Discussion
I have a special with a tuned 1000cc Mini lump in the back, the engine is burning a lot of oil, it clears after a while but to me still seems too smokey.
I have noticed the engine position is inclined towards the front. This means oils sits round the valve guides.
I can also move the tops of the stems on a couple of valves so guessing this could be the problem.
The car was standing for years, but the compressions seem fine approx 125 accros all 4, not sure if a failed oil control ring would effect compression though.
Plugs are well oily,
Struggles to tick over,
Any other tests?
I can get the CO down to 2.5% but it still has visible smoke.
Looked at replacing the head as its the 12G940 model but not sure what valve sizes I can get way with on a 1000cc
Thanks
Joe
I have noticed the engine position is inclined towards the front. This means oils sits round the valve guides.
I can also move the tops of the stems on a couple of valves so guessing this could be the problem.
The car was standing for years, but the compressions seem fine approx 125 accros all 4, not sure if a failed oil control ring would effect compression though.
Plugs are well oily,
Struggles to tick over,
Any other tests?
I can get the CO down to 2.5% but it still has visible smoke.
Looked at replacing the head as its the 12G940 model but not sure what valve sizes I can get way with on a 1000cc
Thanks
Joe
Drive the car, travel downhill on overun and then watch for the blue clouds as you put your foot back in. The compression test has shown that whilst the readings aren't brilliant, most things are pointing to oil coming down the valve guides. The guides and/or stem seals sound like they are shot.
I think you probably have a bit of a combination of knackered bores hence blowby (hence the poor compression test results) and knackered valve stem oil seals.
NB* An A-series oddity - if a Mini (even in rudest health) is left ticking over nose downhill, will suck oil down the guides and will result in a puff at start up or when the car is revved. Noticed this as used to have a very heavily inclined driveway. You don't mention how inclined your engine is - could the oil usage/visible smoke be a factor of the installation?
HTH.
P.S If you use a 12g940 on a 1000cc unit you will need to pocket the block to clear the exhaust valves for saftey if using a performance cam, and use a 1300cc H/gasket.
I think you probably have a bit of a combination of knackered bores hence blowby (hence the poor compression test results) and knackered valve stem oil seals.
NB* An A-series oddity - if a Mini (even in rudest health) is left ticking over nose downhill, will suck oil down the guides and will result in a puff at start up or when the car is revved. Noticed this as used to have a very heavily inclined driveway. You don't mention how inclined your engine is - could the oil usage/visible smoke be a factor of the installation?
HTH.
P.S If you use a 12g940 on a 1000cc unit you will need to pocket the block to clear the exhaust valves for saftey if using a performance cam, and use a 1300cc H/gasket.
Edited by FWDRacer on Friday 9th May 12:03
Edited by FWDRacer on Friday 9th May 12:04
Hello
Havent managed to get it back on the road yet, other than a few quick test drives, I will check the compression numbers again, whats considered good for a mini engine.
I will also measure the incline, to give an idea when the rocker cover is removed, the oil level in the head is a few mm above the rocker cover gasket at the front,it pours out. Changing this incline could be looked at, might mean some chassis tweaks.
You now see my dilema, throw whole unit way which seems a shame as its the original engine for the car built by some tuner years ago, and drop in a new unit, or replace the head.
The engine has only done a few thousand miles from new allegedly but this was in 1990.
Are you saying mini valve guides are not that good a fit hence the oil being sucked down them? or is it a breather type problem in the rocker cover.
I think I need to Identify the block as your last comment indicates, it has no engine number plate, any other marks in the block I could look out for.
Thanks
Joe
Havent managed to get it back on the road yet, other than a few quick test drives, I will check the compression numbers again, whats considered good for a mini engine.
I will also measure the incline, to give an idea when the rocker cover is removed, the oil level in the head is a few mm above the rocker cover gasket at the front,it pours out. Changing this incline could be looked at, might mean some chassis tweaks.
You now see my dilema, throw whole unit way which seems a shame as its the original engine for the car built by some tuner years ago, and drop in a new unit, or replace the head.
The engine has only done a few thousand miles from new allegedly but this was in 1990.
Are you saying mini valve guides are not that good a fit hence the oil being sucked down them? or is it a breather type problem in the rocker cover.
I think I need to Identify the block as your last comment indicates, it has no engine number plate, any other marks in the block I could look out for.
Thanks
Joe
Edited by Joe T on Friday 9th May 12:37
Well stripped the head off, firstly no stem seals on the exhaust valves?
A little bit of side to side at the top of the valve stems, not sure what the tolerance is on these engine. It has double springs.
Some dimensions
Valves Inlet 35.7 mm Exhaust 29.5mm
Cylinder Bore 72mm
Numbers on Piston 21250 .060
Then very small ID6 521
Bores are like new, still see crosshatching, it really dosnt look that old. No step at the top at all.
Might pour a bit of oil in the top and see how long it stays there.
Looking at the head I wonder if I can grind the trough down a bit lower that carries the oil from the valve spring area to the push rod holes.
I could set the head on the same incline on the bench and work out how much to take off, most would be at the push rod hole end.
So worth reconditioning this head or just get another ?
A little bit of side to side at the top of the valve stems, not sure what the tolerance is on these engine. It has double springs.
Some dimensions
Valves Inlet 35.7 mm Exhaust 29.5mm
Cylinder Bore 72mm
Numbers on Piston 21250 .060
Then very small ID6 521
Bores are like new, still see crosshatching, it really dosnt look that old. No step at the top at all.
Might pour a bit of oil in the top and see how long it stays there.
Looking at the head I wonder if I can grind the trough down a bit lower that carries the oil from the valve spring area to the push rod holes.
I could set the head on the same incline on the bench and work out how much to take off, most would be at the push rod hole end.
So worth reconditioning this head or just get another ?
21250 are not 1000 cc pistons, unless it's a rare 970 'S' motor. The 21250 is a medium use Hepolite piston - OK, but not as good as the 21253 which is stronger and will take much higher revs.
The exhaust valves often don't have valve stem seals as current thinking is that they are not necessary. Some of us think differently.
It's worth fitting new valve guides and re-seating the valves. Use seals on all valve stems. You could hone the bores and re-ring the pistons, but if going this route then first check for bore wear at mid stroke. One easy way to do this is to remove one piston ring, measure the gap with the ring in the bore about 1/4" down from the deck, then measure the gap about 1.5" down from the deck level. This will tell you if the bore is worn. Should the gap at mid-stroke be more than about 0.004" greater than at the top, then you need a re-bore and new pistons. If going for new pistons, go for the 21253, they really are excellent and not too expensive. You can spend a fortune on pistons (ask me about my Karl Schmidt ones), but the 21253 are an excellent compromise and are fine for most motor sports.
The exhaust valves often don't have valve stem seals as current thinking is that they are not necessary. Some of us think differently.
It's worth fitting new valve guides and re-seating the valves. Use seals on all valve stems. You could hone the bores and re-ring the pistons, but if going this route then first check for bore wear at mid stroke. One easy way to do this is to remove one piston ring, measure the gap with the ring in the bore about 1/4" down from the deck, then measure the gap about 1.5" down from the deck level. This will tell you if the bore is worn. Should the gap at mid-stroke be more than about 0.004" greater than at the top, then you need a re-bore and new pistons. If going for new pistons, go for the 21253, they really are excellent and not too expensive. You can spend a fortune on pistons (ask me about my Karl Schmidt ones), but the 21253 are an excellent compromise and are fine for most motor sports.
Hi, only have the logbook to go by regards the engine size, I am not familiar with the A Series at all.
So I am assuming that there should be no side to side movement at all in the valve stem. It is only slight and pretty much the same on all of them.
I am not aiming to race this, just want to get it back on the road to test the chassis dynamics, for that it needs an MOT, thats the goal.
There is a 2cm incline across the block face front to back edge. So a lot of oil around the base of the valves when running.
I have measured the bores with calipers they do seem fine, no 004 difference.
Any idea how much I could grind out of the oil gulleys from valve area to pushrod tube, is there a fair bit of material in the head there, if anyone has an A Series head diagram or CAD I can open most formats.
Thanks
Joe
So I am assuming that there should be no side to side movement at all in the valve stem. It is only slight and pretty much the same on all of them.
I am not aiming to race this, just want to get it back on the road to test the chassis dynamics, for that it needs an MOT, thats the goal.
There is a 2cm incline across the block face front to back edge. So a lot of oil around the base of the valves when running.
I have measured the bores with calipers they do seem fine, no 004 difference.
Any idea how much I could grind out of the oil gulleys from valve area to pushrod tube, is there a fair bit of material in the head there, if anyone has an A Series head diagram or CAD I can open most formats.
Thanks
Joe
Whilst the head is off you could measure the actual capacity. I suspect it's a 1275 lump.
With regard to the head, I doubt anyone has a drawing on CAD and grinding bits away other than the usual areas for gas flowing is always going to be a risk. Maybe take about 2 mm out to see if that cures the problem. If you did screw up the head, I've got some spare 12G940 castings and you would be welcome to one for a few quid.
A small amount of play in the valve stems/guides is not a big problem. Better that than valves sticking in the guides if the engine gets really hot, which happened to a friend of mine with a recently re-built head on the M25 yesterday. It's 1330cc engine and the oil got really hot (over 120 deg C) as he has yet to fit an oil cooler (silly boy!). He phoned me as he thought he had a broken valve spring, but it can't be that as the springs ar doubles. The way he described it it sure sounds like sticking valve(s). We shall see tomorrow when the head comes off.
With regard to the head, I doubt anyone has a drawing on CAD and grinding bits away other than the usual areas for gas flowing is always going to be a risk. Maybe take about 2 mm out to see if that cures the problem. If you did screw up the head, I've got some spare 12G940 castings and you would be welcome to one for a few quid.
A small amount of play in the valve stems/guides is not a big problem. Better that than valves sticking in the guides if the engine gets really hot, which happened to a friend of mine with a recently re-built head on the M25 yesterday. It's 1330cc engine and the oil got really hot (over 120 deg C) as he has yet to fit an oil cooler (silly boy!). He phoned me as he thought he had a broken valve spring, but it can't be that as the springs ar doubles. The way he described it it sure sounds like sticking valve(s). We shall see tomorrow when the head comes off.
The stroke comes out at 82.5mm, pretty sure the bore is 72-73mm,
I was thinking of a gradual sawblade cut then I could always tig it up if I go through to something.
I did recheck the compressions 175 was the average, all about the same.
Cooling on this should be fine, has a larger than mini rad at the front of the car, so lots more water also.
SomEthing I forgot to mention was a sort of small end rattle it does during the rev range, just a light clatter only at a specific RPM I think about 3000,
So worth an experiment with the oil trough and stem seals on all the valves, along with a tweak to the engine incline, even if I move it a bit its got to help.
Anything after that I suppose is going to cost.
I will report back when done
Thanks
Joe
Head Gasket number is TAM1521.
Capacity 3.14 * 36.5 * 36.5 * 82.5/1000 =1380cc
I was thinking of a gradual sawblade cut then I could always tig it up if I go through to something.
I did recheck the compressions 175 was the average, all about the same.
Cooling on this should be fine, has a larger than mini rad at the front of the car, so lots more water also.
SomEthing I forgot to mention was a sort of small end rattle it does during the rev range, just a light clatter only at a specific RPM I think about 3000,
So worth an experiment with the oil trough and stem seals on all the valves, along with a tweak to the engine incline, even if I move it a bit its got to help.
Anything after that I suppose is going to cost.
I will report back when done
Thanks
Joe
Head Gasket number is TAM1521.
Capacity 3.14 * 36.5 * 36.5 * 82.5/1000 =1380cc
Edited by Joe T on Sunday 11th May 17:44
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