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V8 engine identification - int serp front cover?


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Hi folks.

After all the help I've been getting on this forum (see my thread), I've started collecting the bits for my engine build.

I'll be having the block (top hats) and heads done before I build it up, haven't decided on induction yet. For now I was just after donor bits and picked up a (very cheap, but incomplete) V8 today. Its come from another modded LR rather than direct from a P38, so has/had a few non-standard bits on it.


The heads are definitely post-1994 10-bolt so I assume these came from the same donor as the block. And the block has the correct number for a 4.6 (46DXXXXXA CR 9.35:1). Though notably, I haven't yet found any red paint in the valley to indicate a red-graded block - might be looking in the wrong place.


I'm aware the PO used a lot of 3.9 bits on it and built it up himself, but I'm not sure if it is 'just' a 4.6 block rebuilt as a 4.0 with 3.9 ancillaries or whether it is the full-fat 4.6.


  • Given it has a hole for a distributor - am I right in thinking that the timing cover is the "intermediate serpentine" one?
  • After that we are into guesswork - I won't have chance to drop the sump until I get my engine stand back in a few months - that would be the ideal time to check the crank to see if it is a 4.0 or the original 4.6. But the pistons should give a good indication about what's going on inside (think it would be unlikely that he used a 4.0 crank and rods with 4.6 pistons - more likely that it was a complete 4.6 with 3.9 ancillaries). The pistons have "Z41" "M6" and "B" stamped into them.
  • Not too sure about whether the cam is 38A or 3.9 either - it has gears that would align with the dizzy, but unsure whether the distributor-less GEMS/THOR cams had the same features.


Thank you for your help.









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Is indeed an intermediate front cover with the crank driven oil pump. Pulley should be wide and flat as it runs on the BACK of a serpentine belt. Water pump also runs anti clockwise looking from the front, so if it has been run with Vee belts the water pump would not have been doing much ?????

Cant tell you about the block without a photo of the side of the block

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Thanks smallfry- I thought it was. Weird way he's built it with the V belt pulley. As mentioned, the block will just be getting dropped in as an exchange unit.


its a bad picture but you can clearly see the crossbolts in this shot:


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And as mentioned it has 10 bolt heads.



4.6 block (confirmed by 46xxxxxxx engine number and crossbolts),

4.0/4.6 heads

intermediate serpentine timing cover and water pump but with v-belt pulley.

i'll check the key way in the crank tomorrow night - that will initially tell me if it's an interim 3.9 or 4.0/4.6 crank (if the latter I'll whip off the sump to differentiate between the two)

the camshaft definitely has a skew gear for the dizzy.

still no idea on the pistons though

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As you've said the block has the correct code for the 4.6 and it has cross bolts the to run a 3.9 crank they would have some how had to add material to the block to run a 3.9 crank. The 4.0 and 4.6 has larger journals than the 3.9.

Stroke will be easy to differentiate:

3.9/4.0 = 71mm stroke

4.6 = 82mm stroke

The pistons will confirm the compresion ratio. Have a look for the capacity of the head online. Estimate the volume of the dish on the piston and then you can get an idea on what the deck height should be once you've compensated for the gasket being composite or original.

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According to ( http://www.gomog.com/allmorgan/40difference.htm ) the dish on the 4.0 and 4.6 pistons are 13.23cc and 22.29cc.

According to ( https://classicroverforum.net/index.php?threads/what-are-these-composite-gaskets.24816/ ) the combustion chamber cc of the head is 26cc

According to ( http://www.v8tuner.co.uk/category.php?id=21 ) the depth caused by the composite gasket is about 1.2cc per cylinder.

[Edit: dodgy maths deleted!]


After all that the last figure looks a little tight. 0.020" in old money between the top of the piston and the deck! 1.2cc for the gasket per cylinder only allows an extra 0.17mm which takes it to 0.68mm or 0.023". Looks like you may need some accurate figures unless someone can verify that the 4.6 pistons are mighty close to the deck.

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## 4.0 ##

Swept volume of 3.9 or 4.0 cylinder = (0.0944/2) * (0.0944/2) * 3.14 * 0.071 * 1000 = 0.497 litres

Unswept volume if 9.35:1 = 0.497 * (1/9.35) = 0.0531 litres

Unswept Volume (without piston to deck volume) (4.0) = (0.0132 + 0.0012 + 0.026) = 0.0404 s litres

Piston to deck volume (4.0) = 0.0531-0.0404 = 0.0127 litres

Piston to deck height (4.0) = (0.0127 / 1000) / ( (0.0944/2) * (0.0944/2) * 3.14) = 0.00182m or 1.82mm

## 4.6 ##

Swept volume of 4.6 cylinder = (0.0944/2) * (0.0944/2) * 3.14 * 0.082 * 1000 = 0.574 litres

Unswept volume if 9.35:1 = 0.574 * (1/9.35) = 0.0614 litres

Unswept Volume (without piston to deck volume) (4.6) = (0.0223 + 0.0012 + 0.026) = 0.0495 litres

Piston to deck volume (4.6) = 0.0614-0.0495 = 0.0119 litres

Piston to deck height (4.6) = (0.0119 / 1000) / ( (0.0944/2) * (0.0944/2) * 3.14) = 0.00170m or 1.70mm


So pretty much stroke to check for capacity and if piston to deck is around 1.7-1.8mm then it's a 9:35:1.

8.13:1 compression ratio gives 2.95mm for the 4.0 and about 3.01mm for the 4.6.

All that said if they were doing things like putting a v belt pulley on a serpentine cover then who knows what else they've done!

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I'm assuming:

"According to ( http://www.gomog.com/allmorgan/40difference.htm ) the dish on the 4.0 and 4.6 pistons are 13.23cc and 22.29cc."

...includes the dish, and the bit around the edge of the pistons to the top of the rings.

Looking at the picture of the bore it looks like the wear patch is only a few mm. Once any carbon deposits are removed I'd expect this to be the bit of the bores the rings don't sweep, and so slightly larger than piston top to deck at TDC.

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I have got a headache..................

Looks like a 4.0/4.6 for sure, BUT I seem to remember seeing something about SOME 4.2 blocks being crossbolted ??? Would have 14 bolt heads though.

Doesnt the 4.0/4.6 crank need a spacer to run this timing cover ?



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