Big cam - piston to valve clearance

[inline6]

I did some searching in the L6 forum and came across a post that said these were the minimum piston to valve clearances to run:

.080" intake, .100" exhaust minimum

 

Has anyone run anything less than this successfully?

 

Here is some info on my combo:

 

• Stock bottom end - F54 L28 with flat top pistons. I measure .017" to .018" piston height above deck (all carbon removed from top of piston).
  
  
• The head (E-88) has been milled a few times over its life, just to straighten. I'm guessing .010 - .015" has been removed from stock. Anyone know the stock thickness?
  
  
• Manley stainless valves - stock exhaust diameter and stock l28 intake diameter.
  
  

 

Cam:

Intake

Seat duration 320 degrees

.050" duration 290 degrees

Valve lift with zero lash .565"

Hot valve lash .015"

Net valve lift .550"

 

Exhaust

Seat duration 315 degrees

.050" duration 274.8 degrees

Valve lift with zero lash = .565"

Hot lash = .015"

Net valve lift =.550"

 

I put clay on the number one piston. I put on the Nissan stock head gasket (a used one that measured .050" thickness). I put the head on with a couple of head bolts just to snug it down. I put the number one and two rockers in with zero lash...

 

Looks like I have about .030" clearance on the intake valve and maybe .025" on the exhaust.

 

By the way, while I was searching through old threads, I came across info that said I should run .022-.025" deck height. That is interesting, because with the stock head gasket from Nissan, I calculate that you end up with .050" minus .018" (piston pop up) which gives .032". A 1mm head gasket would put that around .022"...

 

Garrett

Edited October 31, 2010 by inline6

[z-ya]

I did some searching in the L6 forum and came across a post that said these were the minimum piston to valve clearances to run:

.080" intake, .100" exhaust minimum

 

Has anyone run anything less than this successfully?

 

Here is some info on my combo:

 

• Stock bottom end - F54 L28 with flat top pistons. I measure .017" to .018" piston height above deck (all carbon removed from top of piston).
  
  
• The head (E-88) has been milled a few times over its life, just to straighten. I'm guessing .010 - .015" has been removed from stock. Anyone know the stock thickness?
  
  
• Manley stainless valves - stock exhaust diameter and stock l28 intake diameter.
  
  

 

Cam:

Intake

Seat duration 320 degrees

.050" duration 290 degrees

Valve lift with zero lash .565"

Hot valve lash .015"

Net valve lift .550"

 

Exhaust

Seat duration 315 degrees

.050" duration 274.8 degrees

Valve lift with zero lash = .565"

Hot lash = .015"

Net valve lift =.550"

 

I put clay on the number one piston. I put on the Nissan stock head gasket (a used one that measured .050" thickness). I put the head on with a couple of head bolts just to snug it down. I put the number one and two rockers in with zero lash...

 

Looks like I have about .030" clearance on the intake valve and maybe .025" on the exhaust.

 

By the way, while I was searching through old threads, I came across info that said I should run .022-.025" deck height. That is interesting, because with the stock head gasket from Nissan, I calculate that you end up with .050" minus .018" (piston pop up) which gives .032". A 1mm head gasket would put that around .022"...

 

Garrett

 

Deck height is determined by block height, rod, piston, and crank, not the head gasket thickness. The stock deck height (the amount the piston protrudes above the bock deck) for an L28 is 0.030.

 

I think the test you did is valid. Did you have the timing set installed, or did you just rotate the camshaft?

[inline6]

Thanks for the reply. By timing set, do you mean a degree wheel? I did not have anything like that on it yet. I just mocked everything up and rotated he engine around two full crank revolutions. I do have a degree wheel that I can use... But, I've been reading old posts and came across a comment from Tony that not having the cam dialed in when doing the clay test is ok as generally to get it dialed in usually involves less than 4 degrees one direction or the other, and that amount doesn't make much of a difference in PTV clearence. Thread where he mentions this is here:

http://forums.hybridz.org/index.php/topic/84616-headpiston-clarification/page__p__802326__hl__%2Bpiston+%2Bvalve+%2Bdeck+%2B__fromsearch__1#entry802326

 

If I had something close to the right minimum PTV (whatever that is), I would go through the extra effort to go ahead and time the cam and remeasure. Of course, if I am now looking at putting valve reliefs in pistons, I'll need to do this as a next step anyway.

 

Regarding the piston above deck being .030" - reading through several threads here at least, it looks like there are differing amounts for stock L-28 flat tops... However, Braap indicated in this post that he had never seen less than .019":

http://forums.hybridz.org/index.php/topic/58127-best-way-to-achieve-piston-to-head-clearance/page__hl__%2Bdeck+%2Bbraap+%2Bpiston

 

And then in this post, he gives a much larger range (.012-.022") but I haven't found reference to anything above .025" - until now that is :)http://forums.hybridz.org/index.php/topic/75849-warning-mn47-clearance/page__p__722093__hl__%2Bpiston+%2Bvalve+%2Bdeck+%2B__fromsearch__1#entry722093

 

Mine is measuring out to .017 - .018" above the block deck with my dial caliper and magnetic stand (again all carbon removed - with carbon it was .022")

[TimZ]

This won't answer your question about allowable piston to valve clearance, but I can't help but notice that you are running a lot of lift. You do realize that stock valvetrain hardware won't work with that much lift, right? Have you taken the necessary steps to make sure that your springs won't bind, and the retainer won't hit the stem seal?

[inline6]

This won't answer your question about allowable piston to valve clearance, but I can't help but notice that you are running a lot of lift. You do realize that stock valvetrain hardware won't work with that much lift, right? Have you taken the necessary steps to make sure that your springs won't bind, and the retainer won't hit the stem seal?

 

 

All good there. I got the head back from the machine shop recently. Valve springs are designed and intended for use with the cam. I'm using shorter valve stem seals than stock (Ford Capri V6 as mentioned in threads here on hybridz).

[inline6]

I am still hoping to get some real world experience regarding piston to valve clearance... I saw a post where 1FastZ indicated he had .050" on the intake valves, but he also mentioned he was running titanium retainers...

 

I am looking to order custom pistons... It would be great to have this info before I do that.

 

Garrett

[rayaapp2]

STICKY: NA 3.1L=>head & camshaft questions. No shortcuts, max

 

There is some applicable info in this thread for your valve relief clearance.

 

PTV = Piston To Valve Clearance Im sure.

 

Modeling Clay check is a good place to start. As far as general tolerances I can only give you a vague opinion.

 

The stock L series valves are stainless. I am assuming that aftermarket stainless valves will have very similar expansion characteristics so personally I would feel that the PTV clearances would be extremely similar. The general clearance for a stock L series valve should be the same for yours in my opinion, but you should obviously make sure if you can or error on the safer side.

 

You should be able to ask a reputable L series cylinder head builder what kind of clearances to run for your specific setup. With very little time I found a handful of them using the search feature here and there are a few registered here on hybridzs.

Edited December 30, 2010 by rayaapp2