[ROVERNET - UK] 3500s head compatibility

Kent Kinard kkinard at swbell.net
Mon Feb 20 04:36:54 GMT 2006

Hi Rob,
OK, a new 3.9 at the right price, maybe.  No chance of it having been 
overheated and thus developing main cap or sleeve problems.  But a used 
3.9, never.  You can't be sure it wasn't overheated and there just isn't 
enough aluminum in the cylinder wall anyway(.120"/3.0mm with perfect 
cores). If you overbore a 3.5 and use thinner sleeves (.055" vs. .091) 
you can have .152-.156" wall thinkness with a 3.702" bore.

This being said,Hammill seems to think the top hat sleeve cures all 
ills.  It's worth doing to a 4.6 or a 4.0 with decent cores (although a 
4.0 with good sonic test results would be a rarity according to 
Hammill).  Unless you can find the markings on a 4.0 block or determine 
core shift, it still might not be worth the machine work costs.  Too 
many question marks.  I'll just say I won't buy used 3.9's or 4.0's at 

Since I already have a very low mileage 4.0 with a bad sleeve (and 
presumeably a cracked cylinder behind that sleeve, I'll go ahead and 
have the sleeves removed and the block sonic tested and try the top hat 
sleeves to see if they really will hold up.  I wish I had read the book 
before I had my 4.6 done.  I may have wasted my money having it 
resleeved without using the top hat liners.  It had a loose sleeve also.

Those with 3.702 bore engines that have never overheated will have 
relatively few problems, but most of us on Rovernet are looking to 
re-engine an older vehicle or rebuild one we already have.  If you know 
the service history of a vehicle and the vehicle was wrecked, the engine 
may be one that has never and will never give problems, but statistics 
on the 3.9 are not in your favor.

Given the use we will put them to and the questions surrounding factory 
large bore blocks, we are better off using 3.5 blocks, particularly if 
they have no history of overheating or mysteriously losing coolant. Even 
an unkown 3.5 block with no signs of water jacket erosion, would be a 
better bet statisically than an unknown 3.9 block. The street 
environment is definitely harder on engines in some ways than a race 
environment.  I have had two 3.5's that were chronically overheated and 
developed cracked cylinders behind the liners.

We haven't even talked about the problem of ovality at the bottom of the 

Maybe the IOE engine wasn't such a bad deal.

Kent K.

Robert Thornton wrote:

> Kent wrote : 
>>>you are MUCH better off starting with a 3.5 block, either early or
> late, than you would be investing in a factory 3.9, used or new. I will
> never again buy a 3.9 for any reason. I would only buy a 4.0 if I knew
> the vehicle and it's service history from new and intended to fit "top
> hat" sleeves. <<
> Hi Kent
> What's the difference between investing in a new / used 3.9 or 4.0
> block? They use the same bore, same liners. OK, the 4.0s are cross
> bolted whereas the 3.9s are not, although they have provision for it and
> the later interim 3.9 blocks have the longer crank to drive the oil
> pump. But this does not influence the porosity issue.
> Des Hammill seems to have scared a lot of people off 94 mm blocks.
> There's been much debate about this on the Land Rover Owners forum
> http://www.lro.com/nav?page=lroi.message.list&section=MESSAGE_READERS_FO
> Consensus of opinion, if I interpret it rightly, is that yes, a
> significant number of 94 mm block do suffer this problem, particularly
> if they are allowed to overheat. But a lot do not ever become porous,
> and these may be in the majority. Some other manufacturer's alloy
> engines can also have problems with heads / blocks cracking if they are
> allowed to seriously overheat. 
> Moral of the story seems to be keep your cooling system in top notch
> order, regularly remove and clean out the cores of radiators and closely
> monitor the operation of radiator hoses, thermostat, water pump and
> cooling fan. In the case of P38 Range Rovers a complete re-think of
> their cooling system is really warranted for all the reasons Hammill
> identifies.
> Rob 
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