[ROVERNET - UK] 3500s head compatibility

Robert Thornton R.Thornton at adelaidecitycouncil.com
Wed Feb 22 00:24:40 GMT 2006 

Thanks Kent for your continuing thoughts on all this. I don't profess to
know all (any?) of the answers to this conundrum, and from what I can
gather neither do some of the Rover specialists. 

There seems to be a lot of speculation and hypothesising but no
definitive conclusions. For example, here Triumph Rover Spares who have
been racing and tuning Rover V8s for many years, tell me that they
believe the cracking problem is caused by local hot spots developing
within the engine which don't register as overheating on the gauge.
Others believe it's to do with the ecu under fuelling and running lean
when under prolonged load. Especially on the P38 Range Rovers.
Interestingly TVR with their different fuelling  characteristics don't
seem to suffer the problem. Do you know, Kent, what D&D Fabrication's
experience or view on this issue is?

I agree with most of your views: 

>>"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..."<<

Ok point taken, but main cap bolts becoming loose is not always the
result of overheating. Inferior clamping pressures  causes the cap to
move and some nasty consequences to follow. A situation not helped by
the narrow cap to block registers. ARP studs improve clamping and
prevent the bolts working loose. But if the engine does then overheat
dramatically even these won't save it.


>>"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 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."<<

Agreed, especially the point about keeping things cool. You can get your
tried and tested 3.5 or 4.4 bored and sleeved out, or you can buy a used
(cheap)4.6 and get it fitted with (costly) top hat liners to "future
proof" it. That way you get power, torque, big journal crank and X
bolted mains all in one. Perhaps add some uprated pistons at the same
time...


>>"If you want to take all the guesswork out of it and have room between
your fenderwells, use a Buick 300 short block."<<

Too heavy if you're chasing power to weight ratio like I am (300 bhp per
ton), but I concede a useful and perhaps safer alternative. May as well
swap in an LS1. But that's getting away from the pure Rover/Buick
options. I do however use Buick 300 alloy heads on my 4.6 SD1; pity
Buick didn't do the 300 block in alloy too. Maybe the long stroke 4.4
P76 with the original 3.5 bore provides the solution after all - light
weight, high torque, low risk of the bore cracking... but alas, only two
bolt....

Well, I think we may indeed have reached some common ground on this.

Rob




-----Original Message-----
From: rovernet-bounces at lyris.ccdata.com
[mailto:rovernet-bounces at lyris.ccdata.com] On Behalf Of Kent Kinard
Sent: Tuesday, 21 February 2006 1:07 PM
To: rovernet at lyris.ccdata.com
Subject: Re: [ROVERNET - UK] 3500s head compatibility

Hi Rob,
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.

Strategies:
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?

Roverly,
Kent K.





Robert Thornton wrote:
> Kent
> 
> 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 4.6.
> 
> 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.
> 
> Rob
> 
> 
> -----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 all.
> 
> 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 bores....
> 
> Maybe the IOE engine wasn't such a bad deal.
> 
> Roverly,
> 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
>>RUMS
>>
>>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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