[xk-engine] Blow by?

Hi–Just got my oil analysis back from Blackstone. With only 750
miles on the sample the lead, iron and copper levels where very
high. This obviously shows bearing wear so I am committed to doing
the mains and big ends. The part that confuses me is the oil turns
black very quickly. The comentary from the analysis stated that
insoluables were high and the oil was oxidizing quickly and its
viscosity was low, usually caused by fuel or another contaminant,
but no contaminants were found in the sample. The oil was Pennzoil
20-50.
It has been suggested that the cause of the oxidation could be
blowby or sludge in the bottom of the pan. My brain just can’t
comprehend what is meant by ‘‘blowby’’. My compression is 147-155
(9:1) and the plugs, except for #2 which is blackish but dry,
indicate good chamber condition. It runs quite good with only a
little smoke upon hard acceleration or after ideling at a light.
There seems to be no blueish tint to the smoke. Could it be that
the wiper rings are shot?
I am looking for some advise because if I only commit to doing only
the bearings I will probably give it a go myself. If however these
symtoms are indicating rings and who knows what else, I would lean
towards having it done by someone with expierence and a clue.
BTW I removed the head and had a local shop do the valves last
year. The lash is set @ .005 IN & .008 EX.
Once again thanks in advance for any comments.

John–
John Deren
New Jersey '69 2+2, United States
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In reply to a message from John Deren sent Tue 13 Mar 2007:

Just to clarify John…apart from the oil sample, do you have any
reason to think your engine is running other than fine and strong?–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from Peter Crespin sent Tue 13 Mar 2007:

Peter—No. It does bother me that though that New oil can get
black in 750 mi. When I changed out the cam bearings a good friend
who wrenches busses for New York Transit commented they didn’t even
look broken in yet. When the head was off, after viewing the
cylinder walls and the condition of the pistons on top his comment
was, this engine doesn’t have no 44,000 miles on it, no way, its
still new. Its my first time through with engine inners so stuff
like this can get really confusing.–
The original message included these comments:

Just to clarify John…apart from the oil sample, do you have any
reason to think your engine is running other than fine and strong?


John Deren
New Jersey '69 2+2, United States
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In reply to a message from John Deren sent Tue 13 Mar 2007:

I would vote for doing nothing, driving it another 750 miles and
doing the analysis a second time. Maybe run some high detergent
oil through there once, like add a can of ATF for 100 miles, change
the oil and then run it 750 miles and do the analysis a second time.

Any lab report is subject to a variety of errors. Since you have
good compression and you had the motor apart recently, do not do it
over again only on the results of one oil analysis.
P.–
Peter J. Smith, 1966 3.8S, former 67 MGB
carson city nevada, United States
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In reply to a message from John Deren sent Tue 13 Mar 2007:

John, leave the old girl alone. Oil is supposed to go black by
picking up and suspending carbon - especially modern oils which all
have some detergent, some more than others. How fast it goes black
depends on lots of things like how clean the engine was and what
type of oil and yes, whether there is a bit of blow-by or the motor
is a little rich or often run cold on shorter trips. It is not a
sign of the engine dying on you. If it was a rebuilt engine then
I’d expect those high metal levels and a bit of blow-by as the
parts break in.

I honestly think that doing oil analysis in this situation is a
waste of money and is just giving you data to stress about rather
than helping anything. Once the motor is properly broken in - after
say 5-10 thousand - you could expect wear effectively to cease with
good maintenance for the next six figure mileage. Once fully borken
in if the car was being used a lot it’s not a bad idea to do an oil
analysis every 10K or so and monitor not so much for absolute
levels of anything but for a change or deterioration over time.

After many consecutive analyses (i.e. many tens of thousands of
miles) showing steady numbers, a sudden or steady deterioration
would be an early sign of possibly serious wear somewhere and they
can usually tell whether it’s a bearing or the bores by the
composition of metals discovered. But really this technique is best
applied to very high mileage vehicles like fleets of trucks or
industrial motors where down time is expensive and preventive
maintenance pays to be done by condition as well as just a formula
of miles or hours. For a leisure vehicle I wouldn’t bother because
unless you do it lots of times over many oil changes all you have
is a scattering of single-point data that don’t tell you much. For
the techinque to be worth doing you need lots of consecutive points
to plot a proper graph so you can read the picture of your engine’s
wear pattern.

I’d relax and just do the normal stuff and enjoy the car. The XK is
a tough old engine.–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from Peter Crespin sent Wed 14 Mar 2007:

Blowby, the combustion chamber gas which gets totally past the
piston and ends up in the crankcase, is sort of a fascinating
topic. Blowby raises the pressure in the crankcase and contaminates
the oil with fuel and exhaust gases, and one reference says that as
much as 1% of the fuel may be forced into the crankcase in some
engines.

Here is some fun info on blowby:

The combustion chamber is connected to several small volumes,
called crevices because of their tiny entrances. Crevices include
the clearance between piston and cylinder wall, imperfect fit of
sparkplug threads, and gaps in the head gasket cutout. Gas flows
into and out of these volumes as cylinder pressure changes.
The largest crevices by far are the volumes between piston, rings,
and cylinder wall. When the engine warms up, the crevice volumes
will change.

As cylinder pressure rises during compression, unburnt mixture is
forced into each crevice region. Since these volumes are thin they
have a large surface/volume ratio: the gas flowing into the crevice
cools by heat transfer, and ends up having a temperature close to
the cylinder wall temperature. During combustion, while the
pressure continues to rise even more unburnt mixture, pushed ahead
of the flame front, continues to flow into these crevice volumes.
After the flame front arrives at a crevice entrance, burned gases
will flow into each crevice until the cylinder pressure starts to
decrease, even though the flame becomes extinguished and does not
actually enter the relatively cool crevice region.

The crevice volume between piston, rings and cylinder wall consists
of smaller volumes connected by flow restrictions such as the ring
end gap and ring-to-piston side clearance. The geometry changes as
each ring moves up and down in its grove, sealing either at the top
or bottom ring surface. Gas pressure in the crevices between rings
varies with crank angle in an engine cycle, and there is a time
delay in the pressure change from one ring groove to the next, due
to the restricted flow passage created by the compression rings.

Late in the power stroke, when the piston is moving downward and
the exhaust valve opens, pressure in the crevice volume between the
compression rings will be greater than that in the combustion
chamber, and some gases (which remain unburnt) will be forced to
flow back into the chamber. This is called reverse blowby, and is a
major contributor to unburnt hydrocarbon emissions. The gases
forced downward past all the rings is the normal blowby

Blowby at a given engine speed and load is controlled primarily by
the greatest flow resistance in the leakage flow path between the
combustion chamber and the crankcase. This leakage path (if there
is good contact between the compression rings and the bore, and
between the rings and the bottom of the groves) is restricted
mainly by the smallest ring end gap, which tends to limit blowby.

John, I am not suggesting that your engine has excessive blowby.–
Gary Grant S818919DN
Ottawa, Canada
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Gary,

Great post. This raises the question, do you consider the crevices between
piston wall and top ring in the calc’s for compression ration. I have done
so as in my engine I have a complete 3D CAD model to work from. However,
most posts I see are only using chamber volume. There is a considerable
difference when you include the volume from top ring to piston crown. (I
don’t have the data to hand, but in my case it was the difference between
11:1 to 10.5:1 or there abouts)

Rgds
Mark Eaton

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In reply to a message from Gary Grant sent Wed 14 Mar 2007:

Thank you Gary for a well-written and very enlightening post. I was
aware of most of the principles but mostly in a squish context and
detonation-prevention or ring wear/sealing context. I had not come
across the reverse blow by idea.

Mark, the best way (only way?) of equalising/measuring real-world
chamber volumes is to cc them and if you do that in the assembled
engine you automatically take all around the top ring land into
account.

I would think that by definition the proportion of total effective
chamber volume taken up by the space around the top land would only
be significant in oversquare engines and/or very high compression
ratios (i.e. small chamber volumes) wouldn’t it? In normal motors
the volume of a narrow annular space around the top edge of a
piston is not going to be large compared to the rest of the
combustion chamber volume above it surely? But if you have the
numbers that say different it would be interesting to read them
here.–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from Gary Grant sent Wed 14 Mar 2007:

Gary–Thank you for the insight you provided with what could only
be described as a stellar post. You could have ended it after the
first paragragh with a definition that was accurate and concise and
my brain would have comprehended ‘‘blowby’’. Your fun info. took me
hours to comprehend, especially the last paraghraph. Really
enhanced my appreciation for automotive design and engineering.
Peter–I understand your comparision point, point. The oil
report comes with a ‘‘universal averages’’ comparison from the data
base for the 4.2L on an oil run of 2800 mi. My run being only 750
mi. Just some highlights (in ppm.).
Mine Univ. avg.
aluminum 4 3
iron 29 13
copper 8 3
lead 74 3
tin 1 1

Another factor came into the picture yesterday evening. It was the
first nice day we here in the NE USA have seen in a while, and with
the new date change for daylight savings time, I took a drive down
to my favorite fishing spot to smell the ocean. Ran into a chum,
no, he didnt’ have a bottle of rum, and after a time, while pulling
from the parking spot I noticed the absence of the usual oil piddle
my girl is know for. Once home I got under and the sump area was
dry and oil free. Just before the onslaught of winter here I
wrenched the pan bolts, timing cover bolts,and changed the oil feed
banjo gaskets. I guess it worked.

In the 750 mi. sample I sent, I added 4 quarts of oil, assuming it
was just leaking out. If this is not the case, a relatively closed
system is drinking a good amount of oil.

I think I am going to do a change w/filter and start all over
before drawing any more conclusions. Thanks again—John–
John Deren
New Jersey '69 2+2, United States
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In reply to a message from Mark Eaton sent Wed 14 Mar 2007:

Mark, Peter

Evidently, the total crevice volume can be somewhere from 1 to 3%
of the clearance volume(the volume above the piston at TDC), and
the piston to cylinder wall crevice volume comprises roughly 80% of
the total crevices volume.

I suppose if one were to try to account for the crevice volume
between piston and cylinder wall during compression ratio
calculations, one would also have to use all the rest of crevice
volumes as well. The imperfect fit of the threads of the spark
plug, and the imperfect fit of any fuel injector threads would have
to be used. As well, there is a tiny crevice volume in a circular
shape between each intake and exhaust valve head and the cylinder
head, and also a portion of the space around the centre plug
electrode, as well as a crevice at the head gasket edge.

It would be an interesting exercise (for someone else, not me !) to
try to calculate or model these volumes and use them in CR
computations, but Im not sure of the real world usefulness. These
volumes would change with temperature of the engine. As Peter has
said, actual measurement of the chamber volume provides pretty
useful numbers. It would be fun to model all these volumes using 3D
CAD, and then compare with actual measurements

One book says a typical total piston to cylinder crevice volume of
each cylinder, (for a 3.8 litre V-6 engine having a 89 cubic
centimeter clearance volume) was 2.55 cc, while each plug thread
crevice volume was 0.25cc and each head gasket cutout was 0.3cc.

And dont forget that in a running engine, the valve timing greatly
affects cylinder filling and cylinder pressure, resulting in an
effective compression ratio which may be different from a nominal
calculated CR
For example, a late closing intake valve may allow some of the gas
in the cylinder to be pushed back out of the intake valve during
the compression stroke, thus effectively lowering CR.

So Mark, if you could somehow include numbers representing the
crevice volumes of the plug threads, head gasket cutout, behind the
valve heads and a portion of the space around the centre electrode
in your calculations, perhaps the calculated CR would come out a
bit lower than the 11.1:1 ?

The crevice volume in the space around the plug centre electrode is
an interesting one. First, unburned gas is forced deeply down in
there during the compression stroke. Then, after the plug fires, an
expanding flame front originating from the gap between the
electroded creates a high pressure wave front which forces some of
the unburned gas even more deeply down into that crevice. The flame
trying to enter the space then becomes extinguished, because that
tiny amount of compressed charge is cooled off due to heat transfer
to the sparkplug shell, so that tiny amount of compressed charge
remains unburnt
Then, as cylinder pressure falls, the highly pressurized unburnt
charge then comes shooting out of the electrode crevice with
impunity, comtributing to unburnt HC emissions.–
Gary Grant S818919DN
Ottawa, Canada
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In reply to a message from Gary Grant sent Thu 15 Mar 2007:

Makes sense. I was thinking in the low single digit percents. If
one lung of a 4.2 XK (V6/I6 makes no difference) is 700cm3 then the
clearance volume at TDC for 9:1CR would be about 77 and typically
the burette method on an assembled engine gets you this sort of 75-
80cm3 number, of which 3% would be about 2.5cm3.

If you burette to the bottom thread of the plug hole for
consistency you are accounting for all but the internal plug
crevice and the open thread crevice below it.

I knew a tuner who used to shim his plugs so they always fitted
with the open electrode side facing the centre of the hemisphere.
At the time I thought it was a bit over the top (still do) but I
had to admire him. Bit like the old story about the VIP being shown
round the Rolls Royce aero engine factory in Derby during the war.
He walked though the Merlin assembly section and saw a guy
carefully lining all the flats up for every bolt on a large flange
or something. He said to the fitter ‘Why waste your time doing that
when nobody will ever know they are lined up?’’ The guy looked at
him and simply said ‘‘I will know…’’–
The original message included these comments:

Evidently, the total crevice volume can be somewhere from 1 to 3%
of the clearance volume(the volume above the piston at TDC), and
the piston to cylinder wall crevice volume comprises roughly 80% of
the total crevices volume.
One book says a typical total piston to cylinder crevice volume of
each cylinder, (for a 3.8 litre V-6 engine having a 89 cubic
centimeter clearance volume) was 2.55 cc, while each plug thread
crevice volume was 0.25cc and each head gasket cutout was 0.3cc.


Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from Peter Crespin sent Thu 15 Mar 2007:

Hi Peter
Believe it or not, I have indexed the sparkplugs in my XK140
engine. I was going to make a posting on this, but never got around
to it. It isnt really worth bothering with, though.

Drag racers do it all the time, the idea being that the ground
electrode forms sort of a shield, blocking off a small part of the
advancing flame front which originates from the electode gap. If
the ground electrode faces the middle of the chamber, more fuel air
mixture will supposedly be shielded than if the ground electrode
faces the edge of the chamber nearest the cylinder wall.

For drag racing, thin circular sparkplug gasket/shims are available
to accomplish the indexing. Those guys will go to great lengths to
achieve even a tiny miniscule power increase. But the thickness of
the shims affects heat transfer from plug to head, probably not too
good for a street engine.

I simply bought a couple of extra sets of plugs, marked the
position of the electrode on the hex portion with indelible ink,
then screwed various randomly selected plugs in each cylinder until
I ended up with each of the ground electrodes facing what I think
is the near edge of each chamber.

Of course there is no perceptible difference in power, but at least
now I have some extra sparkplugs lying around.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ACC%
2D1002&N=700+4294854256+115&autoview=sku–
The original message included these comments:

with the open electrode side facing the centre of the hemisphere.


Gary Grant S818919DN
Ottawa, Canada
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Hi Guys,

You’ve caught me out! I am lurking here with a V12 not an XK.

I have to confess I was talking about a big bore V12 with a flat head and
chamber in bowl.

My data as follows:

Bore : 96.3mm x 79mm (6.9L)
Area of Piston Bowl : 44,181 mm^3 or 47,773 mm^3 (with or without ring
cavity)
Head Gasket Bore : 97.50mm 1.15mm thick (8,586 mm^3)
Deck Height : 0.5mm (3,642 mm^3)

Compression Ratio 11.2 or 10.59 with or without ring cavity.

About an 8% increase in volume to include the ring cavity.

Piston bowl is non-standard. Forged pistons with valve pockets for big
valves.

I’m note sure how much the head gasket will squish and that area is
significant (~20%).
11.2 is too high. 10.5 I think I can live with.

Regards
Mark

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In reply to a message from Mark Eaton sent Fri 16 Mar 2007:

There’s more to streetability than the mere numerical value of the CR, however measured or calculated. If you are worried about detonation on road fuel the shape of the chamber (in piston or head) has a big effect, not jusr–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from Mark Eaton sent Fri 16 Mar 2007:

There’s more to streetability than the mere numerical value of the CR, however measured or calculated. If you are worried about detonation on road fuel the shape of the chamber (in piston or head) has a big effect, not just the CR number. There were plenty of sidevalves that pinked horribly at 6:1 until Ricardo showed how to use squish… But I don’t blame you for being careful if your spec of pre-HE engine is known to have issues at highest ratios on today’s fuel?–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from John Deren sent Tue 13 Mar 2007:

John Deren:

My ideas are not as detailed as those expressed by others.

  1. Detergent oil will become black as it picks up the contaminants
    and holds them in suspension, to be disposed of in the next oil
    change.

  2. Blow by is usually easily seen by opening the crankcas filler
    cap with the engine warm and running. A little vapor is normal, but
    not a cloud! One of my old Corvairs had a geyser like column on
    opening the crank case cap. Dependant on the plumbing, it may be
    seen in the air filter.

  3. If bearing wear is an issue, it will manifest in warm oil
    pressure.

  4. The black cylinder may be indictive of a leaking injector.

Just my ideas as a guest on this forum. My JAGUAr is no longer DOHC
powered.

Carl–
The original message included these comments:

Hi–Just got my oil analysis back from Blackstone. With only 750
miles on the sample the lead, iron and copper levels where very
high. This obviously shows bearing wear so I am committed to doing
the mains and big ends. The part that confuses me is the oil turns
black very quickly. The comentary from the analysis stated that
insoluables were high and the oil was oxidizing quickly and its
viscosity was low, usually caused by fuel or another contaminant,
but no contaminants were found in the sample. The oil was Pennzoil
20-50.


Carl Hutchins
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In reply to a message from John Deren sent Tue 13 Mar 2007:

Hi to all,
Wonderful set of posts - good science in there for sure. I’d like
to add a couple of thoughts.
If Previous Owners haven’t been too fussy about oil changing or if
the car has done lots of cold starts or if there’s lots of sludge
in the crankcase from whatever cause you will see these the sludge
deposits releasing crud into your oil as the motor runs hot for
extended periods.
Secondly, XK motors are notoriously hard to get good ring seals
straight after overhauls - and they tend to consume fair quantities
of oil anyway, via inlet valve guides, piston rings etc.
Summary - I fully agree with earlier commnents - oil analyses
belong to condition monitoring in very heavy truck and stationary
engines - it’s the change over time that’s critical in these
applications.
If your engine vital signs are good (like oil pressure, compression
and power) don’t worry.
I would add one caveat - if ONE cylinder on an injected motor shows
signs of plug sooting, I’d certainly do something about the
injector for that cylinder - bore washing will cause wear in that
cylinder, as well as releasing soot and watery deposits into the
crankcase.
Best regards
Shane–
The original message included these comments:

the mains and big ends. The part that confuses me is the oil turns
black very quickly. The comentary from the analysis stated that


SWA1
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In reply to a message from SWA1 sent Mon 19 Mar 2007:

Thanks Carl–Thanks Shane—BTW Carl, my first two cars were
Corvairs. Funny looking back because I never really got into engine
inners in those early years because they both always got me where I
was going. Granted, not very quickly or stylishly, but got there.
My 69 E has the dual ZS’s. Just a little before FI. I am convinced
that it has to be the valve guide leaking, even though the deposit
left is dry rather than wet. #1 & #3 both indicate a lean mixture.
I wish I had some expierience such as seeing the amount of vapor
emmited from another XK engine. There is no cloud when unscrewing
the oil filler, but the vapor can definitly be seen from the tube
at the air canister. Is there a standard pressure built up in a
well running engine, and a way to measure it, so as to perhaps
confirm or negate blowby?
On the last oil change with the drainplug off I took a test tube
cleaning brush, bent the wire to 90 deg., and gave a good swipe all
around the bottom of the inner pan. No indication of any buildup
whatsoever. Also, the oil pools in the head and all the little
crevices around the cams looked factory new. Where else can one
find indications of sludge without dropping the pan?
The vitals all seem good. Oil pressure @ 20 at idle, 40-50 running.
Comp @ 150 psi. and basically running in the ‘‘boy this thing is
lotsa fun’’ range.
As soon as the weather breaks I am going to start with new oil and
just go out and drive. I am hoping to find differnt results, But if
I keep adding a quart every 150 mi. and cant find a leak to explain
it, it will be pan off time.

John–
John Deren
New Jersey '69 2+2, United States
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In reply to a message from John Deren sent Tue 20 Mar 2007:

If you hadn’t said you had to add 4 quarts at 750 John, I’d have
thought you were overfilling.

A lot of people add too much and when they check shortly afterwards
the engine has of course ejected the excess quart or whatever. If
they didn’t top up it would stabilise but they always add the
excess back which the engine then ejects and complain their engine
eats oil a quart per 150! Same with topping off coolant above the
proper header space and puking it out every time…They say ‘My
car’s overheating, it keeps puking water’. In both cases if they
would only add the exact right amount from scratch let it stabilize
they would probably find the car was losing nothing.

However, this wouldn’t explain continued loss to the extent of 4
quarts. It may be the first miles after the rebuild will be far
worse than now if it was a poorly-finished bore. On the other hand,
if it was broken in badly or a ring snapped on assembly, you may
have an oil-drinker ad infinitum. But for me, if it was running
really well and not blowing gobs of blue smoke out, I’d possibly
just start buying oil in bulk and watching for other symptoms.

Your valve guide theory would work out as blue smoke on the
overrun, whereas a broken ring would be blue smoke when flooring
it. The later motors used different guides and valve parts for
inlet guide seals. Sometimes people just put seals on without
swapping guides/collets/valve retainers for the shorter type to
suit the seals. If you mix the wrong parts your valve seals turn
into oil pumps and risk you dropping a valve if the collets work
loose.–
Peter Crespin 66 2+2 E, 74 Daimler 4.2, 86 XJ-S 3.6 manual
Cambridge, United Kingdom
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In reply to a message from John Deren sent Tue 20 Mar 2007:

John,

I don’t think anyone has mentioned this but a 9:1 CR engine
should have about 180 - 185 psi with a compression test.
Have you done the compression test dry and wet? That is add
some oil to the cylinder, I seem to remember about a
teaspoonful ~ 5 ml and do the test again. If the rings are
‘‘leaking’’ you should see the pressure increase with the wet
test.

If you oil pressure is OK then I wouldn’t be too concerned
about the bearings.

It has been mentioned I think that getting the compression
rings to seal can be a problem. For running in, my engine
builder suggested short bursts of wide open throttle up to
4000 rpm with the engine well up to temperature - usually at
least 10 miles, to increase the pressure against the
compression rings and help the seat.

You have convinced me not to get my oil tested though…
Ignorance is bliss!

Regards

Keith–
The original message included these comments:

The vitals all seem good. Oil pressure @ 20 at idle, 40-50 running.
Comp @ 150 psi. and basically running in the ‘‘boy this thing is
lotsa fun’’ range.


Keith Bertenshaw
Rockaway, NJ, United States
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