Burning oil

[97fm]

Hi

Burning a lot of oil, took the head off and discovered all cylinders scored horizontally. Any ideas of the cause?

[Mike C]

That looks like the piston ring ends  scratched the bores during the last assembly , after honing. Buy why all 6 ?

[roy53]

cannot see it being pistons

looks like bad honing or rings to loose and not sealing   ,     No vertical wear shown.

[charlie74]

If rings wouldn’t the marks go the whole length of the stroke?  It’s hard to tell in the photos…

[Mike C]

11 minutes ago, charlie74 said:

If rings wouldn’t the marks go the whole length of the stroke?  It’s hard to tell in the photos…

The original piston  insertion process might have included twisting the pistons, possibly someone that didn't use a good ring compressor. That's about the only process I can think of that will cause the limited helical scratches over the honing.

[PodOne]

Have the correct sized pistons being installed the right way around and with the correct rings and spacing?

[Stagpowered]

Looks like it might have been honed with something very coarse, like a 40 grit flap wheel. Buying a proper honing tool and giving it a quick run over might help, but i would fit new rings in case the old ones are lacking tension

[Motorsport Mickey]

When the engine was running and burning oil...what compression was across all the cylinders ?

What dia pistons have you got against the liner bore dimensions you have ? Remember pistons are not made round measure in 2 planes at 90 deg to each other and swing the piston an inch and measure again to make sure you get the biggest size. Use snap gauges to measure the liner bore dias, measure about 1" down the bore and about 3" down the bore. 

Are there any lips on the top of the liners from a previous owner having reringed the engine ?

The normal running difference between the piston and liner sizes should be about 3 thou, the engine will run ok probably up to maybe 5 thou but power will decrease there and oil consumption increase due to the reduced tangential loading upon the piston rings against the liner bores. The liner bores being a larger size reduced it (unless we are talking competition and forged pistons but that's another story).

Liners that still have concentric machine or honing marks is bad news because the piston rings haven't been pressing against the liners and wearing their own sealing pattern into the liner walls. Ergo...either the liners and pistons are mismatched on sizes or the piston rings are the wrong size for the pistons or liners.

Basic measuring and deduction will show you the way forward, beware trying to increase the piston ring size without refitting new pistons of equivalent size ie 86 + 20 pistons should have the equivalent piston rings sizing with them, (I realise you have a 6 cyl but just quoting dimensions) If the liner sizing is oversize against the pistons maybe relining the block with new pistons complete with rings is the way ahead.

Mick Richards

 

 

[roy53]

On 12/24/2023 at 12:21 PM, charlie74 said:

If rings wouldn’t the marks go the whole length of the stroke?  It’s hard to tell in the photos…

yes but it looks like the rings are not in contact with the bore. Or should i say with no force.

[97fm]

7 hours ago, Motorsport Mickey said:

When the engine was running and burning oil...what compression was across all the cylinders ?

What dia pistons have you got against the liner bore dimensions you have ? Remember pistons are not made round measure in 2 planes at 90 deg to each other and swing the piston an inch and measure again to make sure you get the biggest size. Use snap gauges to measure the liner bore dias, measure about 1" down the bore and about 3" down the bore. 

Are there any lips on the top of the liners from a previous owner having reringed the engine ?

The normal running difference between the piston and liner sizes should be about 3 thou, the engine will run ok probably up to maybe 5 thou but power will decrease there and oil consumption increase due to the reduced tangential loading upon the piston rings against the liner bores. The liner bores being a larger size reduced it (unless we are talking competition and forged pistons but that's another story).

Liners that still have concentric machine or honing marks is bad news because the piston rings haven't been pressing against the liners and wearing their own sealing pattern into the liner walls. Ergo...either the liners and pistons are mismatched on sizes or the piston rings are the wrong size for the pistons or liners.

Basic measuring and deduction will show you the way forward, beware trying to increase the piston ring size without refitting new pistons of equivalent size ie 86 + 20 pistons should have the equivalent piston rings sizing with them, (I realise you have a 6 cyl but just quoting dimensions) If the liner sizing is oversize against the pistons maybe relining the block with new pistons complete with rings is the way ahead.

Mick Richards

 

 

Hi Mike

Season greetings to you and have a happy new year.

Thank you for the benefit of your experience. 
Dry compression test was 

five at 150 and one at 155

wet test erratic, ranging from 150 to180.

Tried new ring at top middle and bottom but could only use feeler gauges( awaiting bore gauge) and all readings within 6 thou of each other.

Will measure the pistons as you said.

When dropped the sump, no metal or grey oil only carbon deposits.

Camshaft lift checked and ok.

cheers

 

[Motorsport Mickey]

The compressions don't seem too bad, but measuring the pistons and comparing against the cylinder bores will give you an idea what's going on.

Mick Richards

[Mike C]

I agree with Mick . The compression test figures look OK. Any damage to the oil control rings?

[trchris]

If the engines been re-ringed has a the carbon been remove from the ring groves on the pistons correctly ? and if so has someone been overzealous and scored the piston within the groves?
Chris