oversized Eccentircs question

[nbristow01]

I have a head I just had redone with an new valves guides seals seats etc etc. I have an IE regrind 292 in the head. I have a set of oversized eccentrics to install but wonder if they are really needed. I have no problem adjusting the valves to .006 or .007. with the stock eccentrics I had the machine shop put in. I believe I read a post and Toby said he runs regrinds and has never had to use oversized eccentrics.

So question is, do I need them if I can adjust the valves with the standard eccentrics?

[AceAndrew]

You do not need them if you can use the standard eccentrics. So in your case, nope, not needed.

They are needed sometimes if the base circle had to have enough material removed (or if the valve seat is moved). On a 292 they are generally not needed, but then again I have come across some who need them. Go any more extreme on a regrind and there's a always a pretty decent chance.

[nbristow01]

You are always a great deal of help..thanks!!

[TobyB]

Toby said he runs regrinds and has never had to use oversized eccentrics.

If I did, I was lying out my a**.

Every reground cam I've ever used

has needed either larger eccentrics or lash caps.

With maybe the exception of the Ireland 'new billet' grinds-

I forget what those needed.

Sorry if I misled you down the golden path of rocker distortion...

t

[Guest_anonymous]

The issue is valve timing. While you can achieve the correct lash gap. Becuse the cam is ground below the billet base circumference, it changes the angle at which the rocker will move the valve, acentuating a valve timing distortion. Seemingly creating an ignition timing issue. Chased myself around a corner with a 300 regrind for exactly this reason.

Daron

[Tommy]

The issue is valve timing. While you can achieve the correct lash gap. Becuse the cam is ground below the billet base circumference, it changes the angle at which the rocker will move the valve, acentuating a valve timing distortion. Seemingly creating an ignition timing issue. Chased myself around a corner with a 300 regrind for exactly this reason.

Daron

But you can't correct the rocker angle by any of these means. Only way is to use a fresh cam (=not re-ground).

-> If you're able to adjust the gap to correct value you don't need to change anything. If not, bigger eccentrics or lash caps will give the same result.

Tommy

[nbristow01]

Toby said he runs regrinds and has never had to use oversized eccentrics.

If I did, I was lying out my a**.

Every reground cam I've ever used

has needed either larger eccentrics or lash caps.

With maybe the exception of the Ireland 'new billet' grinds-

I forget what those needed.

Sorry if I misled you down the golden path of rocker distortion...

t

Toby, you are correct. I misunderstood, you said you have used regrinds with no issues, the eccentric part must have come to me in a dream because you did not bring that up LOL

[TobyB]

Oh, but I DO lie like a rug sometimes, so it's entirely possible I said that once. Or more.

But it wouldn't be true.

heh

As to a valve timing issue with a regrind, in THEORY,when making the cam, the grinder adjusts

for the change in lash pad position and rocker geometry. In fact, they HAVE to, at least to some

degree, to keep the lobe on the pad.

Whether that's done properly- or at all- is another issue altogether.

The L-series Nissan guys take a LOT of time to make sure the lobes

stay on their rockers, but we don't seem to have the problem to the same

degree...

t

[eurotrash]

For the sake of just knowing..

 

 

Stock eccentric:

 

 

 IE oversized.  (Via Le Tran)

 

 

Edited November 11, 2013 by eurotrash