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The car starts and runs really smooth. The more the car is driven the better it runs. It learns while you drive building up a lambda compensation map from the lambda readings. The bypass valve is standing open so there is no boost generated. After a few days of driving, I plugged in the laptop and made some changes to the settings. I made the ECU switch on the supercharger at 50% throttle and close the electronic bypass valve to 50%. After 50% throttle, the bypass valve will close linearly until it is completely closed when full throttle is reached. This is all according to my original strategy.
First, drive with boost.
I took the car for a drive. I drove to an open road just outside the town I lived in. Gradually I opened the throttle until I reached 50% throttle. I heard the charger engage and there was no power gain. As I increased the throttle I could feel the engine is a lot more powerful. When the engine reached 4500 RPM I started hearing a whistling sound. That was the turbo starting to spool with the supercharger. I boost gauge reached 1 bat boost and I tapped off. I thought by myself, this is going to be fun. As the polo was only running on a base map, I didn’t want to run too much into boost. The engine needs to be mapped properly first.
And so the first Issues started…
I decided I needed to get some kilometers on the engine to run it in. This was basically a brand new engine. I took the car for a 3 hour drive on the open road, occasionally going over 50% throttle. There was one or two spot in the map that the car didn’t like so I tried not to go there.
On my way back the car started running funny. When I get to a stop the care would just die, and battle to start again. Once started it felt like the power was down. I had to run a fairly high throttle position to keep the car from dying, of coarse less than 50%. I got another 2 km then the car died and didn’t want to start again. Opening up the bonnet I found that the crank pulley driving the belt to the supercharger was loose. This was not good.
I phoned a friend to come help me tow the car home. I really troubled me why the pulley would be loose. Maybe I didn’t tighten the 4 cap screws properly that hold the pulley to the crank. The trigger wheel is on the back of the pulley so I could understand why the car was cutting out. It just didn’t have a nice constant trigger signal.
Finding the issue
When I got home I got the Polo’s front on stands so that I could see what is going on. I found that the 4 caps screws was still tight. The complete assembly of the timing belt sprocket and the crank pulley was loose. I stripped all the belts off the engine including the cambelt. I could rotate the assembly without the crank turning. Now I knew why the car didn’t want to start. The Cam timing was out completely. Now I started worrying, I know for a fact the valves on the 20 valve engines does not clear if the cam timing is out. I was lucky with my thick head gasket they did clear.
The center bolt holding the timing sprocket to the crank was loose, I know I torqued that bolt as I marked it with a paint marker pen after I did. I turned the bolt out further and took the pulley assembly off. The cast in key on the sprocket has sheared off. Because that sheared off the sprocket turned and loosened the center bolt. The extra loading on that key from the supercharger is just to much.
The fix
I had to go buy another crank timing sprocket, but I know that it would just happen again. Had to do some research on how to fix this issue. I found out that this was a common issue on these crank timing sprockets. All you had to do was to drill 2 of 5-millimeter holes on the pulley. Put the pulley in position on the crank and drill the holes through into the crank.
Once the drilling was done, everything must be cleaned. I also found that the center thread on the crank was damaged from the bolt that came loose. I ran a tap through the center hole and the bolt turned in nicely. The sprocket went back on with two of 5 millimeter hardened dowels. I put the dowels in with Loctite 641. The center bolt got torqued to factory spec. This sprocket was going nowhere. I got the engine on its timing marks and fitted the belts back.
I swang the engine and it started straight away. This was a really good sign. All I had to do now is get this engine mapped.
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