Cylinder 1 low compression - MINI Cooper Forum

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post #1 of 4 (permalink) Old Jul 2nd, 2014, 04:40 PM Thread Starter
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Cylinder 1 low compression

Hi Guys
Our MCS R53 has felt slow for a long time, a few weeks back i thought it would be fun to do some checks to race it against my Corsa 1.2 16V. Funnily enough whoever was driving the Mini just could not get away.
Ok so very down on power.
2 weeks ago we drove from Scotland down to Reading, after about 250 miles of our journey the cars performance came back and it was great and felt very strong
Then after a few miles doing short distance driving the car got very slow again!
This happened a few times whilst we were driving around and felt great after a really long run. I don't get it.
What we did notice in all this time is that we were going through alot of coolant and after each of the long journeys we had lost half of the coolant from the expansion bottle.
The other day after driving 30 miles and stopping in a car park we could hear alot of bubbling noises?
After checking this out we found there to be no coolant and the expansion bottle had split on the seam.
I then did a compression test over the weekend and found cylinder 1 to be very down on compression, the other 3 were exactly the same. This was done with all plugs out with a hot engine and WOT.
The test was repeated after putting a bit of oil on the cylinders, this made a very small difference equally accross all the cylinders, but cylinder 1 was really down still. apologies but i measured 11-11.5 bar on 3 of the cylinders dry and 11.5-12bar when oil was added.
Cylinder 1 measured 8-8.5bar dry and 8.5-9bar when oil put in cylinder.
I did this a few times, because i was in a bit of denial, but the numbers speak for themselves.

I suspect a headgasket issue, i am hoping it is not more serious. Is this a common problem?
With the help of the forum and many searches i am also going to check bypass valve etc for another possible reason why its down on power before we had coolant problems.
I am also going to check and replace the thermostat and housing as this could have been leaking coolant aswell. There was a slight leak at the front so i may also check the radiator joint.

Our gearchange is also slightly stiff so its a good excuse to do the mechanism bolt change thingy.
Our car is at 105k+miles. So i am going to give it a bloody good service and replace SC oil aswell. We are also toying with smaller pulley and few other little things as may as well do as one big job.

Can anyone give any advice on problems, maybe advice on things to look at and replace? Where to by parts from etc etc?

All help be much appreciated

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post #2 of 4 (permalink) Old Jul 13th, 2014, 01:29 AM
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Better mechanics please weigh in but I believe that an engine that fails the "wet" test has a bad valve. I was under the impression that the oil would also seal up a gasket leak long enough to change the results of a compression test but perhaps that's not the case. Either way you'll have to pull the head off. We had a burnt exhaust valve in one of our MINIs and had it replaced and the other valves machined. We're very happy with the results and I'm pretty sure it was cheaper than buying a rebuilt head from another car.


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post #3 of 4 (permalink) Old Jul 13th, 2014, 03:25 PM
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Hi ya

If your expansion bottle has split which is a normal thing, and can be hard to detect sometimes. I would also repair that first and bleed the system first.
I can not emphasise enough how much you must take your time bleeding the cooling system. There's a few threads here at mini2 on the best way to do it.
Run the car and do a hydro carbon test on the coolant this will tell you if you head gasket has failed in to your cooling system.
Check your oil for yogurt this will tell you head gasket has failed towards the oil system.
Putting oil in the cylinder on the MC and MCS will only point at rings as the piston stops well below the cylinder block deck.
If the head gasket had gone between cylinders you would have two bad cylinders next to each other
Personally I would do a leak down check on it this will tell you where the leak is coming from and I have found it more accurate on the MCS
Ie air coming out the dipstick or oil filler good chance it's piston related, super charger horn inlet valve, exhaust exhaust valve

It could be a damage piston or bad valve I would also put a borascope in the cylinder and have a look round as well

You will need to find out why, if it's one of the above, has the car got any mods ?
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post #4 of 4 (permalink) Old Jul 14th, 2014, 11:28 AM Thread Starter
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thanks guys for your replies.
the wet test as stated still leaves valve and gasket open for failure. i do agree a leak down test is better, however i have no way of doing this currently. i know the oil is ok and there is not water oil mix, i am waiting on a hydro carbon tester so i can check the coolant, but this will be done after the new bottle arrives as the car doesn't hold its coolant currently.
i know its not blown between cylinders as i have had this occur on previous cars and it also affects performance and you can hear it clearly if this happens.
the car is stock apart from new cat back exhaust(which affects nothing here).
i think the gasket must be blown between cylinder and coolant or maybe out side of the engine maybe?(although there is nothing noticeable on that front.
its strange because otherwise the coolant leak and excessive pressure etc the engine is running very well. i have done two short journeys in her to get her warm to double and triple check previous results and the car has been driving strong and pulling very well??
i did a boost check and the car seems to making the correct boost as stated from the factory.
boroscope is a good idea although again i don't have anything to use, maybe worth buying on future.
what i am going to do is repalce the coolant bottle with a new aluminium tank i have purchased with a new standard cap and try this and do the hydrocarbon test.
if that appears ok then maybe run the car a bit more and re-check.
But the head is going to have to come off regardless at somepoint if we are down on compression. Just awaiting prices for gaskets etc and other parts
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