Hoping I can find someone that knows so much about slants that they can diagnose an engine noise without hearing it--I'll wait for the laughter to subside.

Anyway, 1983 Dodge B150, 120K, 2 BBL Carter, dumped the lean burn for electronic ignition and early vac. advance distributor, timing is set to spec., carb rebuilt (float level set correctly) decent but not great oil pressure at highway cruise--at least according to factory gauge. At 55-60 mph cruise, the engine sounds like every rod in it is knocking. Depress the accelerator and it quiets down under WOT acceleration, but hit passing gear and it knocks/rattles like it's going to come apart. Faint knock when holding the throttle open under no load at around 2500 rpm--I've run it with the doghouse removed, and it's definitely seems to emanate from the engine when listening under no load.

Disconnecting the vacuum advance seems to make no difference, other than the van is even a bigger dog than before.

Thanks for any ideas. I like the old girl, and I'm trying to keep her on the road. But I'm not sure I'm ready to replace the engine, if that's what it'll take. Trying to explore every other possibility before coming to that conclusion.

Does the engine have good oil pressure? (any metal in the oil filter?)
Where is the timing set with the current ignition? ( initial and total timing)
Is the EGR valve still in operation?
DD

Being a van fan and a slant six fan, I applaud you for keeping it on the road and equipped with the original engine.

Two things come to mind- "timing set to spec" and "dumped the lean burn for...early vac. advance distributor"

The base timing spec on lean-burn ignition vehicles is 16 degrees BTDC. That is fine for the lean burn system because it is designed to advance the timing assuming 16 is the base timing. However, on older vacuum advance systems base timing is set anywhere from 0 to 12 degrees BTDC depending on the application and emissions package. Additionally, the amount of timing advance provided and rate at which it is applied also varied between the original application of the distributor.

The noise you are hearing could be preignition due to the timing being too far advanced. I recommend you back the base timing down to 5-7 BTDC and see if that helps anything. If it does, I recommend you spend an afternoon mapping the timin g advancce curve on the replacement distributor. It could be you have a distributor with a timing curve for a much lighter car instead of a big heavy unaerodynamic van.

I took the time to dial in the timing on my brother's 1983 Dodge van and it has netted good performance and improved economy. It is something worth doing.

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Thanks for the quick replies, guys. It's encouraging.

Good questions, DD, but apart from saying that the EGR valve has no vacuum connection, I don't know the answers--at the moment. The oil pressure starts around 55-60 on a cold engine, but runs around 35 psi warmed up at highway cruise (according to the factory gauge anyway, so I don't know for sure, yet). I'll put a real gauge on it and find out for sure.

It's been awhile since I installed the ignition, but I suspect that I set the initial timing in the 12-16 degree BTDC range, which probably was the lean burn spec. I makes sense, now, that this may be wholly incorrect with the ignition I installed. Mapping the advance curve is a great idea, and I have a Snap On timing light with a dial that makes that fairly easy.

After I wrote this post, I took a minute to run the engine with the doghouse off in order to probe around a bit with a stethoscope. Revving it in the driveway--much to the neighbor's delight--I was able to get it knocking pretty consistently, especially after it started getting hot. I think I hear a couple different noises. At idle there's a faint 'tunt, tunt, tunt' which sounds loudest at the oil pan/block seam around cylinder 2. Then at 2500 rpm and up there's a loud and rapid 'knack-knack-knack-knack-knack' which is just about equally loud in the center of the block under the exhaust downpipe as it is at the head, it's really pretty loud and tough to pin point. The longer I run at that speed the more consistent it gets. BUT, I did notice I was able to mediate the noise when blipping the throttle slightly just above idle when the knock is fairly light. It would pause almost like something was mechanically disconnecting, then pick back up again without me moving the throttle. At a certain throttle opening I could get it to ride in and out like this.

Reed, I with you on the van thing. I really like the look of the '83, kinda reminds me of a VW bus in a way, especially the nose in profile. It's got a factory installed 727 (which I've heard is rare), so at least I'll never worry about the transmission. I took the family (and dirt bikes) to Vegas and back from Portland in mid-July last year (with no A/C, lol) and I'm wondering if that trip did some damage. It ran at 3/4 of the temp gauge a good bit of the trip for many hours at a time.

We're taking the Subaru wagon camping tomorrow instead of the van, so I've got to cull and shoehorn a boat load of gear into less than half the space I'd planned. So, it looks like diagnostics on the van will have to wait until I get back.

Mike

Has the rocker arm shaft ever been removed from the vehicle for any reason?

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I don't have any information on the history of the van. I bought it with a cracked exhaust manifold, so I replaced the single BBL carter with the Super Six intake/carb set-up and changed the ignition, but that's all I've done. I haven't had the valve cover off. Honestly, I can't even say for sure that it's the original engine, although I don't see any evidence that it's been replaced.

OK, well, if the engine is original it should be a hydraulic lifter engine. That means you should be able to eliminate lifter noise. However, you may want to check if (a) it is the original engine and (b) if the rocker shaft is installed correctly. An incorrectly installed rocker arm shaft can lead to oil starvation on the top of the motor and a noisy valvetrain. Hydraulic lifter slant sixes oil the lifters through the rocker arm shaft and down the pushrods. Low oil pressure would lead to potentially insufficiently pressurized lifter and noisy rocker arms.

However, it sounds like you have tracked the noise to the bottom end. Have you checked for an exhaust leak around the heat riser? Is it possible the shaft has worn an oblong hole through the manifold that allows a leak at steady throttle but not when you blip it? Have you tried pulling the dipstick out and seeing if the noise goes away? Check for a cracked flexplate and/or loose torque converter bolts?

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I replaced the doughnut on the headpipe when I did the manifold, so I'm sure it's not an exhaust leak. However, the engine had some serious exhaust leaks when I bought it, and I'm thinking some of the knocking noise may have been there all along. I might not have noticed it. I'd read elsewhere about loose converter bolts, cracked flex plate, etc., which is why I probed around with the stethoscope. It's definitely too far forward on the block to be either of those. The rocker arm shaft, oil delivery theory is worth a shot. It makes sense the lifters could be starving once the oil gets thin and the pressure drops. I could hear some regular valve/lifter ticking with the stethoscope, but that was a separate noise and nowhere near as loud.

Well, looks like you guys nailed it suspecting the timing was off. I retarded the timing this morning and ran it up the highway, still a faint ping/knock under light load at cruise, but basically 'fixed' it. I had to move the distributor 3/4 of the total slot range to find a point where it didn't knock. And no way would it work with the vacuum advance hooked up. I'm gonna check and see where the initial timing is at, but I'm pretty sure it's ATDC. Sounds like too much total advance in that distributor. Any idea which way you screw the vacuum can set screw to decrease advance?

There's a pretty thorough rebuild article located here for rebuilding the Disributor: http://www.slantsix.org/articles/Distri ... %20IIa.htm

I don't run with vacuum advance, so I'll leave the discussion about different cans and adjustments to those better qualified.

CJ

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Thanks for that link, definitely helps to see how it's put together before taking it apart.

I've did a site search for "recurve" etc., there's a wealth of information here, to say the least!

One thing I just read is that a properly functioning EGR system lowers combustion chamber temp by 400-500 degrees, allowing increased ignition advance for increased economy at light cruise. That's a new one. My understanding has always been block the EGR on almost any vehicle.

So I guess my next question will be: how do I rehook-up the EGR system, now that I've ditched the lean burn ignition and original carb, leaving all associated vacuum hoses, etc., laying around unconnected. Again I've got a Super Six manifold and 2BBL Carter on it now. Any link referrals much appreciated.

I owe you guys a beer and a pool lesson (lol), next time you're in Portland.

The EGR system has the potential to be beneficial and allow you to take advantage of the lower cylinder temps, but the EGR system on the slant is six is very rudimentary and is better left abandoned and disabled. Now, if you were to adapt a modern computer controlled system, it might be worth keeping.

One more think to add to your list of things to check is the accuracy of the timing mark oin the vibration damper. The timing mark is oin the outer ring of the damper which is bonded to the hub of the damped by vulcanized rubber. Vulcanized rubber does live long, but it often doesn't prosper and degrades over time. Eventually, the outer ring of the damper will slip in relation to the inner ring and the timing mark will no longer accurately indicate TDC. You can check the accuracy of the timing mark using a piston stop tool.

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Casually looking for a Clifford hyperpak intake for cheap.

If you block EGR off, the engine will not be able to carry as much timing as an OEM non-fixed distributor will provide. When the vacuum amplifier and temperature solenoid are correctly hooked up and working, it can work acceptably. Finding a functional vacuum amplifier these days can be a chore though.

EGR should only flow when the engine is up to operating temp, and it sees cruise vacuum. When you stand in the long pedal, it should close off. If it is leaking it will run poorly at idle, and at power throttle settings.
Depending on how the van is being used, blocking off can be an option, but your going to want to back the total timing way off.

Timing in manuals is given as base, or timing at idle with the vacuum can disconnected/plugged. Full in mechanical is a better way to go, Modify/replace the governor to provide the amount of advance needed to have a clean, un-labored idle with the can connected.
Just a general rule for most builds, limit mechanical advance to ~32 degrees all in. Generally speaking, your timing should be all in at your fast cruise RPM. It should hop out rather quickly when you come above your converter stall, and be all there when you are traveling down the highway, allowing the vacuum can to trim based on power setting.

There were a bunch of different governors used in the slant six, depending on the application. The factory Governor most prefer is the 9R. You'll want to have an idea what your A/F mixture is doing, and at what manifold vacuum. You can modify a governor to deliver the mechanical you need. There have been posts with photos, but I'm not sure where they are. A 9R will give you 18 degrees of mechanical advance in a perfect world. A 13 nets 26ish degrees. Likely not desirable in a van. More often than not, the governors one pulls out of a car will provide more mechanical advance than your going to find desirable.

I could do with a beer and a game of 8-ball! Didn't Bobby just get a new pool table at his shop?

CJ

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Fuel pump's in that area and capable of making that noise.
Outside chance here, but…still got the noise if you remove the engine oil dipstick?

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Okay guys, all the help has gotten me pretty close--I think. After retarding the initial timing to the point that the van would not knock at hwy cruise, but would hardly move fast enough to reach highway speed anyway. I've determined that the vacuum advance is required, at the moment at least. I removed the distributor, but without replacement springs, not much I could do. At minimum, I welded up the slots on the "15v" governor to limit the travel to almost exactly half (I checked this by marking the sweep of advancer rotation on the inside of the distributor housing before and after the change). I also reduced the total advance in the vacuum advance can I far as it would permit. I haven't thrown a timing light on anything, and don't have time until after the camping trip (fingers crossed).

I've set the initial timing by ear to the point that the van has acceptable acceleration, and doesn't knock at cruise UNLESS I tip in and out of the throttle. It knocks like hell for just a couple seconds until I return to steady state throttle. No, or minimal knock under 3/4 acceleration on the hwy, only when cracking into or out of it during cruise.

I've got the vacuum can hooked directly to the port sticking out right in the middle of the right side of the BBD. Something tells me I need something to dampen the vacuum signal, but maybe I just need a different port. This is a Super Six carb and manifold, but it's still got lots of ports, so I'm guessing it must be a later model emissions control carb.

Any ideas greatly appreciated. We're loading up the van tonight, so I guess she'll go or she'll blow. lol

I don't know who Bobby is, or where his shop is located, but I'm willing find it and bring beer, if there's a pool table inside.