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MG Midget and Sprite Technical - Timing a 1275

I recently completed a 1275 engine rebuild for my 69 Sprite and test drove it to Spridget 50 at Lake of the Ozarks. Used the factory seting of 13 degrees advanced at 1000 rpm. It ran smooth, but lacked power and pickup. After I got home I reset the timing the old fashioned way - by ear. I advanced the distributor at idle to the highest rpm and backed it off (retard slightly) about 100 rpm. Now it runs great, but reads 30 degrees advance at 1000 rpm with the strobe light! What gives?
The engine is bored out 20 thousands, has vacuum advance, a 17 degree centrifical advance. It probably has a mild cam, but the cam had no identifing marks - its not original. Vacuum and centrifical advance seem to work by the visual test (advance with strobe light on acceleration).
With the setting by ear, its WARP SPEED BLUE!

69 'Warp Speed Blue' Sprite
B C Hamper

Some here will disagree with what I will say but this is how you should proceed.
You need to set the timing of this car to 32 degrees advance when all the centrafugal advance is in and no effect from vacuum.

That means remove the vacuum tube, rev the engine to 4.5K RPM (Full mechanical advance)and set the timing to 32 degrees BTDC. This is now your IDEAL setting and I suspect it will be slightly retarded from your present setting.
The factory setting of distributors tries to achieve the figures I have described by working them back to a static figure or even the one you quoted, which is alright if the dissy is exactly the same as the one originally fitted.

It is also worth noting however that setting timing in the manner of your description, ie by ear at low revs WILL ALWAYS cause the timing to be too far advanced which may cause detonation, pinking, under load conditions
Bob England

WHAT GIVES???? you ask???....SADly you listened to me at spridget50 when we talked about that,...lol. truthfully concerning pinging(us version) and detenation,,,,there probably many opinions on the issue.....If you you can actully see thur that 1/4 inch gap while standing on your head and be able to adjust the timeing with a light then definatly do the proper method.....but we both have been doing it the same way for years as I recall our conversation....obviously john mangles didnt have a problem with you doing it that way, so...until it blows up...IMHO I dont think its going to be much of a problem....Id be curios if you can get a light on it how far off we really are....


If I could ever figure out how to get a light on mine, thur that small gap. Id probable do it with a light.

prop
Prop

By far, the easiest thing is to fix a new set of timing markers to the upper side of the timing cover where they can be easily seen. (or use the timing cover from a mini)
Turn the crank to an accurate tdc, preferably checked with a dial gauge, cut a corresponding nick in the rim of the crank pully and fill it with white paint. Then you will have a known and accurate tdc for your engine. You will never regret this!

Guy
Guy Weller

BC

When you say 17 deg mech advance, are you referring to the dissy degrees or crank degrees? You should have around 13 dissy degrees which is 26 crank degrees. Add 7 degrees static advance gives 33 max advance above 4,500 rpm - around the 32-34 normally recommended if you time dynamic. (I prefer static, as many here know!)

If dissy has 17 mech adv:
In order to obtain 32 max advance dynamic with your setup, you need to time at -2 degrees static, that is 2 degrees AFTER TDC. This will make your engine seem sluggish until some way up the RPM/advance curve.

If you set the normal 7 before TDC, you'll have too much advance at high PRM (total of 41), which might cause pinking or mild detonation; this is not good for piston life.

You can reduce the 17 dissy adv by putting a sleeve around the post that limits the total movement of the bob-weights.

If your 17 is crank mech adv:
This means you'll only get a total of 17 + static at 4.5K or greater; for example 17 + 7 = 24 degrees: not enough advance to make your engine work properly at high rpm. So you'll be tempted to set a higher static value - say 12 degrees to give total of 29 deg at high rpm. But this compromise will mean:

- too much advance at low rpm (with pinking or detontation around 1K-3K rpm); too little advance above 4,500 rpm; and correct timing maybe around 3.5K.

Either way, your engine will not run efficiently and will have problems due to pinking or overheating if the timing is retarded to prevent pinking.

The solution is the correct spec of dissy, whether by having your current dissy modified, or finding a replacement original.

HTH

Anthony
Anthony

Prop, you need one of these on your engine. Metro timing cover and pulley. You now have the timing marks at the top where you can see them.


rob multi-sheds thomas

How many metros made it to Missouri ?

;)
Dean Smith ('73 RWA)

Anthony and Bob,
Thanks for the suggestions - I'm definitely going to followup on this. Didn't know that 33 degress at 4500 rpm was ideal. That figure helps a lot in trying to figure out if the dissy is doing its job.
The dissy has the number 17 stamped on the weights, so I'm assuming I have 17 degrees centrifugal advance or 34 degrees at the crank. That's a lot based on your figures.
I'm going to set it a 4500 rpm and work backwards. Also need to measure top dead center and get a new mark on the crankshaft pulley. I'm beting that it is off as well.
I'll post the results later.
Here's the Sprite without a bonnet(June 6, 2008) on its first ride around the block after restoration.

Bruce
69 'not quite warp speed blue' Sprite


B C Hamper

Agree 1000% about getting the timing marks to the top. Metro timing covers are good, as they have room for a chain tensioner (another plus of this change) though the bolt pattern is different.

If Metro timing covers are not that easy to come by, remove timing cover and weld on a new pointer as noted above. In doing this, it is important to eyeball the best place for it BEFORE dismantling anything, as other components (esp dynamo or alternator) can obstruct view.

Given that this is not a 5 minute job, as an interim measure turn the engine to TDC on the original marks, then paint a pair of matching lines on the pulley and the rocker cover where they intersect. If you achieve fine straight lines, the accuracy is within a degree or so, which is far better than can be achieved cricking your neck to peer through the notorious 1/4" gap underneath!

As to the timing itself, a major complication for cars of this age is wear in the advance mechanism which can cause the distributor to depart substantially from its original spec. In that case it is impossible to get the advance right under all conditions until the wear is rectified (see Anthony's comments). For this reason I prefer Bob's method of setting at full advance when dealing with a worn or unknown distributor, as having the advance correct at high revs/full load is better for both best power and avoiding engine failure.

I have described what happens with a worn distributor and how to address it on my website at http://www.mgparts.co.nz/distributor.html
While initially written for the MGB, it is equally valid for the midget and shows how to adjust your distributor to perform reasonably correctly without the expense of a full overhaul provided that the relevant advance figures are substituted.

These are:
Full advance - as above, around 32 deg (most important figure)
Intermediate figure - at 2000 RPM advance should be 17 deg. This figure is the important one to achieve in order to avoid pinking.
Original idle figure (ex BMC manual) - 13 deg at 1000. This is not as important provided the engine idles [and picks up from idle] well, so this is the one you can compromise on if necessary.
Once your distributor is performing to all these, work backwards to find the actual static.

Make sure you know when full advance occurs, I note Bob's experience above, but I also note that the BMC manual shows full advance not being reached until 5600RPM. This reflects very well how, at this age, the distributors can vary from the original settings either intentionally or through wear and tear or distributor swaps. I recommend finding where your particular distributor stops advancing as this is another aspect which wear affects (the wear results in the distributor cam hitting its stop much sooner.)




Paul Walbran

>>>>>>>How many metros made it to Missouri ?<<<<<<<<<

5 and 3 didnt have a engines....lol Just kidding, but there as rare here as great white sharks in Iowa...


Im fearful that the mod my take away the orginality of my car and hurt its value....LOL. LOL.

I have been wanting to do this modification, but everytime I have the engine out, I always forget, until after the rad is completely bolted back in...I agree it really would be a great mod.....Ill get around to it someday.....

someone mentioned a mini cooper cover has its marks on top....is that a good option to do this type of mod.....AKA will the bolts all line up, and have a catch tank like the 1275. ...If so which year of mini cooper for the 1275 do I need to source???

prop


Prop

I posted a few pallet loads of bits to the USA about 10 years ago. Quite cheap to do but METRO engines were easier to find back then. I think I must've sent about 4 dozen of them in one go. Where did they all get to????

I could have another go at finding some, if there are enough interested parties. I need a couple for myself, anyway.
rob multi-sheds thomas

The metro bolt pattern may look different but they do actually match up and there is one extra (IIRC) hole that can be added if you wish. A little triming of the alternator strengthening bracket is usually required plus some removal of new paint. Be careful if using a duplex chain since the cam pulley may foul a 'splash ring' welded to the inside near the breather canister hole.
rob multi-sheds thomas

Presumably the changes for metro timing chain cover are the same as in the archives for the Ital in-line one withtiming chain cover.

My nice "new" 1380 already has the later cover but I havent checked where the timing marks are.....of to the garage it is!
Dean Smith ('73 RWA)

The metro cover does have the advantage of a timing chain tensioner. But if it is just the timing marks that are needed it is really very easy just to weld a toothed pointer to the front edge of the cover. You can do it in situ, without having to remove anything at at all. Then turn the crank to tdc and mark your new datum point. Job takes about 15 minutes.

Guy
Guy Weller

And if you can't weld (like me), make up a pointer from a short length of coat hanger wire, bend to shape (a bit of trial and error, use copper wire to determine shape) and put under the bolt head of one of the timing cover bolts.

Steve
Steve Church

This thread was discussed between 04/07/2008 and 05/07/2008

MG Midget and Sprite Technical index

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