Milling a Z-head - what are your thought and how much to take off

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Model T Ford Forum: Forum 2012: Milling a Z-head - what are your thought and how much to take off
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Kelsey on Tuesday, August 28, 2012 - 11:00 pm:

Hi.

My T is blowing a lot of white smoke out the exhaust, moreso when the engine is completely warmed up and very little when the engine starts cold. The engine was rebuilt and running great since 2010, when it was installed. The white smoke has been an issue since this past April and gotten progressively worse since then. If you want to skip my whiney story, please drop down to the last paragraph. ;)

This past July, I pulled the Z-head (which it's had on it since the rebuild) and found that cylinder 4 was completely clean - no carbon. Yet, there was no water in the oil, so the water had to be blowing past the valves and out the exhaust. We put on a new gasket, without any silicone goo, and I took it for a drive. The following day I went to retorque the head bolts and found that #3 bolt had pulled itself out of the block and stripped the threads. A friend and I helacoiled the head and put on another new gasket, thinking that would solve the white smoke issue, but it did not.

We very sure that it's not oil blowing past because of some testing we did last year Bob did a compression test about a year ago because he felt a loss when he tried cranking it through. It measured 70 psi on all of the cylinders but #3, which measured 55 psi. When we took the head off, we checked for scoring on the cylinder walls, just in case it was a broken ring, and all of the walls look brand new. We even pulled off the valve cover and everything is functioning and seating properly.

The GEAA was putting on a car show this past Sunday in Orting, one that I have been looking forward to taking the T to all year. Thinking that there was something wrong with the Z-head, I dug out the original head and wire-wheeled all of the carbon Saturday night, used fine emery cloth on the surface, then pressure-washed it thoroughly this morning and blew it out with air. It took longer than it should have, but I removed the Z-head and put on the original one by 11:00 am, still in time to make it to the show.

I then took the car for a test run and immediately noticed a significant lack of horsepower; however, no white smoke, so that was a good thing. Still planning to go to Orting, I fueled up the car on 176th. I returned home to do another check to see if any white smoke was coming out and the engine boiled over right as I pulled in the driveway. I quickly shut off the car and noticed that the fan belt had broken and I didn't have another one. So, home we stayed and I pouted the remainder of the day.

My thoughts are two-fold: 1) it leaked because I didn’t use a high-heat silicone gasket seaker (Lang’s told me that they had success without using it) or 2) that the Z-head might have a crack or is warped. I’ve taken an aluminum carpenter’s square and feeler gauge to the surface and can slip the .006 gauge under the square in quite a few places, all towards the rear of the head. For those of you more mechanically inclined than me (which is most likely all of you), would you have the head resurfaced? If so, how much can be safely taken off? Thanks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, August 28, 2012 - 11:18 pm:

Jim,
1. High-heat silicone gasket sealer is not recommended for head gaskets. Copper coat gasket compound is recommended for head gaskets if you need any sealer at all.

2. If you really have 0.006" of warp, you need your head surfaced. Just take off what ever is needed, you have no choice. If you have any question about your measurement, the machine shop will check it before milling.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Williams on Tuesday, August 28, 2012 - 11:26 pm:

The Becker Special Z head was milled .030


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison on Tuesday, August 28, 2012 - 11:33 pm:

Hi Jim, There's a pretty good chance your carpenter was more responsible for your .006" than your head. Take it to a machine shop and have them level it using leveling jacks, a test indicator and a surface plate. have them level the head in three different places then sweep the head to determine the flatness. If they have a computer controlled Coordinate Measuring Machine they should be able to check it even faster than dialing it in on a surface plate. I know it sounds like it would be a lot of extra but a good man with the right equipment should be able to do it in less than 10 minutes. If the head checks flat, take it to a competent weld shop and have them do an inspection for cracks using Dye Penetrant. It's also a very easy process and you could do it yourself. The dye, cleaner and developer comes in 3 different spray cans and its extremely simple to use. Some people might tell you to simply lay the head on a surface plate and check it with feeler gauges but it won't check all the way to the center of the head and you might check it and find it's alright and it would still be out of flat.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison on Tuesday, August 28, 2012 - 11:35 pm:

Then if they have to machine the head they should only take off as much as it takes to clean it up.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, August 28, 2012 - 11:43 pm:

You just have to check the clearances to the pistons without the gasket after milling. Some grinding in the compression chambers above the pistons may be needed. When you can crank the engine a full turn without interference you're OK (put some modeling clay on the piston tops and mount the head with a couple of screws for testing)
After final mounting of the head, the gasket should give appropriate clearances for running.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Wednesday, August 29, 2012 - 12:09 am:

You should retorque the head bolts after the engine has run and warmed to operating temperature, and again, with an aluminum head after the engine has cooled back down. I think the 0.006, if that's all there is, should pull down and seat. I wonder if you just didn't have the head bolts tight.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Wednesday, August 29, 2012 - 12:18 am:

I wonder the same thing, Ted. You can get the head squeezed on tighter, without risk of stripping the threads, if you use studs instead.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Wednesday, August 29, 2012 - 12:30 am:

I have a couple of Joe Gemsa cross flow twin spark cylinder heads but their shape is not that of a side valve head. Anyway a T crank can stand a 9.5 compression ratio if you know how to drive it. Don't get silly with it. You must learn how to treat it with kindness and don't drive it like a jerk would and blip the throttle at the wrong time in order to impress folks with the new found hair on your chest.

So I would first learn how to drive a performance engine and then cc your performance cylinder head and get it to 9.5 and go whup-em. Talk to some of the boys that have true performance engines that have held together over the years.

9.5


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Ostbye on Wednesday, August 29, 2012 - 12:31 am:

There is a thread somewhere about taking .050" off to raise the compression to 6.0 to 1 It comes giving you a ratio of 5.8 to 1

It actually might be on the paper that comes with the head.. I will look tomorrow morning for you. You also need to run the correct head gasket. I think it is the new style not copper.

If t is cracked it will not smoke when cold possibly because it sometimes closes the crack though I have seen it both ways.

Also John A. was asking me about this this mmorning.. If you want to check it on weds call john and then call me


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Wednesday, August 29, 2012 - 12:34 am:

Jim - Sorry to hear of your misfortune with the tudor. Wonder if your present problem with the head had anything to do with the slight miss you experienced in one cylinder at the Thun Field Fly-In the other day?

I'm sure you've done this Jim, but while the head is off, check carefully for any possible crack either between valve seat and cylinder or any crack between valve seats. The other thing I was wondering is if there is any possibility that the top of the block is not perfectly flat. My block had to be surfaced in conjunction with the rebuild last winter, however, that had more to do with some fairly deep pits at one corner of the block; I don't think "flatness" was an issue.

I hesitate to make this next comment as I'm sure I'll get some "flak" over this, but I never was too much in favor of an aluminum head on an iron block. I know how successful "Z" heads have been, but there just HAS TO BE a difference in expansion rates due to the two different metals, and if nothing else, I think it makes careful fitting, sealing with copper coat, and torquing (and re-torque) after first run and cool-down even more important with a head gasket replacement with an aluminum "Z" head than with a stock iron head.

Just sorta' "thinking out loud" Jim and I'm sure you'll get some good advice from "those that know" on this forum.

Hope you get it sorted out without too much trouble and expense Jim,......harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Wednesday, August 29, 2012 - 01:01 am:

There is a terrific increase in performance and horsepower with the Z head. Just because of its ability to guide the intake and exhaust gasses to where they belong makes it a good addition as it is. Milling one of them will add compression and so add horsepower and fuel efficiency. As I stated before . . . . . Model T crank shafts can operate with 9.5 compression ratios if they are in good condition. IF and it is a big IF you know what you are doing. If someone let it slip when in the jig you can safely re-align it and mill a little bit off to make all combustion chambers equal but don't get silly unless you know how to treat it like a lady.


Top of pagePrevious messageNext messageBottom of page Link to this message  By mike conrad on Wednesday, August 29, 2012 - 09:25 am:

Hey Jim talked to you sunday, as said before have a good machine shop check that Z head and only mill what is needed. When you do get it back use copper coat to seal the head also do not exceed 50lbs of torque. Any more than this is sure to strip more head bolts. The head will need to be retorqued after a short warm up. Let the head cool then retorque. if you need more help call.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Ostbye on Wednesday, August 29, 2012 - 09:53 am:

Also Jim, Give the head to someone who can bring it here if you like. You can have it resurfaced on a belt sander type resurfacer.

I found the paper about the .050 " by the way. My opinion is .006 will flatten out with 50 pounds of tourque. I have a $ 75,0000 machine here I can measure it for you.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Robison on Wednesday, August 29, 2012 - 11:49 am:

Ditto what Mike Conrad said


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Kelsey on Wednesday, August 29, 2012 - 02:34 pm:

I'm going to take it to where Jerry works tomorrow and see how straight/flat the head is. I've got a new gasket and belt on order from Chaffin's. I'm blessed to have you guys. Thanks for the help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Wednesday, August 29, 2012 - 03:24 pm:

You don't need a fan belt at 5+ mph, unless you're running retarded or something..

rdr


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Huson, Berthoud, Co. on Wednesday, August 29, 2012 - 06:41 pm:

Jim Kelsey:

If you car is right, you do NOT NEED A FAN BELT. I ran the Montana 500 more than once with out one and so do a lot of the over drivers. One of the top T mechanics in the United States, Tom Carnegie, drove his 26 coupe in a trip through EVERY lower 48`States, without a fan belt. Again if your car is right, correct gas mixture, correct timing and a few other things you will not run hot unless you sit and idle. All you need is air through the radiator.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Kelsey on Tuesday, September 04, 2012 - 01:50 am:

Latest update:

First off, I'd like to thank John Aldridch and Jerry Ostbye for their help on this dilemma of mine. Jerry checked the specs on the head with his $80,000 machine. He discovered that there was a displacement of .003 across the head and quite a bit of pitting around the kidney-shaped holes fore and aft. I took it to National Auto Parts in Sumner to have the head resurfaced. They found the same thing. Their measurements ranged from 2.652-2.655. Due to the pitting, it ended up at 2.647.

I spent quite a bit of time yesterday carefully cleaning out the bolt holes for debris, cleaning up the head bolts and used the Permatex Ultra Copper on both sides of the gasket. I torqued it to 50 lbs, took it for a test drive later that evening and there wasn't any white smoke coming out of the exhaust. I retorqued it again after the engine had cooled down. I think the problem is solved, as is the overheating issue. It sat idle for five minutes and the motometer read in it's usual spot, which is at the bottom of the circle.

Thanks again for all of your input and assistance. Every piece of advice helps to make a sound decision.


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