IVA is just the beginning...
BigLee - 23/8/11 at 07:22 AM
IVA passed last month, 1st time (With expert guidence from 2 well known characters near Sheffield!) and road legal a day later courtesy of Preston
DVLA with a nice '11' plate. For those who don't know. I built an MNR Vortx with a Mazda 1600 and a turbo.
Since then, the joy of building a car has turned sour......
1st problem was someone pointing out the oil return from the turbo was touching the manifold. You tend not to consider these things when building
something cold. Its only when super hot that the rubber pipe starts to smell! Anyway, easy fix, rotate turbo housing slightly to create an adequate
gap. Unfortunately, being a little heavy handed I bent the oil outlet bracket allowing small amounts of oil to leak out. On to VERY hot things. Queue
lots of smoke pouring out of my lovely carbon vents, and me flapping like an idiot trying to remove my harness thinking I am about to become toast.
Anyway, to fix it properly, I removed the turbo from the manifold to replace the pipe and ensure everything was as it should be. Came to refit and
sheared a bolt in the manifold! No problem I think, drill the middle of the bolt out, hammer in a pozidrive screwdriver to wind it out, and..... shear
that off too!! At that point I went to bed. Thankfully a mate managed to sort it. Now replaced with studs and bolts.
Finally I thought it was sorted. Went for a blast on sunday. Barely 2 miles from home it all went wrong big style. Under hard acceleration (and a big
grin) it lost power at about 85mph in the outside lane of a busy dual carriageway. Then lost more power and wouldn't rev. I managed to coast into
a safe place and get out whilst the car tried to steam everything within a ten yard radius. Bonnet off revealed the bottom coolent hose had come off.
But had it come off causing the engine to overheat, or had the engine got too hot then blown it off? There was also this strange grey rubbery powder
all over the engine bay from the 'blast.'
Removed the head last night to get everything sorted. I knew there was no compression at all so expected the head gasket to be like something out of a
cartoon, totally destroyed. But it was fine. The edges look to have given up, but nothing around the cylinders. With the head off I noticed it was the
valves that have taken the hit. Totally fried. 2 with holes, the rest with discolouration on the edges where they have melted.
Off to find a new head today. There was loads of the grey stuff bunging up the holes for the water course through the head gasket. Not sure if thats
what has caused it, but it cannot help.
Totally fed up with it now 
tomgregory2000 - 23/8/11 at 07:44 AM
intercooler too small?
boost too high?
BigLee - 23/8/11 at 09:15 AM
Funny you should mention both those things! I took out the intercooler last week as there was a leak on one of the pipes. Refitted the solid aluminium
inlet pipe. Boost was only 0.4 bar, and running a Bipes ACU to retard the ignition. Although it looks like it wasn't retarding it enough. Just
been to an MX5 specialist and says he has never seen melted valves before. I am thinking it could be a compound effect. Lack of proper cooling due to
blockages + a little too much boost for no intercooler + not enough retardation on ignition = fried head (both physically and metaphorically)
Either way I just picked up a new head for £50.
Worse things happen in life.
britishtrident - 23/8/11 at 09:59 AM
Whwn an engine gets that hot there is better than 50-50 chance the piston rings are fried ie the heat treatment of the ring material will be
undone, usually at first no symptoms but 6 months down the line don't be surprised if you get high oil consumption and/or loss of
compression.
britishtrident - 23/8/11 at 10:24 AM
quote:
Originally posted by BigLee
Funny you should mention both those things! I took out the intercooler last week as there was a leak on one of the pipes. Refitted the solid aluminium
inlet pipe. Boost was only 0.4 bar, and running a Bipes ACU to retard the ignition. Although it looks like it wasn't retarding it enough. Just
been to an MX5 specialist and says he has never seen melted valves before. I am thinking it could be a compound effect. Lack of proper cooling due to
blockages + a little too much boost for no intercooler + not enough retardation on ignition = fried head (both physically and metaphorically)
Either way I just picked up a new head for £50.
Worse things happen in life.
From the received wisdom of LPG conversions Japanese exhaust valves are generally made of a lower grade material to that used by European
and US engine manufacturers. This is not a problem in normal tintop use but when the exhaust gas temperature is increased (as in LPG or turbo
conversion) problems start to show.
Retarding the ignition is a double edged sword. Retarding the ignition causes peak combustion temperature to occur later in the power stroke
which causes the exhaust gasses to contain more heat, this raises the exhaust gas temperature by a large margin.
Were the exhaust valves melted or burned ? -- ie burned as in a chunk burned out as if by an ox-acetelene torch. finding a whole sector
burned out an exhaust valve used to be quite common.
This can point to a weak mixture. Because weak mixture ignites more slowly and burns slower than an ideal or rich mixture a weak mixture has
similar effects on exhaust gas temperature as retarded ignition.
BigLee - 23/8/11 at 10:34 AM
Burnt not melted, with a little chunk broken out of 2 of them. It's the inlet valves that look to have suffered from super heat with blue tips on
a couple of edges. If you look closely enough at them, the radius changes at that point as if there is a super tiny piece melted away.
Just looking at the potential damage to the bottom end now!
ashg - 23/8/11 at 10:49 AM
the problem is that the mx5 valves in your head were never really designed to take the abuse of a turbo setup. your going to need a good charge
cooler to keep the temps down.
BigLee - 23/8/11 at 01:37 PM
Oh well, sh*t happens as they say. Just bought a new engine. Its only money and time afterall!
D Beddows - 23/8/11 at 01:52 PM
quote:
the problem is that the mx5 valves in your head were never really designed to take the abuse of a turbo setup. your going to need a good charge cooler
to keep the temps down.
That's not actually true - the 1.6 MX5 engine was originally designed to be a turbo engine in 1980's Mazda 323s............
I feel your pain though Lee, I know all about overheating MX5 engines 
BigLee - 20/9/11 at 08:58 AM
Engine has now been inspected by a seasoned professional. A mixture of CSI and witchcraft! He confirmed the fuelling and boost were fine, simply a
matter of poor cooling. Pressure has built up due to heat and blown the bottom coolant hose off causing temperatures to hit 300 to 400 degrees.
Replacement engine now being built up. Hopefully the alloy rad, oil cooler and proper coolant (and a head not full of radweld) should keep things in
check. Just in time for the weather!