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1986 GM 350 Distributor Installation & Timing Info Needed

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Dave1

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Winter Springs, (Central) Florida
I just had a fresh rebuilt "M" series GM 350 installed in my 1986 GMC 3/4 ton 4WD pick up and have discovered some issues with the installation. One thing I found is the distributor was not tightened down and moved around freely so I know I need to get the engine timed. I also noticed the little vacuum advance cylinder was on the opposite side of the engine than other GM 350 trucks that I have owned.

Is it possible the mechanic could have installed the distributor 180 degrees out and still get the wiring and timing to where it will crank and run?

All I am going on here is the location of the vacuum advance cylinder on the side of the distributor. On my old 1985 GM 350 4WD truck the dist was installed so as the vacuum advance cylinder was on the passenger side of the dist & engine. On this new engine, the distributor was installed so as the vacuum advance cylinder is on the drivers side of the engine exactly opposite from my old truck.

It cranks and runs fine but has serious spark knock when you first step on the gas and it struggles a bit when trying to crank it when it is hot. I am guessing the timing is way advanced right now but I am also wondering if the dist was installed incorrectly. Is there any reason the dist would have to be installed this way such as the cam timing is off?

I susspect I will be pulling the dist, re-installing with #1 at TDCC, and re-running the plug wires.

Thanks for any feedback.

Dave
[email protected]
 
Plug wire location/distributor install doesn't matter. As long as whatever is #1 plug wire terminal has #1 plug on it.

If it runs with the distributor like it is, are you able to increase or decrease timing and make the pinging go away? Do you have access to a timing light? You need to check base timing....it just sounds like that is too high.

Typically, if the distributor is "a tooth off" it will start and run, but you can't get much advance out of it (usually not enough to get timing "perfect") because the vacuum cannister hits something.
 
From what I understand the normal installation of the distributor is such that the vacuum advance cylinder will be on the passenger side of the engine and when facing the front of the engine, the #1 terminal on the dist cap will be right behind the carb just to the right of center when facing the front of the engine.

On my engine the dist has been installed so the vac advance is on the drivers side of the engine or approx 180 degrees out. This would put the #1 terminal in the cap over next to the firewall. They run the plug wires starting at the terminal right behind the carb and just right of center and running that wire to #1 and so on around the cap.

It's kind of hard to explain and I am not sure I am explaining it correctly but hopefully you get the picture of what I have. It does crank and run OK, just a little too far advanced . I do not have a timing light but I know it needs to be timed whether the dist is installed correctly or not. I just need to know if I should pull the dist and rotate it around. If so, I will have to re-run the plug wires then time it.

If it is in 180 degrees out, is there any practical reason they would have had to do that? Was it just a rookie mistake? Does it matter if the dist is in 180 degrees out?

Dave
 
Position of the distributor vacuum advance doesn't matter. it is just preference on where you want it. As far as the plug wires on the distributor, they can be in any location on the distributor cap as long as the rotor is pointing at the #1 terminal/plug wire on the distribtor cap when installed.

As far as your timing is does sound a little off. I would more than likely go ahead and play with it a little while running to see if you can get it right and if not pull it and make sure you have everything the way you want it ran within the engine compartment. Just make sure when you pull the distributor that your #1 cylinder is 8/10* BTDC. I have always went with 8 on my engines but have started running around 10 or so with the fuel injection.
 
Forgive me if I am being redundant with my questions about this distributor installation and location thing but I am having difficulty understanding what is being said.

When looking at the diagrams for a GM 350 it clearly shows the dist on the engine with the #1 terminal on the dist cap being right behind the carb and just right of center when facing the front of the engine. If the dist was installed 180 out, that would put that #1 terminal on the back side of the cap next to the firewall. Are you saying that would be OK as long as I run the plug wire from that same terminal to the #1 cylinder?

OR

Are you saying that any terminal on the dist cap could be the #1 terminal and run plugs wires in the proper order to the corresponding cylinders?

Presently on my engine, because the vacuum advance cylinder on the side of the distributor is positioned on the drivers side of the engine instead of the passenger side, it appears the distributor has been installed approx 180 degrees out from what the diagrams indicate.

The plug wire from the #1 cylinder has been run to the first terminal right behind the carb just right of center. Even though the dist has apparently been installed 180 out, they still used the first terminal behind the carb as the #1 terminal and run all other plug wires around the cap in order as normal.

I guess what is throwing me for a loop here is I am thinking that if the dist has been rotated around and is 180 or so out it seems the #1 terminal would be on the back side of the dist cap next to the firewall and the #1 plug wire should be run to and on that terminal and not on any other terminal on the front. Can the dist be installed in any position and any terminal used as the #1 terminal? Does that make sense? Am I off base here? If so, reel me in.

Sorry for the confusion.

Dave
[email protected]
 
Dave1 said:
Can the dist be installed in any position and any terminal used as the #1 terminal?
Click to expand...

Yes. That is what I was trying to say before. Not sure I made sense on the subject. As long as the rotor button is pointing to the cap where you have the #1 plug wire running it will run correctly.
 
Pull your plugs, stick your finger over the #1 plug hole and have a friend bump the starter until you feel pressure on your finger, then rotate the crank until the line on your balancer lines up with your timing pointer. Pull the distributor cap and distributor. Stick the distibutor back in with the rotor pointed at the terminal that goes to #1. It would bug me too if mine was in 180 out.
 
you dont need to pull the dist.

You dont need to restab the dist. belive me its a pain.
ok first dont worry about the pics in a book. when you stab a dist you put the number 1 cilinder at t.d.c. when you drop the dist in its gear locks in with the the cam gear it doesn't mater where. wherever the rotor is pointed is the number 1 cilinder and you hook up your wires acordingly. if you are having problems with a knock get a timing light, disconct the vacumm advance, drive it with the vacumm advance disconcted. if it still knocks turn the timing back a cupple of degrees, repeat this untill your knock goes away. then plug in you vac advance and take it for a ride if your knock comes back you probly need a vacumm advace.
now if you are really worried about the placement of the vacumm advce you can turn you the number 1 cilinder to t.d.c., unhook the wires from the cap, remove the dist cap. then loosen the dist and turn it to where the vac adv faces where you want. (notice that you can spin the housing and the rotor doesnt move the rotor is locked in with the cam which is why it doesnt mater were #1 is on the cap as long as your firing order is right(18436572). now put the cap back on and reinstall the wires starting with the point the rotor is at as #1. then set your timing.
hope this clears it up for you a little if not feel free to email me and i will be glad to walk you thought it.

"if it and broke dont fix it"
 
This distributor thing doesn't sound too tough. I may try to tackle it one afternoon this week.

I drove it this weekend to the hunt camp and back and noticed a substantial oil leak. Oil had blown around under the rear of the engine and transmission and was dripping from all over. I am going to try and pinpoint that leak before I do the distributor/timing problem. The garage replaced the oil pressure sending unit so I wouldn't think that would be leaking. I just hope it is not the rear engine oil seal that is leaking. They put a new rear seal in the new engine before installing it, hope they got the right seal in there like it supposed to go.

Where else could the oil leak on the rear of the engine be coming from? Oil pressure sending unit, intake gasket leak??? Is there a gasket on the base of the distributor????? The leak is on the rear of the engine but I can't tell if it is on the top or bottom. I will spray it all down with parts cleaner, let it dry, then crank it up and see if I can find it. It is hard to see all back there. I sure hope it is NOT coming from inside the bell housing cover.

Dave
 
Yesterday afternoon I crawled up under the hood again and looked for the timing pointer and timing mark on the crankshaft balancer. I saw a mark/groove on the CS balancer OK but I have a question about the timing pointer(s).

On the top and in the middle of my timing chain cover there is a bracket that extends out over the CS balancer that has four little timing pointers on it. I could not see any markings on it just the four small pointers. To the right (on the drivers side of the timing cover) there a small tube about 2"-3" long 1/4 ID that extends down toward the CS balancer. I am not sure what this is and whether it is used for timing purposes or not.

Can anyone explain which I should use to determine TDC and use to time the engine?

Thanks for any feedback.

Dave
[email protected]
 
heres the deal...

The"tube" thing is used by GM at the factory with a special timing probe to time it at the factory..a normal timing light is aimed at the bracket thing with the "prongs" or pointer looking things on it--it should be marked with TDC(top dead center)-and 2,4,8,and 12 degrees ,"A" for after TDC,"B" for before TDC..some years are marked different,but you time them the same way...

I've had to time a few motors by "ear"--my 86 305 is one--it came from a van,I'm not sure if the "pointer" was lost by a previous mechanic,or if it never even had one!--none there at all!...and its possible to bolt the pointer from the "wrong" year or CID motor on, and you can set the timing to "spec" until your blue in the face,but it wont be right..there are many different "pointers",matched to the balancer size..I just advance mine until it pings slightly and back it off until it just goes away..

If you look real close,there is a scribe or chisel mark on the distributor base,and the intake manifold that should align when the distributor is installed correctly..(might have to scrub them clean to see them--IF you can get a good look at it!)--I noticed them for the first time in my van--easy to see from the drivers seat with the "doghouse"off... :crazy:
 
I cannot see any markings on those four pointers. Which pointer is the one for each setting you mentioned? Do they count from left to right or right to left?

Which way do you turn the dist to advance the timing and retard the timing, clockwise or counter clockwise?

I will look at the dist base and see if there is any marks that can be lined up. With all of the plug wires, fuel lines, throttle and cruise control cables, vacuum lines, etc. it is tough to see back there.

Last night I played with the timing a little bit and when I turned the dist to the left (counter clockwise) the engine shut off.

I am very worried about the oil leak. I made another post about the oil leak i.e. found oil seeping out from behind the flywheel cover right beside the recess for the oil filter. I am afraid it is the rear main seal leaking. That will be a major affair.

Dave
 
..............................

Turning the distributor clockwise retards it,counter-clockwise advances it..

It will likely be nearly impossible to see those marks on the distributor and intake in a K5 or pickup--if the vacuum advance is on the passenger side,and you have the wires arranged as they belong as shown in the chitons book,it should be fine..

I know all the other posters say it does not matter which one you use for #1 cyl,or where the vaccuum advace is,but I feel GM installed it that way for a reason..I'm unsure about the "newer" motors,but small blocks in the 60's would have rocker arm and pushrod failures if the disrtibutor was not installed in the factory position,because it could block the oil passage around the base of it that goes to the drivers side head..maybe it does not matter,but I would prefer to have it in the proper place if it were my truck!...you need a good tune up giude that has pictures of the timimg mark pointers--its difficult to explain in words...usually the deepest "notch" is TDC--it should have numbers stamped into it..

As for the oil leak,I can only say to keep looking--there is a "freeze plug" in the rear of the block behind the flywheel that covers the rear of the camshaft bearing--that can leak--also two or three threaded plugs right in the same area,but they rarely if ever give trouble unless they were removed and not put back with sealer--usually its something stupid leaking that LOOKS like its coming from the rear main--havent seen too many 1 peice rear mains leak,unless they put the seal in backwards...at least its a bit easier to change than the old 2 peice ones if it does turn out to be the rear main seal... :blush: gooid luck! :crazy:
 
Even though the engine cranks up and seems to run OK (except for the spark knock when stepping on the gas), I would really prefer the dist be removed and re-installed to the correct position. As we have discussed my dist appears to be 180 out because the vac advance is on the drivers side of the engine. I intend to correct this when I have time to do it. My only concern about this is, is there a reason they have it installed this way??? Hopefully there are no internal problems with the cam or crankshaft or dist gear timing that would cause a need for the dist to be turned around like that.

Regarding the oil leak, I guess the next step is to remove the flywheel cover and see if I can pinpoint the source of the leak back there. Because of what the mechanic has done on the rest of this engine swap job, it would not surprise me to find the rear main seal in backwards. To replace it I assume the transfer case and transmission have to be removed.

Dave
 
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