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Car Forum / Mercedes-Benz Cars / June 2007

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Why do heads crack on 300 Diesels?

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heav - 09 Jun 2007 14:52 GMT
The engine from my 300 TDT is being remanufactured by Metric Motors
right now.  I talked to Mike at Metric the other day, and found out
that the head on my engine was cracked bad around the "prechamber
hole" in 4 out of 5 cylinders, which Mike says is unusually bad
cracking.

What causes that to happen?

Thanks.
Tiger - 09 Jun 2007 15:12 GMT
No idea... however, I was reading up Bentley's Mercedes Bible from Star
Magazine... it told me that MB rebuilds these old diesel motors at their
Germany factory... everything is inspected and all... for about the same
price as if you were to have Metric do the work... It is fascinating and
wondered if they still do this.

You should check.... Call up MBUSA Classic... about this.
-->> T.G. Lambach <<-- - 10 Jun 2007 01:09 GMT
Starting fluid is known to crack the prechambers themselves causing a
compression leak. That may have occurred at some time and the current
prechambers are in fact replacements - my speculation.

Otherwise, if there needs to be an explanation, I'd suspect overheating
the motor but remember, that motor has done a lot of miles - and nothing
lasts forever!

I believe you'll be happy with the rebuilt Metric motor.
Signature

© 2007 T.G.Lambach. Publication in any form requires prior written
permission.

heav - 10 Jun 2007 12:49 GMT
Interesting.  I just wondered because I don't want to do whatever I
did to cause it to happen again.  I may have tried using starter fluid
a couple of times, but I don't think it ever helped with my engine.
Pretty much it either started or it didn't.  Long cranking is what got
it going when I was visiting Montana or Minnesota combined with
putting hot air in the air intake with a hair dryer and using a block
heater.  My engine had 144,000 miles on it when I got it so I really
don't know what they run and start like when new.  It will be
interesting to find out.

Shipping a motor to Germany and back is not something I would do to
reply to Tiger's suggestion about a factory in Germany.  One of the
best things about Metric besides the helpful, honest guy who runs the
shop and it's small size and staff is that it is close enough for me
to be able to trailer the motor there and back myself.

I really like Mike, the President of Metric.  He was completely
comfortable with me coming in his shop and visiting with him.  He was
working on a block from a 1954 Mercedes when I was there.  It was also
a 5 cylinder diesel.  I don't have my engine back yet, but from what
other people who know Metric have told me and my impressions of the
shop so far I would recommend the place.  I stripped out the heads on
the allen socket bolts that hold the vacuum pump in place and a nut
was missing on a bracket that holds the exhaust pipe on.  I asked Mike
if he could recommend a good place to get metric hardware and he just
went to his hardware inventory and gave me a handful of the bolts I
needed.  I decided to replace the front seal on my transimission and
Mike got me one of those too for 1/2 what the discount on-line parts
places wanted.

I will post on the list when I get the engine back next week.

On Jun 9, 5:09 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at
NoHamorSpamcomcast.net"> wrote:
> Starting fluid is known to crack the prechambers themselves causing a
> compression leak. That may have occurred at some time and the current
[quoted text clipped - 8 lines]
> ? 2007 T.G.Lambach. Publication in any form requires prior written
> permission.
roland franzius - 10 Jun 2007 13:37 GMT
> Interesting.  I just wondered because I don't want to do whatever I
> did to cause it to happen again.  I may have tried using starter fluid
> a couple of times, but I don't think it ever helped with my engine.
> Pretty much it either started or it didn't.

The compression of a diesel engine is around 1:40. For a 3l 5 cylinder
machine with volume 0.600 ml the rest of volume at highest compression
in a cylinder is around 15 ml. If you put a spoonful of fluid in a
cylinder and compess it you will crack the pre-combustion chamber or the
piston.

> Long cranking is what got
> it going when I was visiting Montana or Minnesota combined with
[quoted text clipped - 5 lines]
> Shipping a motor to Germany and back is not something I would do to
> reply to Tiger's suggestion about a factory in Germany.

Ask your dealer for the price of a remanufacured machine. The shipping
to the German factory is a negligible part of the price for a machine
with the status of a new one. In EUR prices vary from 3000-20000.
Warranty is given for 200000 km IIRC.

Signature

Roland Franzius

Tiger - 10 Jun 2007 14:44 GMT
Oh yeah, the factory is actually MB factory... not third party.
Tiger - 10 Jun 2007 14:42 GMT
The rebuilt engines are ready to go in USA... zero wait time if I am right.
Richard Sexton - 11 Jun 2007 02:25 GMT
Ether is supposd to be able to crack the prechambers. I dunno if that really
translates into cracking the head - I just don't know. Usually heat as in
overheating cracks heads if cold water is suddenly introduced. Has it
ever overheated badly?

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  Need Mercedes parts?   http://parts.mbz.org
Richard Sexton       | Mercedes stuff: http://mbz.org
1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net
633CSi 250SE/C 300SD | http://aquaria.net http://killi.net

 
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