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Old 12-21-2004, 04:10 PM
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Join Date: Sep 2004
Location: Canada
Posts: 495
Less Power After Valve Adjustment?

Well, my car has now been graced with first major service since I got it, consisting of new fast glow plugs and necessary wiring changes that go with that, installation of block heater, new thermostat, and valve adjustment. Results are largely positive- glow time is now only 10 seconds, compared with 45, startups are much more positive, I don't need to use glow plugs at all once engine has been warmed up then shut down for 15 minutes, and idling is much smoother. However, I have also noticed a definate decrease in acceleration. When people say how slow these cars are, it made me wonder, because I thought my accelaration was pretty good, even with automatc starting off in 2nd gear. The car still holds its speed good once up to 65 MPH- I've noticed no change on my favourite test hill- still drops to 60 as before, but getting to 65 seems to take much longer.

By the way, he also changed my oil (5W40), and I have an almost new air filter in the car. Fuel filter has not been checked.

The mechanic found that the valves were too tight on three cylinders, and adjusted them. He also thought my timing chain is OK and overall engine health good. I got a definate improvement in warm starting, which could only have resulted from the valve adjustment, but Is it normal to expect correct valve adjustment to actually result in slower acceleration? Doesn't seem right to me. Should there perhaps be an accompanying adjustment in injection pump timng when valves are adjusted?

This mechanic works as an independant on Mercedes and many other imports, but I don't think he's really well studied up on Diesels. When he first checked out my old series glow plug arrangement, he had no idea what he was dealing with- I had to explain it to him. Once he understood, he did succeed in building up a very effective fast glow system for me using a push button and off the shelf high current relay.

Comments appreciated.


1976 White 300D W115 "Pearl"

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Old 12-21-2004, 08:42 PM
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Join Date: Nov 2004
Location: Exit 191, I-25
Posts: 124
as you may have learned, diesel engines are VERY sensitive to valve adjustments. on big engines in trucks after they are adjusted they sometimes run crappy for the first 500 miles then start to run better then they did before the adjustment. probably car diesels are no different.
it may run better after a week or so... be patient.
my little Toyota pickup has less slow speed power after i adjusted the valves but runs better on the highway... just the way i adjust them i guess. everyone has a different "touch' to adjusting and the engine will run differently with different people adjusting valves.
hope this helps a little.
Current money-pits:
96 Passat TDI
78 300D 100k miles(60miles/day)FOR SALE
91 Jetta Diesel 250k miles (80miles/day)
82 Toyota Diesel pickup 150k miles; out of service for a little while with a valve problem.
All on BelenBioDiesel
Past diesels:
01 Golf TDI
81 Isuzu P/U
85 Jetta
89 KW 425 cat
85 Pete 400 cat (currently still running the west coast with over 1.5 million miles)
81 KW 400 Cummins
77 Freightliner CO ???? Cummins (Buttercup)
57 180D lots of miles(gone but not forgotten)
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Old 12-21-2004, 11:23 PM
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Location: Metro Detroit, Michigan
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Lightbulb Hmmm

Linkage needs to be checked for full stroke on injection pump stop.
Vacuum lines need to be checked for correct routing and cracks.
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Old 12-22-2004, 11:22 AM
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Join Date: Sep 2004
Location: Canada
Posts: 495
Thumbs up

Originally Posted by whunter
Linkage needs to be checked for full stroke on injection pump stop.
Hot Damn you're good! On your tip I went back to garage this morning and that was exactly the problem. But it wasn't related to the valve adjustment. He also put a block heater in for me and to get it in he had to slightly re-locate the part of the throttle linkage that goes to the transmission for kickdown. But he forgot to re-adjust the linkage up above afterward. So I just got that fixed this morning, and there's power to burn now!


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