I just had a pre-purchase inspection done on an 83 300D and the first thing they told me was the engine lacked adequate compression. Of the 5 cylinders the compression ranged from 195 - 220. The owner was supprised and I was disipointed because the car seems to crank easily on cold mornings and, according to the owner, cranked first time after sitting idle for 2 years. I've driven the car before and didn't notice any problems. The inspection was yesterday. Today, I found out that valve adjustment may be critical to accruate compressioin testing ( I'm not a mechanic, and don't know much about diesels). So, I called the shop where the inspection took place and asked if they checked the valves or adjusted the valves to insure proper clearance prior to testing compression. They said no, they do not do this. As a novice, my question is-----------will improper valve clearance/adjustment affect compression that much? I've been told that compression is 420 on these engines when new and in this 1983 car with 148k miles you should have a min. of 320. Otherwise, this is a very nice car and I'd like to buy it, but don't want to buy a sick engine. Any suggestions? Thanks for your help.

yup, valve clearances tighten up, not allowing them to close properly it will greatly affect compression testing.
not hard to believe that a inspection place doesn't do valve lash testing, it's kinda involved.
if the motor starts well, and has little blowby, it sounds safe to purchase to me.
barter a bit with the seller based on the low C tests.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Any idea when the valves were last adjusted? 148K is low for ring problems, but possible if the car was run on non-heated veg oil.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

No idea when valves were adjusted. As far as I know, it's never been run on vege oil. In fact, the owner wants to experiment with the vege oil in some of his other cars because he's never used it. This car does not have any conversion equipment for vege oil and is stock as far as I can tell.

Hey, how do you check for blow by? I've heard this term and have a general knowledge of what happens.
thanks

The most common test is to loosen the oil cap with the engine idling and see how much it hops around. An engine with little blow by will not have any movement of the cap. An engine with average blow by will have the cap dance a bit, and a engine with high blow by will have the cap fly off.

You can also remove the cap. An engine with high blow by will look like a old steam train.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

148K is NOT too low for bad rings/compression, especially if the PO (previous owner) was lax about oil changes and used non-diesel motor oil (you don't want to know how I know)

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K