[ROVERNET - UK] P6B compression / carb adjustment - some answers

Kent Kinard kkinard at wcc.net
Thu Nov 30 14:57:29 GMT 2006

Hi Peter,
As John pointed out, it's time to get back to basics and 
one of the "basics" about the Rover V8 is the head bolt 
situation.  All the rover V8 books mention this and we 
talk about it from time to time on Rovernet.

John's dry/wet compression test will tell you a lot about 
the situation with rings and valves in most any engine, 
but the Rover V8 has one interesting and unique 
variable...the head bolts.  Buick made the mistake 
originally, trying to save a few cents by eliminating the 
top four head bolts on each bank.  Oldsmobile versions and 
the current Wildcat heads and blocks from Ian Richardson 
all have six bolts around each combustion chamber, whereas 
the Buick 215 and Rover v8 to 1995 have five.  Five is 
plenty if they are evenly spaced (a la small block Chevy), 
but the Buick/Rover bolts are not evenly spaced.  Torquing 
the outermost head bolts to P6B spec actually tilts the 
head on the block causing a compression leak past the head 
gasket into the valley between cylinder banks.  This leak 
gives the same symptoms as a set of bad rings (commonly 
called blowby) but has an entirely different cause. 
 Unless your mechanic is an old Rover hand, and perhaps 
even if he is, he may not be aware of this.  If allowed to 
go uncorrected, this situation creates a gummy mess in the 
valley and the rocker chambers, adds to the problems of 
design deficiency in the area of camshaft and lifters, and 
impedes oil return from the top end of the engine to the 
sump.  Results: additional camshaft and rocker wear, oil 
starvation when the pickup becomes plugged and lots of oil 
in the intake system (please note this last item).

If the problem is not too bad, replacing the head gaskets 
and retorquing the head bolts to post '95 specs (just 
leave out the outermost head bolts on both banks) can do 
wonders (do the valve job while the heads are off). 
 Beyond this, replacing the camshaft, lifters, and timing 
chain set (always use a true roller chain) and checking 
the condition of rockers and rocker shafts are all "engine 
in place" items.  Cylinders seldom wear enough to need a 
rebore unless they have worn oval at the bottom and this 
will only be appearant upon complete disassembly. 
  Depending on the original CR of your engine, you may or 
may not want to switch to a composit type head gasket.  I 
used to reccommend the composit gaskets for everyone, but 
found that on 8.13:1 engines the compressions drops too 
much.  If the valley and rocker boxes are really gummy, 
its time for a rebuild.  In doing a rebuild, never put new 
bearings in the bottom end without replacing the cam 
bearings and CAREFULLY inspecting the wear on the rockers 
and rocker shafts.  Failure to follow this rule will 
result in tight clearances in the bottom end, loose 
clearances in the top end, and all the oil going to 
exactly the wrong places.  The rod bearings will fail 
within five thousand miles.

Have a nice day:-).  It's snowing here.

Kent K.

On Thu, 30 Nov 2006 21:39:28 +0800
  "Peter Mitchell" <peter_m at amnet.net.au> wrote:
> Hi Nettters
> Many thanks to you all for reading and to Roland Slats 
>and John for their
> replies.
> John asked some searching and relevant questions about 
>the way the
> compression test was done and the condition of the 
>plugs, and I don't have
> the answers at the moment.  My mechanic friend John did 
>say that a number of
> plugs were in poor shape, and I did not think to ask 
>about their condition.
> This morning I went to the carby shop to see the man who 
>rebuilt my SU's. He
> plugged in the exhaust gas analyser which showed a very 
>high 9% emissions.
> He then unplugged the breather pipes that go into the 
>carby and there was a
> lot of smoke.  The expert answer to my rough 
>inconsistent idle is that the
> engine is lunching on its own oil vapour and will soon 
>be ready for a
> rebuild.
> I now have a heavy Penrite oil suitable for older 
>engines, and will keep on
> driving the old girl carefully while I price a rebuild.
> Kind regards
> Peter Mitchell
> Perth WA 
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