Cutting valve reliefs in pistons?

[tbird]

I'm going to be using .030 head gaskets on my build.  My intake's are 1.90's. I need to cut the valve reliefs in the pistons. How much do I need to take off? Anyone w/ pics ? What's the best method of doing this? Any precautions? Only get one shot at it and don't want any screw-ups. Thanks

[Tre_11 FLHX]

Copied from old sight-poster Harleyhog


Open the intake relief further toward the piston edge about .060-.080"
It has to be within .275" of the piston edge.

Make sure it's only the intake's you do, thats the rear piston.
Inside reliefs on both pistons as they are installed/positioned in the cylinders/motor.

Rear piston/front relief....Front piston/rear releif

Modified to add last two paragraphs

[mayor]

I used a round carbide burr bit on a Dremel to do mine. I used blue painters tape to cover everything but the tops.    I was pretty nervous at first, but it wasn't too bad once I got started.  As you can see by the pic, I hit the tops with the bur a couple of times.  If I had it to do over again I might have covered the top with a couple layers of tape too.     Overall it's wasn't a pretty way to do them, but it worked. I used a set of calipers to mark .090" off set from the eyebrows, then kept grindng the edge of the brow to I got to the line.  Even opening the brow up .090", I didn't take the edge to brow distance down to .275" as mz picture states (red arrows). That had me kinda worried since I used that picture as a guide, but I think I would have had to go another .020" or so to get it in that range which didn't make sense.  I smoothed up the openings with a  round pointed grinding stone (applied by hand not in a die grinder), then some fine sand paper.   When you cut the openings keep in mind, you don't need to go deeper just wider. 

[Hillside Motorcycle]

We do that work here in a piston vise, on a digital-readout equipped vertical mill.
2.125" end mill. Looks like it was made that way. (it was )
Scott

[wfolarry]

Scott you need to start posting pictures.
"a picture is worth a thousand words"
On sites like this it can prevent a lot of arguments too 

[jsachs1]

As has been posted numerous times,most MoCo T.C. CAST pistons need to have their valve pockets spread by .100" each.
A critical area is the area where the 2 angles meet at 90 degrees at the bottom of the valve pocket.You need to have a smooth,generous radius there.If not you stand a chance of developing a crack,which can lead into the ring land.
I use a short,stout boring bar(no flex),with a decent radius on it.If you're doing the job with a "Dremel" use a tootsie roll to keep the area smooth,and you can dress a radius on ti as well.
The Pro-Mod pistons I do,from blanks,(picture) will teach you,in a heartbeat,where the problem areas are.
John 

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[PanHeadRed]

I like that last pic, nice work.

[Admiral Akbar]

I like that last pic, nice work.

Yeah,

He got carried away and cut too many valve pockets..  Max

[Jeffd]

This is how Dan Bailey did mine.

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[Hillside Motorcycle]

Scott you need to start posting pictures.
"a picture is worth a thousand words"
On sites like this it can prevent a lot of arguments too 

I've been thinking about doing just that.

[tbird]

Thanks for the info. Is this something I can attempt on my own or should I seek professional help?

[03deuce]

I believe reply #2 sums it up pretty well.  If you have used a dremel before and have the bits, should not be a big deal.  Just make sure you cover up any openings that the grindings might get into.  That's why you tape up the topside.  Also, if you have the pushrod tubes out as well, make sure you cover any openings.  You could always practice on a set of stock pistons, they aren't worth much as take offs.  If you are not comfortable doing it yourself, no reason to not seek out either professional help or someone that has done it before. 

[nc-renegade]

We do that work here in a piston vise, on a digital-readout equipped vertical mill.
2.125" end mill. Looks like it was made that way. (it was )
Scott

Scott,
That is the correct way to do it!

[GoFast.....]

Thanks for the info. Is this something I can attempt on my own or should I seek professional help?

I would have a perfessional do it and I do a lot of stuff on my own, It needs to be done right and you could send them to anyone of the pros above, Altering piston is in anyway is a serious thing. Just miss it a little and you could bend a valve and set off a chain reaction in your motor.

[Scramjet]

Thanks for the info. Is this something I can attempt on my own or should I seek professional help?

I would have a perfessional do it and I do a lot of stuff on my own, It needs to be done right and you could send them to anyone of the pros above, Altering piston is in anyway is a serious thing. Just miss it a little and you could bend a valve and set off a chain reaction in your motor.

I may not be the norm but, I have hand cut, disk sanded and filed spacers and other items to +/-.003" and surfaces parallel to .001".  I do have many years of manufacturing inspection experience.  It can be done with great care, a steady hand, repeated measurement and much blue tape.

B

[tbird]

Not to beat this thread up, but what should I expect to pay to have this done by a shop?

[Sonny S.]

Not to beat this thread up, but what should I expect to pay to have this done by a shop?

$10 per pocket is fair

[mtnmotorrider]

Axtell did mine for $50 and the peace of mind is well worth it!

[Arrowsmit]

If I'd had the pistons out I'd have sent em to Dewey, but I did mine myself (in the engine) & 10K later so far no probs...

**Edited to add a 'thanks for the help' to several other HTT members who had already done this w/good results.

VicW.