Disclaimer
We may earn a commission when you use one of our coupons/links to make a purchase at no extra cost to you. Please support the site by using the links.
So we are back at the workshop with the Porsche 917. We were quite disappointed that the car broke down and the test was cut short. We have never had an issue like this. The only way to find out what is wrong is to start stripping the back of the car again.
What did I find?
It was a mission stripping the side shafts out again. The tripod joints need to be dismantled as the inner’s in solid mounted to the drive shafts. It was about an hour later and the gearbox was laying on the floor. The issue was the input shaft for the gearbox was still in the clutch spline. The shafts snapped off clean.
What we didn’t do or even think of with the rebuild was to get the input shaft of the gearbox crack tested. What we found was the shaft made a stress crack from the crash impact. With the testing and the load on the shaft was just enough to finish the shaft off.
The issue now was to get a new shaft. Xtrac makes there own steel combinations for there gearbox parts. This could mean the shaft was made from “unobtainium”. As we don’t have the exotic steels they use we copied the design of the shaft but improved the thickness. The input shaft on this gearbox is sacrificial, so if anything happens to the shaft it is a quick job to replace the shaft without opening the gearbox.
The fix
We got 2 new shafts made up and got them heat-treated. Now we have a spare encase we brake another shaft. It was about a week later and we had the new shaft complete and the gearbox was back in. The Porsche was once again ready for the track. As I had some time I decided to address the cooling system issue as well.
Cooling system
As I have mentioned, we had an issue with the coolant temp spiking to 125 deg C on the back straight on the track. As soon as start braking for the turn meaning a lot less power from the engine the engine cools down quickly. This could only be due to 3 reasons. Either the radiators are not big enough, not getting enough air to the radiators or the flow rate of the water pump is not sufficient.
Due to space constraints, the radiator size was fixed. Well, we could have made the radiators a bit bigger but didn’t want to spend the money if that is not the problem. At this stage, we were running a Craig Davies EWP 80 pump on the cooling system. I did some research and it turned out the pump was way too small for the power output of the engine. The more power you make the mare heat gets absorbed into the cooling system. On lower RPM the cooling system is fine it is when you hit the high power then it does not cope.
I fitted two JABSCO 100 liter per min pumps in parallel. This gave me a combined flow rate of 140 liters per minute. Running pumps in parallel you never get the full combined flow rate. I was now happy and the car could go back to the track.
Next track session
We once again took the Porsche 917 to the race track as we booked the track for our selves. It was a really nice and warm day and the car looked great. I was really confident that this was going to be a good day. My boss could not make it for the test due to meetings but he said I could run the car and see if there are any other issues.
I took the car out on lap 1 just getting the car up to temp. Everything was going well. On the second lap, I opened up the throttle unleashing the beast. The car was running really great. We were actually timing my laps to see what times I was running. My best time was 1 min 21 sec. This wasn’t too bad as my boss was doing 1 min 18 sec around the track. With more track time this would be able to be reduced dramatically.
On lap 7 something started to feel off. The car was battling to shaft gears, coming down the back straight I lost all shift ability once again and I had to lock the brakes up again to get the speed down for the turn. I know what was wrong just not why it happened again. It was identical to the previous break.
Back to the shop
We took the Porsche back to the shop and took the gearbox out again. The input shaft was off like suspected. The difference was this time the shaft was twisted like a pretzel. The outside skin of the shaft looked like it was shattered glass. I sent the shaft in for hardness testing on my suspicion was right. The outside of the shaft was nice and hard but the inside was soft. When the outside cracked up the inside could not handle the torque and just twisted the shaft off. This was an error made by the people hardening the shafts. We sent the second shaft back and they annealed the shaft and re-harden the shaft to spec.
This was almost like second nature now, taking the gearbox out and putting it back. It wasn’t long and the gearbox was back in. I set up the car on stands without the wheels on it. I ran the car up to 6000 RPM and started to shift my way up to 6 gear. The car sounded insane inside the hanger. I knew my boss was in a meeting in the boardroom but I did the test anyway. It was not even 2 minutes and my boss was standing next to the Porsche with a smile on his face.
Next Track session
We took the Porsche back to the race track for a test again. This time my boss drove the car in anger. This was the first outing since the first track test that we did not have any issues. My boss came in and told me I can take the Porsche out again. Every time I took this car out on the track it blows my mind. This is one serious piece of machine, the way it pushes you down into the seat. You becoming one with the car. Feeling every bump in the road. Through the bends, it feels like your face is busy tearing off your scull from the G forces. There just isn’t any words to describe the feeling of the rush.
Now that we had a successful track test we could enter the car for the next race. Back at the workshop, I will have to run through the car again to see if there are any issues lurking around. This was a really good day.
« Fun and Games or is it? | Going to the Hill climb »
Check out these link buttons!
Parts by Brand Support the website by becoming a Patron Make a donation with GoGetFunding Click here if you would like to Subscribe! Click here to check out some of the other posts Click here to make a contribution to my latest Project car Click here to setup a monthly contribution to website Click here to check out the forum page Click here to check out the Top 100 Auto Blogs
One thought on “So what went wrong!”
Generally I don’t learn post on blogs, but I would like to say that this write-up very compelled me to try and do it! Your writing style has been surprised me. Thanks, quite nice post.
Comments are closed.