Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Slippery Slope Expert
 
Steam Driver's Avatar
 
Join Date: Nov 2012
Location: Hixson, TN
Posts: 635
Garage
Piston to Valve Clearance

Are the numbers given for piston to valve clearance in Wayne's book "hard and fast?" When I check #1 and #4 using that method I get numbers that are essentially the reverse of the 1.5mm Intake/2.0mm Exhaust. Mine are more like 1.75 on the Exhaust and 2.0 on the intake. j Are these acceptable?

I know his numbers on deck height are somewhat conservative relative to the factory numbers. Would the same apply here?

Oh, engine is SC with 9.8:1 Mahles. Stock cams.
__________________
As new technologies become indistinguishable from magic, and I can no longer tinker, the magic goes away for me.

Last edited by Steam Driver; 12-31-2017 at 11:04 AM.. Reason: Add note on cams
Old 12-31-2017, 11:03 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: May 2003
Posts: 3,225
Provided you measured at the closest approach, you’ll be fine. The factory workshop manual mentions.8mm as the minimum.

-Andy
__________________
72 Carrera RS replica, Spec 911 racer
Old 12-31-2017, 03:54 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Slippery Slope Expert
 
Steam Driver's Avatar
 
Join Date: Nov 2012
Location: Hixson, TN
Posts: 635
Garage
Thanks for your reply. Im still mulling it over as to what to do. Still considering pulling the heads on one side and checking with clay.
__________________
As new technologies become indistinguishable from magic, and I can no longer tinker, the magic goes away for me.
Old 01-01-2018, 05:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: May 2004
Posts: 166
There is a very simple way of checking the clearance between the valves and the piston.

You need a degree wheel fitted and zero’ed out to true TDC on the crankshaft. Then a simple indicator and holder. Make sure the indicator is steady and has no movement other than its measuring travel.

Fit 1 piston to the engine along with the cylinder. Fit any base shims etc you think you want to use. At this time you can cc the piston and the head chamber to calculate the engines compression.

Turn the crankshaft so it is at 20 BTDC. You will be measuring from 20 BTDC to 20 ATDC every 5 or 10. This will depend upon how much data you require.

Now fit one head to the engine with both valves fitted but without springs and the rest of the parts. With the engine at 20 BTDC , measure each valve from its seated position on the valve seat to where it touches the piston. This is done by hand with the indicator. Make sure the travel of the indicator is aligned with the valve stems. Record the distance travels by the valve. Also make sure the valve goes into the pocket if there is one without it touching the pocket edges. Otherwise this will give you false readings.

Now move the crank to 15 BTDC or 10 if you want less data. Repeat this until you get to 20 ATDC.

Now if you have the valve lifts your cam produces from your cam supplier at these same degree positions, do some simple math to obtain the clearances. You may find its negative but its on paper and easy to calculate the amount each pocket needs to be machined. But remember your CR will change as well.

If you don’t have the valve lifts of your cam, remove the piston and rod from the engine. Re fit the head with checking springs along with the cam deck and camshaft, timed as you expect to run it. Now re fit the indicator on the back of the rocker adjuster. Make sure it is seated well and cannot move as the valve is depressed. Now repeat the same measuring positions from 20 BTDC to 20 ATDC. This will give you the valve lift numbers that you need to subtract from the valve seat to piston numbers.

This will give you the P/V clearances and this way, if you are fitting new pistons that need the pockets machined but do not know by how much, this method will give you any interference on paper only.

If you wish to side step this last part, you can send us the cams you wish to use and the cam timing you expect to run and we can run the cams and supply you with the lift numbers at that timed position.

Last edited by Neil Harvey; 01-03-2018 at 01:22 PM..
Old 01-03-2018, 01:18 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 10:25 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.