Identifying 4.0 & 4.6 blocks

Pocket rocket · Post by **Pocket rocket** » Wed Apr 08, 2009 9:29 pm

I have just taken delivery of two Rv8 engines.

One is in bits and I was told was a 4.0 engine - the engine number is 42D and the airbox cover has "4.0" on it.

The other is basically complete (without inlet) and I was told it was a 4.6 with a damaged block. However the engine number stamped on the block is also 42D.

According to the various list of numbers (including on here) this means both are 4.0 engines (although they are both stamped with CR 9.35 and not 9.34 s per the listing)

I intend to take the "4.6" apart and look at the pistons. Before I do that, is there any other way to identify a 4.6 from a 4.0?

I am aware that they are both the same cross-bolted block with different crank, con-rods and pistons

sidecar · Post by **sidecar** » Wed Apr 08, 2009 10:26 pm

Hi Robin,

You should get hold of Des Hammills book, it has loads of gumph on the varrious blocks. I'll check it out for you but in the meantime somebody is bound to post the answer!

Pete

ppyvabw · Post by **ppyvabw** » Thu Apr 09, 2009 1:01 am

From the engine numbers on here, both are 4.0 L engines, unless one has been modified.

The physical difference between 4L engines and 4.6L engines is the stroke, nothing more as far as I know, internally and mechanically speaking. I do not know the figures off hand, and after an unknown number of pints of beer I can't look it up right now either. I'm sure someone else will tell you in the meantime but I'll look tomorrow. As far as I know, they are the same bore but larger stroke on the 4.6, so diff length conrods and diff compression height between your 4L and 4.6L engines, as well as the cranks being obviously different. Look up the figures and measure yours.

sidecar · Post by **sidecar** » Thu Apr 09, 2009 8:27 am

I hope for your sake that one of them is a 4.6 and that they are not both 4.0 jobbies otherwise that is going to bugger up your plans some what!

Maybe you could turn the 4.6 one over assuming that the carnk and pistons are still in the block. You should then be able to measure the stroke well enough with a ruler. That will confirm what th crank is.

Pete

RoverP6B · Post by **RoverP6B** » Thu Apr 09, 2009 8:31 am

Rover typically selected blocks with thinner walls between adjacent liners for the 4.0, while those with more metal were built into 4.6 litre engines.

Cranks, connecting rods, pistons and camshafts are all distinct between the two engines.

Ron.

Lehto · Post by **Lehto** » Thu Apr 09, 2009 8:47 am

The 4.6L Crankshaft clearly states 4.6 in it, I have 2x 4.6L cranks and they both say 4.6 in the balance weights. However sometimes they dont say 4.6 in the crank... so only way is to measure the crank in such cases.

topcatcustom · Post by **topcatcustom** » Thu Apr 09, 2009 9:17 am

Even if it is a 4.6 will it be any good with a damaged block?!

Pocket rocket · Post by **Pocket rocket** » Thu Apr 09, 2009 10:49 am

Thanks for your help and suggestions.

Unfortunately the "4.6" is indeed a 4.0 - I've taken the sump off and the crank is clearly marked 4.0 . Bummer - now I'm on the lookout for a crank, rod & pistons for a 4.6. Anyone got spares they want to off load.

Pocket rocket · Post by **Pocket rocket** » Thu Apr 09, 2009 10:51 am

topcatproduction wrote:Even if it is a 4.6 will it be any good with a damaged block?!

The idea was to use the 4.0 block (which has been pressure tested) etc and the 4.6 crank etc to buld a 4.6. The problem with the "4.6" is a slipped liner. From a cursory exam the bottom end appears to be in good shape.

ChrisJC · Post by **ChrisJC** » Thu Apr 09, 2009 12:22 pm

When you've found a 4.6 crank & rods, put the 4.0 pistons on there as that'll give you a useful boost in compression ratio.

Chris.

sidecar · Post by **sidecar** » Thu Apr 09, 2009 4:21 pm

Pocket rocket wrote:
Unfortunately the "4.6" is indeed a 4.0 - I've taken the sump off and the crank is clearly marked 4.0

That's a bit out of order as one of the lumps was sold as a 4.6!

matchmetisse · Post by **matchmetisse** » Fri Apr 10, 2009 9:50 pm

ChrisJC wrote:When you've found a 4.6 crank & rods, put the 4.0 pistons on there as that'll give you a useful boost in compression ratio.

Chris.

As I am running lpg that is what I have done to my engine,although the block was ok I have had it top hatted just to be on the safe side.