MX-5 OC Forum

Hi, Apologies in advance for the rather long post and thanks for the help and info (by email) from Mazda Mender. I wonder if anyone can help with my frustrating problem. I have recently purchased a non running Eunos auto that had been cooked due to a split heater hose. I had the head skimmed, valve seats recut, valves lapped and valves and springs assembled with new valve stem seals (non Mazda) by a very reputable engineering firm in Carmarthen. Having reassembled everything I now have horrendous whitish blue smoke on start up.This takes about 15 secs to appear and is like a fog behind the car and lasts for about 10 mins at tickover (with blipping the throttle). If you turn the engine off after a couple of mins and remove the plugs you can actually see the oil on top of the pistons. I have cleaned this oil out with petrol and a wet and dry vacuum cleaner, Made sure that at least one inlet and one exhaust valve is open and left overnight. Next morning there is no oil in the bores until I start up when it smokes all over again. If driven after the smoke has cleared then all is fine. Compression pressures are reasonable for a 150k mls car and if the oil control ring are naff I would expect it to smoke all the time. I have also removed the tube from the inlet manifold to the vacuun modulator valve in the auto box in case that was faulty and sucking up transmission fluid (thanks Mazder mender) and ditto the servo pipe. I'm now stuck and tearing my hair out and I can't afford to do that at my age. Can anyone throw any more light on this problem. All suggestions will be welcome.

Regards Harvey

 Hi Harvey,

Wrong or wrongly fitted valve stem seals might be a reason but it does sound like a lot of oil doesn't it.

Have you actually ran it on the roads a while? Thoughts are the rings may have stuck due to water down the bores if the head gasket went. A bit of running might free it. Maybe an engine oil flush too, or get it warm and put a few teaspoons of Redex down the plug holes and leave to soak, used to be a favourite trick.

 Hi Rich M. Yes I've driven it about 60 mls in total. The last one was a run of about 45 mls and it got quite a blast too. Compression pressure figures are reasonable so I wouldn't expect ring problems but if it was I would expect oil burning all the time not just on start up. I did put fresh oil in after the rebuild but not flushing oil. Maybe that's the next job.

Note to all who respond to this problem. If my response to any suggestions appears negative or argumentative it's not meant to be. So apologies in advance. It's just that I'.m getting so frustrated !

Harvey

It does sound to me like valve stem oil seals...

 Hi Harvey, No probs, just going through ideas hoping it isn't the valve stem seals. What about the PCV, may be worth changing for what they cost, and check the restrictor is in the tube.

 Hi Victormeldrew and Rich. I wouldn't actually mind now if it was definately valve stem seals - at least  I would know! I have tried sucking and blowing through the PCV and it only works in the right direction. I think at some stage (I've done so many test I'm losing count and my marbles)I tried running it with the oil filler cap removed  - therefore no pressure build up. It was still smokey though.

Harvey

Then that really only leaves the seals, or maybe the head gasket at a push. Have you done a full leak-down test of the compression? And when you say 'good compression for its age' - I take that to mean 'not particularly great' compression?

Hi both, yes agreed and you clearly know what you're on with Harvey. We can only explore the possibilities before pulling the head, followed by pistons if the valve seals are ok. We know it's usually oil being pumped up worn bores or past stuck rings, or draining down valve stems past the seals. The strange thing is how long it takes to clear. I'd have thought stem seals would've cleared after a few seconds. So maybe the oil is coming up the bores and the time relates to the pistons heating and expanding to seal better.

The PCV might give a clue. It is hard to check off the car as it has a spring and shaped parts which cause a balancing act of open/close depending on pressure on both sides of the valve. There should be a small negative pressure in the crankcase during idling which would indicate little piston blow by and tend to keep oil in the crankcase rather than causing it to be pushed up the bores. Worth a quick check; during idle, remove the oil filler cap and hold your palm over the hole. It should be sucked in gently. If the suction is great it suggests the PCV is stuck wide open, if there is no suction or your hand is pushed away it suggests excess blow by or PCV stuck closed.

 Hi, Yes it is looking more and more like the seals. The head gasket was obviously new and was a good one. (ADL/Blueprint)  . Compression figures are all around 170psi. How do I do a leak down test.

Cheers

Harvey

 You could try a proper leak down test Harvey but with those compression figures I wouldn't expect it to tell you much and certainly it won't tell if the oil rings or stem seals are the oil problem. Check for crankcase pressure during idling first which might indicate blow by.

Lokisdad:

Compression figures are all around 170psi

What about after putting a little oil in the cylinders?

Hi Jon, no need to put oil in the cylinders - it's there already! lol. Seriously though- yes oil in the cylinders puts the compression pressures up to about 185psi indicating worn rings, but it's strange that there is no evidence of serious oil burning when warm. Also would that allow so much oil to get into the cylinders so quickly?

Harvey

Hi Rich. I'll try to check for crankcase pressure tomorrow. With a breather from the camcover to the inlet manifold and one feeding the throttle body, would there be any crankcase pressure or would it be sucked into the engine?

Harvey  

Hi Rich, Sorry, in my haste I scrolled down passed your note. I will try what you suggest to check the PCV valve and crankcase pressure/ suction. I'll keep you all posted.

Harvey 

That amount of pressure difference is beyond tolerance, and so suggests there's something going on down in the bores... With the oil in, it's close enough to suggest the head is ok.