SONIC TECH NOTE SERIES

Cylinder Head Work v1.3

FILE NAME:

TNSHEAD.txt

When the time comes to work on your 7M engines aluminum cylinder head
there will be a number of decisions to make. You will have to find a good
machine shop, this will take some asking around. I would talk with the
local drag racing guys. You will have to check out the shops, many of the
shops will not be experienced with your engines cylinder head. They will
tell you they cannot machine it and you should not do this or that. In some
cases they are correct and in other cases they may be dead wrong. I wish
this process was easer to explain, it not.

I hope that this tech note file will help explain some of the thought
process that must go into the decision of: Should I cut the head surface or
leave it? Should I try to have the head straightened or leave it alone? Do I
have to replace the cylinder head with a new one from Toyota or find
another used cylinder head to have check out.

Don't pay cash for a used head until it checks out. Most reputable salvage
yards and parts dealers will allow you to have the head examined by the
shop of your choice. If they will not let you do this take your business
somewhere else. It would be an easy big money business to be selling
scrap aluminum for three hundred dollars a bar. Valve guides in the 7M
engines seldom need to be replaced. If the shop you are dealing with says
you need new ones you should question this!

To determine if your cylinder head is suitable to machine you must have a
good understanding of the following test procedures, and the thought
process relating to warpage. If you do not understand the methods of the
testing, that's ok, leave this to your machine shop. However it is
important that you understand the concept of what I am trying to explain.
Read on as I will try to explain some of this below. I would recommend
that you print this file so you can circle areas you want to ask questions
about.

Remember that the head is not just warped at the deck where you measure
it, the entire head is warped along with the deck. This means that the
ports, valve cover gasket seal area as well as the cam saddles {what the
cams spin in} are all warped x.x thousands of an inch. Following this idea
if you have lets say 10 thou warpage in the deck surface when you
measure it, the cam saddles should also have this 10 thou warpage if the
head has not been machined before. If you bolt the warped head back on the
engine and torque it down this will pull the head straight again providing
your block deck surface is flat. Think of it as a banana on a table, if you
pull the banana flat to the table it will look straight. When you let the
banana go it will look curved again.

Now lets consider what happens if you cut the 10 thou of the bottom of
the head or the banana! The deck surface of the head is now perfectly flat,
but the cam saddles, and basically the entire head is still warped 10 thou.
The banana is still curved but it has one side that is flat. This is ok as
long as the cams still turn smoothly in the head when you have it bolted
down to the engine.

Inspect the cylinder head for warpage in the deck and cam saddles. If the
deck is warped less or more than the cam saddles you have a head that has
already been machined at least once. If the head has not been machined
before you will be able to tell because the warpage will be the same
amount and in the same direction on the cylinder head deck surface and the
cam saddles. It was all straight at some point in time. Because a in line 6
is a long engine a small amount of warpage is normal.

Carefully inspect the deck surface of the cylinder head for any
compression ring groves left by the gasket that are deeper than 5 thou
maximum. The engine block must also be inspected very closely for
grooves in the block surface. If there are marks in the deck surface of the
block they will almost always be on the exhaust side of the deck surface.
If they are deeper than 5 thou you should have the deck of the block
machined as well to get a better than new repair. Remember to have your
timing cover machined along with the block, it also must be machined
down to the height of the deck surface. The shop will bolt it to the block
and cut them together.

If your cylinder head is free of groove marks in the deck from the gasket
that are deeper than about 5 thou maximum and your head is not warped
more than 8 to 10 thou, you will have no problem cleaning the whole thing
up and installing a new stock Toyota gasket.

If your head has grooves deeper than 5 thou from the compression ring in
the deck surface, you must machine the surface of the head in order to
reuse it. The question is can you machine this head safely. 

Checking cam bearings saddles. The factory says that maximum warpage
should be within four thousands /inch. Bearing clearance should be two
thousands minimum, five thousands maximum.

For the most part these specs work out, but I have seen some heads, where
the bearing saddles were warped as much as 20 thousands across the
length of the head. This head only had 12 thou warpage on the deck, this
told us the head was machined once for sure. The cams still turned
smoothly with the valves and followers removed and the head sitting on
the work bench. The warpage in the cam saddles stayed at 20 thou after
the head was bolted down on the engine, this was because we machined
the head flat, removing the 12 thou warpage from the deck surface of the
head. This engines block was only warped 1/2 thou. I believe when the
cams turn smoothly there should be no problem using the head. I have not
had any problems with engines we have used heads like this on, but it is a
calculated risk. If you can afford to buy a new head it may be worth your
time and money in the long run. I will keep the club posted on any new
information in this area.

If you measure the 7M's block deck and it is flat you do not have to try the
bolt down test because it will not tweak the head any different than if the
head sitting on the work bench.

If your engines block deck surface is warped you should check the turning
smoothness of the cams when the head is bolted down to the block, use
your old head gasket for testing purposes and torque the head to 52 foot
pounds. Depending on how much and the direction of the warpage in the
deck of the block and the cylinder head, if it was not machined flat, this
joining of surfaces will add or subtract from the now built in cam saddle
warpage.

If you machined the surface of the head before installing it on the motor
the bolt down test should not change the feel of how the cams turn
compared to when you turned them on the bench. if your engine block deck
surface is not warped. Remember that this test must be done with the
valves and bucket followers removed. If you attempt to do it with the
valve gear in place you will only feel the resistance of the cam lobes
compressing the valve springs. What you are trying to do is feel how the
cam turns by itself when installed in the head.

You should use a good assembly oil or lubriplate grease on the bearings.
Also note that the bearing journals on the 7M cams are coated with a soft
bearing material that is easy to scratch and mark up. Most 7M's will have
these scratch marks when you pull the engine apart. What you may see are
scratch marks on the journal that look like a badly galled up bearing
journal. This may look bad but is normal and will not hurt anything. Do not
attempt to clean the surface of the cam journal. Just inspect it for bad
cuts or grooves in the journal that are into the cam material not just
marks in the soft journal coating material.

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