The V8 Owners Forum -

I've bought an old Rover V8 for $100NZD, about 30-40 quid UK or so, going by the block stampings I've ID'ed it as likely a P6 block, so what would the head numbers be if it is a P6?

the sticky, only shows SD1 and later head numbers... wheres the info for P6's to be found?

cheers

Rhys

Heads fitted to P5B, P6B and early Range Rovers all had double valve springs as standard. All later heads had single valve springs as standard.

P6B heads had 38.0mm inlet and 33.3mm exhaust valves.

The biggest tell tale assuming the heads are still on the block are the spark plugs. Plugs for the P6B are short reach and have a thread depth of 12.5mm.

If your heads have these plugs....then they are in the range of 1967 to 1976.

If not, then they are later heads.

Ron.

The heads are still on the block, but the plugs have been pulled, So it's off i go to pull the rocker cover and count springs

Your name suits ya ask a P6 Q and get a P6 Answerer

I'll take a look for any numbers in the head area as well while the rocker cover is off, just in case it's been modified with later heads. The guy I bought it off didn't know jack poop about it's provenance other than it was rover and 3.5, he bought it a few years ago for a conversion project that never happened and it's just been sitting in his garage since he bought it. There's a fair bit of liquid gasket oozed out between surfaces in places tho and the oil on the dipstick and peering through the oil filler hole in a rocker cover shows clear straw coloured oil and not horrid old black stuff, so it may have been re-done before he bought it.

I'll find out during the strip and re-build I suppose First step is to ID everything on it

cheers

Rhys

Hello Rhys,

Glad I could help

Do lets know how you get on.!

Ron.

Right, I took a rocker cover off and had a look, there are 2 springs per valve, so It looks like it's definitely a P6 motor with P6 heads.

The casting details show <BIRMAL> with an 11 above it and a 6 digit number below it, so I'm guessing it may have been cast in a Birmingham Aluminium foundry?

Hello Rhys,

Had a look at my old P6B 3.5 heads sitting in the garage, and they too have the same marking <BIRMAL>. Could not see an actual casting number anywhere though.

Do be aware that you should not use straight unleaded fuel in the P6B engine. You will need to use premium unleaded to avoid pinging along with a fuel additive to avoid valve seat recession.

Ron.

Hmm... so they're predating hardened valve seats then? I'll have a talk to an engine rebuilder about milling out the valve seat area and pressing in some new valve seats to survive 91 octane, Milling down and high temp coating the face of the piston and a thicker head gasket should drop compression to 91 octane levels while avoiding detonation.

kiwi303 wrote:Hmm... so they're predating hardened valve seats then? I'll have a talk to an engine rebuilder about milling out the valve seat area and pressing in some new valve seats to survive 91 octane, Milling down and high temp coating the face of the piston and a thicker head gasket should drop compression to 91 octane levels while avoiding detonation.

I wouldnt bother, get newer heads as it will be cheaper than getting seats fitted and the heads are much better anyway.

You can also reduce the compression ratio by approx .5/1 using composite gaskets and omitting the outer row of bolts as in the later engines. Suitable heads would be from a SD1 or 3.5/3.9 Range Rover.

Do not use heads from a 4.0 or 4.6 engine as these have smaller 28cc. combustion chambers.

Kevin

I ran an old 10.5CR P6 engined kit for a number of years on 95 ron unleaded without any issues with pinking - when we recently stripped it there was no evidence of any valve seat recession.

Andy

I recall a number of years ago that there was much discussion amongst Rover P6B owners as to whether our cars could run on unleaded, or would we need to use an additive as well.

The Australian Institute of Petroleum advised that Rover V8 engines built prior to 1986 in low compression format,..ie 8.13 : 1 could use unleaded, whilst all others would require the additional additive.

The Land Rover plant in Solihull, England was reponsible for building all Rover V8 engines since 1972, for use in all Rover vehicles of all descriptions. It was my understanding that LR were using hardened valve seats in all cylinder heads built from then on.

So on that score, the P6B with 10.5 : 1 CR could run successfully on unleaded without an additive, and Andy's findings would seem to confirm that.

So in my case, while running my 10.5 : 1 CR 3.5, I used an additive mainly due to the conflicting information, and in any case I figured that it would do no harm, even if it was unneccessary.

Now with my 4.6, I no longer need to worry.

Ron.