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MG MGB Technical - rebuilt mgb engine timing

I have a mgb 18v engine that was just rebuilt for me.I have it installed in the car with everything attached. The last thing i did was to slide the distributor in and tighten the clamp so it will turn clockwise or anticlockwise with a little effort.I have tried a couple of diffirent methods of getting the number one piston at tdc on the compression stroke and have been told that when i do the brass tip of the rotor should be pointing towards the number one spark plug. It does point in that direction when at tdc but the groove on the pulley is pointing towards the ground not the timing marks on the timing cover. What am i doing wrong. How do i get it in time so i can get the engine at least started thanks John.
jb burrows

Assuming the engine is assembled correctly, then you have an early pulley and a late timing cover. On early engines, TDC on the cover is straight down, as is the pulley/damper notch. Later engines have both marks moved to about 10 O'clock.

The thing will start fine with the pulley notch mark straight down = 6 O'clock, and 5:30 would be 15 BTDC. Or about 7/16" before straight down would be 10 BTDC.

Set it straight down very carefully and mark the pulley to match the big TDC pointer on the cover and you are good for further use!

FRM
FR Millmore

Are you sure it's TDC on compression. Take the rocker cover off, at TDC both rockers on cylinder No1 should be rocking! i.e., have valve clearance.
Allan Reeling

Thanks for both of the tips. I removed the valve cover and have the two rockers at the front of the engine in position where i can slide a feeler at 15 thousands in freely on both of them. With number one plug removed i can see the piston at the top. The rotor is pointing down opposite from number one cylinder. About 8 o,clock and the groove in the pulley is straight down at 6 o,clock. i have marked it with a spot of red paint.
I tried starting it with the rotor pointing at number one cylinder and the pulley groove straight down at 6 o,clock and i could see the piston at number one plug hole.The engine just backfired through the exhaust. Now that i have both number one rockers rocking why isnt the rotor pointing at number one cylinder. thanks John.
jb burrows

John

It sounds like your distributor drive has been installed in the wrong orientation.

As long as you have No1 on compression and at TDC, make sure No1 plug lead is where the rotor is pointing. If that means moving it, so be it. Then move the other plug leads to their correct locations and...fire!
Dave O'Neill 2

As Dave suggests, the easy way is to move the leads to suit. If you are intent on getting the rotor to match the leads you could always pull the dissy drive and rotate it 180. It's not difficult, screw in suitable bolt and rotate slightly as you pull out. Getting it back in exactly 180 around is a little bit trial and error.
M McAndrew

Mine is that way any way, it's just the way it has been assembled. The plug lead runs aren't ideal but makes no difference to running.
Allan Reeling

With your engine rotated to TDC as confirmed by the valves and piston, connect the coil leads to the distributor and with the cap removed, rotate the distributor until you get spark across the points and note the position of your rotor. The distributor is not supposed to be capable of inserting 180 degrees out because the ends of the "key" on the bottom are slightly different thicknesses. However, it could have worn sufficiently to do so.
Rick Penland

I have turned the engine over on the under hood solenoid with my thumb on the no one plug hole until it blows my thumb off, then checked to see where the timing mark on the crank pulley is . I also put a plastic straw into the plug hole to be certain the plug was at tdc. The timing mark was pointing at 6 0clock and the brass tip on the rotor in the dist cap was pointing at 8 oclock. I tried attaching the first plug wire from where the rotor was pointing , 8 oclock to no one plug and then from there on to 3 4 and 2. Still no start.The dist is new the rotor is new the condenser is new and when i place a plug in any of the plug wires and lay it on the block then turn the engine over i can see a bright blue spark.I am baffled as to why i cant get it even close to a start. I even sprayed easy start into the carb intakes, nothing. ????? thanks John.
jb burrows

JB The locating blade on the dizzie dose not run directly across the diameter of the shaft but slightly to one side so that the dizzie can only be located one way, could there be a problem with the cam shaft being located 180 degrees out maybe its worth taking the timing cover of and checking that the timing marks are opposit each other then checking no 1 cyl is at tdc. if that was the problem the dizzie would be sparking on the exhaust stroke.
Just a thought.

PT
P.T. Tighe

Hi JB,

Just a thought sparked by PT's comments, above.

For some reason the timing marks on the cam gears are funny. They line up on #4 TDC, not on #1. The manual doesn't specifically state which piston is at TDC compression. In the attached picture it is set up for #4.

Herb

Herb Adler

Another thought sparked by PT's and Herb's comments, perhaps you could check whether the cam timing is 180 degrees out by turning over the engine and watching the movement of the valves on No.1 cylinder as it comes towards the TDC position on the (supposed) firing stroke.
The exhaust should be closed and the inlet closing after Bottom Dead Centre (or thereabouts).
Does this make sense? I need my morning coffee!

David
David Overington

Thanks for your help, i will try everything and see what happens.It may take a few days as i am disabled but i will have a go , thanks John.
jb burrows

FR Millmore Has a good point about the crank shaft pulley and timing cover being from different engines,the timing cover from a later engine and pulley from an earlier one. I think your going to have to go back to basics.
1 you have proved you have a spark. and the plug leads are on in the right order.1342 looking at my haynes manual
2 you have compression having blown the end of your thumb off.
3 have you got fuel, how old is the fuel old fuel may not ignite,
I hope this dose not come accross as patronising.
One other thing you can do is turn the distibutor clockwise a bit at a time and try and start the engine most engines are set at about 13 degrees BTDC
Let us know how you get on.

PT
P.T. Tighe

If the cam is in 180 degrees out, all you have to do is to install the distributor 180 degrees out also, to compensate for it. As long as you have the valves, on #1 cylinder at TDC, with no clearance between the rockers and valves and the rotor pointing to #1 terminal, on the distributor cap, the engine should at least fire. RAY
rjm RAY

Again, assumimg the engine is re-assembled correctly and you are at TDC,The distributor turns anti-clockwise.

with the rotor on:
#1 in the 8 o'clock position, next,
#3 at the 5 o'clock position, followed by #4 in the 2 o'clock position and finally #2 at 11 o;clock.

Is this how your spark plug leads are set up???

And obviously are you getting spark.??

cheers

Gary
79 MGB

PS I run my MGB with a Lumitronix Ign. and a Crane 270 cam. My dist cap leads are at:
Timing set at 17 BTC @ 1500 RPM

#1 = 3 o;clock
#3 = 12 o'clock
#4 = 9 o;clock
#2 = 6 o'clock

Hope this helps
gary hansen

JB. The first question is who rebuilt the engine? Does it have a warranty? If, as Fletcher suggests, the engine has been built up with the later model timing chain cover and the earlier model harmonic balancer, I should think the rebuilder should be responsible to supply the correct parts. It would be useful to have the correct parts, working together, when trying to do the initial start up.

The concept of top dead center is an interesting one because it applies to the crankshaft, not the piston. The piston will rise to the top of the cylinder bore and remain there for a number of degrees of crankshaft travel. Thus, the proper procedure for finding the true top dead center involves the use of a dial indicator and a degree wheel with the dial indicator zeroed when the piston is fully up. Then, the piston is rotated until the dial indicator shows about .001" before zero. At that point, the degree wheel is moved to zero degrees and locked in place. The crankshaft is then rotated, clockwise when viewed from the front, until the dial indicator just touches the .001" mark before the zero mark. The number of degrees difference between the two points is noted, divided in half, and this measurement is the actual top dead center of the crankshaft and the reference point for cam and ignition timing. It is, also, possible to make marks on the crankshaft pulley, then split the difference between the two marks, but this method is far less precise than using a degree wheel.

When determining the compression stroke, the intake valve is the second valve from the front. Remove the rocker arm cover, rotate the engine by hand (1 5/16" inch wrench or socket--from memory) until you watch the intake valve open (intake stroke) and close (compression stroke). There begins the ignition firing sequence where the distributor fires the spark plug just before the crankshaft hits its top dead center position to allow the fuel to be burning properly as the crankshaft passes through the top dead center position and begins its downwards movement. Fired too early, the crankshaft has to force the piston upwards against the expanding gasses. Fired too late, the expanding gasses do not develope their full thrust against the piston and efficiency is lost.

Thus, having the proper parts would be of great assistance in allowing you to determine exactly what the problem preventing your engine from starting is. And, if I had paid for a rebuilt engine, then found mismatched parts, I would have some very real concerns about the quality of the engine rebuild and how the entire engine had been set up.

Les
Les Bengtson

Now, Hopefully when you have all this timing lark sorted, be sure oil is in and filter charged with oil then fire up, or crank over engine fast without firing to get an oil pressure reading on the oil pressure guage, then fire up and run for good while 30 minutes? at 2000 rpm to break in the cam etc if there is any mishap, close down, adjust the re-start an do the run -in. Mike
J.M. Doust

Worth thinking through your timing set up. The dissi rotates ccw so you need to set it with no1 at 10 degress BTDC and then move the body CW until the ponts just open. Nip it up and if you have fuel and spark it should run. you can refine things from there. You can get true TDC with a measuring stick, get a point before and after,then set the piston to 1/2 way between. Now mark that and the turn the crank back 10 degrees. This doesnt have to be exact, once you get it running you can play with the timing to get the best performance/ping compromise.
Stan Best

Would the engine run if the cam was 180 degrees out? Wouldn't that cause the valves to have their TDC positions at BDC? If both No.1 valves have play when No.1 piston is at the top then counting anti-clockwise from which cap contact the rotor is pointing to 1.3.4.2 is the way to go, even if the distributor gear has been inserted incorrectly (incidentally Haynes has got this wrong, Leyland correct). You usually get popping and banging if the plug order is incorrect. After cranking a bit do you smell fuel on the plugs? Are they wet? Maybe there is no fuel getting through or it is flooding. Did you set the carbs to their initial positions?
PaulH Solihull

This thread was discussed between 20/05/2011 and 27/05/2011

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