I may do it for just a tad bit higher compression when i port and polish my head, and have the ECU reprogrammed.

 

Well I guess no one has as of yet. Does anyone have opinions about it though??

 

Howdy all, new to the forums here with my SVT Focus purchase this past week, but I've learned a fair bit about Ford OHC engines from working on my 4.6L SOHC Mustang. I've been looking for a competent technical resource for the Focus the last few days and this certainly seems to be the place. Back to the question at hand...

My understanding is that milling the heads is not a good thing to do on an OHC because it will alter the cam timing. Milling the head moves the crank and cam sprockets closer together which creates slack in the timing chain. This slack gets taken up by the crank advancing relative to the cam. The Ford service limit for milling the head face on a 4.6L is 0.010". I'm not at all familiar with the cam drive set up on the Zetec but I'm assuming it's similar to the modular V8's. If not, hopefully someone will step in here to educate me.

Cheers,
Matt

 

Plus the SVT engine is an interferance engine and milling the head will greatly effect the piston valve clearance.

 

Ok about the 4.6 timing chains, i know alittle about this, because Im building a 4.6 DOHC. The chains are chains. the zetec motor has a belt, which has a tensioner, thus can be adjusted accordingly.

As far as the head being in interferance with the pistons ... that wouldnt be an issue unless you screwed up your timing extremely bad.

 

Howdy all, new to the forums here with my SVT Focus purchase this past week, but I've learned a fair bit about Ford OHC engines from working on my 4.6L SOHC Mustang. I've been looking for a competent technical resource for the Focus the last few days and this certainly seems to be the place. Back to the question at hand...

My understanding is that milling the heads is not a good thing to do on an OHC because it will alter the cam timing. Milling the head moves the crank and cam sprockets closer together which creates slack in the timing chain. This slack gets taken up by the crank advancing relative to the cam. The Ford service limit for milling the head face on a 4.6L is 0.010". I'm not at all familiar with the cam drive set up on the Zetec but I'm assuming it's similar to the modular V8's. If not, hopefully someone will step in here to educate me.

Cheers,
Matt

Welcome, and nice first post...good info.

 

Ok about the 4.6 timing chains, i know alittle about this, because Im building a 4.6 DOHC. The chains are chains. the zetec motor has a belt, which has a tensioner, thus can be adjusted accordingly.

Well, both engines do have a tensioner but I don't think it affects this problem. The cam is pulled on one side of the belt/chain loop by the crank gear. The pull of the crank keeps this side of the belt/chain loop tensioned. The hydraulic tensioner is on the opposite side of the loop to take up the slack on the undriven side. So, on the driven side, I still think you wind up with the crank advanced relative to the cam. Am I missing something?

 

Well, both engines do have a tensioner but I don't think it affects this problem. The cam is pulled on one side of the belt/chain loop by the crank gear. The pull of the crank keeps this side of the belt/chain loop tensioned. The hydraulic tensioner is on the opposite side of the loop to take up the slack on the undriven side. So, on the driven side, I still think you wind up with the crank advanced relative to the cam. Am I missing something?

Well if you retime your cams to TDC, then would be just fine then. As long as your running the same amount of teeth on the gears and belt as previously, and not changing the length of the timing belt, or chain ... everything would be alright.

You are right about the hydraulic tensioners on the 4.6, i forgot about them, oops.

 

Well if you retime your cams to TDC, then would be just fine then.

Good point! If you have an adjustable cam or crank gear then you're good to go. I'm not used to thinking in terms of adjustable gears since I haven't seen a set offered for the 4.6 yet so you don't have any adjustability to fine tune TDC on that engine.

 

Good point! If you have an adjustable cam or crank gear then you're good to go. I'm not used to thinking in terms of adjustable gears since I haven't seen a set offered for the 4.6 yet so you don't have any adjustability to fine tune TDC on that engine.

Actually , doesnt steeda offer a timing gear on the crank for the 4.6's?

 

Actually , doesnt steeda offer a timing gear on the crank for the 4.6's?

They do make an adjustable trigger wheel, but that's only used for adjusting spark timing. It doesn't affect the cams.

 

Ok, let's be realistic. There is no possible way to mill the head without removing the cams. So in the event you do mill your head, you WILL be retiming your cams, and retensioning your belt. And the ZETEC is a NON-interference engine, unless SVT changed something with the SVT head, this car should still have a non-interference setup, and it should not be a problem. Gude has already milled their head, I am aware of another company who has milled their head, so the issues being stated here, I do not believe to be something to truly worry about. I think the biggest problem will be the tuning, and IF there is even any power to be had.

 

Ok, let's be realistic. There is no possible way to mill the head without removing the cams. So in the event you do mill your head, you WILL be retiming your cams, and retensioning your belt. And the ZETEC is a NON-interference engine, unless SVT changed something with the SVT head, this car should still have a non-interference setup, and it should not be a problem. Gude has already milled their head, I am aware of another company who has milled their head, so the issues being stated here, I do not believe to be something to truly worry about. I think the biggest problem will be the tuning, and IF there is even any power to be had.

Im sure with an increase in compression, there will be gains, that happens with any motor. But the limits on Octane at pump stations will be a concern. As far as tuning, Unnaturally-Aspirated has tuning from Diablo sport, and will be offering, very soon, SVT programs for the Predator ECU flasher. As soon as I can get my head off the car, I will port and polish it, if needed, and mill the head for higher compression, and have it tuned accordingly.

Bela, ill be PMing you sometime today.