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Thread: Engine swap timing issue G54B

  1. #1

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    Engine swap timing issue G54B

    Hello everyone, new to the site! I was hoping for some guidance from all of you fine folks. I have a '79 D50 4X4 with the G54B. A few weeks ago someone (not saying it was me, but it was probably me) started the truck with no oil in it and blew up all of the rings. I was able to source a free engine from a local fellow that said his dad had rebuilt it but it had no oil pressure. So I removed the engine from the truck and swapped over the oil pump and replaced all the gaskets I could. I had to use some other stuff from the old truck like the Weber carb, oil pan (free engine came from a Plymouth Arrow and the pan isn't compatible with the four wheel drive) and the distributor. Now the problem I'm having is when I set up my distributor with the vacuum advance hose connected to the non-ported port like it was on the old engine I can get it timed to 7 BTDC, but if I hit the throttle it drops to around 10-12 ATDC before advancing and has no power. If I set it up with out the vacuum advance not hooked up the closest I can get in timing is 17 BTDC or 2 ATDC just by moving it one tooth on the cam gear. Is it fine to run at 17 if I have the advance hooked up to the ported vacuum?

  2. #2

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    Base timing should be set with the vacuum advance disconnected. Remove the hose and plug it so there is no vacuum leak. Then set your timing to 7BTDC and reconnect the vacuum.
    When running manifold vacuum to the distributor you will get full vacuum advance at idle. I don't know what the pull from the vacuum mechanism is, but i suspect when you retard your timing all the way to get 17BTDC, your actual base timing is somewhere around 5ATDC.
    There are two brass ports on the side of the Weber, one ported and one manifold. All you have to do is take the plug out of the ported side, swap the hose, and put the plug in the manifold side. I wanted to be a believer in running full manifold vacuum, but I found that the biggest drawback is a large loss in engine braking performance. I tow with my truck with some frequency and the service brakes aren't that big!

  3. #3

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    Quote Originally Posted by Giovanni89 View Post
    Base timing should be set with the vacuum advance disconnected. Remove the hose and plug it so there is no vacuum leak. Then set your timing to 7BTDC and reconnect the vacuum.
    When running manifold vacuum to the distributor you will get full vacuum advance at idle. I don't know what the pull from the vacuum mechanism is, but i suspect when you retard your timing all the way to get 17BTDC, your actual base timing is somewhere around 5ATDC.
    There are two brass ports on the side of the Weber, one ported and one manifold. All you have to do is take the plug out of the ported side, swap the hose, and put the plug in the manifold side. I wanted to be a believer in running full manifold vacuum, but I found that the biggest drawback is a large loss in engine braking performance. I tow with my truck with some frequency and the service brakes aren't that big!
    Thats the problem is that if I try and set it without the advance hooked up I can't get close to the 7 BTDC. I can only get 17 BTDC or 2 ATDC

  4. #4

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    Quote Originally Posted by scottadams14 View Post
    Thats the problem is that if I try and set it without the advance hooked up I can't get close to the 7 BTDC. I can only get 17 BTDC or 2 ATDC
    Ahh, I misunderstood. Sorry. Have you checked the cam timing? Not with a degree wheel, but made sure the timing marks are lined up. I believe when it is at TDC on compression on cylinder 1, the pin the aligns the cam gear with the camshaft should be at the 12 'o clock position. Make sure to check this after rotating the engine by the crank pulley bolt clockwise.
    Also, check that the timing mark on the crank pulley has not moved. Put a wooden down or similar in the spark plug hole and spin the engine slowly by hand until it reaches it reaches the point where it is sticking out the most that it can. Your crank pulley timing mark should be close to TDC When the rubber between the inner and outer portions of the harmonic balancer gets old, the outer portion can slip. This will make your timing mark useless. Buddy of mine bought a municipal f350 with central hydraulics and a dump bed with a "blown engine" for $300. It had a brand new distributor in it. Once I discovered the timing mark had spun about 90 deg we timed it with a vacuum gauge and and ran like new. The new distributor was stabbed in a few cylinders off because the timing mark had moved.

  5. #5

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    a wooden *dowel* in the spark plug hole

  6. #6

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    Quote Originally Posted by Giovanni89 View Post
    Ahh, I misunderstood. Sorry. Have you checked the cam timing? Not with a degree wheel, but made sure the timing marks are lined up. I believe when it is at TDC on compression on cylinder 1, the pin the aligns the cam gear with the camshaft should be at the 12 'o clock position. Make sure to check this after rotating the engine by the crank pulley bolt clockwise.
    Also, check that the timing mark on the crank pulley has not moved. Put a wooden down or similar in the spark plug hole and spin the engine slowly by hand until it reaches it reaches the point where it is sticking out the most that it can. Your crank pulley timing mark should be close to TDC When the rubber between the inner and outer portions of the harmonic balancer gets old, the outer portion can slip. This will make your timing mark useless. Buddy of mine bought a municipal f350 with central hydraulics and a dump bed with a "blown engine" for $300. It had a brand new distributor in it. Once I discovered the timing mark had spun about 90 deg we timed it with a vacuum gauge and and ran like new. The new distributor was stabbed in a few cylinders off because the timing mark had moved.
    Thats a good idea that I haven't tried yet. To be honest I'm a little scared that is the problem. I'm at work today, but I will examine that tomorrow and report back. Thanks again for all of your input Giovanni!

  7. #7

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    No problem. If it is one tooth off, it can be done with the front timing cover and oil pan still on. If it's just the mark has moved, file another notch in once you find TDC, until you get another harmonic balancer.
    Giovanni

  8. #8

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    so this is TDC on the compression stroke. I don't understand how it could be this far off and still run. Whoever put it together must have just winged it. Click image for larger version. 

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  9. #9

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    I feel like it should move one tooth clockwise. I looked at the old engine and the hole on the cam gear holder was right at 12'o'clock.

  10. #10

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    I can't tell from the photo. You can set up a pointer on any other sprocket tooth, and rotate the engine until it lines up on the next sprocket tooth. The cam gear dowel should be right at 12 o clock then. That will simulate the change before going through the hassle. If you move it over one tooth, just be sure to spin it over by hand a few times.
    You can take a long prybar and tape a rag around the end. Shove it down the front cover and wedge between the chain at the tensioner and the right side of the front cover. Try and pull up on the chain as you're doing this to get all the slack up top.
    Make a witness mark on the chain and cam gear ( I used the silver link ) unbolt the cam sprocket and you should be able to move it over one tooth and bolt it back on. I did this last year. I replaced the head with a new fully built mechanical lifter head that ended up leaking out of the rear freeze plug from poor machining. I sent that back and built a replacement with a new parts from Engine Machine Service out of Ohio. I figured it was worth trying before removing the oil pan, fan, water pump, alternator, power steering pump, and front cover again. Worked for me, just don't let that tensioner pop out. Of course if it's off one tooth you may want to take it all apart and check everything else out to make sure nothing else is gaffed.
    Giovanni

  11. #11

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    UPDATE: I used my borescope (my most favorite tool. seriously, buy one.) and found true TDC which was within half a degree on the harmonic balancer. Then I used the technique outlined by geezer in this awesome post and fiddled with the leads and their position in the distributor cap. I was able to get the base timing at 7 BTDC with the vacuum advance disconnected.

    Now my question is, do I use the ported vacuum or the manifold vacuum? I was also reading that the Weber's are crazy with how much vacuum they pull, but mine is seems to run fine with the ported line.

  12. #12

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    Awesome! Glad you got her running good. I personally would leave it on ported vacuum. I tried switching mine to manifold vacuum, and while it idled and transitioned to off idle better, I lost a great deal of my engine braking. I really noticed it trying to stop on a downhill interstate highway off ramp. Enough so that I pulled into the next parking lot I passed and switched it back.
    It's easy enough to try out. After the throttle plates are open a bit both vacuum signals are the same. You're only going to notice the difference at closed to near closed throttle. Other people may have different experiences, but that's mine.
    Giovanni

  13. #13

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    Quote Originally Posted by scottadams14 View Post
    UPDATE: I used my borescope (my most favorite tool. seriously, buy one.) and found true TDC which was within half a degree on the harmonic balancer. Then I used the technique outlined by geezer in this awesome post and fiddled with the leads and their position in the distributor cap. I was able to get the base timing at 7 BTDC with the vacuum advance disconnected.

    Now my question is, do I use the ported vacuum or the manifold vacuum? I was also reading that the Weber's are crazy with how much vacuum they pull, but mine is seems to run fine with the ported line.
    How much difference has the ignition re-tune made? It's also interesting to note that TDC was incorrect when you were setting the timing (one of the reasons why my observations of tuning 'by the book' isn't always optimal) Ignition tune should be done with the vac advance connected but there's always a chance that the increased vacuum generated by the Weber would fudge the advance (it has to be connected if you're aiming for a dynamic tune). It's probably worth experimenting with...
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  14. #14

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    The biggest difference is that I can drive uphill in 2nd or even 3rd gear! Before I would have to keep it in 1st and burned a lot of oil to what I assume was blowby pressure forcing oil into the cylinders. Now it drives like the old engine that I pulled. I did notice that when I didn't have the advance hooked up and the timing was at a static 17 BTDC the engine felt more responsive and would pull quicker uphill, which I would assume the manifold pressure would make the engine perform the same way. I'm going to swap the line before I head to work and see if its better.

    Thanks again for all of your help guys! This truck is my daily driver and i'm happy to have it back on the road.

    p.s. I would like to know if anyone on this forum is close to my elevation with the Weber 32/36 and know what kind of jetting they're using. I'm at 4,200 ft.

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