WR450 head cracks?

[BrendonS]

Hi Guys,

I'm having a bit of an issue with a couple of Yamaha WR450 heads (2005), and I was hoping some of you may have seen this before or know what we are doing wrong!

To power our student built race car, we use a WR450 re-packaged into a custom billet machined crankcase/transaxle arrangement. Here is a photo of our crankcase:

http://iforce.co.nz/i/d5l5cbkl.dij.jpg

We run EFI with an Autronic ECU, and to tune this set up we use a second standard WR450 engine on the Universitiy's engine dyno.

Recently we have noticed cracks in both cylinders, on the head bolt ridge, closest to the exhaust outlet. Below is a photo of the crack on our dyno engine (standard engine), however the camera was shocking at picking up the crack!

http://iforce.co.nz/i/jthxp5g3.1iu.png

The only running we have done on the dyno engine is around half an hours worth of tuning with our new Link G4 ECU; admittedly the EGT got a little hot at one point, which we originally thought was the cause of the crack. However we then noticed an almost identical crack on the custom package, which has only been running on the well tuned Autronic ECU.

The heads are always torqued correctly, as per the Yamaha manual, and the head bolts are always checked against the specifications. However they have had a fair amount of assembly and disassembly over the last couple of years.

If anyone out there has seen anything like this before, and may have an idea of what has caused this, any help would be greatly appreciated!

Thanks!

Brendon

[Pussy]

Hi Guys,

I'm having a bit of an issue with a couple of Yamaha WR450 heads (2005), and I was hoping some of you may have seen this before or know what we are doing wrong!

To power our student built race car, we use a WR450 re-packaged into a custom billet machined crankcase/transaxle arrangement. Here is a photo of our crankcase:

http://iforce.co.nz/i/d5l5cbkl.dij.jpg

We run EFI with an Autronic ECU, and to tune this set up we use a second standard WR450 engine on the Universitiy's engine dyno.

Recently we have noticed cracks in both cylinders, on the head bolt ridge, closest to the exhaust outlet. Below is a photo of the crack on our dyno engine (standard engine), however the camera was shocking at picking up the crack!

http://iforce.co.nz/i/jthxp5g3.1iu.png

The only running we have done on the dyno engine is around half an hours worth of tuning with our new Link G4 ECU; admittedly the EGT got a little hot at one point, which we originally thought was the cause of the crack. However we then noticed an almost identical crack on the custom package, which has only been running on the well tuned Autronic ECU.

The heads are always torqued correctly, as per the Yamaha manual, and the head bolts are always checked against the specifications. However they have had a fair amount of assembly and disassembly over the last couple of years.

If anyone out there has seen anything like this before, and may have an idea of what has caused this, any help would be greatly appreciated!

Thanks!

Brendon

In an aircooled aircraft engine, you can get the exact same problem with rapid temperature changes, insufficient cooling, and excessive exhaust gas temperatures.