Ouch..... That's sounds drastic!

The head was from a Metro with oversized valves and valves were reseated, a 1.5 ratio roller tip rocker was fitted. The block was decked and over bored 60 thou, the Hypertec pistons did protrude .7mm on the first fitting and I needed to get them skimmed .035 in so they now sit .02mm below the deck.

This is how they now sit when TDC:

You can calculate actual compression ratio without removing the head.

To do this, you need the CV (clearance volume), this is volume of the head chamber + gasket + piston crown to deck of block.
This can be found the same way as motorcycle builders do it.
1. Face car uphill.
2. Turn engine to TDC on compression stroke.
3. Use a measuring glass or burette or horse syringe to fill the chamber with ATF or similar, to 1/2 way up the plug hole. Rock the engine to get accurate TDC (max fluid level) during this.
4. Measure the amount poured in, this is the CV.
5. Cover the front of the motor, slam panel and floor with rags and crank the motor to expel the ATF.

ENJOY.

C/R = [cylinder displacement + CV]/CV
where displacement is engine size/4. eg for a 1310 it's 327.5cc.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Marty, I would start with spark plugs, timing check and then fueling mixture, if that doesn't solve issue, I will be around Sat arvo if you would like to have a crack at calculating CR as per Doc's method . Mal

There is also an app called mini head to calculate CR

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1965 Riley Elf
1974 Ex Army Moke
1997 Rover Cooper
2002 JCW Cooper
2003 JCW Cooper S

I have had to tune a few cars that run-on. Usually retarded timing, flooding or hot spots.

Cheers Jas,

According to the app my compression ratio is: 10.94

My 1360 is 11.0:1 C/R now, it doesn't ping but does run on when hot.

The bigger the cam duration, the more C/R you can get away with.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Mine is 1340 and 10.94 is close enough to 11:1 I might just try the clutch trick for now

Cheers Drmini


P.S. Is 11:1 too high to handle a supercharger?

Yes you want less than 9.0:1 if putting a decent huffer on it. Like a Sprintex.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I agree.
Same with my cars.
Usually worse when hot, but let clutch out soon stops it. Just remember to keep your other foot on the brake or the handbrake is on tight.

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Running on in the Majority or cases is caused by too much Air and Fuel at Idle.

There is too much air and fuel simply because the Butterfly has to be, relatively, a long way open to allow the engine to Idle at an acceptable speed.
There for it is supplying Air and Fuel to the engine which allows it to run on.

So How do we stop the engine Dead when we turn off the ignition, Simple!!!

We have to turn off the Air and Fuel as well.
Late model Japanese cars With Carburettors ALL used this method/
They had a fuel shut off solenoid fitted to the idle circuit on the carburettor as well as a solenoid which allowed the butterfly to close completely.
I understand that some later model cars fitted with SU's used this butterfly solenoid as well to shut off the Air. With an SU no air no Fuel so kills 2 birds with one stone.

Anyway Back to the Old fashioned Mini Engine.
The reason Most Mini engines have to Idle with such wide open butterflys is simple/
It All comes back to the Lucas Distributor with its Advance Curve.
Most Mini Lucas Distributors have 15degrees of Mechanical Advance which equates to 30 degrees at the Crank,
The total Advance for the Average Mini Engine should be Around the 30 to 32 degree mark.
So with the standard mini Distributor you are stuck with an initial Timing setting of 2 degrees BTDC to give a total advance of 32 degrees.

Now, to get an Idle with only 2 degrees of initial advance requires the butterfly to be relatively a long way open. This creates a condition of excess fuel and air which causes the engine to run on when the ignition is switched off .
On the other hand if the Initial is set to 10 degrees BTDC the idle speed Speeds up Very Considerably which allows the engine to Idle Smoothly with the butterfly closed down to the almost fully closed position.
No More Running On...

But with a standard Distributor 40 degrees of total advance is way too much.
The Distributor must be modified Mechanically so it has no more than 11 degrees of mechanical Advance and then the curve has to be set up for your particular engine.

So 10 initial, and 11 in the distributor which equates to a total of 32 degrees
Obviously these figures will not suit all engines but one thing is for sure,
Run as much Initial advance as practical and Keep those Butterflys Closed................

Dave

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Mine idles at 1300rpm...!
Static advance with the Accuspark black box is now 10 deg, it was 20 with the Pulsar dizzy in. Run-on is still the same. No change.
This motor runs lots of advance because the chambers are bathtubbed.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Kevin,

1300 rpm is a very high idle, Butterflys must be wide open, no wonder it runs on!!!

Set up a solenoid on the throttle stop, so when the ignition is switched off it allows the butterflys to shut fully.. That will stop it....

Dave

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running on was quite a problem with a lot of engines. and with a lot of solutions.
the brits just fitted an electric valve that opens up an air bypass if ignition is turned off, IIRC first on some MGBs. and just this valve was found again at the carbed, high CR, 1300 minis from the 1990s to stop run on. so it was even a problem for the factory

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Rover 214 atm ....