Checking Cylinders For Cracks - PeachParts Mercedes-Benz Forum

thebenstenator · #1 10-07-2011, 02:25 PM

Ok, so I´ve recently removed the head on my om602 1992 300D and I took it to a machine shop to be inspected. They couldn´t find anything wrong with it and want me to check the block for 1) cracks in the cylinders and 2)complete flatness. They gave me a "flatness checker" and it seems to be fine in that respect. We could not get any sort of measurement feeler gauge under the ruler.
Now my question is checking for cracks, they say that it´ll be difficult to find the crack, but should I be able to feel it? I´ve gotten in there with a light and can´t find anything. Are there any techniques to finding cracks?

Air&Road · #2 10-07-2011, 02:33 PM

I'm not familiar with the particular engine, assuming it's the one in your sig. I don't know if it's a dry sleeved engine.

You need to look closely around each head bolt hole to see if it is spider webbing.

NJ300sdl · #3 10-07-2011, 03:01 PM

Wiping prussian blue on the area to be checked may help identify a crack.

engatwork · #4 10-07-2011, 03:15 PM

What makes you think there are cracks? That engine can be resleeved.

leathermang · #5 10-07-2011, 05:18 PM

Were you just standing around one evening and decided to take your head off ..... or was there some reason you took it off which you could share with us ?

whunter · #6 10-07-2011, 05:30 PM

Quote:

Originally Posted by LarryBible

I'm not familiar with the particular engine, assuming it's the one in your sig. I don't know if it's a dry sleeved engine.

You need to look closely around each head bolt hole to see if it is spider webbing.

Picture attached.

whunter · #7 10-07-2011, 05:32 PM

Video: Cracked Cylinder Diagnosis: Finding the Cracks | eHow.com

compu_85 · #8 10-07-2011, 11:23 PM

As I understand it those sleeves were developed for the for the .970

-J

Diesel911 · #9 10-08-2011, 12:27 AM

If they Crankshaft and Pistons are still assembled in the Block; on non-mercedes Engines Blocks are not checked for Cracks unless there was previous symptoms of Cracking and they symptoms were not being caused by the Cylinder Head or Cylinder Head Gasket.

However, a Dye Penatrant Type Test can be done on a Block to check the portion of the Cylinders and upper Deck (see the internet for a better description).

The other way is to make adapter plates to block off the Coolant Passages in the Block and fill the Block with Hot Water and pressurize the Block (how much pressure?)

And, having the Water you are going to use Hot; like 180 decrees F hot Makes a difference. I have seen a bunch of Cylinder Heads that have passed the Cold Pressure test but when the after got hot little crakes opened up (in the Case Detroit Diesel Cylinder Heads.).

leathermang · #10 10-08-2011, 09:47 AM

How about DIY magnafluxing ?

thebenstenator · #11 10-08-2011, 03:51 PM

Alright, here's why I think it has some sort of problem. Two years ago I did have a serious problem with the head/head gasket. The engine was overheating a lot and it ended up water locked. So we took off the head, took it to a machine shop, got it cleaned up, inspected, planed and all that stuff. Reassembled it and everything, then took it to the dealership to get it running properly. Then after a while (7-8 months) we had another problem which turned out that the positive cable had grounded, thus taking all the electrical power from everywhere and that threw us through a loop hole for about a year, in which the car sat. Then we finally took it in and they figured it out but also said that we were loosing coolant still. They ran a pressure test on it and it passed that, so they thought it was the head. They said that it was rare for a head gasket to blow (previous reason for water locked engine) without cracking the head, so we took it off AGAIN (this is now) and took it back to the same machine shop and they reinspected it. They said that they couldn't find anything wrong with it and wanted me to check the block out.
I told them that when we took the head off, one of the pistons was clean and the others were black (just like in that video) and they said they'd bet money that the block was cracked. By chance, the piston in question is at bottom dead center and we've checked that out and I can't find anything that looks like the crack in that video. Can't find any spider-web cracks around bolt holes. I have yet to rotate the engine to look in the other pistons but . . this is just over my head.

thebenstenator · #12 10-08-2011, 03:54 PM

but where could I get that Dye to do the dye penetrant inspection?

engatwork · #13 10-08-2011, 04:12 PM

Quote:

They said that it was rare for a head gasket to blow (previous reason for water locked engine) without cracking the head, so we took it off AGAIN (this is now) and took it back to the same machine shop and they reinspected it.

This is not an accurate statement from my experience.

If the car is run real hot (contined to run until it stops on it's own after loss of the cooling system) it will cause cylinder head issues and a need to go through the bottom end (no compression). I'd be surprised if it would crack the block though.

whunter · #14 10-08-2011, 04:54 PM

Quote:

Originally Posted by thebenstenator

but where could I get that Dye to do the dye penetrant inspection?

Dye penetrant inspection
Dye penetrant inspection - Wikipedia, the free encyclopedia

Look here.
Dye penetrant inspection - Google Search

.

jt20 · #15 10-08-2011, 05:07 PM

I did not read mention that the cylinder head was pressure tested. Does this shop have MB diesel or any IDI diesel experience?

If the prechambers are not removed during pressure testing, they might not find the leak. The head does not need to be cracked to leak. Fissures in the PC area can be created by carbon buildup and regular exposure to combustion.

The cylinder liners are a dry fit, if you don't see a very visible crack, its hard to imagine that is the failure point. But, if the casting behind it is cracked, it could, potentially, run up the space b/w the liner and the casting then below the HG into the bore. That would be a trip. Look for signs of discoloration around upper bore on the affected cylinder.

There was a thread a while back about a cylinder liner that lifted up above the deck of the block.... all your liners should be flush with the top of the block.