Valve to piston clearance.

Some interesting info. I was looking at a few spare engines today and I noticed little marks on the pistons (TRW forged 10:1) from valve to piston contact. These happened when the guy who bought my old turbo car did a cam swap. He didn’t have the cam degreed properly. The pistons sat 20 thou in the hole and the heads were stock 58 cc not milled. The cam was a mild 114 Poston. The engine went on to make 460 hp to the tires on low boost, ran low 11s in the quarter. 140 mph on the freeway with 3.42 gear, 2004R, just a great cruiser. The guy wanted more and went to a 1200 hp 383 with turbos, sold me back the drivetrain.

I just thought it was interesting that it’s less about cam size and more about how the cam is degreed when in comes to valve to piston contact. Ironically there are a few other marks from a previous engine build where someone did the same thing with the pistons on a previous build.

 

Valve notches would've helped.

 

When the cam is degreed right they aren’t needed.

 

I think I see where your talking about, top left of the piston?
If so, why is the ding filled with carbon?
Do all the pistons have that mark?

 

Yes all of the pistons have these marks. The carbon is on the mark because the engine was ran for 5000 miles after the valve to piston contact. A better pic:

 

So how was it degreed? You aren't saying that was done during assembly are you?

Jim

 

The engine was built initially with a stock cam, and then the owner wanted a bit more RPM so he swapped in a 114 cam. But when he installed the cam it must have been way off on the timing set. So when he tried to start it the pistons hit the valves. He re degreed it and had no further issues.

 

Only +8 to 0 to -8 available on a 9 keyway set. Maybe he was an add'l tooth off?

 

Yes, not sure how he managed it but that was the end result....