8 replies to this topic

[1968cooper]

I have an old 998 Cooper that appears to be down on power. It starts and runs lovely accelerates reasonably well on the flat, but show it the slightest hill and the engine dies I try to accelerate it bogs. Now this engine hasn’t run for 30 years so I know I was expecting a bit much for perfection. I borrowed a compression tester today, cylinders 1 and 2 around 120 psi cylinders 3 and 4 60 to 70 psi squirted a little oil in these cylinders which gave around 20 psi increase. I am hoping to get away with a head off and valve regrind. She is not blowing oil from the filler or dipstick holes and she doesn’t smoke so I am hoping the piston rings are okay, but there appears to be considerable crankcase vacuum, if you remove the oil filler cap the engine speeds up, if you place your hand over the open hole the engine stops, why does this happen? Is this normal? I should know better but I can’t remember doing this before! I appreciate the closed circuit breathing system is creating the vacuum but if it is sucking oil fumes from piston blow by would I not have a smoky exhaust. Any thoughts on this.

[sonikk4]

Judging by those figures the bottom end is due a overhaul. Pressure going up with a squirt of oil in each bore points to worn, damaged rings or wear in the bores.

[Dusky]

Seems like you're running too rich as well. When you remove the oil cap you allow the carb to (indirectly) suck in more fresh air through the breather hose.
 

[carbon]

If the engine has not been run for 30 years you may need to be patient, it's possible that some of the piston rings are sticking in the grooves.

 

What oil are you running?

[greenwheels]

Have you checked the carb pistons are not sticking?

Edited by greenwheels, 06 May 2016 - 06:14 PM.

[1968cooper]

If the engine has not been run for 30 years you may need to be patient, it's possible that some of the piston rings are sticking in the grooves.

 

What oil are you running?

I thought the same. I don't remember the engine having any problems when I stopped using it in 1986. I have had it running in my workshop and been half a mile up the lane. I am using a 20/50 from the local motor factor, do you think I should put something special in?

[carbon]

Might be worth a couple of squirts of diesel or similar into bores 3 and 4, leave for a few days and then take it for a good run.

 

Greenwheel's suggestion of checking the carb pistons is good, might be worth first checking the carb which feeds cylinders 3 & 4 in case this is sticking.

[1968cooper]

Might be worth a couple of squirts of diesel or similar into bores 3 and 4, leave for a few days and then take it for a good run.

 

Greenwheel's suggestion of checking the carb pistons is good, might be worth first checking the carb which feeds cylinders 3 & 4 in case this is sticking.

Thank you, I will try the diesel. I did pour some Lusol down the plugholes and left it to soak before putting fresh oil in. Even though the engine had been left for so many years it turned freely. I did strip and rebuild the carbs, as they were gummed with old fuel, but even after resetting by the manual she is running rich, so I intend having another go at adjustment

 

 

.

[carbon]

If carbs are still running rich then worth checking the jets are returning fully when choke is in, they can sometimes stick.

 

Also if you don't already have an in-line petrol filter fitted just before the carbs this is worth having, as rust from the tank can stop the float valve sealing properly and cause rich running (or if bad carb flooding). The cheap clear plastic ones are ideal, you can see when they need replacing.