Things to watch for when milling heads

[trbig]

Just a word of caution for anyone considering milling on their head. Just remember that as you mill the head, you're taking away meat from where the exhaust studs go into the head as well as on the intake where your carb boots screw in...






If you have the later model heads with the bigger valves like these, notice how close they are to the edge after milling.






In the second photo you'll also see how I tapped and blocked off the YICS tubes (Black arrow). If for some reason I decided to ever go back to that system, those allen screws will come out.



I had quite a bit of work done to this head. Most of it was done in opening up the area immediately before the intake valves. The roughest of the casting was knocked down, but it was left rough. Nothing was done to the exhaust side except that both intake and exhaust valve seats were opened a bit to where the valve faces were hitting more towards the edges than in the middle of the face like the book calls for. I'm doing all this with the new 1179 bore, so if I make more power, I won't be exactly sure where it came from: The milled head, the porting, or just more CC's???


Tod

[mro]

How much did you have shaved off the head?


mro

[trbig]

LOL... I'm not exactly sure. I did a piston to valve check with the head and the 82 pistons that have a higher dome to them before all this work and had almost double the minimum clearance, so I told him to take a little and not worry about it too much. I think it's somewhere between 5-10 thousandths is all though. I just didn't want it boosting the compression up so high that I could only run 91 octane or higher.


Tod

[TADracer]

Tod

I am certainly not a machinist but just looking at the pictures, the amount of metal removed from the bosses to fasten the intakes and exhaust looks like maybe alot more than just .010" was removed from the head surface. I would figure a way to check this out against a known head that has not been milled.

Since you are into it this far, find someone that will lend you a burette and check your combustion chamber volumes then you can take your bore, stroke and head gasket thickness and calculate your actual compression ratio. It might surprise you. Also, when you set this head up I would be very careful checking intake and exhaust valve clearances making sure you have at least .050" and check it at 5 degree intervals for 15 degrees before and after TDC keeping in mind that the closest piston/valve clearance probably will not be at TDC. With a milled head this is especially critical on the intake valve.

Just my suggestions

[fredintoon]

0.010? and the rest.

Hi Tod,
Mike may not be a machinist but I was.
Looking at the photo, if that delta-shape plateau on the exhaust stud boss was not there before I reckon they took ~1/16" off the head to make it. Just you double check the actual compression ratio as well as if the valves still clear the pistons before you fire it up. You may be looking at choosing between fitting double head gaskets and running on alcohol.

[planedick]

Flycutter

Being a machinist for years I would not have used such a large flycutter for the process, instead concentrated on the indicating of the mill head for absolute perpendicular. Seeing the cutter marks shows the head was not absolutely true. Using a large diameter flycutter is a way of cheating so as not to have to spend a lot of time indicating or for compensating for older machines that may be a little worn. The flycutter should be only slightly larger than the width of the head being cut, and any more than .020" would not be done without written consent from the owner.

[mro]

Looks XSive

I'd put a straight edge across the intake and have look at the gap where it got shaved. Not scientific but will give you an idea how much was removed.


mro

[trbig]

Naw, he didn't take that much material away. Here's a few pics of a stock head 82....










And you can see in this pic that the valves are pretty close even stock...





So these spots are milled already. I was just making the point that it's taking even more of this area off when/if you do mill one.

As for Piston to valve clearance, I measured this once with these large valves and the higher domed 82 pistons which are just a tad higher than the Wiseco big bore pistons. The magic number for minimum clearance is debateable, but I've heard anywhere from .040-.060" on the intake and up to .080" on the exhaust. The closest measurement I got when I measured was .132 inches... so MORE than enough room to play with milling. It's just the other stuff ya gotta watch for! lol.

The guy doing this doesn't do motorcycle stuff normally. He has a machine shop set up and builds racing motors for dirt track cars, but yeah, most of his stuff is pretty old, but he tries to get by with what he has. I was pretty satisfied with the work he did for me. I just let him have the head for a few weeks to tinker with on his spare time. He did the 3 angle grind, milling, and all the porting work for less than $200. He did an excellent job with the cylinders he bored also.


Tod

[79XS11F]

Originally posted by mro
How much did you have shaved off the head?


mro

I was going to ask the same question? On the stock head those areas are already flattened out like that from the factory. So unless you took off a lot of material there should be no issue. When I had mine done they only took off a few 1000s to remove oxidized metal at the outer edges
Rob