DIR Return Create A Forum - Home
---------------------------------------------------------
The Mighty Nuovo Falcone VOC
HTML https://nuovofalcone.createaforum.com
---------------------------------------------------------
*****************************************************
DIR Return to: Engine and Transmission
*****************************************************
#Post#: 1571--------------------------------------------------
Re: Preparing for a Long Trip
By: huub Date: September 7, 2016, 2:24 pm
---------------------------------------------------------
the engine barely reaches working temperature, unfortunately the
exhaust valve does.
#Post#: 1572--------------------------------------------------
Re: Preparing for a Long Trip
By: cloggy Date: September 8, 2016, 2:25 am
---------------------------------------------------------
I don't believe heat is the sole problem. I have a couple of
sidevalves. Run them hard at night and the exhaust port is
glowing cherry red. They dont seize or break valves. In an
annexe to this website it's states that the camshaft only gets
fed oil when the revs rise enough to get the oil above a certain
pressure, thus the cam's quietening ramps can wear making
valve movement abrupt and stressing the valves. Certainly if the
tips of the lobes wear the change in profile can be abrupt,
though that doesnt always happen. Even so I've worn cams on
japanese motors and they still dont break valves. I've heard
that the original valves on these are two part friction welded.
I've never heard of that before but then if valves dont break
it's not something one gets into.
Is it always the exhaust valve that breaks?
#Post#: 1574--------------------------------------------------
Re: Preparing for a Long Trip
By: banquo Date: September 8, 2016, 2:47 am
---------------------------------------------------------
I guess as the failure is catastrophic, it's difficult to know
the root cause of failure, but I'd always assumed that the valve
stuck open, got clouted by the piston, and the head broke off
from the impact. I'd never considered the possibility that the
head came adrift first.
My opwn theory, based on very little, is that new guides control
the direction of valve movement well. We already know from
experience that the valve guides suffer from wear, and once that
occurs, the valves will tend to move in an axis that's no
parallel to the original guide bore. Once the angle is steep
enough, there's the potential for the stem to dig in and jam,
resulting in failure to close.
If that were true, then replacing the guides on a regular basis
would resolve the problem?
Never heard of an inlet valve issue, but that means nothing....
#Post#: 1575--------------------------------------------------
Re: Preparing for a Long Trip
By: huub Date: September 8, 2016, 6:34 am
---------------------------------------------------------
last time my NF suffered a dropped valve the guides were fine,
so was the (upgraded ) oil pump and the camshaft.
due to its position the exhaust valve gets pretty little cooling
oil, the expansion from the valve stem and the pushrod reduces
the clearance when the engine heats up.
my theory is the valve starts to leak because of too little
valve clearance , cant loose its heat to the seat, overheats and
snaps.
i cant imagine the valve sticking open with the spring pulling
it shut, and hardly any contact with the guide.
i might try steel pushrods ,
steel has half the expansion rate of the original alloy...
i did a quick calculation, the difference between a steel
pushrod and a alloy one is 0,25 mm with a hot engine.
i dont think the NF valves are welded , but welded valves are a
industry standard.
usually the highly stressed head is made using different alloy.
#Post#: 1576--------------------------------------------------
Re: Preparing for a Long Trip
By: cloggy Date: September 8, 2016, 7:00 am
---------------------------------------------------------
You'd need the guides to be worn to hell before the angle
changed much. I didn't see any sign of seize marks on Huub's
valve stem. Another relevent theory is that the valve springs
are too strong but since it happened to Huub's uprated valve
then that theory should be out the window too. The engine being
horizontal probably makes a difference to how much oil gets down
the guide. I noticed that great dollops of oil got delivered to
the rockerbox every time I turned the engine over when I was
setting the valves. They go click clack at all running
temperatures I've managed to run so far. But my engine appears
superficially to have a good oil delivery system. One half
heared push on the kick start and the oil pressure light goes
out.
Be interesting to know if any motors with upgraded oil
seals/pump/auxilery oil line ever have valve failure.
#Post#: 1577--------------------------------------------------
Re: Preparing for a Long Trip
By: huub Date: September 8, 2016, 7:13 am
---------------------------------------------------------
[quote]Be interesting to know if any motors with upgraded oil
seals/pump/auxilery oil line ever have valve failure.
[/quote]
mine did
#Post#: 1578--------------------------------------------------
Re: Preparing for a Long Trip
By: cloggy Date: September 8, 2016, 7:54 am
---------------------------------------------------------
Right then, I'll try and make sure the tappets don't close up,
not bother with any "upgrades". Noticed elsewhere that a better
big end feed seal means less oil bleeding to other parts of the
motor, causing further "modifications".
Also read elsewhere that dealers say the engine is bulletproof,
but to keep an eye on the tappet clearances.....
If it happens after hard running maybe the heat weakens the
valve and then when tappets return to normal on a cooler motor
it can't take being thumped back into the seat
#Post#: 1585--------------------------------------------------
Re: Preparing for a Long Trip
By: banquo Date: September 9, 2016, 2:27 am
---------------------------------------------------------
There's that mismatch between the recommended valve clearances
between the riders manual and the workshop manual. The narrower
clearances give a quiet engine, but I lost compression after
climbing a steep hill, and had to wait until it cooled off
before it would start. Since then I've run with the wider (and
much noisier) clearances, although it was burnt valves I was
worried about, not broken ones. What we need is hydraulic
tappets!
#Post#: 1847--------------------------------------------------
Re: Preparing for a Long Trip
By: cloggy Date: March 7, 2017, 1:20 pm
---------------------------------------------------------
I've been pondering this and wonder if the massive size of the
pushrods don't store a huge amount of heat and that's where the
valve problems emanate from. Also an engineer mate has
reiterated that lead helps dissapate heat from the valves. Just
wondering if hydraulic tappets wouldn't help. Bit bored as
recovering from double hernia op, more annoying than anything
else. Think one's fine and then twang! bugger.
#Post#: 1848--------------------------------------------------
Re: Preparing for a Long Trip
By: huub Date: March 7, 2017, 2:47 pm
---------------------------------------------------------
i have actually looked at using hydraulic lifters...
modified dodge/jeep lifters would fit, you would just need to
drill a extra oilway into the lifter tunnel to provide the oil
pressure
just the exhaust would probably be enough, i've never seen a
inlet valve fail.
i am first going to try steel pushrods. that should provide
enough valve clearance with a hot engine.
if not , hydraulics are the way to go.
i wish you a fast and full recovery,
i've had back problems and i was basically immobile for a couple
of months, pretty hard if you are used to 6 hours of workout a
week.
*****************************************************
DIR Previous Page
DIR Next Page