Subject: Diesel engines--valve adjustments
From: (Engineman1)
Date: 25/07/03 08:17 GMT Daylight Time
Message-id:

Several days ago I posted a query about what to look for when buying a boat
with a diesel engine and got lots of useful advice. When looking at the boat,
the owner said "I just had the valves adjusted" I thought "huh? automotive
engines have had hydraluic lifters for about 50 years." The salesman told me
that he used to be a diesel mechanic and verified that the valves had been
adjusted. I'm not that familiar with marine engines but wonder why a Hino
diesel would have to have adjustible valves?
Engineman1

To achieve compression ratios of the order of 20:1 you end up with very little
clearance between pistons and valves in a diesel engine. Any fault with a
hydraulic lifter such as "pumping up" would wipe the valves out in short order.
That's not to say it's a good thing to happen in a petrol engine but usually
there's a few mm of clearance to provide a safety margin even in an
"interference" engine. On many 2v per cylinder petrol engines you don't even
get valve/piston contact if the cam belt breaks. So most diesel engines have
shimmed valve lash. Given the lower operating rpm this isn't much of a
maintenance issue as valve wear at low rpm is fairly limited and the valves
stay in adjustment for very high mileages.


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
"How's life Norm?"
"Not for the squeamish, Coach" (Cheers, 1982)