Re: [Chrysler300] Compression pressure , 300H
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Re: [Chrysler300] Compression pressure , 300H
- From: "Gary Barker" <gbarker@xxxxxxxxxxxx>
- Date: Tue, 13 Nov 2012 20:40:21 -0800
Hi Mike, I had a good friend that had a Mopar with a 360 in it. He put in
a roller cam, high compression pistons, Roller rockers and much more. It
ran like a snail with arthritis. Well he called me and told me what he had
done , So I asked him to bring it over and I would take a look at it.
When he pulled down my driveway, I ran over and grabbed a bucket. I
thought it was going to throw up. Hearing the way it sounded I knew there
was something really wrong in side. After checking the normal things, I
told him we were going to have to pull the engine down. We started with
the upper end and pulled one head so I could cc the the chambers, then the
cc's of the piston tops and then the piston to head cc's. After all the
additions and subtractions it turned out his compression came out to be 7.6
to one.
He said that was impossible. They were TRW 10.5 to one pistons. He showed
me the Receipt and it said 10.5 to one. So now I felt I made some mistake,
so I cc' the cylinder again. It was 7.6 to one. Now whose right or wrong.
So we pulled the pan and removed one piston and rod. Looked inside the
piston casting and there was a number. Called TRW with the number, They
said that was a Motor Home piston that was 7.6 to compression. So we sent
the pistons back and replaced them with the right compression. Reassembled
the engine and reset all the adjustments
You never know what a day is going to bring. Gary Barker
Sent: Friday, November 09, 2012 5:01 AM
To: <mgoodknight@xxxxxxxx>
Cc: <c300@xxxxxxx>; <Chrysler300@xxxxxxxxxxxxxxx>
Subject: Re: [Chrysler300] Compression pressure , 300H
> Marshall,
> I have been gradually getting my 300H, which I have owned since 1964, back
> into a more drivable condition. Some of the major problems which kept me
> from driving it much (brakes, steering) are resolved, but the engine
> issues, while better, are still with me. In general, it has suffered
> from a lack of power dating back to the engine rebuild I had done many
> years ago. The rebuilder, a highly respected race engine builder,
> misunderstood California (where I was moving to) requirements. He also
> knew high test was going away. Among the mods he made was to lower the
> compression with a custom Barnes cam, rejet the carbs with richer needles
> and install a smog valve. The car had power, but ran so rich your eyes
> burned. The carbs were rebuilt and rejetted to stock needles and it began
> to run better. I know it still does not run as strongly though as it did
> even in the 90's.
>
> I obtained a correct 300H camshaft from a member and have a new set of
> lifters. My plan is to replace the camshaft with the stock 300H camshaft.
> Recently though, I have been wondering if the rebuilder may have installed
> lower compression pistons. If so, now would be the time to replace the
> pistons also.
> I also don't fully appreciate how the custom camshaft lowered the
> compression ratio other than he adjusted the overlap.
> Thanks,
> Mike Moore
> Morgan Hill, California
> 300H
> On Nov 9, 2012, at 3:44 AM, mgoodknight@xxxxxxxx wrote:
>
> Thanks for your research Rich,
>
> That's a good write-up on compression testing. One might conclude from
> that reading that too much emphasis is often put on the results of
> compression testing and that proper (valid) compression testing is not
> often accomplished.
>
> Much can be learned about the condition of an engine from studying the
> results of a valid test, but inaccurate diagnostics are more commonly the
> main outcome.
>
> My recommendation is to avoid such a test unless you have strong evidence
> of a problem that can be easily identified by a test. If the engine runs
> well and performs properly, don't do the testing. You might see results
> that will cause you undue worries.
>
> Marshall Goodknight, engine failure analyst
>
>
> Please note: message attached
>
> From: "Rich Barber" <c300@xxxxxxx>
> To: "'Michael Moore'" <mmoore8425@xxxxxxx>, "'300'"
> <Chrysler300@xxxxxxxxxxxxxxx>
> Subject: RE: [Chrysler300] Compression pressure , 300H
> Date: Thu, 8 Nov 2012 22:47:28 -0800
>
>
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> From: "Rich Barber" <c300@xxxxxxx>
> Subject: RE: [Chrysler300] Compression pressure , 300H
> Date: November 8, 2012 10:47:28 PM PST
> To: "'Michael Moore'" <mmoore8425@xxxxxxx>, "'300'"
> <Chrysler300@xxxxxxxxxxxxxxx>
>
>
> Individual compression pressures on a long non-operated, 85,000 mile,
> cold,
> ram K block ranged from 100 psi to 140 psi. I found this interesting text
> on analyzing compression pressures. According to the 75% criterion, the
> engine failed, although a properly operated and warmed up engine with
> properly adjusted solid tappets would have probably tightened the range
> and
> marginally passed.
>
> C300K'ly,
> Rich Barber
>
> COMPRESSION TESTING
>
> Note: although this is written primarily for 4cycle gas engine testing,
> 2cycle gas and diesel follow pretty much the same sequence of procedures.
> Also, many diesel engine companies do not publish specific compression
> readings so the values, in the chart, at the end of this section will be
> too
> low for use with a diesel, you'll have to do the calculation.
>
> 1. Be sure the crankcase is at the proper level and the battery is
> properly
> charged. Operate the engine for a minimum of 30 minutes at 1200 rpm, make
> sure that the choke has opened, and the engine is at normal operating
> temperature. Putting a load on the engine for at least 10 minutes, can
> increase the accuracy of your test. Turn the ignition switch off; then
> remove all the spark plugs (injectors on the diesel). If the engine has
> closed cooling, (green anti-freeze) relieve pressure in the cooling
> system.
> (carefully)
>
> 2. Set the throttle plates and choke plate in the wide open position. On 4
> cycle gas engines: Try not to pump raw fuel into the intake with the
> accelerator pump.
>
> 3. Install compression gauge in No. 1 cylinder.
>
> 4. Install an auxiliary starter switch in the starting circuit. Ground the
> coil wire on gas engines. Next, using the auxiliary starter switch, crank
> the engine (with the ignition switch off) at least five compression
> strokes
> and record the highest reading.
>
> Count the approximate number of compression strokes required to obtain the
> highest reading.
>
> 5. Repeat the test on each cylinder as was required to obtain the highest
> reading on the No. 1 cylinder.
>
> If the readings degrade from front to rear, re-check the battery and
> possibly re-run the test starting at cylinder #1. In this way you can have
> a
> set of two tests to compare an average.
>
> TEST CONCLUSION
>
> 2 Cycle Engines:
> Your test results need to be within 15 psi range to be considered an
> engine
> worth using. For example; a 3 cylinder with readings of 130, 135, and 120
> would be considered a good engine. Some might argue that there should be
> no
> more than 5psi difference between high and low cylinders. But, obviously,
> the closer the readings are to each other, the better.
>
> 4 Cycle Engines:
> The indicated compression pressures are considered normal if the lowest
> reading cylinder is within 75% of the highest. Refer to the following
> example and chart.
>
> Seventy-five percent of 140, the highest cylinder reading is 105.
> Therefore,
> cylinder No. 7 being less than 75% of cylinder No. 3 indicates an
> improperly
> seated valve or worn or broken piston rings.
>
> If one, or more, cylinders read low, squirt approximately one (1)
> tablespoon
> of engine oil on top of the pistons in the low reading cylinders. Repeat
> compression pressure check on these cylinders.
>
> 1. If compression improves considerably, the piston rings are at fault.
>
> 2. If compression does not improve, valves are sticking or seating poorly.
>
> 3. If two adjacent cylinders indicate low compression pressures and
> squirting oil on the pistons does not increase the compression, the cause
> may be a cylinder head gasket leak between the cylinders. Engine oil
> and/or
> coolant in the cylinders could result from this problem.
>
> Note: An engine compression test is easy to do but, your results need to
> be
> tempered with the knowledge of testing conditions that reduce the accuracy
> of your test. As the battery gets weaker, starter gets hotter, and the
> engine cools down, your results from any one cylinder will change. It is
> important to do the test a quickly as possible, with as little cranking as
> needed to complete the test.
> Circumstances arise where a more accurate leak down test should be
> utilized
> before you start tearing the engine down. Readings that are at the
> extremes
> of the chart, (meaning over-all very high or very low readings), may
> indicate conditions inside the cylinders that a compression test won't
> depict properly.
> You can do the math yourself but, the following quick reference chart
> should
> be used when checking cylinder compression pressures. ( to avoid
> mathematical errors) The chart (below) has been calculated so that the
> lowest reading number is 75% of the highest reading.
> Special note: Although the "actual" compression readings are not all that
> important, keep in mind that very few engines will run with a compression
> under 100 psi. However, there are some engines that will test with
> readings
> in the 90 psi range on a regular basis. If you're not sure if you have one
> of these engines, contact your servicing dealer before you get excited.
>
> Although 75% range is tolerable for an older motor, keep in mind that most
> modern engines are designed at much closer tolerances. Also, on a V8
> engine,
> if 7 cylinders test at 150psi and only one tests at 113psi, this is not a
> good sign...
>
> -----Original Message-----
> From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
> Behalf Of Michael Moore
> Sent: Thursday, November 08, 2012 11:13 AM
> To: 300
> Subject: Re: [Chrysler300] Compression pressure , 300H
>
> Sorry, that would be engine compression.
>
> Mike Moore
>
> On Nov 8, 2012, at 11:00 AM, Michael Moore wrote:
>
> Does anyone have available the pressure I should read for a stock 300H
> when
> cranking (with all plugs out) ?
>
> Thanks, Mike Moore
>
> [Non-text portions of this message have been removed]
>
> [Non-text portions of this message have been removed]
>
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