christopher 5 1 Cars Posted April 14, 2008 (edited) I've done some measurements on valve lifts on 8v TU before a dry build and am now worried about piston valve clearance . Doing some basic measurements I'm seeing that the valve seems to protrude into the cylinder 0.9mm at 2.7mm of lift @TDC. I'm unsure how much this clearance changes after TDC I can only do a basic check without doing a dry build. Now that I am considering using flat top pistons this doesn't leave a lot of clearance. What is the recommended clearance? I know Sandy relieved the pistons on his build. I suppose this is an option. Question is does this a piston out job? Has anyone bulit a 8v using flat top pistons (TU5J4) is so what kind of lift @ TDC were they running? Edited April 14, 2008 by christopher Share this post Link to post Share on other sites
Sandy 191 Posted April 15, 2008 I have recently built an 8v with TU5J4 pistons, but I machined cutouts on the mill before I built it up. What you can do with the pistons in place, is use a gash head, cut up a valve to make it into a rotary cutter, smear grease around the edge of the piston to trap swarf, (lock the crank at TDC), put the valve in the head, drop the head on without a gasket, put a drill on the valve and GENTLY spin the valve "cutter" down onto the piston. It's bloody tricky, but a fairly common method which i have used satisfactorily for minor cut outs several times. Obviously the clean up must be undertaken very carefully and the cutting edge/bacedge on the valve is crucial to the success. Share this post Link to post Share on other sites
christopher 5 1 Cars Posted April 15, 2008 I have recently built an 8v with TU5J4 pistons, but I machined cutouts on the mill before I built it up. What you can do with the pistons in place, is use a gash head, cut up a valve to make it into a rotary cutter, smear grease around the edge of the piston to trap swarf, (lock the crank at TDC), put the valve in the head, drop the head on without a gasket, put a drill on the valve and GENTLY spin the valve "cutter" down onto the piston. It's bloody tricky, but a fairly common method which i have used satisfactorily for minor cut outs several times. Obviously the clean up must be undertaken very carefully and the cutting edge/bacedge on the valve is crucial to the success. Hi Sandy, Thanks for that. Do you have any pictures of the TU5J4 piston milled down and the valve cutter? I think the cutout needs to be relativly minor. But I'm not 100 % sure Share this post Link to post Share on other sites
Sandy 191 Posted April 16, 2008 Here's the machined TU5J4 piston: I don't have a pic of the valve cutter handy. Share this post Link to post Share on other sites
christopher 5 1 Cars Posted April 16, 2008 Here's the machined TU5J4 piston: I don't have a pic of the valve cutter handy. Thanks that makes it a bit clearer. That looks quite a lot to shave off with the valve cutter method. What kind of lift @TDC where you using and valve piston clearance? Share this post Link to post Share on other sites
eeyore 0 Posted April 16, 2008 Sandy did those with an end cutter on the mill. I think that one allowed about 3.5mm plus clearance safely at TDC. Share this post Link to post Share on other sites
