P38A Changing pistons & crank

I have a 4.6 thor which needs a new block (crack behind liner).
I just picked up a cheap 4.0 block to replace it.
I understand that the crankshaft, rods, and pistons have to be put in the 4.0 block from the 4.6.
Is this a big job? Garage thought it was just a straight swap of the blocks, but when I informed them of the things that needed swapping, they told me I was talking 'stupid money' to get it done.
Is this true? Is it really a lot of work to swap these parts?
Thanks for your advice.

Think the stroke is longer on the 4.6 so check carefully before committing to any work.

tomcat59alan said:

Think the stroke is longer on the 4.6 so check carefully before committing to any work.

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Yes this is why I need everything swapped, I'm wondering how much work it is

Pretty much an engine out job if I was doing it, crank, pistons and rods I believe are different, most everything else is the same.
At that stage I'd be tempted to take the block to Turners and get a new cset of liners fitted.
Apparently cracked blocked are recoverable when top hat liners are fitted, check with Turners, I was talking to Freda when this was mentioned.
Peter

p38swansea said:

I have a 4.6 thor which needs a new block (crack behind liner).
I just picked up a cheap 4.0 block to replace it.
I understand that the crankshaft, rods, and pistons have to be put in the 4.0 block from the 4.6.
Is this a big job? Garage thought it was just a straight swap of the blocks, but when I informed them of the things that needed swapping, they told me I was talking 'stupid money' to get it done.
Is this true? Is it really a lot of work to swap these parts?
Thanks for your advice.

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Your post is a bit confusing or I'm being thick, which is quite likely. Do you mean take out your original Pistons, con rods and crank from the 4.6 and put them into the 4.0 block?

Col

Colthebrummie said:

Your post is a bit confusing or I'm being thick, which is quite likely. Do you mean take out your original Pistons, con rods and crank from the 4.6 and put them into the 4.0 block?

Col

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Yes this is what I mean. Both blocks are out of the car, I just want to know if it's a big job to get the pistons and crank from the old 4.6 into the new 4.0

Just time, two dismantle, one rebuild

With both engines out and on a bench/engine stands, I would have thought a couple of hours top whack. But I'm still being thick. How do get Pistons from a 4.6 to fit in the bores of a 4.0? I'm obviously missing something so apologies to those in the know.

Col

The 4.6 pistons will be a straight fit into the 4.0l bores - same diameter (are you fitting new rings). You could also think about putting the 4.0l pistons onto the 4.6 crank to up the compression. Would need to remove the conrods though.
Edit : sorry just re-read you only have the 4.0l block.
Also, if the 4.0l & 4.6 are not both gems or thor you will need to change the CPS fitting.

Colthebrummie said:

With both engines out and on a bench/engine stands, I would have thought a couple of hours top whack. But I'm still being thick. How do get Pistons from a 4.6 to fit in the bores of a 4.0? I'm obviously missing something so apologies to those in the know.
Col

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The 4.6 has a longer throw crank so pistons travel a bit further down the bore compared to the 4.0 thus increasing bore capacity.
4.0 = 500cc per cyl
4.6 = 575cc per cyl

myfirstl322 said:

The 4.6 has a longer throw crank so pistons travel a bit further down the bore compared to the 4.0 thus increasing bore capacity.
4.0 = 500cc per cyl
4.6 = 575cc per cyl

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Ok, so the plan is to use the old Pistons and crank but get shorter con rods?

Col

I was answering simplistically, but I believe the rods are particular to each motor.
Shorter sound right.

myfirstl322 said:

I was answering simplistically, but I believe the rods are particular to each motor.

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Thanks, phew, I can sleep soundly tonight knowing that.

Col

You need to use the 4.6 crank,4.6 con rods,4.0 or 4.6 Pistons,the 4.0 Pistons will give you a higher compression ratio,than the 4.6 ones originally fitted,however if you are using a high lift cam you might need to check clearances between valve and piston at full lift,I used the 4.0 Pistons on my engine build with a piper high lift cam ,I pocketed my Pistons a little just to make sure they wouldn't touch,as mentioned above crank position sensors are different mounts between gems and Thor,pretty sure the rest will just swap over

Thanks for all your help. Crank, pistons and conrods from the 4.6 all going to the 4.0. Also it's thor to gems so I know the CPS and timing cover need changing. How many hours of labour roughly do you think it would take?