MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - TDC - Brain Clarification!

Hi all,
Sorry to post this, but just need to check that what I think .......is what really happens!
midget mk 3 1275
To set TDC compression / firing stroke on 1,
1/. I remove plugs
2/. I remove rocker cover
3/. I turn by hand the pulley clock wise until the cut out on the crank pulley is on the big pointy timing mark( or very near it)
4/. look down plug hole on 1 & see piston top
5/. I take off the dizzy cap
6/. Rotor arm should point to # 1 lead in the dizzy cap & also to no. 1 cylinder which is nearest to the radiator.
7/. Both rockers on cylinder 1 should wiggle very slightly
8/ . Both Rockers on number 4 should be rock solid.

Thats TDC compression stroke on 1.

Sorry to have to ask like a git but I'm still a little confused - I'm NOT a mechanic ( clinical Chemist) so I just need to get it straight between my ears for the future.
If I've made any big clangers . could someone kindly point it out to me?
Cheers all
Col
colin frowen

You're brain is fine.

With No.1 piston at the top of it's travel, as shown by the timing mark and you're own visual check, with both No.1 inlet and exhaust valves closed, you are indeed on the compression/firing stroke for No.1

You didn't really need to take the rocker cover off.

Assuming the engine has been running ok, then the distributor will be sitting in the correct position, and the HT leads will be connected correctly too.

So all you need to do is look at the rotor arm just as you did, to confirm that the No.1 valves must be shut and the engine about to fire on No.1

Congrats. :)

Any special reason you are doing this check?
Lawrence Slater

Edit.
Well actually, before someone corrects me, I should have said ---

---- the No.1 valves must be shut and the engine would already be firing on No.1, as it happens B(efore)TDC. 7 deg static, dependant on how your timing is set for your engine.
Lawrence Slater

Colin. The only reason to remove the valve cover is to watch the intake valve open and close. The intake valve, the second valve from the front of the engine, will open late in the exhaust stroke, be open the intake stroke, and will close early in the compression stroke. If you see the intake valve closing, you know, absolutely, that you are on the compression stroke. Run the timing marks to the appropriate static timing mark, check the rotor position, and you are ready to set the static timing/verify the orientation of the distributor.

Les
Les Bengtson

Yes, the only thing I wonder if you realise is that with the notch on the pulley pointing at the timing mark, it could be EITHER cylinder 1 OR 4 that is going to fire. That is the reason for checking the valves. The cylinder that is about to fire has a slack valve train, whereas the other one will have at least one of the valves depressed, in fact it will be the exhaust valve - the very front one for cylinder one and the very back one for cylinder four.

You want it to be cylinder one that is about to fire, hence, as you say, Both rockers on cylinder 1 should wiggle very slightly, Both Rockers on number 4 should be rock solid. Turning the crank pulley isn't simple on a Midget because the chassis cross-member gets in the way. I put the car into 4th gear and push it forwards to turn the engine over.

Otherwise everything you say is right. Oh, and by the way, I was a clinical biochemist myself until I retired three years ago.
Mike Howlett

Easiest way to find TDC on the compression stroke is remove the plugs, put your thumb over the #1 spark plug hole and and have someone turn the engine over. As soon as #1 piston starts up on the compression stroke, your thumb will be smartly pushed off the spark plug hole - no having to determine if valves are rocking or not. Cheers - Dave
David DuBois

I agree with you David, but for someone who seems new to this, I figured not to mention the finger/compression method.

You could also have the ignition on, and lay No.1 plug, connected to it's lead, against the head to make sure it's earthed, and then rock the engine back and forth, while you watch for the spark. Or flash the lt lead on the coil.

Quite a few ways to do this, that don't require the rocker cover off.
Lawrence Slater

This thread was discussed between 11/02/2012 and 12/02/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.