Suspected piston ring issue

[coolchris]

Hi there,

Just looking to pick the brains on here on a smoke issue on my car. It is burning a bit of oil and I am getting what looks like smoke out of the oil catch can breather pipe that goes to atmosphere and a bit out of the oil filler if I take the cap off.. I did a compression test all cylinders were a between 100 and 110 but one was 84 I i put a teaspoon of oil down the chamber re tested and it shot up to 148.

I know all this does point to a piston ring issue as I have 2 symptoms of that ( low compression and blow by) but the car to drive there is no missfire no flat spots the car pulls cleanly right through the rev range no hesitation under load and from what I have read on the net missfire and loss of power is something you would expect with a loss of compression issue is that the case or not necessarily ?.I know there is an issue there is there anything I am possibly missing ? car is a two point five noble m12.

regards

chris

[Chemapi]

Hi coolchris, the symptoms you are talking about could be due to two possible explanations, either a shot fire ring issue (as you think) or a blown cylinder head gasket. I think the latter would be more likely because of what you say about you can see smoke coming from the oil filter. In the following link you can read something about it:

https://haynes.com/en-us/tips-tutorials/5-signs-yo...

Both cases you will have to pull the cylinder head up to check the problem.
Regards

[paintman]

Be interesting to see what you get out of the other cylinders with the oil test.
Sounds like a well worn engine.

[coolchris]

Hi Chemapi,

Thanks for your helpful advice.The car does not run hot the temp is constant and it does not use any coolant so I am thinking possibly not head gasket.I was advised if it is a ring then it would be a re bore and bigger pistons and rings but if it was just the rings couldn't the old pistons just not be used again ?.

[DVandrews]

If it was a head gasket failure you would see other symptoms, cooling issues / coolant loss etc. If you have crankcase pressure and low compressions then it is more likely to be a problem with the rings. I would arrange a leakdown test which the results of which will prove conclusively where the problem lies. BTW the ‘fire ring’ mentioned earlier is a misnomer, the fire ring is part of the head gasket.

Dave

[Chemapi]

Hi all, this is getting very interesting!!! It could be both but a head gasket has passages for coolant, oil, bolts and obviously pistons and around all of them there are "beads" that generate the enough force (coming from the bolts) to close all of these passages so that all the fluids do not mix up and the pressure inside the combustion chamber is kept. Over the years these beads tend to flatten and lose sealibility around what they seal. Depending on where it first happens you will have different symptoms. And as DVandrews says fire ring is a part of the gasket around the combustion chamber, sorry for the misundertanding. I would like to help you more but surely as I said earlier you will have to pull the cylinder head up to discover the problem.
Regards

[coolchris]

I do suspect that if it was rings and head gasket that the car would run like a bag of nails.I have been running the car in its current condition for about a 1000 miles and apart from the blow by and having to keep an eye on the oil level the car still pulls like a train.

I do feel though it is at a stage being winter that it makes sense to get it sorted as I know it wont get any better and a mechanic I spoke to said I could blow the engine carrying on driving it. If it is just rings would it be a case of just replacing them or would you do other work while engine is apart ?.Would the engine have to be lifted to do that job and I have no idea what a job like that would cost would one expect to have change out of five k to do the job ?. It is a v six ford duratec.

[steveo3002]

id test it hot ....84 vs 100 isnt extreme

headgasket wouldnt improve with oil , could be sticky rings that improve when warm...any ring will seal better when warm

[DVandrews]

On a hot engine anything greater than a 10% variance is worth investigating, as I’ve stated before a leakdown test conducted by someone who has experience will give a conclusive answer and put to bed any speculation (however well intentioned).

If it is worn rings then it would just smoke a bit, produce excessive crankcase pressure and the performance would gradually drop off, maybe gradually enough for you not to notice.

Head gasket failure normally renders the engine unviable in short order ether by misfire , coolant loss, overheating or coolant/oil mixing.

I have experience of over 250 head gasket failures, in most cases the symptoms were a world away from what’s you are experiencing, the only time I have seen a gasket breach with no other symptoms but low compression on two adjacent cylinders was on a Pinto where the gasket was incorrectly formed and popped over a very small area where the cylinders Siamese.

Dave

Edited by DVandrews on Monday 11th January 15:40

[coolchris]

Hi Dave,

Really appreciate your expect knowledge and advice on the symptoms I'm getting with the car like you say the difference between compression on the highest one and the lowest is too big to just ignore.I am going to speak to a couple of noble specialists and see if I can get the car recovered to them to diagnose the issue only problem is there north way and I'm in the south.Or thinking about it is it something that any respected car builder could do or would you stick to those who know the car.

Cheers Chris

[catman]

I don't think that you need a Noble specialist tbh, as it's a Ford engine in a really nice car. You just need someone who really understands engines. I'm sure that you will get many recommendations on here.

[coolchris]

Ok thought I'd put the feelers out on what a rebuild would cost.Maybe I'm not in the real world but nearly 7k excluding vat (that doesn't include the removal of the engine and putting it back in).

[Boosted LS1]

If this was me I wouldn't pull the engine just yet. I'd redo the compression readings, throttle open and maybe 6 cranks per cylinder. As you say, the car's running well so I suspect it'll continue to do so for a fair while yet.

[coolchris]

To be honest apart from the blow by it is running well on one hand couple of people have said oooh engine rebuild time while others have said if it runs fine doesn't run hot still pulls well with no lack of performance just keep driving it and keep an eye on oil level.

[SturdyHSV]

coolchris said:

Ok thought I'd put the feelers out on what a rebuild would cost.Maybe I'm not in the real world but nearly 7k excluding vat (that doesn't include the removal of the engine and putting it back in).

So to give someone your engine, and have it 'rebuilt' (meaning what? A quick hone, some new rings and some gaskets?) they want £8,400? Wow.

I mean, I'm no expert but that seems a lot for a Mondeo V6.

Alternative suggestion, have you used spanners before? Buy yourself an engine crane and stand for £300, get a big Halfords socket set for £150 or so and pull it out yourself taking pictures of everything and labelling things as you go.

By the time you've got to that stage, might as well take the bottom end out yourself, get a decent torque wrench and some rings, pay someone a couple of hundred quid to hone it etc. save yourself £7,000 or so and have something fun to do during lockdown If it all goes wrong, get another 2.5 V6 off ebay for £250...

[coolchris]

Basically carry out machining work component preparation and fully rebuild engine.I can only just about use a knife and fork let alone a set of spanners so doing a diy home engine rebuild is way beyond limited talents.

[SturdyHSV]

For under £250 for a used motor I'd be tempted to give it a go anyway, something to do eh?

Can the 3.0 be swapped in if the old one's coming out?