I would be gratful for people’s thoughts on this.
I swapped my engine for a 1.8 BP from a MK 2 and I put forged rods in, all new gaskets and lapped the valves. Most of the time it drives ok but when lifting off the accelerator pedal after hard acceleration there is a big cloud of white smoke from the exhaust, bear in mind my car is running 0.9 bar boost with about 250bhp and the smoke only happens when I nail it.
I thought maybe this could be piston rings or valve stem seals, I hadn’t replaced the rings but did replace the valve seals with Victor Reins ones. To diagnose further I did a down test on each cylinder, the results I THINK were good at TDC for each cylinder however I tried going just off TDC (when the valve would be open a tiny bit) and saw air pressure build up in the oil so much so that oil splashed out of the dipstick sheath and made a gurgling sound.
I’m not sure what to do next, I was thinking to pay a garage to do a leak down test to diagnose for me as I didn’t trust the gauge on the ebay tester that I used, but if anyone on here thinks the cause is obvious then I won’t bother.
Many thanks in advance.
- My model of MX-5 is: 1993 MK1 with 1.8 BP engine
- I’m based near: Bristol
- I’m looking for technical help or recommendations on: details above
White smoke is usually coolant.
Possible your boost is lifting the head slightly. Or many other reasons!
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I assume you’re doing a TDC leakdown test on the compression stroke, in which case the valves will all be closed for at least 150 degrees of crank rotation, not ‘open just a tiny bit off TDC’.
White smoke is either coolant as Nick alludes to, or less likely brake fluid being pulled in from a leaking master cylinder and servo.
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pretty sure it’s oil as the oil level drops by a noticable amount but the coolant level does not drop at all. The air also smells a bit oily from the exhaust gases
that’s an interesting point, I hadn’t thought that the valves would be closed for so long arond TDC. To be honest I don’t know if I had it at TDC on the compression stroke, we just tried both TDC positions for each cylinder and found that one TDC position had a big leak so we assumed that to be the wrong TDC. I haven’t noticed the brake fluid level going down but certianly have noticed the oil level reducing.
White smoke is burning oil, nothing else. If it’s steam, it’s water.
could a broken PCV valve cause these symptoms?
Dodgy PCV won’t help. As you know, easy to discount.
Have a third party start it from cold while you gaze lovingly at the exhaust. Blue whiffs from cold could indicate tired bore-rings. I doubt in your case it would be worn valve stems.
Maybe even slightly cracked rings. That’s what did for mine.
Very possibly…as the engine is apparently still on it’s OEM bores and rings (?) it would be a Huge Ask for it not to burn some oil ?
End of day it’s an elderly & 0.9 boosted very hard worked twincam after all.
Lotus TwinCams pretty much did it from new to the sweet toffee scent of burning Castrol.
I’m going all weepy & nostalgic. 
But I’d set aside, till proven guilty, the oil burn. Wrong signals as said above.
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I replaced the PCV and I haven’t noticed a problem with white smoke since then… although I still don’t know why the oil made a gurgling sound when i pressurused the cylinders just off TDC