Leaking piston rings?

[MichelvdM]

Hi Guys,

My Spitfire 1500 is burning quite some oil. I have lifted the head and while looking at the bores and the pistons I am
wondering what could be wrong. I have measured around 8,5 bars compression and this seemed to be kind of low. As a test I have put some gasoline on top of the pistons and was quite suprised that it was gone on all of the pistons after a couple of minutes. I even heard the gasoline dripping in the sump. Is this a test a valid manner to see if there is a loss of compression?

Thanks,

Michel

[Rallyspit]

Whoa.... don't use gasoline (petrol). Use engine oil to check if the rings are leaking, petrol has very low viscosity and will drip straight past the rings and not seal them sufficiently to do any reliable diagnosis. Even oil will slowly seep past the rings. Use a quick squirt of oil and do your compression test (with all spark plugs removed, coil disconnected and throttle pedal down) for a more reliable reading.

That engine also looks very clean, is it recently rebuilt? If so did you hone the cylinder bores, 'cos if not it will exhibit all the symptoms you describe.

[Sheepy]

I agree with R.S. don't use fuel for the test, use oil.

While the head is off check the side movement in the valve stems! (before removing the valve spring do a valve leak test, use fuel for that! As you looking for the slightest leak)
Turn the head over, get it level (two blocks of wood is good) then poor some fuel into the combustion chamber and see if it leak out.

Is it a recon/rebuilt head? Then it should be ok, if not the valves may need lapping in.

When you say it used oil, was it smoking? Usually if she smokes it's a sign that the rings are worn, if it just puffs when you declutch, it points to worn valve stems.

Have you not got a leak on the engine? A failing gasket or something? When it's parked do you see a puddle of oil?

[MichelvdM]

Hi Shawn

Quite a story. When I started restoring the car (7,5 years ago) I knew that the engine had been revised earlier and very few km's have been done after that. While dismantling the engine I saw that the pistons still looked quite shiny. Also the bores looked very smooth, even still showing the hone marks. That made me thinking that the engine didn't require much attention. I had the valves checked and the head and lower block flattened. Pistons were cleaned and been put back in. Now that the restoration is finished and I was making the first km's I noticed quite some smoke (blue) coming from the exhaust. I also noticed the oil level lowering from Max to Min after 60 km's and turning black.
On accelerating and especially driving away after waiting for a traffic light gave quite some smoke. Also on idling too.

I decided to check the compression this and seemed low (8,4 – 8,7 Bar range) what made me decide to strip the engine (real tough decision :'()to find the cause. Besides leakage through the valves and piston rings, also the head gasket could be to blame for taking oil. As you probably now the 1500 engines have recessed cylinder bores. The block itself also has been flattened what means that the depth of the recessed bore has become less and I am wondering if there could be a leak between the bore and the oil channels. If I am looking at the metal rings in the old gasket you can see this has been nicely compressed.  I haven’t noticed any external head gasket leakage and didn’t see any cooling fluid in the oil.

Any suggestion is very welcome. I already learned that removing pistons and turning the pistons rings and then put back has not been the smartest decision...

4058 wrote:

I agree with R.S. don't use fuel for the test, use oil.

While the head is off check the side movement in the valve stems! (before removing the valve spring do a valve leak test, use fuel for that! As you looking for the slightest leak)
Turn the head over, get it level (two blocks of wood is good) then poor some fuel into the combustion chamber and see if it leak out.

Is it a recon/rebuilt head? Then it should be ok, if not the valves may need lapping in.

When you say it used oil, was it smoking? Usually if she smokes it's a sign that the rings are worn, if it just puffs when you declutch, it points to worn valve stems.

Have you not got a leak on the engine? A failing gasket or something? When it's parked do you see a puddle of oil?

[Steve AKA vitessesteve]

Probably too late now but did you two compression tests.  First as is and then a second wet test. To do wet test add a teaspoon of oil to each cylinder via the spark plug hole and then redo the test. The oil makes a temporary seal so if the pressure is still low the compression is probably being lost to the top of the engine ie valves or gasket rather than past the piston rings.

[Sheepy]

When you fit the rings, have the gaps offset to each other, (I.e. not all in a line)

Also you say it is a recessed block, was the correct recessed gasket used? (there are two different ones, a recessed and non recessed) just a thought.

That's a lot of oil being burnt, if the engine has been sat for a while, the rings could stick in the piston, but If it was recently built, I would not suspect that.
You say you can see the honing marks, that is good, but it may be good to try measuring the ring gap, place a ring in the bore and set it square with the piston (up turned and pushing it in the bore from above, a little way in, then remove, and it will leave the piston square, and a good way into the bore) then measure the gap with feeler gauge comparing to the technical specification for that engine.
If after they built it, and it has stood for a while, perhaps the oil used during build up has drained away from the rings, and when it was run it was "dry" for a while, therefore prematurely wearing the rings.
(I'm just trying to throw ideas at you)
I would suspect rings, as you say it smokes alot and the oil goes black.

Hope this helps, and not scare you!  ;)

[MichelvdM]

Hi Shaun,

Thanks for thinking with me. This is the only way to come to a solution.
I just measured my valve OD's and valve guide ID's and I have double check but these all seem to be within the tolerance.
While doing this is also noticed that the inlet ports are oily,pls see picture. This shouldn't be the case. This means that oil is being sucked through the valve clearance. I indeed installed the special head gasket. I need to continue and remove the engine from the car and remove the pistons. I am planning to buy new rings and have the bores honed once more. I don't think I have another choice... ??)

4058 wrote:

When you fit the rings, have the gaps offset to each other, (I.e. not all in a line)

Also you say it is a recessed block, was the correct recessed gasket used? (there are two different ones, a recessed and non recessed) just a thought.

That's a lot of oil being burnt, if the engine has been sat for a while, the rings could stick in the piston, but If it was recently built, I would not suspect that.
You say you can see the honing marks, that is good, but it may be good to try measuring the ring gap, place a ring in the bore and set it square with the piston (up turned and pushing it in the bore from above, a little way in, then remove, and it will leave the piston square, and a good way into the bore) then measure the gap with feeler gauge comparing to the technical specification for that engine.
If after they built it, and it has stood for a while, perhaps the oil used during build up has drained away from the rings, and when it was run it was "dry" for a while, therefore prematurely wearing the rings.
(I'm just trying to throw ideas at you)
I would suspect rings, as you say it smokes alot and the oil goes black.

Hope this helps, and not scare you!  ;)

[WIMPUS]

Michel told me that he had an external rocker shaft oil feed kit installed.
Can it be that he was burning oil because of that ? (Heard a few story's about those kit's .. )

[GT6 M]

could be the  oil feed, as this does increase oil use
need a restrictor init,  aboot 1/64"

other thing is, if its burning oil, is this cos yer oils to thin, as its been thinned by the
fuel ye lost doon the bores,!!!

try some new oil, 20/50 /60 nd see if it does make a diff.
as oil get older it goes thinner, reverts back to just a 20 grade, and gets thru rings

M

[JohnD]

Skimimg the face of the block will reduce the depth of the recesses.   That would compress the 'fire rings' around the bore even more, but could prevent the head-to-block compression sealing any other passages.   The areas on the block face around the passages in the water jacket look very corroded, Micheal - are they?  But for oil to be lost in this way it would be from the ascending oil passage to the rocker shaft, and you would have a leak from the rear of the head/block joint.   So I don't hink it's that.

I think that, as usual, it is the external oil feed that is Ye Spawne of Ye Deville!    So wrong in so many ways!
The oil passage in the block appears to be unblocked, Michael.  Some who fit the external supply block it, which does nothing to deal with the devillement that the supply causes, so refit the head without the external, and observe for oil flow into the rockers.  Ony a little is required, unlike the flood that an un-restricted external line supplies.

Also worth on re-assembly and running, check that there is no excess blow-by into the crank case.  Take off the oil filler cap with it running and see if there is much of a gas flow out.  A gentle breeze is normal but a lot means poorly sealing piston rings.

Lastly, respect to Sheepy, but don't worry about off-setting the rings on assembly.  They rotate as the engine runs, approximately a thousand times more slowly than the engine, so wherever you set them, they won't stay there!

JOhn