[ROVERNET - UK] Rover P6B - compression test query

John Burkhard burkhaj at earthlink.net
Thu Nov 30 09:15:17 GMT 2006

Hi Peter,

I think we need to get back to the basics.  First lets look at what we know 
or do not know.  What sort of shape were to old spark plugs in?  Gasoline 
or oil fouled or lean burned?  Was the gap too wide?  Was the compression 
test done wet or dry?  Did John put a vacuum gauge on the engine and check 
manifold pressure?  This tool can tell you a hole lot such as carburetor, 
USA spelling, problems, sticking valves and so on.

Next check for manifold leaks.  Use a can of aerosol carburetor cleaner and 
spray it around the throttle shafts, gaskets and along and at the ends of 
all the vacuum lines.  If the engine speed increases you have found a leak. 
If no faults were found up to this point I would think it's time to check 
out the carburetors as the other Rover owners have recommended.

Now about the compression test, why did you have it done.  Is this engine 
using more than one quart of lube oil every 600 to 800 miles or did the 
spark plug look oil fouled?  As general rule the difference between 
cylinders should be no more than about 14 psi or not less than 80% between 
the highest and lowest.  Just a few pointers about getting good 
information.  The engine should be fully warmed up, first test done dry, 
each cylinder done three times and with the throttle wide open.  Recheck 
the low cylinders a second round wet.  That is to say a small amount of oil 
down the spark plug hole.  If the pressure comes up it's ring time.  If no 
or very little change it's valve grind time.  Be sure to check the 
crankcase pressure and if John has the tools do a leak down test.  For this 
test the engine should be cool and will take a few hours to do.   Please do 
remember the old adage about the weakest. link.

Well I hope this is of some help and to you and yours a happy holiday 

----- Original Message ----- 
From: "Peter Mitchell" <peter_m at amnet.net.au>
To: <rovernet at lyris.ccdata.com>
Sent: Wednesday, November 29, 2006 1:41 AM
Subject: [ROVERNET - UK] Rover P6B - compression test query

> Hi Netters,
> I dropped my P6B off to mechanic near my work today so he could have a 
> good
> look at some serious problems that I have been having with an 
> inconsistent
> idle and difficult starting.
> I asked John, the mechanic, to do a compression test to establish whether 
> I
> was facing major problems with a completely worn out engine and high
> crankcase pressure. At the same time he fitted new plugs and set the 
> timing.
> This sorted the starting problem instantly, but the engine will not idle 
> at
> a consistent number of revs - I have had to resort to left foot braking 
> so
> that I can keep some throttle on when waiting at traffic lights.
> Since the new plugs were installed and the timing adjusted, the car is 
> more
> lively under power, and tomorrow we are going to check the carburettor 
> float
> level (the carbs have just been overhauled), John feels that the most 
> likely
> source of the idling problem will be traced back to the float level.  I 
> am
> also going to put in a better oil than I am using at present, and will go
> for a Penrite brand suitable for older engines.
> Have members experienced these problems with the float level being too 
> high?
> My brother is a mechanic (originally a Land Rover apprentice with Faulls 
> in
> Perth) and agrees with my mechanic's viewpoint.
> For your information the compression test results were:
> Cyl psi
> 2 125
> 4 125
> 6 110
> 8 100
> 1 125
> 3 125
> 5 115
> 7 115
> Thus the lowest cylinders were no 8 at 100 psi and no 6 at 110 psi.
> May I ask those more experienced than I, am I safe to expect a few more
> years of modest weekend use, or do I need to start saving for a rebuild?
> Opinions would be most welcomed.
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