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Old 03-28-2007, 05:26 PM
Registered User
Join Date: Dec 2004
Posts: 554
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

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Old 03-28-2007, 10:28 PM
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Join Date: Feb 2007
Posts: 176
Rockwell Tester

I've had pertty good luck on ebay, wetting up a search with daily reporting and have found a bunch of very pricey test gear and rock bottom prices.
Skidmore Wilhelm, Hilti/Hydrajaws pull test unit, Panametrics Epoch 4 UT Flaw detector.

I ahve seen the handheld Rockwell units go for $250-500 and the bench units at $750
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Old 03-28-2007, 10:30 PM
t walgamuth's Avatar
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 38,527
good idea, larry.

tom w
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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Old 03-29-2007, 09:16 AM
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Join Date: Feb 2007
Location: Knoxville, TN
Posts: 30
Ok, I made a C in metallugy. How do you re-harden Al? Heat and quench?
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Old 03-29-2007, 09:48 AM
david s poole
Join Date: Mar 2005
Location: dallas
Posts: 1,822
larry,i'm extremely interested in your say you took the head loose on a running 103 engine and the bolts did'nt feel right,but those are steel bolts into steel block[going thru an aluminum head].i'm interested in knowing if the loss in hardness is caused by engine overheating or age.the junk heads you aquired are prob from o/heated engines?
David S Poole
European Performance
Dallas, TX

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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Old 03-29-2007, 10:02 AM
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Join Date: Dec 2004
Posts: 554

all my inital testing is leading to the fact that if these heads are heated to 320f and allowed to cool slowly like an engine would do then there is softening of the aluminum.
larry perkins

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