As posted I was breaking in another new 355 when one of the valves touched a piston a little too much and broke off. You can barely make out where every valve was kissing the the piston. There is no indent or or knick on the piston, just a pin print where there is no black soot. These were my Trickflow heads that I had just finished porting out. Only one of the valves broke off, damaging only one piston and combustion chamber, everything else is perfect. I did not measure valve clearence because I was using a cam with less lift and felt/heard no interference when turning it by hand.

My real question is what do I need to do to put this engine back on the road, other than measure valve clearences? Of course I pulled the engine and took it all apart. I am guessing that I need to replace all of the intake valves, possibly the bronze valve guides, I will replace all pistons any way, new bearings. I am wondering if I can use the same piston rings if I keep them in bore order since they were only used for break in. Combustion chamber will need some more porting and smoothing now....New valve seat.

I can post any picture needed.

 

The piston is NEVER supposed to contact the valve under any circumstances. In fact, there should be a minimum clearance between the two. You put a motor together and didn't check piston to valve clearance???

You could try using the thickest head gasket you can find. You might also want to get a machine shop to fly cut the valve reliefs in the piston top a wee bit deeper.

 

Ya just leaned the hard way that peak open valve lift has nothing to do with V to P clearance. Duration and overlap do.

Trickflow recomends that any cam bigger than 216@.050" duration needs to be checked. Your cam has 235deg duration @.050". Where did you get the idea it would be a boltin? Every component will have to be checked for damage. Cam, roller lifters, pushrods, rocker studs, rockers, retainer and locks, pistons, pins, rods and all bearing. Essentually you'll be rebuilding the whole thing.
To flycut the new piston to clear the custom valve angles of TW heads will require U use the head on the block as a guide for the fly cutter ( Isky tool) unless TFS can supply specs for a mill setup that will work. You're going to have more$$$"s tied up on this (machinist setup labour) than these heads are worth by the time you've corrected the VTP clearance problem. Rebuild it and dump the heads. Get new conventional 23deg heads.
There are many that flow as good or better and cost less and "bolt on"
The custom valve configuration of the TFS twisted wedge design is just not worth the bother.

 

The heads are not the "twisted wedge." They are the Kenny Duttweilers. I believe that the heads can be saved pretty easily, only one combustion chamber was damaged, and it was minimal at that. I am already getting a new cam, pushrods, locks, pistons and pins. Matter of fact I have half of that ordered already.

I would just assume that all of the valves were bad along with the guides and possibly seats. Is that machine shop able to check that valves and seats though. Or pushrods?

Of course I will rebuild it, I am wanting to know what I can pitch for sure and what is more than likely still good. Also, how do I check lifters or the cam? Would it be a good idea to get new cam bearings?

 

I wouldnt reuse the rings. They mate to the bore AND the piston. Toss them.

Machine shop should be able to check the rest like cam bearings, etc. and see what needs throwing away. I'd for sure chuck the lifter and pushrods on the cylinder that broke the valve, might as well replace all the pushrods to be safe. The other lifters might be ok.

Unless you were running lots of lift, dome pistons, and tight clearances, I dont think you should have had contact. Did you degree in the cam? I wonder if it was in right.

 

Also, double check your cam degreeing. If you're hitting intake valves then the valve is "chasing" the piston down the bore (and catching it, obviously, in your case). A cam that's advanced will only make this situation worse. You didn't happen to advance the cam 4* at the timing chain when you put the motor together, did you? Many cams have about 4* of advance ground into them from the manufacturer (for instance, 110* LSA on a 106* Intake Centerline is common for many Comp cams).

 

Yes I did install the cam advanced 4*. I had heard that GM ground them "straight up." I was running flat top pistons with a quench of .045."
Will get new rings then, thought they could be reusable. How do I check the lifters? Is it safe to say all of the intake valves are bad? Lift on the cam was .480/.480.

Why is it that you can't find a hydraulic roller cam ground on a 108 LCA with less than 240* duration? Is it because the faster opening rates allow for a tigter LCA? Or because as mentioned earlier they are already ground in to it?