7 replies to this topic

[dschwartz1957]

My '68 Mini Traveller has a 1275 cc engine with an HS4 carb and is probably from an Austin America or Austin / Morris 1300. The engine number is 12H159A / H175882 and was probably built around 1971. I understand the 'H' means high compression, but have not been able to find additional specs for the engine.

 

I recently participated in a 100 drive with my Mini club which included “summiting” a 2000 foot mountain. On the descent I used engine compression to keep speed under control. At a stop to regroup, a club member told me my car was burning oil on the way down the mountain and this indicated I need new valve seals.

 

A few days later I pulled the spark plugs and found the insulators as follows:

 

Cylinder    Plug
 1                White / grey / tan
 2                White / grey / tan

 3                Lightly covered in oil.
 4                Heavily fouled with black gunk, plus a small chip in the insulator.

 

I installed new plugs and drove 20 miles on country roads at speeds of 20 to 40 mph. After the engine cooled down I pulled the new plugs and found the insulator condition is consistent with the old plugs:

Cylinder    New plug
 1                White
 2                White
 3                Tan
 4                Black
 

I then ran a compression test on the COLD engine. I know it is better to run on a hot engine, but didn't want to handle hot spark plugs.

Cylinder    Compression
 1                100
 2                110
 3                105
 4                110

As you can see the compression was fairly consistent across all four cylinders. Though given that the plugs from cylinders 3 and 4 show signs of oil, I expected the numbers to be lower. According to the Mini Workshop manual, compression on a brand new warmed up engine should be in the 150 to 190 range depending on the engine / car model. The workshop manual does list an early 1970s Canadian Mini 1000 with compression of 120. I have no idea what the compression should  be for an Austin America or 1300 engine from 1971.

What can I conclude from the spark plug condition and compression numbers? Could this just indicate leaking oil seals in 3 and 4, or does it mean the rings are leaking and it is time for a full rebuild?

 

Thank you,

 

David Schwartz

Framingham Massachusetts

Edited by dschwartz1957, 04 August 2014 - 07:47 PM.

[KernowCooper]

If you used the engine braking down the hill then the vacuum is at its highest and indicates either work guides or seal or both, have no info on the Austin America but those reading you did are low, but they should be done hot and with a wide open throttle

[philip663]

Evening, Im in a similar pickle to you. Suspected the same as you so had new guides and seats on the head done, helped a little with the burning of oil. The only thing i can really help or just point out that when i comp test my engine the readings are 145-155 cold and 195-200 hot. Try doing on hot and compare the differance, could help tell if its rings i presume?

[dschwartz1957]

I did the cold compression test with a wide open throttle. I'll try again with a hot engine.

 

Thanks,

 

David

[carbon]

David, for info the 1971 BL 1100-1300 factory manual gives spec range for compression pressures on 1275 as :

8.8:1 CR = 155 to 180 psi at 300 to 400 rpm

9.75:1 CR = 185 to 210 psi at 335 to 485 rpm

 

How often do you need to top up the oil, and are you using 20W50 grade?

[dschwartz1957]

Thanks for posting the specs. I wonder if the 'H' in the engine number indicates the higher compression ratio.

 

I am using 20W50 grade and have driven about 400 miles since the last oil change. Currently the dipstick reads exactly halfway between the lines, but it started a hair over the top line.

 

It is difficult to tell how much oil the engine is leaking versus burning. In August 2013 I replaced the rear main seal, but there is still a lot of oil dripping from the front of the engine and around the gear shift tunnel. I changed the oil in early July and was afraid of over-torquing the oil drain plug so I lost a bit there as well.

[dklawson]

The compression numbers are low but you have to ask yourself how much money you want to spend at this time if the engine runs "OK" otherwise.  If you do a minimal cost engine rebuild where you pay the shop to do the machine work and you do the assembly, figure on about $2k for a rebuild.  

 

The white plugs on 1 & 2 suggest a lean condition.  However, since you are running a single carb it further suggests as you say that 3 & 4 are burning richer, probably from oil.  

 

You've done a compression test.  If you have an air compressor, make or borrow a leak-down tester and carry out a leak down test.  It will tell you where any problems are.  It won't tell you if the valve guide seals are worn out but it will tell you if you have leaky valves, rings, or other failing components.  As a footnote to the valve guide seals... you can replace them but typically when they are worn, the guides are worn and new seals are only a temporary fix.

 

It's common to transplant AA engines into Minis.  Take a look at the front plate behind the timing cover.  If the plate has evidence of ears (for engine mounts) being cut off, then it is probably an AA engine.

[dschwartz1957]

I last pulled the spark plugs a year ago and three plugs were white/tan and the fourth had a little oil. When I replaced the plugs two weeks ago, the plug from cylinder 4 was completely fouled with black goo, and 3 was black and wet. I have a mechanic friend with the equipment to do a leak-down test.

 

I bought the car in May 2013 and spent some time trying to determine the history and donor vehicle for the engine. The car is right hand drive and started life in the UK. It then spent 30 years in New Zealand. Some time after 2000 it disappeared from the New Zealand Motor Vehicle Records. It had a different engine number when last inspected in 1999.

 

The current engine number is 12H159A / H175882 and the best I could determine is an A series engine from around 1971. The donor vehicle was likely an Austin America or Austin / Morris 1300. I couldn't find much history from the Mini's time in the US, and don't know whether the engine was swapped in New Zealand or after it was imported. The car spent several years in New Hampshire before I bought it. Based on the numerous quick and dirty repairs I have discovered, I suspect the engine was swapped before the car left New Zealand. Someone probably needed cheap basic transportation and just wanted to keep the thing running.

 

    David

Edited by dschwartz1957, 05 August 2014 - 02:03 AM.