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Old 11-21-2012, 01:30 PM   #1
rebelyell
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Default Cylinder head machining

Hello everyone, my name is Greg. I am the lead tech at a school bus company that has 6 04-06 dodge 2500 CDI sprinters in its fleet. One of which has been giving me some major head aches.

Here's my question. According to the factory service manual, the cylinder heads are not machinable. Does anyone know why? Because the service manual doesn't explain why.

The sprinter that is giving me problems is a 2004 2500 sprinter. It ran great but was losing coolant. Where it was going could not be found. So I pulled the head off and sent it out to get checked out along with a copy of the factory service manual. Machine shop told me that the head was warped and that they resurfaced it. I come to find out that the guy that runs the machine shop is very good at machine work when it comes to cutting rotors and working on old cast iron heads. However, when it comes to anything new or complicated he is clueless.

Assuming he knew what he was doing I put the head back on and try to start the sprinter. Won't start. Reason? Only 2 of 5 cylinders had good compression. The other 3 had only 35% compression.

Then I decide to read the service manual. Something he obviously didn't bother to do despite me sending him a copy. After 5 minutes of reading I learned that the head is not machinable. But I don't understand why, and I don't understand how that would cause compression loss. Unless of course the knuckle head that machined it screwed it up.

Anyone with any insight or knowledge on this subject?

Thanks in advance.

Greg
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Old 11-21-2012, 02:37 PM   #2
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Default Re: Cylinder head machining

http://sprinter-source.com/forum/sho...06&postcount=4 from one of the best in the business.

Pictures here show lack of clearance: http://sprinter-source.com/forum/sho...1&postcount=10

Last edited by hkpierce; 11-21-2012 at 02:49 PM.
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Old 11-21-2012, 05:30 PM   #3
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Default Re: Cylinder head machining

That was my thought, I think my older head can be machined but the allowable amount is very small because there simply is not much clearance between pistons and valves/injectors/glow plugs. However it is possible with mine to buy thicker gaskets to maintain the gap. Probably this has all been done away with on newer models. My engine was phased out before sprinters started being sold in the US!

As for compression loss - did the shop pressure test the head after they machined it?
Have you inspected and gauged all the cylinder bores and checked the pistons for damage - I had one cracked and I've seen photos of others on here too.
Also my head was written off because the pressure test showed a leak within an inlet port which the shop couldn't fix, the head specialists took it in exchange and seemed to think they had the technology to repair it and return to stock (or was that the other guys who didn't have one in stock?), I am actually not sure if I have a remanufactured head or new one now! I never got as far as looking at whether or not it could be skimmed.

You could try a leak down test before you pull the head off again, it might help you work out if the loss is through the mating faces/gasket or some other component (valves, pistons, rings). I have one cylinder slightly low and I am trying to find time and good weather to do a leakdown myself, my first time so I have no idea if I will interpret it right, but can only think of one way to learn!
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Old 11-21-2012, 06:16 PM   #4
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Default Re: Cylinder head machining

I'm quite certain that I also remember comments about any machine work causing camshaft alignment issues which will lead to premature camshaft failure.

http://sprinter-source.com/forum/sho...9&postcount=21
http://sprinter-source.com/forum/sho...ight=sad+story

The bottom line is that the heads should not be machined. vic
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Last edited by hkpierce; 11-21-2012 at 06:27 PM. Reason: Citations to warped head and cam issues
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Old 11-22-2012, 10:02 AM   #5
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Default Re: Cylinder head machining

Greg
The camshafts run directly in the head with very small clearances, if the head is warped when you take it of it means it had stress in the casting caused by being driven when it was to hot. When the head is bolted to the block it is held straight by the block and the cams are able to rotate, when you take it of, the head bends due to the stress and the cams will lock up. If you then machine the head in the bent shape the cams are still locked, so the repairer may bore out the cam bearings to allow them to spin, this destroys the head because the cam shaft is no longer in the correct location to open the valves and allow them to close again. As others have said the head or any other overhead cam head are not machineable. Eric.
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Old 11-22-2012, 11:26 AM   #6
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Default Re: Cylinder head machining

Happy Thanksgiving Day Everyone!!!

I can attest to this condition. In earlier posts and conversations with Dr. A, we had discussed the fact that after a major overheat (burnt motor oil) the shop I took my van to had the head machined...... I have had a noise in the engine since that sounds like a lifter rattle that comes and goes. Sometimes it is gone for days and other times it is really loud. This head had been warpped 15 thousands and wasn't supposed to be milled I find out after the fact.
This shop replaced all the lifters and timing chain assembly including tensioners etc.
I have great power and get about 19-20 MPG, down from the 26 MPG I was getting.
Just living with the interminant noise that has not changed really in over a year since the repairs were done. The frequency of the noise going away is getting better all the time.

But to get back to the main point here.....This head should never have been machined. All prior comments I agree with totally. The head will warp up in the middle taking the camshaft journals with it. Milling the head to block mating surface only does just that. Now the clearances between the valves, pistons, injectors and glowplugs have changed, all at different capacities as you follow the contour of the cylinder head.
I've run compression tests with my MB Star and found a variation between all cyls. # 3 has the greatest and #2 and #4 lessen as do #'s 1 and 5. I also have a intermitant rough idle. The camshaft and journals are still warpped putting undue stress on them. This can also translate to excessive lifter compression causing a lifter to not pump up or making it bottom out (assuming that the lifters are hydraulic....I don't know). AKA maybe my mystery noise.

All injectors are remans from the Dodge dealer. The injectors showed no signs of hitting the pistons, but I'm guessing that if the tolerances are that tight for this engine and the head was milled, I'm getting inconsistant injector spray cones causing injector knock.

My advise is that if anyone says that they can machine your cylinder head, beat them in the head with it.
Just sayin'..........
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Old 11-22-2012, 02:15 PM   #7
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Default Re: Cylinder head machining

Quote:
Originally Posted by Eric Experience View Post
... and the cams are able to rotate, when you take it of, the head bends due to the stress and the cams will lock up. ... Eric.
I'm not at all a rebuild expert. For practical purpose what is the max irregularity of the head which will bolt back in, conform and provide proper service? There must be some tolerance or rule of thumb gauge. vic
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Old 11-23-2012, 05:11 AM   #8
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Default Re: Cylinder head machining

The terms "planned obsolesence" and "value engineering" come to mind.

A good example is those Braun Oral B electric toothbrushes, the rechargeable battery eventually fails
and a replacement is impossible to install everyone just buys another new one.
Don't ask me how i know this.
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Old 11-23-2012, 10:13 AM   #9
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Default Re: Cylinder head machining

Vic.
I do not have any figures for the sprinter, but I have fixed this style of head by straightening it in a press. not many shops have a press large enough. You may be able to do it by by bolting it to an old block with shims under the "high" spots. I would be happy with 100microns warp. Eric
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Old 11-23-2012, 01:59 PM   #10
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Default Re: Cylinder head machining

Quote:
Originally Posted by Eric Experience View Post
Vic.
I do not have any figures for the sprinter, but I have fixed this style of head by straightening it in a press. ... Eric
Interesting. Aluminum castings seem to want to return to shape.

We would always try straightening the old opposed 4 VW warped heads by carefully holding them very flat waist high over a concrete floor and dropping them. The head copper ring gasket was recessed so no worries of damage to that sealing surface. We had nothing to lose. The theory was that it jarred the casting and caused it to go back to original shape. Sometimes it took more than one drop. It was surprising how often it worked.

Thanks for the reply. vic
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