Login    Forum    Search    FAQ

Board index » Racing Forum » Engine & Cylinder Head Tech




Post new topic Reply to topic  [ 6 posts ] 
Author Message
 Post subject: Cold Lash
 Post Posted: Thu Jun 17, 2010 3:55 am 
Offline

Joined: Thu Jul 19, 2007 11:08 am
Posts: 400
Looking to come up with a figure for setting my lash cold.. Cam spec suggests .026 hot lash. Motor is iron block and aluminium heads, full roller. I'm not a fan of setting lash hot as the motor is normally cooling off whilst doing it from around 200 down to 170 or so, also I like to do it with the plugs out and am pissed off getting burnt ! What figure do you guys use to compensate for cold versus hot lash tolerances ?

_________________
Image


Top 
 Profile  
 
 Post subject: Re: Cold Lash
 Post Posted: Thu Jun 17, 2010 5:35 am 
Offline
User avatar

Joined: Wed Dec 09, 2009 5:43 am
Posts: 12
subtract .004 - .005 for cold lash

_________________
Seven second action
Image


Top 
 Profile  
 
 Post subject: Re: Cold Lash
 Post Posted: Thu Jun 17, 2010 6:07 am 
Offline

Joined: Mon May 17, 2010 9:34 pm
Posts: 115
Location: Georgia
I always like running the engine up to operating temperature then shut it off. Whichever cylinder is easiest to get to, I quickly set the valves on that one. After engine totally cools off, I check & see how much lash has changed and use that as a guide for that paticular engine.


Top 
 Profile  
 
 Post subject: Re: Cold Lash
 Post Posted: Thu Jun 17, 2010 8:36 am 
Offline
Site Admin
User avatar

Joined: Tue Apr 18, 2006 6:38 am
Posts: 11804
Location: Coming At Ya!
BarryW wrote:
I always like running the engine up to operating temperature then shut it off. Whichever cylinder is easiest to get to, I quickly set the valves on that one. After engine totally cools off, I check & see how much lash has changed and use that as a guide for that paticular engine.


I used this method and it was .004 across the board. Now I take the lash listed and subtract .004 and use that number with the engine cold.

I'll give you another one too. I use to set lash at TDC on each cylinder but that doesn't work out for me. Now I check the exhaust when the intake valve is near max lift. Then I check the intake valve when the exhaust is just starting to open. I found that lash varies a bunch from TDC to this method. What I believe I found is that the cam will move some simply because it has about .003 bearing clearance. When one valve gets opened I do believe that the cam gets pushed away some and that actually increases lash over what it was at TDC with both valves closed.

Another thing to keep in mind is that 99% of the time a valve is going to get loose rather than tight so if you have been running this engine for some time and you find one you think is tight, then bump the engine around some to see if that changes. Certain spring harmonics can cause damage to valve seats and "might" result in lash tightening up but they will normally go to the loose side.

If you find a valve that is loose then it's a good idea to make a note of which one it is and then check it again after a few passes to see if it has loosened up again. That might indicate that a lifter or rocker arm has a bearing going bad.

_________________
Big Boyz Toyz!

Image

Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

William Pitt, British Prime-Minister (1759-1806)


Top 
 Profile  
 
 Post subject: Re: Cold Lash
 Post Posted: Thu Jun 17, 2010 9:01 am 
Offline

Joined: Thu Jul 19, 2007 11:08 am
Posts: 400
thanks guys I'm gonna try .004 and check it after my first pass next week.

Interesting what you say Ken about the bearing tolerance affecting lash, I would have though the forces acting on the cam we're pretty much even as the the springs from every other cyclinder will be acting on it ?

_________________
Image


Top 
 Profile  
 
 Post subject: Re: Cold Lash
 Post Posted: Thu Jun 17, 2010 9:38 am 
Offline
Site Admin
User avatar

Joined: Tue Apr 18, 2006 6:38 am
Posts: 11804
Location: Coming At Ya!
PSweeney wrote:
thanks guys I'm gonna try .004 and check it after my first pass next week.

Interesting what you say Ken about the bearing tolerance affecting lash, I would have though the forces acting on the cam we're pretty much even as the the springs from every other cyclinder will be acting on it ?


In your case Phil it might not be that much of an issue but on my engine, cam bearing clearance along with the fact that I'm running a small base circle cam (.930 dia) I do think there is flex involved as well. I can assure you though that if I set lash at TDC, it changes (increases) when the valve opens.

_________________
Big Boyz Toyz!

Image

Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

William Pitt, British Prime-Minister (1759-1806)


Top 
 Profile  
 
Display posts from previous:  Sort by  
 
Post new topic Reply to topic  [ 6 posts ] 

Board index » Racing Forum » Engine & Cylinder Head Tech


Who is online

Users browsing this forum: No registered users and 1 guest

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron