Timing and Dieseling

[hatzie]

Alright, so I finally got around to finding TDC and found that the original mark was off by 26.5°! I'm glad someone mentioned the rubber dampener allowing the outer cast ring to move. I found this using the piston stop. The orange dot is the original mark and the 2 small silver lines are where the piston hit the tool on either side of TDC. Then the long mark is splitting the two. I estimate 13° between each mark for a 7" harmonic balancer.

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Time to replace the balancer. A moving harmonic ring will not stay in the same place and it will eventually break your crankshaft. The 6.2 6.5L Diesels are very very bad about that. I used fluidampers as replacements on all my diesels.
Be sure to get the right one for your engine and timing tab.

 

[1987 GMC Jimmy]

The reason I mentioned vapor lock is because improper routing near an extreme heat source (i.e. exhaust manifold) is a good recipe for vapor lock. Someone brought this up the other day, and this is the one for $23. I confirmed the application on the Classic Industries site. I’m not against the look or function of a braided line. I guess I’m just a stickler for the way the OEM approached it.

https://www.summitracing.com/parts/rsd-tpc8101s

 

[HotRodPC]

Time to replace the balancer. A moving harmonic ring will not stay in the same place and it will eventually break your crankshaft. The 6.2 6.5L Diesels are very very bad about that. I used fluidampers as replacements on all my diesels.
Be sure to get the right one for your engine and timing tab.

I had the same problem with my 454. I timed by ear so no biggie really, but it's not good to run without a correct balancer. So I got a brand new one and it idled smoother and then I was able to confirm my timing with a light too. Mine had slipped about 1/3 the way around is a pretty significant slip.

 

[74 Shortbed]

The reason I mentioned vapor lock is because improper routing near an extreme heat source (i.e. exhaust manifold) is a good recipe for vapor lock. Someone brought this up the other day, and this is the one for $23. I confirmed the application on the Classic Industries site. I’m not against the look or function of a braided line. I guess I’m just a stickler for the way the OEM approached it.

https://www.summitracing.com/parts/rsd-tpc8101s

But if you route it in the same area it's no where close to an exhaust manifold.

 

[74 Shortbed]

I had the same problem with my 454. I timed by ear so no biggie really, but it's not good to run without a correct balancer. So I got a brand new one and it idled smoother and then I was able to confirm my timing with a light too. Mine had slipped about 1/3 the way around is a pretty significant slip.

Anytime I put a new balancer on I put two identifiable punch marks with a little dab of paint, this way a quick glance at any time will tell me if the ring has moved..

 

[74 Shortbed]

I like the look of a braided one and it seems easier to install so Im on your side. The only reason Id justify another solid line is that I dont intend to take the carb on and off and wouldnt mind saving $20. I welcome part suggestions.. maybe even with a filter/gage combo.. I like to make sure all my bases are covered if Im going to take the time to replace all this stuff.

Not so much the looks, just makes it easier to work around other stuff since the hose flexes that hard line can get in the road of a wrench sometimes.

 

[maxtwms]

Time to replace the balancer. A moving harmonic ring will not stay in the same place and it will eventually break your crankshaft. The 6.2 6.5L Diesels are very very bad about that. I used fluidampers as replacements on all my diesels.
Be sure to get the right one for your engine and timing tab.

Holy cow, thats a chunk of change. Im looking at a $56 Balancer and then check out your Fluid Dampener for $230! Whats the benefit here? Just extreme reliability?

 

[HotRodPC]

Anytime I put a new balancer on I put two identifiable punch marks with a little dab of paint, this way a quick glance at any time will tell me if the ring has moved..

That's a great idea.

 

[1987 GMC Jimmy]

But if you route it in the same area it's no where close to an exhaust manifold.

Yes, you’re right.

 

[hatzie]

Holy cow, thats a chunk of change. Im looking at a $56 Balancer and then check out your Fluid Dampener for $230! Whats the benefit here? Just extreme reliability?

Don't bother with a Fluidamper for a regular smallblock. Wasn't suggesting you should. Just commenting on the engines I've seen this happen on and what I did to fix em. Sorry I wasn't clear about that. The $50-$70 rubber balancers are just fine for a basic smallblock motor. I might consider Fluidamper on a 383 stroker or some other special motor where some coin was spent on the build. My Dodge Polara 500 has one but again I spent plenty on that original 383 Chrysler motor around 30 years ago and it's only lightly driven in the summer.

The 6.x Diesel balancer and damped accessory pulley are known issues. They fail between 70,000 & 100,000 miles or around 10 years. When they fail they quickly break crankshafts on the expensive 6.x diesel motors. Fluidampers are permanent parts because they don't have a rubber piece to breakdown from vibration or time. I've owned my 2000 GMC C2500, 76 K20 6.5L, & M1008 6.2L for around 20 years each so mine have paid for themselves at least once.
The stock 6.x Diesel Balancer is around $110-$130 and another $110 + for the damped serpentine pulley on the 2000 & 76. I only have to swap out the accessory drive pulley on the 6.5L engines now.

 

[maxtwms]

I reinstalled the rebuilt carb, installed a new dizzy, rotor, plugs, and wires, found/fixed a valve cover leak, and set the timing at 12btdc. Engine ran at 750rpm. Idle screw backed all the way out and then screwed just enough to move the throttle (to achieve the ~.050" transfer slot), and I'm still getting run-on which is prob from the ethanol free 87 octane I'm running.

If I advance the timing any more, the idle will rise and I won't be able to lower it from the idle screw. At the moment the metering block mixture screws do little to nothing and I have about 12inhg of vacuum so that's not good.

If I raise the idle by advancing timing, will the mixture screws be able to increase the vacuum and lower rpm?

I ask it now instead of trying since I melted one of my plug wires during idle... My luck

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[1987 GMC Jimmy]

Refresh my memory, but was it doing something wrong at a lower timing setting? 12 is just too much for that motor. It’s tough to say and exact number, but I’m thinking more like four or five to run 87. Maybe mine’s a little more sensitive than most, but I think 12 is universally too much, and you should back it down. I think the lower octane fuel and the high timing are exactly why it’s dieseling. If you can drive it and get on it without audible detonation, that’s surprising to me from my experiences. The curb idle mixture will make an incremental difference in vacuum level and stability, but that’s not what they’re designed to do. A vacuum that low with an initial timing that high throws up a red flag for me. What have you checked in terms of leaks? It’s gotta be several small ones or a big one to cause that (warped carb, intake leak, brake booster, etc.) kind of drop, and your relatively high idle is byproduct of that. You lack at least 5” to be in a nominal range.

 

[maxtwms]

It's an 85 so no fuel injectors (I say that since yours is an 87) but I'm sure you picked up on that. I have the dizzy adv plugged, and all other vacuumed ports plugged except the pcv, brake booster, and choke. Those are all hooked up and the choke is on the manifold port. All emmission items have been removed before I owned it. It's apparently a rebuilt 305 with a different cam. The balancer had wiggled out of clocking so I found TDC with a piston stop by finding the piston hitting on both sides and split the difference to find center. I lined it up at 12 deg on compression stroke and looked at the dizzy rotor and placed my 1 cylindar spark plug terminal at the rotor point. Then the rest is confusing. I'm reading that I should advance away from 12 to something more like 18 but I agree it seems that I should be more like 8. That's what the engine reqs recommend. I was only wary because of all the emission items being removed which I'm ok with.

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[maxtwms]

Refresh my memory, but was it doing something wrong at a lower timing setting? 12 is just too much for that motor. It’s tough to say and exact number, but I’m thinking more like four or five to run 87. Maybe mine’s a little more sensitive than most, but I think 12 is universally too much, and you should back it down. I think the lower octane fuel and the high timing are exactly why it’s dieseling. If you can drive it and get on it without audible detonation, that’s surprising to me from my experiences. The curb idle mixture will make an incremental difference in vacuum level and stability, but that’s not what they’re designed to do. A vacuum that low with an initial timing that high throws up a red flag for me. What have you checked in terms of leaks? It’s gotta be several small ones or a big one to cause that (warped carb, intake leak, brake booster, etc.) kind of drop, and your relatively high idle is byproduct of that. You lack at least 5” to be in a nominal range.

I'm surely going to back it down... It seems to run too rough at this point. Will any of this cause it to run cooler by chance? Just curious.. I haven't seen it run hot or anything, it just seems to get warm really quick

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[1987 GMC Jimmy]

If the cooling system is working correctly, it should be running at the right temperature, but it’s likely getting to work sooner because of the way things are. Lean and potential detonation equal heat, plug wear, piston wear, etc. The key here is the vacuum. If you can that up, the idle will go down, you can tune the correct mixture and the correct curb idle setting, you can back the timing down, and it’ll run right. Before you knock that out, trying to establish operating parameters when it’s not running right is pointless. I think you’ll get it, but you have to check for those leaks very thoroughly. A set of port plugs, pliers to clamp hoses, and starting fluid are all good tools to get that done. I’d plug off the carb and manifold ports and see if the vacuum comes up. If it does, you’ve got a whole bunch of little things to examine. If not, you can pretty much narrow your search to the carb itself and/or gasket and the intake. This is where the starting fluid sprayed around these areas come in, and you check for a change in idle speed. This is the easiest route to get the ball rolling, but there can be other factors, too. I’ll attach a “how to” on reading a vac gauge, and you can see what I mean. It can tell you a lot of stuff.

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