17 replies to this topic

[Austin mini 30]

Evening everyone, 

 

Got a problem with my 1989 mini 30, 110000 miles, 998cc standard engine

 

It seems to be running on 3 cylinders and going very lumpy now and again. The spark plugs were changed a month ago, and the points gap has been set properly. coil and condenser were changed less than 6 months ago. rotor arm/distributor all in good condition  

 

When the engine is running, pulling the HT lead off cylinders 2,3,4 (one at a time) - each one makes the engine drop rpm as it should. (cylinder 1 being closest to the radiator) 

 

Pulling the HT lead off cylinder no. 1 when the engine is running there is no decrease in rpm. 

 

Tried swapping the spark plug/changing the HT lead but no difference at all.

 

Car is loosing some water (which is a funny colour, unsure weather its oil or just a build up of rubbish)

Car is loosing some oil - no sign of any "mayo" in the rocker cover. 

Car is also my daily.

 

had a 100 mile trip yesterday, 50 miles there 50 miles back, temp gauge was sitting just above half way on the flat, unless i went up a hill and it would increase to 3/4 up the scale, and downhill it would be normal. 

 

Unsure what to do.

 

Any help is much appreciated 

 

Angus

 

 

[AgentHubcap]

Have you tried a compression test?  

 

To confirm spark, you can pull the plug for cylinder 1 and see if the spark is arcing to the block when the car is running.

 

What colour is your coolant?  Is it a rusty brown, or is it milky?  Old coolant can turn brown from rust.

[Austin mini 30]

I haven't tried a compression test, but I could do because I know someone who has the tools for that. 

 

The coolant is a brown colour- no sign of milky so i guess it needs flushed and changed-  possibly causing the engine to run warmer on longer drives.

 

I did actually try pulling the plug for cylinder 1 out to see if it sparked against the block, it did but it was a very weak spark compared to the other 3. 

[lrostoke]

first I'd swap the plug on No 1 for one of the others.

 

If problem moves its the plug.

 

Then try swapping the lead for one of the others, same thing if it moves found the problem.

 

After that its the head gasket or worn valves on that cylinder..either of these its head off, which isn't that big a job

 

Worst case ring problems on that cylinder

Edited by lrostoke, 07 August 2016 - 07:55 PM.

[Austin mini 30]

Ok so I've swapped the plug and lead but no difference unfortunately.

The oil pressure warning light is now also on permanently, car is using oil, got blue smoke on start up with a constant but slight misfire, this is pointing towards piston rings isn't it?....

[Austin mini 30]

Going to do a compression test tonight

[sonikk4]

Compression test and leak down test after. Add a drop of oil into the bores. Increase in compression = damaged rings / piston. No increase points to valves not sealing. But do a standard compression test first.

 

However if a oil scraper ring is damaged this may not show up on a compression test.

[tiger99]

Piston rings have nothing directly to do with oil pressure, but do not run the engine at all until the loss of pressure is fixed. The damage has probably already been done, but more running may result in some vital part such as the crankshaft becoming worn beyond regrind limits.

First check the oil pressure switch by swapping it for a known good one, or preferably connect a gauge if the car doesn't have one already. Then check the oil pressure relief valve.

If it turns out that there is actually good pressure, proceed with the diagnostics. Otherwise you may as well go straight to engine out as there is no other way to assess and fix the problems, which will be at least worn big ends or main bearings and/or oil pump.

But it does seem that you will at least need to take the head off for a look at the bores, even if oil pressure is present.

[Austin mini 30]

thankyou for all your advice this is great you know so much. everything has been taken on board- ill check the oil pressure tonight and see whats going on, and proceed from there . 

 

Compression test results... (no.1 being closest to the radiator): 

 

Cylinder 4 - 145psi 

cylinder 3 - 160psi 

cylinder 2 - 145psi

cylinder 1, 40 psi (not a typo) actually 40 psi! has that narrowed the problem down at all? 

[AgentHubcap]

Did you add a squirt of oil to the cylinder that has low compression?  That would help narrow it down to head vs rings, but either way, the head needs to come off for an inspection of that cylinder.

[Austin mini 30]

Not done that yet but i will go and do that this very minute and get back to you, yeah it has to come off just want to have a fairly good idea at what could be wrong before doing so! 

 

Thanks for your help 

[Austin mini 30]

squirted oil into the low compression cylinder, hardly any change at all, not even 10psi more - bad valve is a main suspect then ? 

[tiger99]

Most likely valve or head gasket. But either way the head needs to come off.

[Austin mini 30]

Ok great will get onto that this weekend and let you know what i come across! 

 

Cheers everyone

 

Angus

[Austin mini 30]

 valve.jpg   24.16K   13 downloads 

 

Well everyone pulled the head off tonight, chipped inlet valve on cylinder 1!

 

(see photo) 

 

Also the oil pressure light i have found to be on for no reason at all everthing is fine there too. 

 

Cheers for everyones help

 

Angus