[Hal]

The Zetc is supposed to be a non-interference engine. To me this means that even if the timing belt should break and the cams stop with a valve at max lift it will not hit the piston as the engine keeps rotating.

Question 1 - Am I correct in my interpretation of non-interference?

Question 2 - What is the max valve lift you can have and maintain the non-interference feature?

 

[teamDFL]

1 - yes that is correct, and don't let some engine manufacturers tell you that non-interference means that the pistons don't need clearancing.

2 - no one who has it will share that info. I have Crower I's and I put the cams at TDC and spun the crank (no t-belt) and no problems.

 

[Uriah]

A few hours and some Plasti-guage would answer this question. You don't even need to change cams. If you get the clearance between the piston and valve at TDC and max lift you can extrapolate from there.

 

[teamDFL]

Originally posted by Uriah:
A few hours and some Plasti-guage would answer this question. You don't even need to change cams. If you get the clearance between the piston and valve at TDC and max lift you can extrapolate from there.

<font size="2" face="Verdana, Arial">I am not sure that you could use plastigauge, as it is designed to measure very tight clearances and I think that you should have a minimum of .030" clearance to take into account expansion and rod stretch. You would also need a way to measure the angle that the valves are compared to the head face so that you can do the trig to figure out how much a change in lift would reduce your clearance. It could be done, but I am not sure if it would be just a couple of hours.

 

[Hal]

Plastigauge wouldn't work, but modeling clay would using the same idea. If someone had a engine they were rebuilding they could put some modeling clay on top of #1 piston, set the head on with the cams at max lift on #1 and rotated the crank thru a turn. Then you could measure the thickness of the modeling clay where the valves touched it. That wouldn't be exact but would put us in the ballpark and give a figure to use the trig on.

Anyone out there with an engine tore down???

[ 01-16-2003, 03:13 PM: Message edited by: Hal ]

 

[Blue01Street]

I have Crower Stage IIs and had my head milled .040". I have interference. Of course this is only a problem if the belt breaks.

 

[Hal]

OK Blue, Thanks

The Crower II's have gross lift of .374. If the valve inclination angle is 30 degrees (I'm guessing on that), by milling the head .040(A on diagram)you reduced the available valve clearance by .032(B). So adding .374 and .032 to get .406 gives us a figure that we know creates interference.

Going by that, it looks like anything with a gross lift over .385 would be an iffy propostion if you want to remain non-interference.

[ 01-17-2003, 03:12 PM: Message edited by: Hal ]

 

[FocusGhiaFFOC]

For any UK peeps reading this thread, our engines are not of the "non interference" design.

 

[redneckZX3]

i know that on the crower II the exhaust cam is 392 lift and that clears the head but the stage III it is like 415 lift and you have to grind around the valves to get the exhaust cam to clear the head but the intake on the III is 392 so you shouldnt have to grind that down. If you have any questions i know tnat Nader at FC is knowledgable with the st III, i believe he had them in his car.

geoff

 

[CTZX3]

well i know for a fact that if you have a stock block, and a stock head with stock cams and valves, when you turn the cams they DO touch the pistons.