Engine smoking badly after rebuild... HELP PLEASE!...
Discussion
Greetings Ladies and Gentlemen!
I would like to ask Your help.
I have two BMC mini related cars under restoration, a Wolseley Hornet and a Cox GTM. I have rebuilt two pre A+ non „S” 1275 engines for them.
I have done some engine rebuilds in the past few years with success. Not this time though. Each engines are smoking very badly. The smoke is blue, deffiniatly oil burning.
The sympthoms:
The car does not smoke when cold. The oil (mineral 20W50) needs to heat up before smoking starts. If You leave it to idle, a thin blue smoke appears. But if You drive it a bit, the smoke gets a way worse. And if You stop and let it idle again, the smoke is worse then before. If You stop the engine for a while (5 minutes enough), then after restarting it, at first it does not smoke, but after a few minutes, it starts again. The oil gets burned (deep brown) after a few hours idling/reving or 1-200kms ont he road. There is not too much crankcase gas present. When I remove the head, there is oil everywhere (ports, valves, inlet manifold etc). At the first time it was even worse, there were puddles of oil on the pistons. Now the pistons simply look black.
The pressure in the cylinders is good (14-15bars). The car is starting fine, running good, pulling strong, reving willingly. The oil pressure is good (hot, cold, idle, reved).
No oil in water, no water loss, but some marks of water in oil (on the cap only).
The engine specs:
The first engine is a 1275GT, sleeved back to std., bored and honed. New AE pistons, rings, new bearings, CR 9.75, SW5 cam, ported bigvalve head (reconditioned with new steel guides, valves, oil seals.
The second engine is from an Austin 1300. It was bored out to accept Minispares evo 73 pistons. New bearings, CR 11:1, Kent275 cam, ported bigvalve head with 31 rimflow exhaust valves. Head also reconditioned.
What I have done recently to find the problem:
- changed heads (two rconditioned and one old). Also had the heads double checked and tested (vacuum tested the ports)
- changed the oil (20/50 mineral, 15/40 mineral, different brands)
- removed the crankcase vents (clutch side, valve cover) from carb. Checked, they flow free, vented out to a catch tank.
- replaced mechanic fuel pump
- replaced head gasket (Payen, composite)
- replaced piston rings (new to another new)
First engine dismantled (after 4 hours running, plus 200kms road test).
- Piston-bore clearance 0.06mms-0.07mms (0.0025in)
- Bores round, not tappered (within 0.01mms)
- Rings were checked, gaps not lined up, rings facing the right direction, the oil ring started to get shinny on the bottom third.
- Ring gaps: 0.25-0.35mms (0.01-0.014in)
- No bad marks on pistons
- Honing very light, but present. Near TDC shining areas front and rear – honing nearly gone here, only maybe 0.003-0.005mms wear can be measured after a few hours of running
Second engine dismantled (after 500kms)
- Piston ring clearance 0.07-0.08mms (app 3 thou)
- Bores like the other
- Slight scoring to pistons (front/rear)
- Below TDC same shinnig areas, honing gone.
- Pistons top covered in black carcoal, but the piston crown is clean on some areas (mainly front and rear side) Piston skirt/ring area clean
And here I stand after struggling for 7 weeks day-and-night.
Please help me if only possible. What could go wrong with thesse engines? I am totaly out of ideas…
I would like to ask Your help.
I have two BMC mini related cars under restoration, a Wolseley Hornet and a Cox GTM. I have rebuilt two pre A+ non „S” 1275 engines for them.
I have done some engine rebuilds in the past few years with success. Not this time though. Each engines are smoking very badly. The smoke is blue, deffiniatly oil burning.
The sympthoms:
The car does not smoke when cold. The oil (mineral 20W50) needs to heat up before smoking starts. If You leave it to idle, a thin blue smoke appears. But if You drive it a bit, the smoke gets a way worse. And if You stop and let it idle again, the smoke is worse then before. If You stop the engine for a while (5 minutes enough), then after restarting it, at first it does not smoke, but after a few minutes, it starts again. The oil gets burned (deep brown) after a few hours idling/reving or 1-200kms ont he road. There is not too much crankcase gas present. When I remove the head, there is oil everywhere (ports, valves, inlet manifold etc). At the first time it was even worse, there were puddles of oil on the pistons. Now the pistons simply look black.
The pressure in the cylinders is good (14-15bars). The car is starting fine, running good, pulling strong, reving willingly. The oil pressure is good (hot, cold, idle, reved).
No oil in water, no water loss, but some marks of water in oil (on the cap only).
The engine specs:
The first engine is a 1275GT, sleeved back to std., bored and honed. New AE pistons, rings, new bearings, CR 9.75, SW5 cam, ported bigvalve head (reconditioned with new steel guides, valves, oil seals.
The second engine is from an Austin 1300. It was bored out to accept Minispares evo 73 pistons. New bearings, CR 11:1, Kent275 cam, ported bigvalve head with 31 rimflow exhaust valves. Head also reconditioned.
What I have done recently to find the problem:
- changed heads (two rconditioned and one old). Also had the heads double checked and tested (vacuum tested the ports)
- changed the oil (20/50 mineral, 15/40 mineral, different brands)
- removed the crankcase vents (clutch side, valve cover) from carb. Checked, they flow free, vented out to a catch tank.
- replaced mechanic fuel pump
- replaced head gasket (Payen, composite)
- replaced piston rings (new to another new)
First engine dismantled (after 4 hours running, plus 200kms road test).
- Piston-bore clearance 0.06mms-0.07mms (0.0025in)
- Bores round, not tappered (within 0.01mms)
- Rings were checked, gaps not lined up, rings facing the right direction, the oil ring started to get shinny on the bottom third.
- Ring gaps: 0.25-0.35mms (0.01-0.014in)
- No bad marks on pistons
- Honing very light, but present. Near TDC shining areas front and rear – honing nearly gone here, only maybe 0.003-0.005mms wear can be measured after a few hours of running
Second engine dismantled (after 500kms)
- Piston ring clearance 0.07-0.08mms (app 3 thou)
- Bores like the other
- Slight scoring to pistons (front/rear)
- Below TDC same shinnig areas, honing gone.
- Pistons top covered in black carcoal, but the piston crown is clean on some areas (mainly front and rear side) Piston skirt/ring area clean
And here I stand after struggling for 7 weeks day-and-night.
Please help me if only possible. What could go wrong with thesse engines? I am totaly out of ideas…
"if You stop and let it idle again, the smoke is worse then before" and "There is not too much crankcase gas present"
adding the two together it screams valve stem/guide problems to me. I would be inclined to clean up the inlet ports, backs of the inlet valves and manifold then run it at idle till it smokes then have a good look into the ports and see if there are signs of fresh oil dribbling out of the valve guides. Just possible they have been reamed too big and if they are wobbling around then the stem oil seals will be ineffective. The piston to bore clearance seems a bit tight to me too if they are forged pistons which tend to grow more than cast ones when hot but I am not an A series expert and the bores are smaller than the stuff I usually work on so I could be off the mark there. In any event it seems clear than it is coming from the top not the bottom. Your compression test seems to rule out piston sealing problems as well as the lack of excessive crankcase pressure.
adding the two together it screams valve stem/guide problems to me. I would be inclined to clean up the inlet ports, backs of the inlet valves and manifold then run it at idle till it smokes then have a good look into the ports and see if there are signs of fresh oil dribbling out of the valve guides. Just possible they have been reamed too big and if they are wobbling around then the stem oil seals will be ineffective. The piston to bore clearance seems a bit tight to me too if they are forged pistons which tend to grow more than cast ones when hot but I am not an A series expert and the bores are smaller than the stuff I usually work on so I could be off the mark there. In any event it seems clear than it is coming from the top not the bottom. Your compression test seems to rule out piston sealing problems as well as the lack of excessive crankcase pressure.
I think you probably have a valve guide stem seal problem, I would fit seals.
It is now too late to do anything about this but next time I would use a far lower piston to bore clearance. You can see where you are getting contact and that is going to affect ring sealing performance. Confirm which way round the pistons go to make sure the thrust side is correctly oriented.
When you assemble the engine I would wipe the top of the bores out with a piece of kitchen paper, after the pistons are in.
I would recheck the breather system and verify the oil level is set appropriately. It does not want to be hight.
It is now too late to do anything about this but next time I would use a far lower piston to bore clearance. You can see where you are getting contact and that is going to affect ring sealing performance. Confirm which way round the pistons go to make sure the thrust side is correctly oriented.
When you assemble the engine I would wipe the top of the bores out with a piece of kitchen paper, after the pistons are in.
I would recheck the breather system and verify the oil level is set appropriately. It does not want to be hight.
stevieturbo said:
Valve guides, or what have you done with the breather system ?
I have had the cylinder heads reconditioned with new valve guides, valves, seals. I had them tested (vacuumed the ports) and two different testers told me they are ok. I also have tried an old head on the engine, and it still smoked.
The breathers were disconnected from the carb at the first time and vented out to the air. But I have tried repluging them o create vacuum, but no use.
Well I suspect you're no wiser so far given that from different posters you have either too much or too little bore clearance and both think it's a valve guide problem. So what's the actual answer? Well it's nothing to do with valve guides.
You've almost answered your own question in the initial post with the information given.
(1) The oil is getting burned after just a short road mileage. That means it's circulating into the combustion chamber and also getting back into the sump rather than just being blown out of the exhaust.
(2) The piston to bore clearance is far too high in both engines. It should be about 0.0015" in the first engine with standard cast pistons and no more than 0.002" in the 73mm bore one with Evo pistons.
(3) You can see from the bore pictures, especially at the bottom of the bores that the main machining marks are almost horizontal not at 45 degrees. I suspect they are actually remnants of the boring operation rather than honing marks. Higher in the bores there are no honing marks left.
4) The smoking starts after a few minutes running. That's because the oil is now hot and thinning out.
The bores are not properly bored and honed. I suspect the machinist has bored too big to start with thus preventing him honing out enough stock to get a proper cross hatch finish. He's then just tickled over the bores with a fine stone to make it look like it's honed and not honed right down to the bottom of the bores. It's always harder to get the bottoms of the bores honed properly because you can't pass the hone down very deep without hitting the main bearing webs. In this case the tops of the bores are too shiny with little cross hatching because a coarse stone was never used and the bottoms are not really honed at all.
You have no proper oil control. The oil is coming up past the rings, burning and then some of it is being scraped back down again. You have high compression readings because the excess oil itself is sealing the rings.
You need to start again with new blocks and a new machinist. Bores should be taken to no closer than 1.5 thou from finished size on the boring bar, coarse honed (120 grit) to within a couple of tenths of finished size and then fine honed (220 to 280 grit) to size, all honing to be done using a 45 degree cross hatch angle by matching vertical stroke to rotation speed. A light plateau hone with a 400 or 500 grit stone can then be done if wanted. Even that 1.5 thou assumes a good boring bar which doesn't leave tool marks. If not then you might have to hone out as much as 3 thou. On my own bar I can go as close as 1 thou at a pinch but usually leave 1.5 to be safe.
Running in then needs to be done properly as explained on my web site.
http://www.pumaracing.co.uk/runin.htm
You've almost answered your own question in the initial post with the information given.
(1) The oil is getting burned after just a short road mileage. That means it's circulating into the combustion chamber and also getting back into the sump rather than just being blown out of the exhaust.
(2) The piston to bore clearance is far too high in both engines. It should be about 0.0015" in the first engine with standard cast pistons and no more than 0.002" in the 73mm bore one with Evo pistons.
(3) You can see from the bore pictures, especially at the bottom of the bores that the main machining marks are almost horizontal not at 45 degrees. I suspect they are actually remnants of the boring operation rather than honing marks. Higher in the bores there are no honing marks left.
4) The smoking starts after a few minutes running. That's because the oil is now hot and thinning out.
The bores are not properly bored and honed. I suspect the machinist has bored too big to start with thus preventing him honing out enough stock to get a proper cross hatch finish. He's then just tickled over the bores with a fine stone to make it look like it's honed and not honed right down to the bottom of the bores. It's always harder to get the bottoms of the bores honed properly because you can't pass the hone down very deep without hitting the main bearing webs. In this case the tops of the bores are too shiny with little cross hatching because a coarse stone was never used and the bottoms are not really honed at all.
You have no proper oil control. The oil is coming up past the rings, burning and then some of it is being scraped back down again. You have high compression readings because the excess oil itself is sealing the rings.
You need to start again with new blocks and a new machinist. Bores should be taken to no closer than 1.5 thou from finished size on the boring bar, coarse honed (120 grit) to within a couple of tenths of finished size and then fine honed (220 to 280 grit) to size, all honing to be done using a 45 degree cross hatch angle by matching vertical stroke to rotation speed. A light plateau hone with a 400 or 500 grit stone can then be done if wanted. Even that 1.5 thou assumes a good boring bar which doesn't leave tool marks. If not then you might have to hone out as much as 3 thou. On my own bar I can go as close as 1 thou at a pinch but usually leave 1.5 to be safe.
Running in then needs to be done properly as explained on my web site.
http://www.pumaracing.co.uk/runin.htm
camelotr said:
Pistons are symmithric items, not oriented.
No they are not! Look (measure) properly and the gudgeon pins will be closer to one side of the piston than the other. The pistons should be fitted with the gudgeon pin closest to the thrust side of the engine i.e the left hand side looking at the engine from the front pulley.I am realy gratefull to everybody, especialy Pumaracing for giving me of Your time.
Just today I have collected a small company of specialist (engine builders, race car mechanists, car restorers) and we have concluded just about the same as You told me earlier.
You helped me to make my decision to get my sleeved engine redone. It I succeed with this, I will get another engine and have it bored to 73mm to take the EVO's.
Realy thanks alot! I will report on the engine when I get it back and fitt it.
Pumaracing: the running in article is brilliant. I have added to my favorites.
BMC forever.
Just today I have collected a small company of specialist (engine builders, race car mechanists, car restorers) and we have concluded just about the same as You told me earlier.
You helped me to make my decision to get my sleeved engine redone. It I succeed with this, I will get another engine and have it bored to 73mm to take the EVO's.
Realy thanks alot! I will report on the engine when I get it back and fitt it.
Pumaracing: the running in article is brilliant. I have added to my favorites.
BMC forever.
Edited by camelotr on Friday 9th April 20:14
Edited by camelotr on Friday 9th April 20:34
I suggest you also read the other article on my website about running in camshafts. I may be wrong but from some of your text and the pic you have of engine 1 with the head removed after you say only 1 hour running I'm hoping you didn't just leave either of these engines to idle for long periods immediately after being rebuilt or you will have contributed greatly to your own problems by not running them in properly or at all.
Cams must be run in at fast idle (2000 to 2500 rpm) and the bores and rings need high throttle application several times to get gas pressure behind the rings to bed them in. You can only do this on a dyno or on the road.
Even after running in is complete I'm not a fan of letting performance engines idle for long periods as loads on the cam nose are highest like this. You'd better check your cams are not already buggered.
In the olden days it wasn't unknown for bores to not be honed at all. My own boring bar (40 plus years old) is designed to have enough precision to achieve a finished bore without honing although you'd never do this nowadays. The cross hatch is essential for oil control but if you run the engine in right you can just about manage without it. In fact if you consider a very worn engine with no cross hatch remaining it stills works ok up to a point.
However you must run the engine in to suit the bore finish. Very fine finishes with little cross hatch pattern require aggressive throttle application to bed the rings in. Coarse finishes sort themselves out over time but with more wear to the rings before bedding in is complete. On race engines that couldn't stand much mileage I used progressively finer finishes but you had to work the engine hard from the start and then it was fully run in after as little as 30 miles. Try that on a coarse finish and the engine will seize before it's run in.
I suspect many of your problems have been caused by incorrect running in and too much idling. The extra thou of clearance won't have stopped the pistons working ok although it wasn't ideal but too much idling with no cross hatch pattern is probably what finished things.
Cams must be run in at fast idle (2000 to 2500 rpm) and the bores and rings need high throttle application several times to get gas pressure behind the rings to bed them in. You can only do this on a dyno or on the road.
Even after running in is complete I'm not a fan of letting performance engines idle for long periods as loads on the cam nose are highest like this. You'd better check your cams are not already buggered.
In the olden days it wasn't unknown for bores to not be honed at all. My own boring bar (40 plus years old) is designed to have enough precision to achieve a finished bore without honing although you'd never do this nowadays. The cross hatch is essential for oil control but if you run the engine in right you can just about manage without it. In fact if you consider a very worn engine with no cross hatch remaining it stills works ok up to a point.
However you must run the engine in to suit the bore finish. Very fine finishes with little cross hatch pattern require aggressive throttle application to bed the rings in. Coarse finishes sort themselves out over time but with more wear to the rings before bedding in is complete. On race engines that couldn't stand much mileage I used progressively finer finishes but you had to work the engine hard from the start and then it was fully run in after as little as 30 miles. Try that on a coarse finish and the engine will seize before it's run in.
I suspect many of your problems have been caused by incorrect running in and too much idling. The extra thou of clearance won't have stopped the pistons working ok although it wasn't ideal but too much idling with no cross hatch pattern is probably what finished things.
Edited by Pumaracing on Saturday 10th April 06:23
You may be all right. Although I have succesfully ran in quite a couple of engines in the past. Plus the two engines were treated quite differently.
The first was stated up, ran at 2500 for 20 minutes for the cam, them lowered the revs and set the carb and the ignition.
Then stopped for a night. Next day I have stated the engine. This time I noticed the smoke (although it may have been present last time as well, just I was busy with other things). After this I did not wanted to go out without finding the souce of the smoke. I have revved the engine a bit and ran it on higher revs (3000+) for a while. Removed the head, made a dozen tests/changes (replacing head, gaskest, mechanic fuel pump, oil, etc). After no success, I have done some road tests (on the first couple of runs. I have treated this engine gently. 200kms - no use.
The second engine was run on high idle (2500) for a longer period, maybe 30 minutes. Then taken out and given load on the engine. I have treated this engine harder. 500kms - no use.
Although I have not checked the mixture with WBO, but I am pretty sure it was not "out of scale". The engine ran without hesitation - realy well.
I dont know. But after reciving the engine back, I will try to be more precise.
The first was stated up, ran at 2500 for 20 minutes for the cam, them lowered the revs and set the carb and the ignition.
Then stopped for a night. Next day I have stated the engine. This time I noticed the smoke (although it may have been present last time as well, just I was busy with other things). After this I did not wanted to go out without finding the souce of the smoke. I have revved the engine a bit and ran it on higher revs (3000+) for a while. Removed the head, made a dozen tests/changes (replacing head, gaskest, mechanic fuel pump, oil, etc). After no success, I have done some road tests (on the first couple of runs. I have treated this engine gently. 200kms - no use.
The second engine was run on high idle (2500) for a longer period, maybe 30 minutes. Then taken out and given load on the engine. I have treated this engine harder. 500kms - no use.
Although I have not checked the mixture with WBO, but I am pretty sure it was not "out of scale". The engine ran without hesitation - realy well.
I dont know. But after reciving the engine back, I will try to be more precise.
Edited by camelotr on Saturday 10th April 07:52
Ok that's good you did the camshaft running in properly. Anyway even so I think you stood no chance of running the rings in against those bores. It's interesting looking at the scuff patterns in the bores. You can see sets of vertical scuff lines all ending at the same horizontal position which is either the topmost position of the oil rings with the piston at TDC or it's where boring tool marks were still standing proud and the rings were knocking the edges off them. I think the former.
Whatever it's highly abnormal and clear evidence of how bad the boring and honing was. I suspect the oil rings were already finished within a few minutes of start up going by how severe those scuff marks are.
Good article on boring and honing here.
http://autospeed.com/cms/A_109105/printArticle.htm...
Nice pic of what to look for in a freshly honed bore here.
http://theoldone.com/articles/badtothebone/Cylinde...
I used to go to ridiculous lengths to try and achieve perfection with the bores in my race engines. I tried to work to 0.0001" on taper, ovality and diameter for all bores but rarely got better than 0.0002" or 0.0003". The honing would take place over several days because of heat build up each time you honed any material out. After 30 seconds honing you might think you'd removed 3 or 4 tenths of a thou but after the block had sat overnight and cooled down you'd find it was only 1 tenth and the rest was thermal expansion of the cast iron. I'd just sneak up on target size over several days and several honing operations.
More coolant and a bigger drill would have helped but you work with what you've got. The tolerance from general engine reconditioners is often no better than +/- 0.001" although I did know one guy I could rely on to within about 3 tenths if I had to farm a job out. Trouble was that was all he could do properly. His valve and seat work was awful.
Whatever it's highly abnormal and clear evidence of how bad the boring and honing was. I suspect the oil rings were already finished within a few minutes of start up going by how severe those scuff marks are.
Good article on boring and honing here.
http://autospeed.com/cms/A_109105/printArticle.htm...
Nice pic of what to look for in a freshly honed bore here.
http://theoldone.com/articles/badtothebone/Cylinde...
I used to go to ridiculous lengths to try and achieve perfection with the bores in my race engines. I tried to work to 0.0001" on taper, ovality and diameter for all bores but rarely got better than 0.0002" or 0.0003". The honing would take place over several days because of heat build up each time you honed any material out. After 30 seconds honing you might think you'd removed 3 or 4 tenths of a thou but after the block had sat overnight and cooled down you'd find it was only 1 tenth and the rest was thermal expansion of the cast iron. I'd just sneak up on target size over several days and several honing operations.
More coolant and a bigger drill would have helped but you work with what you've got. The tolerance from general engine reconditioners is often no better than +/- 0.001" although I did know one guy I could rely on to within about 3 tenths if I had to farm a job out. Trouble was that was all he could do properly. His valve and seat work was awful.
Edited by Pumaracing on Saturday 10th April 09:13
Thanks again. This is a real "Engine academy". I though I know something, but deffiniatly not.
I thinks my engines were done not 100%. I will try to press the machinist do a better work next time. He has the right equipment, and knowledge. I think he was not keen enough on his employee.
The articles are perfect.
Can You advice me more? I think if I would like to come out of this problem, I should at least try to leanr as much as possible.
I thinks my engines were done not 100%. I will try to press the machinist do a better work next time. He has the right equipment, and knowledge. I think he was not keen enough on his employee.
The articles are perfect.
Can You advice me more? I think if I would like to come out of this problem, I should at least try to leanr as much as possible.
Many years ago I suffered a similar problem on a 1380. Turned out that was down to poor ring bedding/bore glazing, caused by a too prolonged and gentle running in period (and poor pattern). Ever since I've adopted a less sympathetic approach to running in (increasing and varied load/rpm)and used a different machine shop, I've not had a problem.
One point I can confirm - there's definately no pin offset on AE A-series pistons.
If you decide to take one of the blocks further, I've got a brand new set of 73.5mm pistons complete with rings & lightweight pins which are surplus to requirements (I think with a 9cc dish, but would have to check). These are Minispares Mega pistons manufactured by AE. Drop me a line if you're interested.
Good luck with the rebuild
One point I can confirm - there's definately no pin offset on AE A-series pistons.
If you decide to take one of the blocks further, I've got a brand new set of 73.5mm pistons complete with rings & lightweight pins which are surplus to requirements (I think with a 9cc dish, but would have to check). These are Minispares Mega pistons manufactured by AE. Drop me a line if you're interested.
Good luck with the rebuild
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