Here is a picture of a Prelude Type S piston that was notched recently. The engine was started ran and when vtec engaged, shut down. The cylinder head was removed and we found that for the second time, the same exhaust valve in chamber #3 is bent. Look where the valve hit. Can anyone give me some professional feedback as to what caused this? Also, remember, the valve reliefs were modified for more clearance before these pistons were reinstalled and the same thing happened.

The cylinder head is from an H22A and had the following procedures done to it:
deshrouded valve area
welded chambers
port/polish
stock valves with JUN valvetrain and JUN cams





Any feedback will be greatly appreciated as i would like to put an end to this and tell the guy who did this what he did or did not do. [IMG][/IMG]

 

sorry guys, having some trouble getting the image to show here

 

We will be measuring the lobes and see if there is some variation to determine if that might be the case. I have never heard (at least i haven't) of a JUN cam being defective in such a way, but anything is possible. Strange thing though is that we ran this engine with a completely stock H22 head (we used the JUN valvetrain/cams) and ran it for about two weeks with no problems whatsoever in and out of vtec engagement. That kind of raises doubts in my mind as to the state of this cylinder head. I would think that mabye if it were the cam, the stock cylinder head would have run into the same problem. What do you think?

 

anyone else?

 

i really doubt its the cams or valve springs... i say the guide may be messed up for that valve. that is the only thing that aligns the valve. unless you were using the same bent valve as before? did you clay the motor before assembling?

 

Assuming you're using stock diameter exhaust valves, as that's all the type s pistons will allow, the problem comes from the "flip" that the piston does at TDC, when the rod changes direction, forcing the exhaust-side "up". This is a problem with H22's, especially those running large cams with the type s pistons.
While the B series also do a "flip", it's not a s pronounced as with the larger bore H series engines.
You might want to remove the pistons and have the exhaust-side reliefs enlargened a bit to the outside of the piston.
If you are running .5mm oversize exhaust valves, you'll definitely need to make the reliefs larger because the type s pistons won't accomodate them.

 

im going to go with valve guide to as stated above

 

hey Larry's back Have a good xmas buddy.

 

ever figure out what the problem was?

 

Hi there:

Well, the only problem that was found was that the exhaust valve guide clearance was off and thus this specific valve and only this specific valve would stay open and thus cause the damage. We set cam gears at 0,0 and plan on leaving them like that for a while. As Junbb1 stated, he got the best power results at 0,0 after playing with his cam gears so i am just going to keep them at that for now. I just want to enjoy the car a bit before anything else is done to it.