Head milling: At what point does cam degreeing become advisable?

[TheRadBaron]

This is sort of an offshoot from my earlier post about the possibility of surfacing the cylinder head.
I dropped my head off at the machinist today and after taking a few measurements he estimated that he'd need to take about .007 or .008" off the surface to get it properly cleaned up and true.  In my last post it was stated that taking .004" off the head would cause the cam timing to be retarded by approximately .5 degrees.  If my head comes home with .008" off it, the timing would then be retarded by 1 degree, right?
I also imagine that my 51,000 mile timing chain is causing a slight retardation of the cam timing.  I really don't want to lose any of the low-end that the FJ is known for.  Will the degree or two of retarded timing make a noticeable difference in the power? 
I've also read here that there is added performance to be had from advancing even the stock cam timing.  I'm thinking about getting adjustable cam sprockets, but I don't at all like the idea of the slotted sprockets due to the possibility of slippage.  Would there be any major reason not to get the slotted sprockets mocked up where you want them, then tack weld the bolts to the sprockets to ensure that there will be no slippage?
Sorry about all the questions and thanks in advance.

[SlowOldGuy]

I've been running slotted cam sprockets for over 10 years with no "slippage" problems.

DavidR.

[andyb]

Loctite the bolts once you've triple checked and know you've nailed the positioning.

Really cam chain stretch imo will give a bigger change than milling the head will to the timing with standard gears, if nothing else, using the slotted cams to put the timing marks exactly in alignment should give you all the power you want and then some.

[fj1250]

These heads frequently get milled .020"-.030" on a regular basis for the Legends cars.
Most street FJ's Will only make around 90rwhp on the dyno.
Mill the head, do a valve job (clean up the step in the port pocket), slotted cam sprockets with the timing @ 106 degrees
and it'll go to right 120rwhp!
My street 1250cc has done close to 140rwhp, but I eased it back down to 130rwhp for reliability/noise/touring duty issues.

Mike C

These engines love a bump in compression. It takes a fair bit of milling and pistons to get these to pump 180psi (10:1 compression)
Your engine will really come to life once it pumps 180psi!

[andyb]

Did some looking and some math. I'm going to start by saying my research may be wrong, but it's too damned cold to go and measure properly in the garage!

The FJ cam chain as spec'd by INEX (legends) is PN# 79RH2015.  Some searching says that this chain has a pitch of 0.250" (6.35mm).  It was posted someplace here that each cam sprocket has 46 teeth on it.  threejagsteve did the math and said that each tooth then has 15.652174 degrees of rotation relative to the crank (which spins twice as fast, remember).  From here with some lucky guesses at remembering how to do math, it seems that cutting .010" off the head will change the timing by 0.626 degrees, but I'm not accounting for the fact that they lie in different planes vertically (because I'm too tired to remember/google enough geometry to see if it matters or not)... the chain run isn't perpendicular to the surface being shaved down, in other words.

So a cut of .016" will change the timing by at most one degree.  It's not a huge difference, really.  I looked for about ten minutes and couldn't find a service limit for stretch on the timing chain (GYSM 3-23 will get you close, but I didn't see much), just to replace it if it looked stretched.  Thanks Yamaha, that's helpful.  I'm exhausted or I'd go try to dig up what another bike using a comparable chain spec's stretch at and work that out, but it isn't happening today.  I'm still guessing that stretch/wear is going to play a bigger role overall in where your cams actually end up as compared to the change that shaving a head will cause (and to say nothing about tolerances during manufacture!).

If someone wants to look bright, double check my math and give me all the answers here   Preferrably on a silver platter!

[andyb]

Now that I'm a pinch more awake:

Definitely shortening the distance between the crank and cams (shaved head, thin gasket, skimmed block, thin base gasket) will change things less than what I said above.  I'd have to measure the angle of the cam chain at the angle of the head:block surface and map a right triangle from that to figure out by how much.  Still isn't a huge amount, anyhow.

That being said, adjustable sprockets to just put things back to factory timing by aligning the stock punch marks with the caps to TDC will probably be a great boost to most FJ's out there still on factory sprockets.  As the cam chain stretches and the guides wear as the miles pile up, the timing moves around, and with factory tolerances also in the mix, there's probably a fair bit to gain for most riders.

[TheRadBaron]

I decided to go with the APE adjustable gears.  I like the idea of the cam timing being spot-on, and it sounds like very few people have had problems with the gears slipping and throwing of the timing.  I'm just waiting for them to arrive and I'll be wrapping up the motor. 

[carsick]

What octane does this require for street usage, i.e. heat and extended load, to avoid detonation?