MGB Ignition timing issues....I'm getting confused!

[Jagguy]

OK, I've been messing around with this issue long enough for me to get completely confused!


I bought a 67 MGB a couple months ago. Pretty nice driver but has a nagging running hot issue.
At first I figured it was a cooling system problem but after replacing the thermostat and having the radiator rodded and the block flushed it still runs hot.
Hot meaning after 30 minutes driving the gauge is about pegged..
Oh, and I do have an IR thermometer and have checked the accuracy of the gauge.


So I check the timing. The marks are at 6 o'clock on the timing cover.
The timing mark on the pulley idling at 750 rpm with the vacuum advance line plugged is at about 4 o'clock using a timing light.
Humm...


I turn the dizzy clockwise to set the timing and it barely runs. Not really driveable.


I check for tdc with the #1 piston at the top of the stroke and the marks on the pulley line up with the marks at 6 o'clock.


I turn the dizzy back to where it was and its running well again but hot.


I'm starting to get confused.


Turning the dizzy clockwise advances the timing right?
With the timing mark at 4 o'clock it's retarded right?


When I turn the dizzy clockwise the rpm goes down! Shouldn't it increase?


One thing, it has a Pertronix unit on it. I'm not a real fan of those. I got a set of points and a condenser to check for any improvement but I also need the low tension lead adapter so I have that coming before I can try it with points.


I need to replace the front seal so I will be able to check for a cam-timing problem. Never know with a 50 year old car...


Does any of this make any sense? I would like to drive this for longer than 30 minutes!


Thanks for your time and your thoughts.

 

[Rut]

I’m guessing that the engine was rebuilt at some time? They may have the timing chain off by a tooth or so giving you the symptoms you describe or the dizzy may have the wrong springs/weights in it messing with your timing. These are just wags on my part, but it’s something I would check.
Good luck, Rut

 

[DrEntropy]

With the 18 GB engine (assuming yours is original), advance should only be around 10*~13* BTDC. If the notch on the crank pulley is set to somewhere near four O'clock, that is waay too advanced! With a Pertronics iggy you can't static time it without taking the chance of burning the unit out, either. So, it should be timed running and the pulley notch should be no further than the second small "tooth" past TDC on the oil pan toothed guide (10* BTDC). And, yes, going clockwise with the dizzy advances timing. Small
increments make a big change.

Plugs correct? RN-9Y Champions are the "standard" for the 18 GB series. Gapped at 0.028".

You are right to suspect cam timing, but getting that crank pulley off in that chassis presents a challenge. The steering rack is in the way, engine must be raised off the mounts, the interference with the firewall by the gearbox is a consideration, too. Once begun, you may as well consider replacing the motor mounts if they look at all aged.

Good luck and report back! And AFAIC the change to a points iggy is a good thing. :thumbsup:

 

[Jagguy]

Thank you for your reply DrEntropy. And you touched on some of my confusion.
With the notch on the pulley at 4 o'clock, by turning the body of the dizzy clockwise it brings the the notch toward the 6 o'clock position...
So, if the notch is at 4 o'clock, turning the dizzy clockwise should advance it more toward the 3 o'clock?

Re: removing the pulley, the manual says I can remove the mounting bolts on the steering rack and pull it forward enough for clearance which I was planning to do...
The motor mounts were replaced last year by a British car Shop according to receipts I have and look in good shape.
This same shop installed the Pertronix iggy so I don't know what to think about them...They also rebuilt the carbs, then when I got the car the carb dampers were completely dry!
This is why I don't trust repair shops!

 

[DrEntropy]

With the notch on the pulley at 4 o'clock, by turning the body of the dizzy clockwise it brings the the notch toward the 6 o'clock position...
So, if the notch is at 4 o'clock, turning the dizzy clockwise should advance it more toward the 3 o'clock?

Now I'M confused! I'll drop the X o'clock references and go for a more 'conventional' explanation:

If you are using a timing light, and there's really no other way to time a Pertronix setup, set the dizzy at the place the car starts/runs. Start it up and witt Timing light, see where the notch in the pulley is in relation to the pointers. To be at 10*~13* BTDC, the strobe light should indicate when the #1 plug fires: The notch ideally should be ~just~ right of the second small tooth. The pointer for TDC is the first one on the left and larger than the others. Again: the #1 plug should be firing on the second of the smaller ones. To advance (move it further Before Top Dead Center) the spark, turn the dizzy clockwise (very little) until the plug is firing at the correct pointer. If it needs to go closer to TDC turn the dizzy counter-clockwise.

And be aware that the locking plate holding the distributor CAN be over-tightened and break the dizzy housing. Just snug it enough to keep it from turning after you get the timing where it should be.

And I do understand the distrust of some production shops for Brit and Euro cars. I've seen shoddy fixes on everything from MG's to Ferrari's and had to correct 'em. It was always my goal to earn the trust of our clients.

 

[Jagguy]

I'll need to get back to you with this because we are having a bit of a weather event now and can't verify my notes nor memories today but...
If I remember correctly, on my dial back timing light it runs well at about 38 degrees advanced at idle...
Moving the dizzy body counter-clockwise moves the timing mark clockwise. I adjusted it to an indicated 13 degree setting and ran very poorly.

I did note that the rotor arm is pointing at 3 o'clock (there's that o'clock thing again) when at tdc when I read it should be at 2. Seems like the drive gear is off a tooth or the cam is.
I won't get the front of the engine off until the weekend. Looking forward to getting that done.

 

[Brinkerhoff]

Just a thought... rotate the engine while its turned off so that you have the timing marks lined up at 10 degrees BTDC on the #1 compression stroke . Now check the position of the rotor in relation to the #1 post on the cap . It should be right on it. The shop manual shows a picture of the proper fitment of that drive gear. A quick check to see if your cam timing is close would be to pull off the valve cover and check the valves on #4 cylinder , they should both be open about the same amount ( due to the overlap of the cam lobes , the intake valve on #4 should be opening at 10 degrees or so ( I don't have a shop manual in front of me , so just a wag), when #1 is on its compression ( firing) stroke. The exhaust valve on #4 should be almost closed at the same point , give or take. The closer to TDC it takes for both the valves on #4 to be open the same amount , the more retarded your cam timing is ( stretched chain or off a tooth).

 

[DrEntropy]

It will be interesting to find out what's awry in there. Sounding more and more as if the cam timing is off.

 

[Jagguy]

Brinkerhoff, I appreciate your thoughts, I'll check it out when I can.
DrEntropy, I'm looking forward to seeing what's going on also.

Will update when I have something to report!

 

[Joe Schlosser]

38 degree BTDC at idle???
This seems to be very advanced. Most motors are 10-15 degrees at 1000 rpm or so. 38 degrees would be full advanced at 2-300

 

[Jagguy]

38 degree BTDC at idle???
This seems to be very advanced. Most motors are 10-15 degrees at 1000 rpm or so. 38 degrees would be full advanced at 2-300

Yes, very odd to be running timed like this with no pinging, or kicking back when started.

Anyway, I had some time yesterday.
I swapped out the ignition module for a set of points and condenser. Fired right up.
Got out the timing light and set the timing at about 15 degrees. Adjusted the idle back to 800 rpm and took it for a ride.

Runs better, and best of all with an ambient temp of 100 the engine never went over 200 deg. A real improvement.

Still the rotor points to 3 o'clock so either the cam timing is off or the drive gear is off a tooth.

So, I still need to change the front seal and still want to look at the cam chain and marks.
I had a couple hours today so I was just going to pull the radiator...
I got far enough to pull the crank bolt and the leaking seal is obvious! Looking forward to getting that fixed.

Going to spend Friday with my Grandson at the shooting range but will pull the timing cover Saturday.

Updates to follow and thanks for all the help and suggestions.

 

[DrEntropy]

Rotor position doesn't much matter as long as the #1 plug fires at the 10*~13* BTDC mark. But it may be indicative of cam timing being off.

 

[Jagguy]

Understand, but must verify the cam timing is spot on.
Thanks!

 

[Jagguy]

I had the time yesterday to finish up on R&Ring the front cover. The cam timing was correct and the chain wasn't too stretched so I just changed the seal, cleaned and painted assorted bits and put it together.
I had forgotten how simple and easy these old engines are to work on.

The primary reason I did the work discussed in this thread was because of a running hot condition that's plagued this car since I bought it a few months ago.
So in preparation for the front seal replacement I bought an aluminum radiator and fan shroud since they were on sale at Moss.
Unfortunately the fan shroud won't fit because the filler neck is in the way so I just installed the new radiator and seals.

Checked the timing at idle and set it for 13 degrees and went for a ride. Cool! The car is running cool enough to see the temp gauge move with the thermostat opening and closing staying at 180 and no more. (It was a much cooler day today than it has been)
Don't think I'll miss the shroud.

I'm thinking I had a problem with the Pertronix ign since the car wouldn't run unless the timing was way advanced. As soon as I replaced it with points and condenser I was able to time it to where to book says and have it running great.
The seal needed replacing anyway and was a good excuse to check the cam timing and chain.

Of course, after taking it on a good run today I discovered a puddle under the differential.
OK, another project.
What- me worry? I'm retired.

Thanks again for all the assistance.

-j

 

[DrEntropy]

Glad to learn you've solved the issue. And with regard to the Pertronix; it is much easier and more economical to keep a spare set of points in the glovebox than to carry a spare Pertronix unit. :wink:

Diff leak? Front seal on that is a PITA, the gasket on the back not so much. If it's the seal and the drip is slight, gear oil is cheap, so is a cookie tin. :smirk:

I was hesitant to mention the Moss aluminum radiator. I fitted one to our '65 and rigged up an auxiliary electric fan with both an over-ride switch and a thermocouple. It works well. The July ambient temp and humidity here (mid-state Gulf coast of Florida) are brutal on old cooling systems.

Pix in the "new additions" thread I just "bumped".

 

[Joe Schlosser]

Any thoughts as to why the motor would not run with the Petronix without tons of advance.
I have Pertronix on my 1275 Sprite and everything is fine at the 1275 specifications.
The Petronix system is very simple and usually bullet proof

 

[Jagguy]

Any thoughts as to why the motor would not run with the Petronix without tons of advance.
I have Pertronix on my 1275 Sprite and everything is fine at the 1275 specifications.
The Petronix system is very simple and usually bullet proof

Not a clue.
I imagine at some point I'll reinstall it and see if the problem returns.
I'm not in any rush though, I'm pretty happy with how it's running and there are a lot of other things that need attention..