Setting timing on 18GK engine

[wkilleffer]

Hello,

In the last few days, we've had some hot, humid weather, and my 74 MGB's temp gauge is reading just on the other side of the N. You can see the whole letter when driving 55-65 mph, and the top of the right side of the N is covered when driving slower. I'm using a 190deg thermostat.

I'm trying to get the car to run cooler and better. This has involved valve clearance and carb adjustments, and now ignition check up. Probably should have saved the carbs for last. I changed and set the points gap and spark plug gap, and decided to check the timing.

In the Haynes book, an 18GK engine is supposed to be at 10deg BTC at 600 rpm, which looks like the third tooth on the engine timing mark. With the vac advance disconnected and the manifold tap plugged, the engine was running at roughly 600 rpm. The timing mark was down between the first and second tooth. So, I turned the dizzy to move the groove up even with the third tooth, and the idle slowed down. I adjusted it up, and the timing looked to be in the same place.

After putting everything back to rights and reconnecting the vac advance, it looked like the timing mark dropped down to between the first and second tooth, and a throttle rev sends it up to maybe around the fourth tooth.

So, I guess my questions are did I do this right, and could the possibly overadvanced state of the engine be responsible for the engine's temp seeming a bit high?

Any advice and suggestions would be appreciated.

Thank you,

 

[Tom_Fisher]

Hi, William:

I'm new here - so bear with me. First of all, are you absolutely sure about the 10deg advance? The reason I'm asking is that on my 69 MGB, the advance is supposed to be 20 deg.

The other thing is that I would't get "locked in" on the 600 rpm idle (even though that's what the manual specifies). I keep mine about 1000 rpm. This makes for a more even idle and promotes better oil pressure.

 

[tony barnhill]

William - I'm away from home & my manuals so I'll leave the timing specifics to other guys...however, on the ooling issue: have you determined if its the guage reading incorrectly? If guage is correct, is radiator clean & holding pressure? If so, are your hoses in good shape (i.e., not collapsing internally)? If so, when was last time you back-flushed engine? &, lastly, how old is water pump?

 

[wkilleffer]

[ QUOTE ]
Hi, William:

I'm new here - so bear with me. First of all, are you absolutely sure about the 10deg advance? The reason I'm asking is that on my 69 MGB, the advance is supposed to be 20 deg.

The other thing is that I would't get "locked in" on the 600 rpm idle (even though that's what the manual specifies). I keep mine about 1000 rpm. This makes for a more even idle and promotes better oil pressure.

[/ QUOTE ]

Hello Tom,

Welcome to the forums, and thank you for your response.

As far as being sure about the 10deg advance, I'm not. I might have done it wrong. In the Haynes book, their are two numbers for timing, one for high compression and one for low. I think I used the one for high compression, but American spec engines might have been low.

As far as idle speed goes, I typically idle mine just under 1000 rpm. Sometimes it goes lower depending on engine temperature. The reason I was using 600 is because that's what the Haynes book called for when checking and setting timing dynamically using a strobe light.

Sounds like I'm on the right track, but need to make sure I've done the job correctly.

Thank you,
Bill

 

[wkilleffer]

[ QUOTE ]
William - I'm away from home & my manuals so I'll leave the timing specifics to other guys...however, on the ooling issue: have you determined if its the guage reading incorrectly? If guage is correct, is radiator clean & holding pressure? If so, are your hoses in good shape (i.e., not collapsing internally)? If so, when was last time you back-flushed engine? &, lastly, how old is water pump?

[/ QUOTE ]

Hello Tony,

You may remember my earlier posts about getting the gauges to work right and finding the voltage stabilizer. I got that taken care of, so I know the fuel and temp gauges are working the way they're supposed to even if they're not pinpoint accurate. Before I found and connected the stabilizer, the fuel gauge read high and the temp gauge went all the way to hot. I'd be willing to consider that it could be reading hot, but don't know how to test it.

I used foaming a/c fin cleaner on the radiator, but it looks like it could have a small leak. The coolant level isn't down, but there's residue on the back of the right side of the radiator like it is leaking. Can these radiators be boiled out and patched? A new one's almost $200.

All hoses are new within the past three months, as is the thermostat. As far as backflushing the system, I ran water through everything, and ran it through the heater core backwards. Everything *appeared* to be clean, and the none of the fluids that came out seemed to have a noticeable amount of dirt in them. But this is all based on appearances to a semi-untrained eye.

The water pump's about five years old. It's aluminum, and ordered from Vicky-Brit before I knew better. I still have the old pump, but it leaks.

Thank you,

 

[Bret]

Assuming an original stock equipped 18GK engine – according to my Haynes manual “static” timing should be 10 degrees BTDC. But the “Dynamic” should actually be 14degs at 600 RPMs.

For clarification:
“Static timing” is a manual procedure what you’d do if you tore the engine down and/or if you completely lost the timing setup. Basically rotating the engine manually until it reaches the 10deg setting above.

“Dynamic timing” is what most of us think of when we mention setting the timing using a (strobe) timing light.

FYI Timing & Idle speed will interact with one another and might necessitate repeat adjustments to dial things in properly.

 

[tony barnhill]

William - now I remember...sorry I dredged up all the old stuff again.

Yes, I have radiators boiled & repaired all the time....I've even heard of guys repairing the original water pumps though I don't know how they did it.

 

[wkilleffer]

The Haynes manual says an 18GK engine high compression should be 11deg BTDC and a low compression should be 14deg BTDC, both at 600rpm. Frankly, that's kind of hard to measure with the timing marks being what they are. I checked it at lunch time with and inductive light, and it could be anywhere in that range. The owner's manual has another spec, can't remember it except for 1500 rpm.

Another thing that bothers me is that the timing mark doesn't look like it moves much when I rev the engine. The books all say it should move counter-clockwise, which to me says it's moving toward the passenger side of the car. It does some of that when the vac advance is connected. Maybe I'm not revving it enough, but is it possible that the centrifugal advance is stuck?

 

[Bret]

[ QUOTE ]

The Haynes manual says an 18GK engine high compression should be 11deg BTDC and a low compression should be 14deg BTDC, both at 600rpm. Frankly, that's kind of hard to measure with the timing marks being what they are. I checked it at lunch time with and inductive light, and it could be anywhere in that range. The owner's manual has another spec, can't remember it except for 1500 rpm.


[/ QUOTE ]

Hmmm? My Haynes manual (Chapter 4 Ignition System p95) says the 14deg BTDC is for High compression and 12degs for Low compression.

The only B’s that call out for setting their timing @ 1500rpms are the later 18V

[ QUOTE ]

Another thing that bothers me is that the timing mark doesn't look like it moves much when I rev the engine. The books all say it should move counter-clockwise, which to me says it's moving toward the passenger side of the car. It does some of that when the vac advance is connected. Maybe I'm not revving it enough, but is it possible that the centrifugal advance is stuck?


[/ QUOTE ]

I’d follow that thought about the advance being stuck & pop off the rotor cap and check if there is something blocking and/or keeping it from advancing. Early on after I’d installed a Petronix ignition kit in my 78B’s 45DE4 I noticed it’d fall off at higher RPMs. Turned out that the service loop of the wiring in the dizzy was actually too tight & keeping the advance from functioning properly. You could have something in there doing the same thing.

 

[piman]

Hello William,

yes you should see a noticeable movement of timing as you increase the engine speed. The reason an idle speed is specified when timing is that the timing alters (Should alter it sounds like in your case) as the engine speeds up.
Another poster mentioned 1000 idle speed, if you set the timing at that speed it will actually be retarded.
Certainly I would check that the mechanical advance has not seized as this will have a very detrimental effect on your running.
In my opinion, you should be able to get a smooth idle at 650 to 700 rpm. A higher idle tends to make gear selection from rest more difficult.

Alec

 

[wkilleffer]

[quote
Hmmm? My Haynes manual (Chapter 4 Ignition System p95) says the 14deg BTDC is for High compression and 12degs for Low compression.

[/ QUOTE ]

This is what happens when I don't have the book in front me. But you knew what I was talking about /ubbthreads/images/graemlins/grin.gif
But I don't see how there could be that much difference between the two the way the timing marks are set up.

[ QUOTE ]
The only B’s that call out for setting their timing @ 1500rpms are the later 18V

[/ QUOTE ]

That's strange, cause I could have sworn my owners manual was for a '73. I ordered a '74, but that's another story.

[ QUOTE ]

I’d follow that thought about the advance being stuck & pop off the rotor cap and check if there is something blocking and/or keeping it from advancing. Early on after I’d installed a Petronix ignition kit in my 78B’s 45DE4 I noticed it’d fall off at higher RPMs. Turned out that the service loop of the wiring in the dizzy was actually too tight & keeping the advance from functioning properly. You could have something in there doing the same thing.

[/ QUOTE ]

Now, I can think of three wires inside the dizzy, one goes to the terminal on the side, the other is for the condensor, and the last attaches to the plate somehow. That one could be the problem. Is there some kind of wiggle test for this? The vac advance works.

 

[Bret]

[ QUOTE ]
[ QUOTE ]
The only B’s that call out for setting their timing @ 1500rpms are the later 18V

[/ QUOTE ]

That's strange, cause I could have sworn my owners manual was for a '73. I ordered a '74, but that's another story.


[/ QUOTE ]
Wasn’t trying to say that you where wrong. Only that it is my understanding that the 18V 797 AE engines onward call for a timing setting @ 1500 RPMs. 13deg for 75-76, 10degs for 76 & on.

While I don’t know for sure - it could be that the settings for 74 you are thinking about might be for a 74.5 that employed the same single Zenith Stromberg carb setup as the later Rubber Bumper Bs did? Seems logical to me that they'd have similar timing settings as the 75-76 B's did.

But looking at the Haynes it shows earlier B's (pre-74.5') timing set at 1000rpms.

[ QUOTE ]
Now, I can think of three wires inside the dizzy, one goes to the terminal on the side, the other is for the condensor, and the last attaches to the plate somehow. That one could be the problem. Is there some kind of wiggle test for this? The vac advance works.

[/ QUOTE ]
Not sure about points & condenser dizzys – but in my 45DE4 CEI that I’d installed the Pertronix ignition kit in, I didn’t give enough service loop in the wiring inside the rotor cap. This restricted movement causing the timing not to advance with the RPMs the way it should. Likewise too much service loop can be just as restrictive and might bind restricting movement.

 

[wkilleffer]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
The only B’s that call out for setting their timing @ 1500rpms are the later 18V

[/ QUOTE ]

That's strange, cause I could have sworn my owners manual was for a '73. I ordered a '74, but that's another story.


[/ QUOTE ]
[ QUOTE ]
Wasn’t trying to say that you where wrong. Only that it is my understanding that the 18V 797 AE engines onward call for a timing setting @ 1500 RPMs. 13deg for 75-76, 10degs for 76 & on.

While I don’t know for sure - it could be that the settings for 74 you are thinking about might be for a 74.5 that employed the same single Zenith Stromberg carb setup as the later Rubber Bumper Bs did? Seems logical to me that they'd have similar timing settings as the 75-76 B's did.

But looking at the Haynes it shows earlier B's (pre-74.5') timing set at 1000rpms.

[/ QUOTE ]

Ok, to satisfy curiosity, I looked it up in my Bentley, and it says for an 18GK (which is 1971-72, I thought they were 72 only), the timing is 15deg BTDC at 1500 rpm. We all know the Bentley's the be-all-end-all authority /ubbthreads/images/graemlins/jester.gif The engine has to turn fast, but at least I'll know exactly where to aim the groove.

[ QUOTE ]

Not sure about points & condenser dizzys – but in my 45DE4 CEI that I’d installed the Pertronix ignition kit in, I didn’t give enough service loop in the wiring inside the rotor cap. This restricted movement causing the timing not to advance with the RPMs the way it should. Likewise too much service loop can be just as restrictive and might bind restricting movement.

[/ QUOTE ]

I forgot you had a different setup. Now, I took mine apart, and everything was coated in crud. The weights were frozen. It's a wonder it worked at all. I've cleaned it and am preparing to put it back in.

Now, what effect should the vac advance have on everything once it's hooked up? Last time, it advanced everything from around the 10-13 BTDC to close to the TDC mark. Not sure how yours works, but that seems to be alot. The Bently says something about setting the vac advance micrometer to the midway point, but I don't know where that is.

Thank you for your assistance so far. It's been very helpful. /ubbthreads/images/graemlins/yesnod.gif

 

[wkilleffer]

I'm finally done. It involved taking the dizzy out and apart. Everything inside was gummed up and frozen. I gave it all a good clean and lube. Set the timing at about 14BTDC at 600 rpm, and the final idle speed at around 800 rpm.

Car runs like a different animal now. Lots of pep, smooth up to 3300 (as high as I could get away with on the test drive), feels like it could drive across the country.

Thanks to everyone who gave advice and time.

 

[jlaird]

Vac advance micrometer is on the other end from where you hook the vac line to the dizzy.