomic clocks for gov't, etc) review my injector project. He's a huge car nut and done some really interesting things with his cars. We spent a little time going over torque curves for the various injectors (7E55, N60, N65, N70) and, now remember the input from the old timer mentioned about, they both essentially said the same thing: "Torque is Torque".  Even though the peak torque shifts upward about 300 rpms from the 7E55 injector up to the N70, torque and HP cross at 5252 rpm, and because 5252 is what it is, an engine with N65 injectors will produce more torque at 1200 rpm than an engine with N60 injectors, even if the "peak" torque has moved from 1200 to 1400 rpm.

Now, the old timer said the "hot" setup was a 8V71N with N70 injectors, advanced timing, 1.484 injector timing, 19.5:1 compression ratio, 2350 No Load rpm.  335 HP.  He spent a half hour explaining why that setup will get better fuel mileage than the N60 and N65 setup.  After talking about the four speed Spicer, towing a 7500 pound trailer, gearing (tall) we agreed that he N65 setup would work well if I set the No Load rpms at 2400 and downshift to third at 65 on hills.  He thought I'd be able to pull most any hill around here riding the governor in third, which was my goal in the first place.  BTW, he has customers that are running their 2 strokes at 2700 rpm!!!!  He's built engines for a truck racing team that spins at 3700 RPMs!!!!!!!!  He showed me a picture of the truck.  Quad turbo 12V71. Yikes.

He had several engines on the bench in different states of rebuild.  He showed me how to advance the timing and gave me a refresher on adjusting the valves, injectors and Jakes.

I'll let you know how it turns out!

[OneLapper]

Well there are two cams, so you have to do it twice...  But fundamentally advancing the cam timing is as simple as setting the gears per the book for advanced timing, and then completely re-running the rack.  resetting everything in the injector and governor to accommodate the change, and doing the valve lash as well.  In my engine manual, timing is covered in chapter 1.7.1.



Brian

Brian, thank you!  You are right.  Even though I read that section, it didn't explain it in the detail I needed.  I now understand that it's the crank that phyiscally get's "advanced" in relation to the cam timing.  I'm good to go!  I got my hands dirty and I now completely understand the process.

Thanks!

Mark

[bevans6]

Well, I was wrong when I said you have to do it twice, you do only make the change at the crank gear, the others simply line up as normal.  I agree with you on the torque thing.  Perusing the charts I have access to, N60's and standard timing produce 770 ft lbs of torque at 1200 while N65's and advanced timing produce 785 ft lbs of torque at 1200, and 800 at 1600 rpm.

Brian