Make sure all the headstud threads are clean, smear them (and under nuts) with some molygrease, eg Castrol LMM.
Stops the nuts sticking as you retorque them after running.

_________________
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.

id check the head and bloclk faces are both flat as well and no little crack in the head

I'd do a leak down test as well as a compression test to see if there are any other problems in that area before you take the head off.

Cheers,

smithy

Hi,
Smithy
Can you please explain what a Leak Down Test is or how to do one?
Thanks

Hi Gezo,

A leakdown tesr basically checks the efficiency of the engine's sealing ability. It requires compressed air and two pressure gauges in series. The actual pressure doesn't really matter (it has to be reasonably decent, say over 80 psi) as you're comparing readings on one gauge to the other. There are leaks in all engines, it's the amount that is worrying. From memory an F1 efficiency is up around 99%. a Super V8 about 97%, normal car 94%.

So. pick a cylinder and turn the engine until both valves are closed and lock the crankshaft from turning. Remove sparkplug and replace by screwing in an airline adaptor. (I made mine out of an old sparkplug) Joined to the sparkplug adaptor is a gauge (for ease of understanding, let's say it goes to 100psi) that is joined to another 100psi gauge by a .060" resrictor. That second gauge is joined to an air compressor. (I may have misssed a tap or something but it's bloody hot in my shed so I'm not going to check it unless some really wants to make one)

Crank up the compresser and get the gauges up to 100psi. As air leaks from the cylinder the gauge closest to the head will go down. The gauge closest to the compressor is kept at 100psi As per above, nothing's perfect. If it goes below 90% you've got the startings of poor sealing. If it gets down to 85% you have got problems. (See why I picked gauges of 100psi. It's a comparison/percentage thing so the actual pressure doesn't matter, you can work it out mathematically but having 100psi gauges makes it much easier.)

Now having found out that a cylinder is bad, listen. If it's an exhaust valve you will hear ait escaping out the exhaust pipe If it's an inlet valve you'll hear it through the carb, if it's valve stem/guide wear you'll hear it out the valve guide, if the gasket has blown between 2 cylinders (you have all the sparkplugs out) you'll hear the air in escaping into the adjacent cylinder and so on.

Mind you, you can do all this listening just by stuffing air into a cylinder it's just that the gaugs will pinpoint how bad it is in terms of effeciency.

A compression test will tell you if there is a problem. A leak down test will tell you how bad that problem is and listening and interpreting quite often tells you what it is.

So, find someone who does these tests regularly as it shouldn't cost a lot and in most cases you should know what the problem is without taking the head off and how bad it is.

smithy

Hi,
Just warmed the vehicle and did a compression test. There was 165 in all four cylinders.
I could have sworn when the motor had first been started ( after complete rebuild) the compression was 190 all cylinders. A while back a took it to the Carbie place and on the invoice it had-
adjust carb,fit new points, set timing and set tappets. On all the mini literature I have, it states poor valve timing can effect performance and cooling of the vehicle. Is it possible that the engine builder set the valve timing correctly and when I took it into the carbie place when they adjusted the tappets they through the valve timing out. As the car was unreg I trailered it to & from the carbie place and just started in the shed.
This motor has not done more than 20kms since professionally in Aug 02. The carbie place was done a while ago, not the same place I used the Dyno recently.

Could valve timing explain Overheating and poor performance?
Thanks

Hi,
Should I change the headgasket even though the compression is the same on all cylinders or shall I check the valve timing first?
Or should I do both?
Thanks

some qs is it using any water
under the oil cap is there any sign a milky type mayo substance or is it clear
when the engine is running and the rad cap is off give it a little rev and then drop the revs to idle and watch if any bubles come through the water
if any of these happen good chance head gasket

If not overheating, and equal compression on all 4 cylinders, and no bubbles in rad, good chance the head gasket is OK.
I'd check/adjust the valves first, but if anything bad there, compression would be uneven.

`set timing' on that invoice is ignition timing- not valves- there's no easy way the valve `timing' can be adjusted on a Mini during a service.

Ignition timing would have no affect on the compression pressure- maybe when first built the pistons and bores were well lubed up, which would give a higher reading.

BTW at any particular C/R, the bigger the cam (ie more duration & overlap) the less compression pressure you will have, due to poorer `trapping efficiency'.

_________________
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.

Hi,
Underneath the oil cap is clear and on the dipstick is clear. I will have a look tomorrow afternoon at the radiator to see if there are any air bubbles.
Thanks

yeah check for the bubbles but as the doc says if there isnt any bubble no milky stuff and even compression id be leaning against a head gasket
ive had two blown headgaskets one used heaps of water i mean heaps and the other ran like it was on 2 cylinders hardly any power at all

Hi,
How much compression should there be on a 1275 motor. The book supplement I have says , it should haveno less 150 for the compression. I have spent a small fortune on this vehicle all I want is it to run and rev right.
Thanks

Important thing is pressures should be even, within 10psi.
If it has a big cam in it but a low C/R, it will not perform well.
For a road motor using 98 octane unleaded with cams around 270* duration, I like it to be ~10.5:1.
Bigger cams can have more, smaller cams less.

To check C/R either the head has to come off, or.....
you can face car uphill with motor cold. Put #1 piston at TDC mark with its valves closed, then fill the cylinder thru the plug hole with ATF (auto tranny fluid) until 1/2 way up plug hole. You need to measure this amount ACCURATELY using a burette, horse hypodermic syringe or whatever.
This measurement is the `clearance volume' CV. You know the `swept volume' SV, which is engine CC/4. eg 1275/4.
C/R = (CV + SV)/CV

to get the ATF out, put a bunch of rags in front of plug hole, start engine on 3 cylinders, stop, refit plug.

_________________
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.

But get your mother in law to stand in front and ask her to keep an eye on plug hole to see if any fluid's leaked in there ......

I shouldn't be mean but I've always found people have to stand in front of a motor if there's oil in it , I bought one from an old bloke one time who'd filled the bores with oil , hooked a battery up to the starter to pump it out and a mate stood right in front "to see if the oil would spurt out" ......... It did , he wore all four cylinders worth . Just remember , this will make a mess ....

_________________

It won't be in there long, you could use water or coolant- as long as you start and run it straight afterwards....
Still make a mess....
But it is the only truly accurate way to do it, IMO.
With the head off you would have to add the vols of piston dish, deck height, top ring land, gasket, and head chamber..... to achieve the same thing, an accurate measure of CV.

_________________
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.