I was driving my '91 Sovereign around 60mph this morning and
suddenly felt vibration in engine & idled rough, but didn’t die. I
took it to a mechanic & he diagnosed it as having low compression
in cylinder #4. The car is around 106K miles. Is this normal with
this amount of mileage? Please help! It will cost me an arm & a
leg if the diagnostic test result is true.
thanks!
JagMan999–
JagMan999
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Sounds like you may have burned a valve. Its not normal for any mileage but
it happens.
You need more diagnostics to confirm this though. How low is low?----- Original Message -----
From: “JagMan999” jeff_castro@peoplesoft.com
To: xj40@jag-lovers.org
Sent: Wednesday, March 31, 2004 6:37 PM
Subject: [xj40] Low Cylinder Compression ??
I was driving my '91 Sovereign around 60mph this morning and
suddenly felt vibration in engine & idled rough, but didn’t die. I
took it to a mechanic & he diagnosed it as having low compression
in cylinder #4. The car is around 106K miles. Is this normal with
this amount of mileage? Please help! It will cost me an arm & a
leg if the diagnostic test result is true.
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting
services and resources including Photo Albums, Event Diary / Calendar, On
Line Books and more !
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from JagMan999 sent Thu 1 Apr 2004:
Hi Jagman
I had a similar experience and lost all compression on #6. Turns
out that I had lost part of the exhaust valve and blown it out of
the exhaust. no other damage, everything else was perfect so I just
replaced the broken valve and redid the head gasket at the same
time. This was at about 205K, may have been done before, I bought
it with 170K on the clock. cost me a few nights and a new valve and
head gadsket kit plus the bolts as I didnt know if they had been re
torqued before. Its a pretty easy job if you want to do it
yourself, just follow the book
cheers
Barri–
1988 XJ40, 74 Triumph Spitfire, 69 Lotus 7, 01 Landrover
Seattle WA, United States
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In reply to a message from Barri Herman sent Thu 1 Apr 2004:
Barri, I had exactly the same thing on my 3.2litre. PArt of the
exhaust valve head was missing with no other damage in the #6 (rear
of engine) cylinder at 146,000km. I’d like to know why it happened
but it allowed me to buy an otherwise immaculate car at the
auctions for very little money. As you say the replacement job was
straightforward.
ciao
Peter–
The original message included these comments:
In reply to a message from JagMan999 sent Thu 1 Apr 2004:
Hi Jagman
I had a similar experience and lost all compression on #6. Turns
out that I had lost part of the exhaust valve and blown it out of
the exhaust. no other damage, everything else was perfect so I just
replaced the broken valve and redid the head gasket at the same
time. This was at about 205K, may have been done before, I bought
it with 170K on the clock. cost me a few nights and a new valve and
head gadsket kit plus the bolts as I didnt know if they had been re
torqued before. Its a pretty easy job if you want to do it
yourself, just follow the book
–
MARK IX, E type, SI XJ Manual, MARK II, XJ40
newcastle new south wales, Australia
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In reply to a message from JagMan999 sent Thu 1 Apr 2004:
Jeff, If youve Burnt a Valve,ie:the missing piece has been melted
away, I would go ahead & replace just the one offending Valve, &
then investigate the cause & correct it.BUT if youve had a piece
break off the Valve, I would reccomend you check out all the other
Valves, & if any have cracks, replace all 12 Valves at least, if
not all 24! I had this experience with a Truck once & when I
checked the rest of the Exhaust Valves, 3 of them had hairline
cracks, & were about to go the same way! In this case, the Engine
was badly damaged & I opted for a secondhand Engine as the Block
had been damaged. The Valves were suffering from fatigue due to a
combination of high mileage & over revving(worn governors & an over
enthusiastic Driver, ahem, who me?) I have built many Engines
especially XK Jaguars, but never an XJ40, so wouldnt know if this
has been heard of before with these Engines, but remember, all the
Valves have done the same mileage & if it looks like a piece has
cleanly broken off the Valve, its likely to be Metal Fatigue, if it
looks melted, its likely to be an air leak/weak mixture on that
cylinder.No doubt the more experienced XJ40 Engine Builders will
advise you of their views but that is what I would do if it were
mine. Good luck, Bernie–
mesh grilled kiwi wheeled xj40Daimler1990
Dover, United Kingdom
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One thing to note is that if the valve was burned and all the other
valves do not show stress cracks (use a magnifier to check) it is a good
idea to check the seats and valve edges. If no damage, it is definitely
a good idea to lap them while you have the head off. Also lap the new
ones with lapping compound. Lapping is cheap, don’t take much time and
will definitely be helpful on any engine that has run 100k or more and
perhaps less.On an aside, I had a exhaust valve (they are the ones that fail usually) burn on the first cylinder in from the front on my 82 S3 4.2 Litre. Could find no damage other wise but it was like half the valve was gone. I suspected that it broke from a stress crack and the burn over was from the fact that I drove it back from California on 5 cylinders. Ran OK but would not go over 114 mph and the Z28 Camarros would blow bye me making rude noises and gestures in the Mojave Desert. The more of that story is that if there is a big piece missing and it looks burned it could have broke off and then burned so check the other exhaust valves carefully regardless. Also check the cylinder face for nicks and retract the piston in the cylinder to check for scratches on the walls. The cylinder walls on my S3 still had the honing pattern marks at 120,000 mile. This could be the reason a car uses oil. If the engine in ot broken in correctly (as many American owners would be likely to do) the rings may not seat in the cylinder properly and you will have hone marks at high mileage. What you can do about this other than replace the rings I do not know. I just put mine back together and lived with the fact I used a quart of 20/50 W every 700 miles and moved on. Jay 90 VDP Majestic Archie Bernard wrote:
In reply to a message from JagMan999 sent Thu 1 Apr 2004:
Jeff, If youve Burnt a Valve,ie:the missing piece has been melted
away, I would go ahead & replace just the one offending Valve, &
then investigate the cause & correct it.BUT if youve had a piece
break off the Valve, I would reccomend you check out all the other
Valves, & if any have cracks, replace all 12 Valves at least, if
not all 24! I had this experience with a Truck once & when I
checked the rest of the Exhaust Valves, 3 of them had hairline
cracks, & were about to go the same way! In this case, the Engine
was badly damaged & I opted for a secondhand Engine as the Block
had been damaged. The Valves were suffering from fatigue due to a
combination of high mileage & over revving(worn governors & an over
enthusiastic Driver, ahem, who me?) I have built many Engines
especially XK Jaguars, but never an XJ40, so wouldnt know if this
has been heard of before with these Engines, but remember, all the
Valves have done the same mileage & if it looks like a piece has
cleanly broken off the Valve, its likely to be Metal Fatigue, if it
looks melted, its likely to be an air leak/weak mixture on that
cylinder.No doubt the more experienced XJ40 Engine Builders will
advise you of their views but that is what I would do if it were
mine. Good luck, Bernie
mesh grilled kiwi wheeled xj40Daimler1990
Dover, United Kingdom
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In reply to a message from Jay sent Mon 5 Apr 2004:
Hi Jay, yes mate, I would always lap all the Valves after removing
them for inspection anyway, I should have added that to the post,
silly me! And I agree it will almost always be the Exhaust Valves
that Burn out or Crack as they are the ones subjected to the most
heat. When fitting new rings to Bores that are as you describe, I
used to ‘‘Glaze-Bust’’ the Bores with an inexpensive Honing Tool, to
allow the New Rings to bed in to the Bores, Works a treat!
Incidentally, before you remove the offending Valve, check the
Valve clearance on it, if its tight, youve probably got the cause
if its burnt out!
Bernie–
mesh grilled kiwi wheeled xj40Daimler1990
Dover, United Kingdom
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In reply to a message from Archie Bernard sent Mon 5 Apr 2004:
Fatigued Valves often have a piece missing that resembles a ''Bite
out of the Head ‘’, Whereas more often than not a Burnt Valve will
have a piece missing that is ‘‘V’’ shaped! Bernie–
mesh grilled kiwi wheeled xj40Daimler1990
Dover, United Kingdom
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The more of that story is that if there is a big piece missing and it looks burned it could have broke off and then burned so check the other exhaust valves carefully regardless. Also check the cylinder face for nicks and retract the piston in the cylinder to check for scratches on the walls. The cylinder walls on my S3 still had the honing pattern marks at 120,000 mile. This could be the reason a car uses oil. If the engine in ot broken in correctly (as many American owners would be likely to do) the rings may not seat in the cylinder properly and you will have hone marks at high mileage. What you can do about this other than replace the rings I do not know. I just put mine back together and lived with the fact I used a quart of 20/50 W every 700 miles and moved on. Jay 90 VDP Majestic Archie Bernard wrote: