[ROVERNET - UK] 3500s head compatibility
kkinard at swbell.net
Tue Feb 21 02:37:08 GMT 2006
Wow, this is really brain bustin'! I love a good technical discussion
and we are really not that far apart.
Main cap fretting on two bolt mains is not solely due to inadequate
register surface and is only a problem with engines that have been
overheated, causing the aluminum block to expand too much and leaving
the cap unsupported laterally, at which point it begins to fret. It is
not inevitable. Moreover, it is easy to discover.
If you have a large bore engine that hasn't overheated or shown
symptoms, keep it cool and count your blessings.
If you have a small bore engine that hasn't overheated or shown
symptoms, keep it cool and know that at rebuild time you have the option
of using a larger bore for better torque and breathing at relatively
little cost without chancing an unknown block.
If you must start with an unknown block, a 3.5 or 4.6 are your best
choices statistically. The 4.6 is much more expensive, but you will
save the cost of resleeving...at least initially...and you will have a
stronger bottom end. Do the math and take your choice.
If you want to really make power, you have to have a crossbolt block.
You are going to spend big bucks anyway, so you might as well start with
a block that has the best cores (usually a factory 4.6).
If you already have 3.5, 3.9, and 4.0 blocks which are all suspect,
build the 4.0 because of the stronger bottom end and use top hat liners.
If you want to take all the guesswork out of it and have room between
your fenderwells, use a Buick 300 short block. You can bore it .10,
.20,.30,.40,.50 (Standard 350 pistons), or .60 using cheap pistons.
Are we getting closer?
Robert Thornton wrote:
> I appreciate what you say about this. However it seems to me there is
> little point in choosing a 3.5 block over the bigger bore items. If what
> Hammill says is right, then all two bolt mains blocks (i.e. virtually
> all 3.5 blocks) will suffer fretting due to inadequate cap register
> surfacing rendering these blocks scrap. They cannot be repaired. While
> ARP studs help they do not absolutely overcome the problem. Rover fixed
> it when it introduced the 94 mm X bolted blocks in 1995, i.e 4.0 and
> The problem with these larger blocks is the one of cracking. BUT there
> is a solution in the form of top hat / flanged liners which effectively
> overcomes this problem. Unlike the two bolt 3.5 / 3.9 blocks the larger
> ones are salvageable. The 4.0 / 4.6 blocks seem to be the lesser of two
> evils because they can at least be fixed, whereas the 3.5s are history
> once the bearing caps start to fret.
> A used 4.0 / 4.6 would be ok if you were going to re-sleeve it using
> flanged liners. Then even if it had cracked the new liners would prevent
> coolant escaping into the combustion chamber or crankcase. Hammill
> claims this is a 100% effective cure for a cracked block, albeit a
> rather expensive one.
> I suppose the worst case scenario is a 3.9 which has two bolt mains and
> a 94 mm bore - 50% chance of the main caps fretting, 25% chance of the
> bores cracking (according to DH's calculations).
> Having said that my own 3.9 Disco, now ten years old and used as my
> daily transport, has run faultlessly, never uses a drop of coolant and
> has never overheated, despite the 40 degree plus C temps we often
> experience here in summer. I don't know what condition the mains are in
> because I've never had it apart. But I do keep the cooling system in
> good order and routinely take the radiator out and have the cores
> cleaned thoroughly.
> -----Original Message-----
> From: rovernet-bounces at lyris.ccdata.com
> [mailto:rovernet-bounces at lyris.ccdata.com] On Behalf Of Kent Kinard
> Sent: Monday, 20 February 2006 3:07 PM
> To: rovernet at lyris.ccdata.com
> Subject: Re: [ROVERNET - UK] 3500s head compatibility
> 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. <<
>>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
>>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.
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