I am in the process of putting on new AFR 180cc Street Heads on my 350. I originally had the stock 411 heads with the 1.94 intake. I think I now have a problem with the radial clearance. The intakes are now the larger 2.02". The pistons are TRW 2256 (now Speed Pro L2256F). The info online is sparse, but it seems to suggest that the piston reliefs aren't made for/large enough for 2.02 intakes. I did a clay test and clearly the vertical distance is fine, but I am measuring around .040" radially. And it's right on the relief edge as shown in the pic. Wondering if anybody has had a situation like this, or heard of just taking a Dremel and grinding down some of the relief edge. I clearly don't have to take much off. Thoughts?? Thanks!! [Other info: rockers- keeping the 1.5 lift, and the cam is 232@50 with .485/.485 lift also same as before]
It's close. I was learnt many years ago to shoot for 050" radially, .100" piston to valve on the exhaust and .080 minimum on intake if you have good valve springs. I would think that I would go with .040" for a "bread & butter", or mild street motor. Unless you plan on buzzing that thing up past the spring limit and get into valve float.
I’d hit it with a dremel to give you some breathing room. Unless it’s full blown race motor and is balanced it won’t hurt it.
Should you decide to do some grinding, when done don't leave a sharp edge. Recreate the small radius on the transition edge so not to create a hot spot.
I would relieve the intake valve pocket a bit with an aluminum cutter with an air grinder - using a "flame tip" type pattern. I'd also then use about a 120 grit sand-paper roll to smooth out the modifications and blend the edge just a bit. Tape off around every piston and mask off the valley area to ensure you get no aluminum or sand-paper grit into the engine. This should be an easy fix! Here is a link to a 1/4" carbide bur - is what I use: Carbide Bur for Soft Metals and Plastics, Round Tree, 3/8" Head Diameter | McMaster-Carr
If you have a Spar striped head ,& One intake Valve no matter size , With measuring Braze a carbide to, To make a Fly cutter , Use head as a guild jig No head gasket Drill & Fly cut piston's
And use a locking collar/usually with an Allen set screw on the valve stem to adjust just exactly how for down you want it to go. And I have actually used an abrasive disk glued to the valve face in a tight. The cutter brazed or other cutters would be best. . Mask everything off. Even piston top. Etc. Put the jig /head /cutting tool on and go to it. Wes actually used to have a head cut in two just for such things. And as he said it’s not sexy but it sure works and you can see exactly what you want
To expand on what @19Eddy30 said...........people take an extra/scrap/used valve and attach a cutter to it. I like another similar way. Probably have to find/buy an extra valve thats larger than your 2.02. You can grind radial slits in the face of it. Use a thin small wheel on a Dremel or air jig grinder. Instead of vertical with the slit , tilt it slightly so it makes a crude cutting edge. Don't slit all the way thru the valve, just maybe .030/.045 deep. Then in the area between the slits, carefully grind that area down lower than the cutting edge. Then the valve is inserted into the head and the head set back on the engine. The valve touches the piston where its going to cut it. Put a bushing or collar around the valve stem and tighten a set screw to hold it in place. Leave a little room so that the valve can make a slight cut. Remove the head and see how much you need to move the collar to get the correct depth. Now scribe a line or make some kind of reference on the valve stem above the collar so you can reinstall the collar to the same point as you move from cylinder to cylinder. I would also put masking tape around the edge of the piston so no chips get wedged in that space. Be sure you make the cutting edge face the correct direction unless you can reverse your drill. This will allow you to make some consistent cuts so all pistons will be the same. I don't like the idea of grinding it by hand as that will surely leave grit on top of your rings. Its really hard to be consistent doing something like this by hand, and the valve cutter will provide you with better consistency. Good call @19Eddy30........I had forgotten about doing it this way until you brought it up. By the time I read 19Eddy30 and replied, @Mitchell Rish had responded with a similar post, so credit him as well. Edit: If you put some spray dykem blue of the valve and scribe some lines to represent the cutting edge, then grip the stem in a vice .....put some tape on the stem to protect it. Take a "thin" cutting wheel like you cut an exhaust pipe with. Simply tilt the grinding wheel when you make the slits. By that I mean put the wheel parallel to the face of the valve and then tilt it and follow the layout lines. It will cut an angled trough in the valve. You still need to relieve the area behind the cutting edge some in order for it to cut, but that should get you what you need. Might try it on an old valve first just to get the knack of it.
This is a topic I’d never thought about. I’m getting ready to have a SBC zero decked, and running heads with 2.02 intakes as well. I think I’ll have the shop open up my valve reliefs beforehand. Thanks for the thread!
The Jalopy Journal
