Piston to Valve Clearance w/Clay

Steam Driver · Steam Driver's Garage

Has anyone figured out an easy (I.e less labor-intensive) way to do this on the 911? I need to do this because I need a more precise measurement than the adjuster screw method because the exhaust clearance is too tight for comfort.

There doesn’t seem to be anything on YouTube or the like. I have a way in mind, but it’s not going to be quick.

Ideas appreciated.

356RS · 356RS's Garage

I have used good quality clay on several valve to piston clearance measurements. Also have used soft rosin core solder 3mm OD for good measurements. I'm sure there are other ways but this works for me.

jpnovak · 01-23-2018, 05:10 AM

I have never figured out a better way. Yes, its a full dry build including cam timing but if you are running tight enough to question, you have to measure to verify.

Tippy · 01-23-2018, 05:18 AM

Crayons?

MBruns · 01-23-2018, 05:57 AM

I use light springs and start with the adjuster, if you are that close and the cam timing is where you want it and after confirming the valve is not touching the radius of the pocket or somewhere other than the pocket floor, cut the pocket and then if you have the setup use a dial indicator to measure from the retainer by pushing on the rocker or using the adjuster, be sure you have found the closest v to p on a degree wheel and not assume it's at Z1, with proper spring pressures I use .080" on exhaust and .040" on intake for minimums. I have used solder for piston to head across the dome, using clay works but the above reduces alot of back/forth labor
Hope this helps, Mike Bruns

boyt911sc · boyt911sc's Garage

Assemble your engine and set your cam timing. Remove the valve springs using a P7I and P7E or similar tools. This will give you the valve’s maximum travel or clearance. And @Z1, you have the piston at its highest peak of travel. Then you could compare the values of the distance traveled between using the cam setting and manual test. Only when you get the the values very close to each other should you worry about valve and piston contact. The piston dome pocket’s configuration is very critical to prevent contact. Tests and measurements will determine if you have the correct set up.

Tony

JohnJL · 01-25-2018, 03:02 AM

Quote:

Originally Posted by boyt911sc

Assemble your engine and set your cam timing. Remove the valve springs using a P7I and P7E or similar tools. This will give you the valve’s maximum travel or clearance. And @Z1, you have the piston at its highest peak of travel. Then you could compare the values of the distance traveled between using the cam setting and manual test. Only when you get the the values very close to each other should you worry about valve and piston contact. The piston dome pocket’s configuration is very critical to prevent contact. Tests and measurements will determine if you have the correct set up.

Tony

TDC isnt the point of closest interference with the valves. Many cams open faster or close later andso are closer to the piston before and after TDC.

The fast and dirty way is to install cams and heads amd time them correctly. Then screw the lifter in another 1.5 turns (1.5mm) and carefully turn the motor over. if it turns over then you have at least 1.5mm clearance throughout the revolution.