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Discussion Starter #1 (Edited)
EPISODE 1 - THE CASE OF THE ANGLE GRINDER PISTONS

I've decided to start this thread showing some of the reasons we decided to start our own private workshop.

Our team is not professional mechanics but 'enthusiastic amateurs' , I've been working on my own motorbikes , go carts and cars for 40 years now (since I was 12) , Taffy is an expert aero-modeler, hasn't worked on cars too much but has a good understanding of automotive engineering theory, Indra is an aircraft engineer (jet and turboprop engine and airframes) and Agus (his assistant) is an aircraft engineer graduate and then started working on cars.

We don't have good independent workshops such as Davidoli's shop and the BMW dealer workshops don't have the tooling , spares, experience with 20+ year old BMWs (lots of young mechanics) or time to solve some of our problems.

One of our BMW friends (2 x E30 M3s, E9 3.0CSi, E24 M6) asked us to take a look at his M30B30 engine from the 3.0 CSi , it went to a BMW dealer shop then an Indy shop for a cracked head replacement and it's been running rough and using oil since the work was done.

Here's what we found on the teardown yesterday ...

1. The E28 535i head that was used on the M30B30 block hadn't been torqued down properly , it was on average 60 NM per head bolt

2. Then I noticed a couple of valve to piston impact marks on the top of the piston

3. As I looked closer I couldn't believe what I saw , almost a third of the piston dome on each of the Mahle pistons had been ground down with an coarse disk angle grinder. On no.5 piston there's one area where the top surface probably 1mm thick and about to fail.

With different weights ground off the top of the pistons no wonder it was running rough , we'll weigh them later.

The block will be sent out for a rebore due to some gouging on the cylinder wall and some new CP pistons put in.

Enjoy the photos !
 

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Discussion Starter #3 (Edited)
On cylinder 5 where this piston is located we found tiny little specks of piston material in the combustion chamber

Lots of small scratches in the bore, I think the pistons were ground while still in the block dropping abrasive material in the cylinder bores

You can also see the the outline of the inner wall of the piston skirt starting to show

 

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Discussion Starter #6 (Edited)
An E9 M30B30 block with an E28 M30B35 head should be ok I would have thought as the valve sizes (46mm intake/38mm exhaust) and the combustion chambers are all the same up until about 1988, is this correct ?

In principle this should have been a good mod for a cracked original cylinder head (yes another overheat) as the later heads were beefed up in the cooling galleries

I think they messed up on the timing chain set up , we found some paint alignment marks in a different position to the factory markings.

I like the M30 , what an easy engine to pull apart compared to the S38 !
 

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Discussion Starter #7
+1M

You can anticipate the hack that did it was thinking!! THIS IS A GOOD JOB!!
You hit the nail on the head , these hack masters are quite arrogant about their skills and don't appreciate being challenged.
 

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it's only the fault of the hack after the fault of the customer first. You see, if the customer did his due diligence on this indy shop, maybe he wouldn't have felt so comfortable leaving his m30 there for the work. All you have to do is ask to see previous work done/speak with previous customers, etc. Good shops have nothing to hide.
 

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it's only the fault of the hack after the fault of the customer first. You see, if the customer did his due diligence on this indy shop, maybe he wouldn't have felt so comfortable leaving his m30 there for the work. All you have to do is ask to see previous work done/speak with previous customers, etc. Good shops have nothing to hide.
I can't agree. How many owners have openned their engines after having them rebuilt? I have no data, but I would say only a very small minority. This would have gone unnoticed by the majority of us even on this enthusiast site.

It is the professional who should make clear his abilities and processes to the client. Doing your due diligence as a customer can only get you so far. Shops with great reputations will put out bad work too.
 

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Discussion Starter #10 (Edited)
It also gets down to quality control.

An owner of a good small Indy shop that then grows due to it's reputation and puts new people on to match the expansion needs to watch carefully what's going out the door.

This particular shop does a lot of work on Porsche , Mercedes and BMW and was held in reasonable esteem here in Jakarta.

Something has gone terribly wrong either at the workshop or the "machine shop" that they sent the engine out to and rather than inform the owner (and incur a lot of expense) they tried to bury their mistake by putting the head back on.

This sort of botch engineering is normally seen on the crappy privately owned trucks and buses we have here.

This particular E9 owner owns about 30 cars and puts a lot of work through this shop and he was shocked when we opened the engine up , I wanted him there when we did it.
 

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Discussion Starter #12 (Edited)
Other problems found with the M30B30

1. 6 of the 14 main bearing cap bolts were under specified torque

2. All the con rod bearings were about 20% to 25% under torque

3. The sump is filthy , there is lots of oil sludge in there. The sump has been off and I'm surprised they couldn't be bothered to clean it out. The sludge in the bottom of the sump is 1.5 cm deep.

4. Main bearings are finished , lots of damage from grit.

5.The front of the crankshaft has been damaged where the harmonic balancer installs and the crank journals are scratched and scored.

Most shops here don't use a torque wrench , they use a 'calibrated wrist'.

Other than the problems we found I'm really impressed with the M30 engine , simple , strong and well put together. I said to the boys that with some CP pistons this would make a great budget turbo engine or NA track car engine in a lightweight vehicle.


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That's some crappy work right there! Wow...glad is taken in the right hands now that poor engine.

:byee55amg
 
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