dummy injector for compression testing - Page 2 - PeachParts Mercedes-Benz Forum

scottmcphee · #16 08-06-2011, 10:57 AM

Quote:

Originally Posted by funola

I don't have a clear picture of what your adapter looks like, but if you have an actual nozzle to pass the compression to your gauge, then you need a good seal between the nozzle and the head, i.e. a new heat shield or equiv, otherwise it would leak out the injector body to cyl head threads if it was not well sealed.

Oh and BTW, if your gauge slowly drops after you stop cranking, you have a leak

Here's what I made side-by-side with a standard injector for same engine. It appears as an actual nozzle to the car.

You can see the enlarged center hole that took a diamond bit to do.

I'm also showing the nylon washer comparing it to a heat shield. The washer only skirts the nozzle, whereas the shield covers the nozzle seam. No matter, any pressure entering the injector body will find its way to the gauge.

funola · #17 08-06-2011, 11:04 AM

Looks nice. On the tiny screen of my phone I can't see if there's a schrader valve at the nozzle hole. Where is the schrader valve? If you have it anywhere other than at the tip of the nozzle, you will lower the compression ratio and get a lower reading. If you do not have a schrader valve, you do not have a functional compression tester.

scottmcphee · #18 08-06-2011, 11:18 AM

The schrader is inside the quick connect you see on the top. And you're right, if the gauge shows a drop (leak down) there would be a leak somewhere between the schrader and the gauge (inclusive). Compression readings should only go "up"... until you press the release button on the gauge.

If you take the schrader out of the equation then you'd have a lousy compression tester, but a useful cylinder leak-down tester. Maybe I should make another one of these for that purpose.... Hmm. I'll grab another one of these perfect brass fittings while there's still one on the shelf. Since it's seasonal "sprayers" type gear... and summer is ending.