1275 timing marks

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philthehill
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Re: 1275 timing marks

Postby philthehill » Mon Mar 23, 2020 4:25 pm

Just make sure that No: 1 inlet and No:1 exhaust have clearance with No: 1 piston approaching TDC and you will be on No: 1 cylinder compression stroke which leads to TDC and ignition firing.


paul 300358
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Re: 1275 timing marks

Postby paul 300358 » Mon Mar 23, 2020 5:01 pm

Also, ensure that the rotor arm is pointing to the number 1 plug terminal in the distributor cap and not number 4.

alawrence10360
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Re: 1275 timing marks

Postby alawrence10360 » Tue Mar 24, 2020 10:41 am

All done now
Many thanks for your support Phil

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Re: 1275 timing marks

Postby alawrence10360 » Wed Mar 25, 2020 6:26 pm

Regarding the adjuster on the distributor how much does it adjust the timing in terms number of clicks/turns per degree
I advanced it half a turn and could not feel any discernible difference

philthehill
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Re: 1275 timing marks

Postby philthehill » Thu Mar 26, 2020 7:58 am

The adjuster on the distributer is for the very fine adjustment of the timing therefore you will not feel or see a discernable difference in the timing other than by using a timing light with the engine running.
Half a turn will not make much difference.


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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 9:57 am

I’m 100% sure I’ve found TDC. That’s the mark with cross on it
Wether I’ve gone the right way withe the 7 and 22 degrees is another matter
If I have then at 1000 rpm my timing is a country mile away
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philthehill
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Re: 1275 timing marks

Postby philthehill » Thu Mar 26, 2020 10:03 am

If your engine is running the timing cannot be 'a country mile out'...….
Just set the timing so as to get the engine running sweetly and not pinking. That is all you can do. The timing settings are there as a base line - final setting has be done by road testing or using a rolling road.


alawrence10360
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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 10:23 am

Will do
Looking at the pics have I gone the right way with the marks phil ?

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Re: 1275 timing marks

Postby philthehill » Thu Mar 26, 2020 11:57 am

So long as you have identified TDC on the compression stroke of No: 1 cylinder the timing mark (both pulley & timing cover) can be placed where you find them most convenient to view. Placing the cross on the RDC mark is a good idea, saves any confusion.
As the engine turns clockwise the actual firing mark(s) should be just in front of your TDC (with cross) mark which they appear to be.
Phil


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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 12:35 pm

Thanks Phil
I decided to bite the bullet and rotate the distributor and was surprised how much the marks/timing moved so perhaps I wasn’t that far away initially after all
I did notice that whilst adjusting the distributor the point at which the revs were highest was quite a bit away from the marks I had made. I’m not sure if this is relevant
Anyway I have set the timing such that at idle it’s 7 and when the revs are raised to what I estimate to be 4000 its 22
I will see how that feels when I dare go out into the world

philthehill
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Re: 1275 timing marks

Postby philthehill » Thu Mar 26, 2020 2:21 pm

As I have already said - the setting of the timing marks is only the beginning. Obtaining the smoothest running and best performance overtakes getting the timing marks to align as per the manual.


Hopefully we shall see a day when we can all get back to normal - whatever normal is.
Take care and keep safe.

Phil


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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 4:11 pm

So I’ve played with the timing and I’ve found the best setting is actually as per the book.
I never really got it pinking even when retarded as much as I could but the performance definitely suffered.
Now it’s running better than before and sweet as a nut with an even steady tickover.
Next is the fuel mixture
Now I’ve given it a good blow out the plugs are like this pic (they were black as coal before hand )
I’m guessing that’s a bit lean so I’ve give it half a turn on the mixture
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mobylette
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Re: 1275 timing marks

Postby mobylette » Thu Mar 26, 2020 4:46 pm

Pinking occurs when the timing is over advanced, not retarded.

philthehill
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Re: 1275 timing marks

Postby philthehill » Thu Mar 26, 2020 4:57 pm

With everything right the plugs should be a nice digestive biscuit brown.

Over advancing the ignition causes pinking or pre-ignition.

Excessive retarding of the ignition can lead to melted pistons.

There is a fine balance to be struck between advance and retard.


alawrence10360
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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 7:07 pm

mobylette wrote:
Thu Mar 26, 2020 4:46 pm
Pinking occurs when the timing is over advanced, not retarded.
That will be why it didn’t pink then.
I knew that all along. Just trying to test you all...

alawrence10360
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Re: 1275 timing marks

Postby alawrence10360 » Thu Mar 26, 2020 7:10 pm

philthehill wrote:
Thu Mar 26, 2020 4:57 pm
With everything right the plugs should be a nice digestive biscuit brown.
I think mine are more rich tea

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Re: 1275 timing marks

Postby Chipper » Fri Mar 27, 2020 3:29 pm

Which 1275 engine do you have? It would appear that you have the extra holes in the cylinder head for bolts at each end of the rocker cover, as per Mini Cooper 'S' and Austin 1300GT...
Maurice, E. Kent
(1970 Traveller)

philthehill
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Re: 1275 timing marks

Postby philthehill » Fri Mar 27, 2020 4:08 pm

Non of the in line engines had the additional stud (at the rear) and the bolt (at the front).
It is a common conversion to fit the additional stud and bolt. The 940 cylinder head even without the stud and bolt has the casting boss's inside the head which can be drilled through.
Most conversions to 11 fixings fit a stud at the front but care must be taken not to over tighten (max torque 25 lbf) the stud (or bolt) as the top of the block is very thin in the area of the additional front stud/bolt. Overtightening can cause the stud/bolt to break out of the top of the block
There is no detriment to fitting a 11 fixing head to a 9 stud block and leaving the two additional fixings open/unused.

It should be noted that not all Cooper S cylinder heads were secured to the block by the 10 studs and 1 bolt. Early Cooper S heads were just secured by 9 studs.
Latterly it was found that the Cooper S engine tended to blow head gaskets between the two rear studs and the two front studs. To overcome the problem the additional stud and bolt were incorporated.

Personally I would leave well alone as if the additional taped holes in the block are not there it will require an engine strip to incorporate them.
Below is a picture of a 940 head (top) with 9 stud fixing and a Cooper S 12G185 head (bottom) with 9 stud fixing.
12G185 head 4.JPG
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You can also see the additional brass plugs fitted in the 940 head so as to deflect coolant to the rear of the head as 940 heads tend to run hotter at the rear.


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Re: 1275 timing marks

Postby les » Fri Mar 27, 2020 4:28 pm

I’m amazed to see how small the valves were in that early S head. Certainly enough room between to avoid the cracking that later heads suffered from.


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Re: 1275 timing marks

Postby philthehill » Fri Mar 27, 2020 4:45 pm

Les
The valves in the 940 head (top) have been replaced with larger items so should not be used as a comparison.

The valves in the 12G185 head (bottom) have the same head size 1.4" inlet & 1 5/32" exhaust as those in a standard Cooper S / 1275GT 12G1805 head.
The valve stems of the valves fitted to a 12G185 head are shorter and the valves made of better quality material.
It was the early heads that suffered from cracking especially the 12G185. To overcome the problem the valves were moved further apart (approx 1/8") in the 940 casting so giving more metal between the valve seats. The internal water channels of the 940 head also were reprofiled to aid coolant circulation around the valve seats.
The best of the early heads was the AFG163 (same size valves) which if available commands a premium price - that is if you can find one?

Phil



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