Non Interference in VVTi

[Lextreme II]

There were few cases in CL where members damaged their valves due to faulty timing belt installation. Would this problem be solve with dished or a change of compression height? The newer engines are 10.4:1 vs the over engines are 10:1.

So dished custom pistons would solve the interference problem?

 

[Lextreme II]

There were few cases in CL where members damaged their valves due to faulty timing belt installation. Would this problem be solve with dished or a change of compression height? The newer engines are 10.4:1 vs the over engines are 10:1.

So dished custom pistons would solve the interference problem?

 

[cribbj]

David, I'd think to keep that fairly high CR, it's going to be tough to make enough room on the piston crown to keep the valves from kissing it under all conditions. Cutting reliefs on the crowns would do it, but then you'd be altering the CR, and changing the chamber's characteristics. Who knows how well that would work. I'd try your contacts at Ross and/or Wiseco, JE, etc. and see if they have any ideas.

At some point, I think to keep high CR's and good valve lift with aftermarket cams, we'll have to accept that the motor is going to become an interference design. What we have to guard against is it becoming an interference design under "normal" conditions. So when you put your hot cam in that 11:1 motor, don't forget the clay test!

 

[cribbj]

David, I'd think to keep that fairly high CR, it's going to be tough to make enough room on the piston crown to keep the valves from kissing it under all conditions. Cutting reliefs on the crowns would do it, but then you'd be altering the CR, and changing the chamber's characteristics. Who knows how well that would work. I'd try your contacts at Ross and/or Wiseco, JE, etc. and see if they have any ideas.

At some point, I think to keep high CR's and good valve lift with aftermarket cams, we'll have to accept that the motor is going to become an interference design. What we have to guard against is it becoming an interference design under "normal" conditions. So when you put your hot cam in that 11:1 motor, don't forget the clay test!

 

[LondonBenji]

Clay test?

 

[cribbj]

The clay test was a crude but easy test to see how much clearance you had between the valve and the piston. You simply put a layer of clay on the crown of the piston, put the heads on, then turned the engine through a couple of cycles. When finished, you pulled the head, peeled the clay off and measured its thickness where the valves had penetrated it.

I did a search just now to see if people were still using this test or if they'd come up with something better, and I found this informative article on a Ford hotrodding site. It describes the clay method, and another even easier way of doing it:

http://www.fordmuscle.com/fundamentals/pistontovalve/