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MGB Setting the timing on an MGB

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wkilleffer

wkilleffer

Jedi Knight
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I tried searching the forum before asking, and really hope I haven't asked this before...

I'm a little confused as to how to read the timing mark scale on my MGB. It's an 18GK engine, and the mark is on the passenger side of the car. Looks sort of like a comb with a few thick teeth.

Don't ask why this is confusing me, but where on that scale is the place where I should be aiming? If the spec calls for 16deg BTDC @ 1500rpm, which part of that timing scale represents that? Is it closer to the top or bottom of the scale?

As it stands right now, I've either got it way advanced or way retarded.

Hope that question makes sense.

Thank you,
-Bill
 
Bill -

You have a PM.

Mickey
 
Thanks for that Mickey. There's just one problem. My car is a Chrome bumper, 1974, with an engine # beginning with 18GK, and the timing mark is on top. No sign of the underneath one that I was able to see.

Thank you,
-Bill
 
But if my marks are set up correctly, then I need to be aiming more for the lower end of the scale.
 
No, don't have a timing gun with adjustable settings.

If my marks are set properly, my timing is as well.
 
No need for it, William. Determine TDC with #1 plug out and (iggy OFF please!) hand rotate the engine (or a fourth gear "bump" by rolling the car using the R.F. tire) while lookin' down the hole. Once you have that, mark the balance wheel and the TDC pointer. The other "fangs" should be five degrees apart, IIRC.
 
You probably have the '74 timing cover and balancer installed on your '71 GK. The top matk is TDC, each lower is 5 degrees. Set your timing at idle w/o the vac advance to 10-14 BTDC. Its gonna be WAY too retarded if yu follow factory specs, unless you've had it rebuilt with new advance springs.

Once you get the baseline right, you'll want to power tune it. Go for a quick wide open throttle load test. If its too far advanced, you'll get pinging between 2500-3000 rpms when accelerating under a load. You want to be about 2 degrees retarded from pinging.
 
JeffS said:
You probably have the '74 timing cover and balancer installed on your '71 GK. The top matk is TDC, each lower is 5 degrees. Set your timing at idle w/o the vac advance to 10-14 BTDC. Its gonna be WAY too retarded if yu follow factory specs, unless you've had it rebuilt with new advance springs.
Click to expand...

Ok, I'm not running the original dizzy. I've installed a Pertronix Flame Thrower and Flame Thrower coil. When I set the timing, I set it to 15deg BTDC at 1500 RPM. That's between the last two teeth on the marker.

My car's a mongrel for sure...

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Once you get the baseline right, you'll want to power tune it. Go for a quick wide open throttle load test. If its too far advanced, you'll get pinging between 2500-3000 rpms when accelerating under a load. You want to be about 2 degrees retarded from pinging. [/QUOTE]

I was driving up a grade today and shifting around 3500 RPM. I don't remember hearing any pings, but will have the chance to try it again soon.

Thank you,
-Bill
 
Bill, the timing specs I gave you will work for the Pertronix unit as well. The curve on that Pertronix IS NOT as listed I promise you! I've sold dozens and NEVER had one that was "as listed." In fact , the range of advance I saw from them was HUGE! Use the 10-14 BTDC at idle, w/o the vacuum attached. Right now I guarantee your timing is retarded at least 4 degrees.

Since you have NO IDEA if your TDC mark is perfectly accurate, power tuning is definitely your best option. Drive the car in 4th gear, wide open throttle from 1500-3000 rpms. Keep advancing the timing until you hear the engine ping, then retard the timing 2 degrees. You may end up with a setting of 14-17 BTDC at idle and that's perfectly fine. That's around a total timing figure of 36 degrees - perfectly safe!!!

If you can't hear any pinging no matter what you do, pop the square rubber plug out of the firewall on the passenger side - the one that's there for RHD brakes. That will transmit noise into the cabin VERY well! If you hear pinging, it most likely going to be between 2200-2600 rpms.
Good luck!
 
Bill..believe Jeff.

Jeff's an expert of MG ignition. And one of his rebuilt stock distributors is less expensive and better than one of the Pertronix (or "Eurospec") units.
 
Bill..believe Jeff.

Jeff's an expert of MG ignition. And one of his rebuilt stock distributors is less expensive and better than one of the Pertronix (or "Eurospec") units.
 
I don't doubt it. But I have to use what I've got at least until it dies. I was never able to find anything cheaper. Where are these distributors sold?

Yesterday, I checked the timing as advised and ended up advancing it two or three degrees. But I've had to postpone the test run till today.
 
Bill, I can tell you flat out that the '73-73 model year MGB distributors used the worst igniton curve that MG ever offered. They give 36-39 degrees of crank advance, which is obviously WAY too much for good performance. Hopefully your advance springs are quite fatigued as that will decrease the amount of advance you'll see above idle rpms. You can read some info in regards to my rebuilds at: www.advanceddistributors.com
jschlemmer1@comcast.net
 
Well, on top of using a Flamethrower now, my car has an 18GK engine from around 1971. Not sure what kind of effect that has on what you've told me. Can't remember the model of dizzy that was in the car when I got it. It had some problems, like all the weights being frozen and frozen vac advance mechanism. I was able to free all that up, only to find that the shaft was really wobbly which made it impossible to set the gap consistently.
 
A wobbly shaft is ~death~ to higher RPM wellness!!!

..think on it: as the RPM's build, the silly thing is thrutchin' around in there like a bean in a tin can!!!
 
Bill, I also run a '71 GK engine, as original to my B. It came with the 41339 25D distributor with 13 degrees of advance - not a bad base unit to rebuild. Better performance (in good condition) than the 41491 distributor that was original to your car, but not by a landslide.

I stand by my recommendation of 10-14 BTDC, using 14 degrees if possible with no pinging present under load. I just set my Magnette at 16 BTDC, assuming the TDC mark on the pulley is correct...

Keep in mind that there are a LOT of factors that could make your timing marks inaccurate! A stretched timing chain, worn timing chain tensioner, bent degree tabs on the timing chain cover, canted timing chain cover as it was bolted in place, improperly cut keyway on the crank or damper, or slipped ring on the harmonic damper can all lend your car to having inaccurate timing marks. I'd guess that half of all cars are off by 2 degrees or more. That's why power tuning is the ONLY wasy to set your timing accurately, unless you're deaf and can't hear pinging! Then hire a passenger - I'm sure they'd enjoy the ride!!!
:smile:
 
Hi Guys
I've been advised to throw away the timing light and use a vac gauge, timing to the highest reading.. Bad practice ?
(B series 1500 engine )
Have to say it drives OK and no sound of pinking noticeable..
If the pulley is measured it equates to 16 degrees BTDC
 
Jik said:
Hi Guys
I've been advised to throw away the timing light and use a vac gauge, timing to the highest reading.. Bad practice ?
(B series 1500 engine )
Have to say it drives OK and no sound of pinking noticeable..
If the pulley is measured it equates to 16 degrees BTDC
Click to expand...
I don't think there is a right answer to this question, whatever works and whatever you are comfortable/ experienced with. I would say, if it ain't broke don't fix it - if it is running fine, get out and drive.

PS the thread itself is from 2008. Sometimes it is easier to start a new one. Jeff Schlemmer hasn't posted in years - though he i an amazing choice if you need you distributer rebuilt or recurved

cheers
 
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