Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

LinkBack Thread Tools Display Modes
Old 12-18-2003, 01:30 AM
Registered User
Join Date: Dec 2003
Location: Festus MO
Posts: 762
New info - leakdown test results

Well, I did a leakdown test using a rubber-tipped blow gun and my air compressor. After "bumping" the engine around to make sure both valves were closed on cyl #1, I pressurized the cylinder only to hear air rushing up from the crankcase. The same results on cyls 2,3,and 4, although I did have to adjust some of the valves for clearance. Cylinder # 5 had no detectable leakdown, and would turn the engine until this piston was at BDC. This is the same cylinder that showed over 300 psi on a compression check.

My problem is in the bottom end of this engine. What I don't understand yet is why cylinder #5 is still so good. The PO reported that his wife was driving the car at 70 mph when it just died and coasted to a halt. If I assume that it overheated and the pistons got into contact with the cylinder liners, why does
#5 still check out OK?

I guess I'll pull the head off as soon as I get a chance, and have a closer look.

Pistons for these engines sure are expensive, what are the odds that I won't have to buy a set?

Reply With Quote
Old 12-18-2003, 02:31 AM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150

The pistons are expensive because they are both precision die cast (with a steel ring for the top compression ring to sit in) and extensively machined for the oil cooling system -- there are oil jets in the block that spray oil onto the bottom of the piston around the rod to cool the crown. Otherwise, they would melt under high load.

When you get it apart I expect you will find evidence of badly siezed rings having chewed up the cylinder walls. The pistons may be OK, but I'd not plan on it. To check them, inspect the ring lands carefully. Any visible of palpable evidence of a "lip" extruded out from what should be a nearly square edge of the ring groove means the piston is no good. Ditto for scuff marks larger than one third of the skirt area, or any place except the thrust faces. Any other damage (burns, melted areas on the crown, etc), condem them.

If they are visually OK, get a new set of rings and check the side clearance on the ring grooves with the new rings. If over the wear limit, get new pistons.

You have a choice if you need new pistons: bore the existing liners oversize (if they are thick enough) and fit oversize pistons, or press them out and install new ones, then bore to standard size and get new standars size pistons.

Just running down the road and it quit, eh?

Wonder if it ran out of oil first or overheated first?

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 07:01 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page