So, unfortunately we joined the small but expanding club of smashed rockers, bent valves and damaged camshafts at the weekend! Cylinder 3 is 40psi down on compression with significant leak off through the exhaust valves. We were not even on the full power map, but our higher rev limiter of 7600rpm seems to be a stretch too far for the stock valve train.
Full engine strip down to assess for further damage and find all the contents of the rocker bearings which are currently AWOL! Then we can look to improve other things whilst we are in there.
We also observed significant dips in oil pressure under braking that was eliminated by over filling the oil by 1L so we need to investigate the oiling system too to see if there are improvements we can make.
It has taken a little while to gather up all of the parts required to fix it from around the globe. Holy moly there are some serious price discrepancies and lead times for oem parts on these around the world. I hope that settles down for the future!
We also had a great chat with the guys at Kelford around the valvetrain, tossed around some idea of converting over to solid lifters etc and in the end decided to just change the valve springs. The stock valve springs are very very weak, lots of tuners around the world are now coming out and saying the same. You will notice a lot of dyno graphs dropping off around the 6500rpm mark, this in most circumstances is valve float with increased boost and exhaust gas back pressure.
When we started increasing the boost beyond 1.6bar we ran into a misfire at 6500rpm, at the time changing the cam timing away from the stock logged values losing a bit of overlap in this area allowed us to lose the misfire and continue through. In our rushing to make an event and desperation to make the most powerful GR Yaris in the world first we brushed over it and carried on tuning with our "fix". Well we hadn't fixed anything we had just masked a problem because it turns out it was a heavy dose of valve float not just a reversion issue with all the exhaust and inlet changes we made. You saw the result above, it also bent 2 exhaust valves.
The theory is the extreme valve float was causing the camshaft and the rocker rollers to smash into each other in high boost high rpm situations rather than gliding nicely together which eventually caused the bearings to fail. All pistons show some small amount of evidence of valve contact on the inlet and exhaust pockets. In summary the valve springs are the very first limiting factor of stock components. For anyone going beyond just a bolt ons I strongly strongly recommend you change your valve springs. Shameless plug, we will be carrying the Kelford springs at all times where possible but honestly its not just a sales ploy, let our findings save you money and upgrade before they cause you much more expensive problems.
It also split open the alloy intake manifold! Because the exhaust valves didn't open, combustion still happens it just had nowhere to go......until the next intake stroke where the hot exhaust gasses came back out the inlet valves, combined with fuel made a nice boom blowing the intake open. It was the first time I have ever seen exhaust soot in an intake port!
In the end replaced parts were - Exhaust camshaft, 2 x valve stem tips, 3 x roller rockers, 2 x exhaust valves, 2 x hydraulic lifters 4 x collets then springs, retainers and bases.
Most of the damaged parts managed to find themselves neatly in a corner of the sump once flipped over
The rest of the engine was entirely stripped for inspection and was all found to be within serviceable limits. The extra power does not seem to be having an effect on anything else. The metal debris from the destroyed parts had floated through the system causing some light marking to the bearings and other contact surfaces but not enough to put them outside of tolerances or be worth replacing at this stage........lets be honest its not the last time this engine will be apart.
You will also remember we had oil surge issues under reasonably heavy braking with all the extra grip with big dips in oil pressure shown on the logs. The baffling in the bottom end is not great for the small quantity of oil the car carries. It has a small dip in the steel part of the pan to try to retain some oil in that area but the pickup pipe is at the back of the engine which a huge expanse of open area at the front of the sump for the oil to slosh into
So we have built a small plate into the steel part of the pan which slots up between the pickup pipe and the balance shaft area to hold the majority of the oil in to the lower half of the pan under braking. There are drain down slots between each rib of the lower pan as well as down the sides. The main oil drain from the turbo, cylinder head and block also run into the back half of the pan right behind the oil pickup pipe so it should now have plenty of oil in all situations. I expect somebody will come along and make a baffled lower half at some point, if not and we can prove this design to work we will look into having them manufactured. It would be an incredibly easy fit.
The eagle eyed amongst you will also notice the balance shaft is missing. Just something we are trying to increase response, lose some weight and gain some oil pressure(as the bearing feed is now plugged). We will see what affect this has soon and might turn out to be a poor choice but its very easily reverted and can be reinstalled without removing the engine from the car. Definitely not something you will ever want to do to a road car, its already bad enough with a single mass flywheel!