OK, I'm shopping for both a compression and leak down tester for an OM617 diesel engine. This is a new venture for me so a question, what size fittings do I need to look for in a compression and leak down tester?

It used to be that harbor freight had the compression tester and you also need the adapters from the compression tester to adapt the leak back tester which only comes set up for gasoline engines.

The harbor freight compression testers occasionally had quality issues but if you go on say eBay and look at the cost of a single compression tester adapter for a Mercedes and I mean a generic one not a real Mercedes one and compare the cost of that to having to by that adapter and get a quality diesel compression tester for that adapter you will be amazed at the cost.

You also need an air compressor that can put out sufficient volume for the leak tester.

On eBay there is also diesel compression tester kits and likely the leak back testers. However, on this forum it is the harbor freight one that most have used and hence more reviews on it.

One of the frequent areas the harbor freight one fails is the valve stem type Schrader valves can have the rubber seals burn. They are cheap to replace.

To get the detailed info you will have to spend some time reading old threads on the subjects.

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84 300D, 82 Volvo 244Gl Diesel

Well.....I have read on more than a few car forums that el-cheapo, harbor freight made-in-china testers can give false readings.

question: Do we want false readings or do we want accurate readings?

I'm thinking of purchasing either a Snap-On, Matco or Cornwell compression tester and leak down tester. I'm hoping to purchase testers that give accurate readings. Does anyone know what size fittings will work for an OM617 diesel engine?

Glow plug hole is M12x1.25
Injector hole M24x2 I think

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

If someone goes to the harbor freight site and looks up one of the diesel compressing test kits they can access the .pdf instructions and I believe in the instructions it has a list of what adapters for what vehicles it will work on, and I believe it also has the thread size.

It used to be the kit had the injector adapter and also the glow plug adapter though it also used to be users on the forum said the glow plug adapter 90-degree thing was fragile.

When you pull the injectors (even to do the compression test), you are supposed to replace the heat shields. In order to get the heat shields at a cheap price they need to be bought on the internet.
You don't need to replace the heat shields to do the compression test.

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84 300D, 82 Volvo 244Gl Diesel