When cutting valve reliefs in pistons...

[RonA]

Sounds like the position of the valves in relation to the piston has a large margine of error so the ideal way would be to actuall make a spotting tool that is nice fit in the valve guide and drill a small spot through each gude into the top of the piston. then indicate the spots and cut the valve reliefs one at a time. Do they really vary so much that you can't just mark one piston, figure out the pattern, make a program, and do them all the same?

 

[Blueboy]

After you make 1st one you are right, you can make a
program, but you need to find a way to load each piston
the exact same way. they would need to load in relation
to your wrist pin.

 

[SINNER]

Take a steel rod slightly smaller than the valve guide and grind a point onto one end. Tap it with a hammer to give an exact center of the valve on the piston.

 

[Timebomb]

How big a dia are you cuting in the piston .100 larger then the valve ?

 

[XLR8R]

We cut .050" radial clearance for street trucks.

 

[Muddin_dude06]

A 5/16" transfer punch works great for going through the valve guide on a 12v, but it won't work on all pistons. My #286210's bowl is to large of a diameter to center punch it, so I used transfer paper and a sharpie afterwards to mark the valve OD. I sent mine to XLR8R for the flycuts.

 

[GRotman]

You can also take an old valve and cut the head off of it,then sharpen it to a point.

 

[RonA]

Starting to sound like alot of trouble for what little gains one might see from a more aggressive cam.

 

[morkable]

xlr8r, do you have the ability to fly cut the pistons without a person marking them (as in do you have a jig?

 

[XLR8R]

Not really Ron - it's basic stuff... folks tend to overcomplicate things.
Machining as required to fit the right cam is well worth it to maximize power.

In view of the low lift & negative overlap, the radial clearance covers a multitude of sins concerning indexing/marking inaccuracy.

Chris, forgot to ask - what part # are those valves?

 

[XLR8R]

xlr8r, do you have the ability to fly cut the pistons without a person marking them (as in do you have a jig?

Yes Kevin, although if they have the ability to mark them we request it as a double-check (amazing what can get lost in translation with too many chefs in the kitchen), especially considering the various combinations of valve swaps/replacements.

12V & 24V cuts are indexed a bit differently due to setup efficiencies.

 

[morkable]

What kind of dollars to do that? If you could pm me a price that would be awesome!

 

[RonA]

Pistons ship from Pa to Ca. assemble the engine minus valves in the head, bring pistons to tdc one at a time and mark them with a long custom made spotting tool, disassemble the engine and indicate each spot on each piston and cut the valve reliefs one at a time.Then send to NY for coating and back to Ca. Then send pistons and block to machine shop for fitting of the now .002 larger pistons(TC9 coating). Does FedEx know about the profit potential in engine building? Maybe a sponsership?LOL

 

[XLR8R]

Needless complication.

 

[RonA]

Yep. I just changed the cam order and will not need the flycutting. Cancelled the trip to get the pistons coated too. I don't think my engine runs hot enough to need the coating and I'm pretty sure it will meet my HP goal with one of the milder cams I run now.

 

[Scooter's Roofing]

you can modify a valve into a cutter, set the head on the deck, chuck the valve into a drill and scuff the piston and extrapolate the center point

 

[RonA]

Thank you for all the information. After today I am only a set of studs, front cover and housing, and a fuel pump away from having everything for the 6.7.

 

[Timebomb]

Then send pistons and block to machine shop for fitting of the now .002 larger pistons(TC9 coating).

I see it can be .015 for puller stuff from Swain....

 

[RonA]

I see it can be .015 for puller stuff from Swain....

I asked how much change to the piston od and this was the reply.

(PC-9 usually adds about .002” to the diameter of the piston. If you have more than .004” of clearance to start with you rarely need to add extra clearance to compensate for the skirt coating. If you have less than .004” to start with you would want to run on the low side of the recommended clearances for those pistons or about .0005” under the recommended clearances.)

 

[Hamilton Cams]

Ron, if you have the piston protrusion and valve face depth, I still might be able to fit the larger cam in with one of the different LSA's I have in stock. Don't feel like you are without options. Even still, if you decide to stick with the cam you bought, it is quite an upgrade over the old designs.

Zach