the process to a soft head
 

lol, i told my wife the title to this thread and you know her response,ok course she suggested that i should write about hard heads.
ok forum, this one should last a while.
i have been trying to determine why so much trouble with heads on the mercedes engines.
i got a couple heads from locals that were about to be scrap and had a couple of my own to experiment with.
i tested the free heads and found that the aluminum had softened (down to average of 20 on the rockwell b scale as compared to high 80's as per mercedes specs)
the soft heads had all kinds of problems,stripped threads at the rocker arm hold down bolts,and on one that i removed from a running engine(91 300e 3 liter) the head bolts were loose to the point that there was no snap at all when removing. i even re tightened to specs and removed again and got that soft feel as the bolt released.
i dont see how anyone could afford a new head for one of these engines ,so i am experimenting with the process of re-hardning the soft heads and have completed one was 20 rockwell b and now is 85.
i am having to borrow a rockwell tester,so if anyone knows a source for a used one(i can calibrate it)let me know.
also anyone who has any aluminum heads that i could get i would pay the frt and a reasonable value.
would be interesting to hear of some of the forums special projects.
larry perkins lou ky 15027276903
thought i would give you oil folks a shot at this

Wow, good thread, Im sorry I have no heads I can donate to your experiments, but on behalf of every mercedes owner thanx.

I have a degree in materials (metal) engineering and softening aluminium suggests to me that mercedes (or supplier) chose to cast the material with an aloy that ages. If you are able to heat treat the aluminum, ie heat it and then quench it to harden the aluminium, then the alloy that was used is not really the best choice on mercedes part. My concen is the head is liable to warp if this is not done on a fixture.

ice
 

man am i happy to see you on board with this one.
i tried to research and determine the mercedes brew,i drew blanks so settled on the proceedure for 6061 t6,at least i read all i could find.
i am in the process of determining the degree of warpage,and will post the results.
maybe you could suggest more on this fixture if it is needed.
thanks for the plug on heads,
larry perkins lou ky

Easiest cheapest fixture might be a bare cast iron block, Or A steel I beam drilled and tapped for the headbolts.

I think this is a very worthwile project. I have some metalurgical texts, let me know if i can help you out.

their is a 617 in my junk yard but it has a cast iron head correct.

Larry, this experiment you have gotten into might indicate a used head is not a good ideal in general. Unless hardness tested before purchase. Those spanish aftermarket heads are starting to look better and better all the time. If it is a material aging process as mentioned especially. I hope you keep posting as you work your way through this. Interesting thread.

barry
 

would you post any link or source for the heads you mentioned from spain?
i agree,it looks like no one is making any allowance for the hardness test on rebuilts. seems to me that would be a gamble i wouldnt want to take. i would suggest to anyone who was about to recieve a so called rebuilt to look at the area of contact where the head bolt contact the aluminum and if there is evidence that the bolt head-washer has left a indention in the metal then its soft. of course the hardness tester is the real way.
larry perkins

Larry, contact appears to be a Mark Degroff in california I believe. Phone # is 818-701-5274. In fact for the thread that covered this initially perhaps just dial in spanish head in our sites archives and the thread will appear. Price seems reasonable to boot as well. I do not have the actual physical address.

Just so I get e-mail notices on this post.

P E H

not too much to report
 

forum, well i spent most of the week extending my 1950's furnace out 6 inches so that all my heads would fit into it.
did test one new head #22 for the 3.5 liter 350sdl and its brand new, it test 55.5 0n the b scale. will have to read some but dont mercedes say that 60 is the low limit?
i did use the test block on the tester after seeing the lower number on the new head and the tester is right on at 93.8 b.
an earlier question about how to harden aluminum, yes all i can read that is feasable is to heat to 1000f for 6 hours and quence it in a aguasolution. i used tap water. icefire, would you comment on the cooling liquid that would produce the best results for the quence??
will keep you all updated
larry perkins

Larry let me know what you think of my email RE. Age hardening aluminium alloys, As for quenching, Usually there is a water quench or an oil quench, Oil quench provides a lower cooling rate.

I dont think there is a permenent solution to this problem, I think that if you heat the entire head and cool it quickly, that would simulate the casting process which the head was made with.

dont bother "tempering" the head after quenching, it will age naturally, and get harder for the short term then eventually get softer as the alloy precipitates out.

from da wiki...
 

Rockwell scale
The Rockwell scale characterizes the indentation hardness of materials through the depth of penetration of an indenter, loaded on a material sample and compared to the penetration in some reference material. It is one of several definitions of hardness in materials science. It involves the application of a minor load followed by a major load, and then noting the hardness value directly from a dial. Its chief advantage is its ability to display hardness values directly, thus obviating tedious calculations involved in other hardness measurement techniques. Also, the relatively simple and inexpensive set-up enables its installation in college laboratories.
It is typically used in engineering and metallurgy and is most common in the USA. Its commercial popularity arises from its speed, reliability, robustness, resolution and small area of indentation.
There are several alternative scales, the most commonly used being the "B", and "C" scales. Both express hardness as an arbitrary dimensionless number.
The B-scale is used for softer materials (such as aluminum, brass, and softer steels). It employs a hardened steel ball as the indenter and a 100kg weight to obtain a value expressed as "HRB".
The C-scale, for harder materials, uses a diamond cone, known as a Brale indenter and a 150kg weight to obtain a value expressed as "HRC".
The depth of penetration is converted to a scale in which a harder material gives a higher number.
Common values
Very hard steel (e.g. a good knife blade) HRC 55 to HRC 62 or so
Axes, chisels, etc. HRC 40 - 45
Readings below HRC 20 are generally considered unreliable, as are readings much above HRB 100.
Several other scales, including the extensive A-scale, are used for specialised applications. There are special scales for measuring case-hardened specimens.
Good practice includes:
Cleaning indenter and test-piece to be clear of dirt, grease, rust or paint;
Measuring on a perpendicular, flat surface ("round work correction factors" are invoked to adjust for test-piece curvature);
Ensuring that the thickness of the test-piece is at least 10 times the depth of the indentation;
Maintaining an adequate spacing between multiple indentations; and
Controlling the speed of the indentation.

test results
 

ok, i finally determined that 600f was a good temp to straighten a alum head,worked the +.020 in warp down to .-002in, heated the sucker to 893degf(+- 5 deg) 5 hours later, dunked her in a water bath.
i wanted to see the total distortion, icefire you are correct ,i will call my .002in arc_-.002 as the feeler gage would fit under the straight edge at the center of the head.after quencing in 60deg tap water i remeasured and got -.008in at the center,so i have to build a member that will hold the head straight at the quence cycle.
anyone have an old 103 block they want to donate?
i will have to wait till tomorrow to report the hardness results as i am still borrowing a rockwell tester. anyone have one to donate?lol
btw,good write up on the hardness tester and proceedures,i didnt have any operating instructions but soon determined that the release lever had to just be touched to get the weight traveling,if you help it too much the results varied.
larry perkins

too early
 

forum i know its way too early to make positive statements,but as i heat this alum to 900-1000degf and cool it in less that 15 seconds to the touch,and heat it to 500-600deg for bending i have to ask myself,how do you crack a head.icefire can join anytime,but i think there has to be a connection to the head bolts loosing up and then the combustion is shooting the head up slightly and getting a bending action resulting in work hardening,so could this be why the head cracks??
will tell u this i cant crack the thing and there dont seem to be any fractures at all.
the reason i mention this early is that if i was running a alum head i would make sure my head bolts were torqued especially if i had experienced any over heating.
larry perkins lou ky

dang forgot
 

forgot to ask, anyone with a past cracked head,where did the cracks happen at?
logic would tell me that #1 and 6 would be the weakest point to allow more motion to occur if it had loose head bolts.
larry perkins lou ky