Thread: new 3.9 block

oops forgot to mention its an 84 with a 3.9 pre 94 i'm pretty sure tony

The key features of the RV8 block in terms of the subject of cooling are as follows noting block cracking behind liners was not a problem with the small bore Rover 3.5 litre/P76 4.4 litre engines.

1. When bore size went from 88.9mm to 94.0 mm with advent of the 3.9 and larger engines the hole bored to take the liner went from 93.25mm to 98.6mm or block wall thickness was going to be 2.67mm thinner on each side unless design was altered.
2. However while the block core was altered to increase the wall thickness it was only increased approximately 1 mm on each side.
3. This made the wall thickness of the big bore block more than 1.5mm thinner on each side on account the original water gallery width remained much the same (nominally 3.5mm).
4. Cast perfectly the wall thickness of the big bore block is a minimum/nominal thickness of 3mm.

However because block casting and boring was still being done using old techniques it was difficult to control the core "position" within the mould. As a consequence the core could “shift” so that the wall thickness surrounding the liner was ultimately not uniform.

The attached sketch of a large block bore X section shows the outcome of that potential “core shift” whereby minimum thickness of aluminium is in the order of only 2mm+ not 3mm or a 1/3 reduction to design in the big bore block. The block wall is thinnest on sides A and as such is more likely to crack there and not side B. Rover only scrapped blocks when thickness was less than 2.1mm but that was only after about 1994 when ultrasonic testing was first done and a lot of blocks started to be scrapped. That makes using pre-94 big bore blocks in rebuilds more of a lottery.

By way of further specific reference to this thread, according to Hammill and others the block grading system after 1997 had 4 litre engines being allocated 2.2 – 2.5mm thick minimum blocks and 4.6 litre 2.5 – 3mm .Unfortunately that extra thickness was little help with the RR's very ordinary cooling system.

The commonly found cracks are shown at points 1 – 4 on the attached diagram. The rear two adjoining cylinders seem to crack more than others. Vertical Cracks 1 & 4 are less common compared to Horizontal Cracks 2 & 3. The latter appear to be associated with cylinder head bolt locations and noting their horizontal height within the bore sits within the height of the coolant gallery. I have already noted a head bolting fix for that above.

this is all very interesting...and I'm worried now as I've just bought a brand new 4L short motor from Triumph Rover Spares.

On advice from an expert I asked for a top hat motor, but was talked out of that by the TRS rep. He said there will not be a problem with the 4L provided head studs are fitted. He said he'd built hundreds of these and never had a problem.

His reasoning is that the head bolts pull the block metal aroung the cylinder upwards due to the massive tension caused especially by stretch bolts and even by normal head bolts.

Sales spin??? Well I hope not!!! TRS are trustworthy and knowledgeable are they not? Ah well looks like another LR experiment is in progress at my place

Originally Posted by INter674

this is all very interesting...and I'm worried now as I've just bought a brand new 4L short motor from Triumph Rover Spares.

On advice from an expert I asked for a top hat motor, but was talked out of that by the TRS rep. He said there will not be a problem with the 4L provided head studs are fitted. He said he'd built hundreds of these and never had a problem.

His reasoning is that the head bolts pull the block metal aroung the cylinder upwards due to the massive tension caused especially by stretch bolts and even by normal head bolts.

Sales spin??? Well I hope not!!! TRS are trustworthy and knowledgeable are they not? Ah well looks like another LR experiment is in progress at my place

Probably as he has removed one kind of stress raiser, the other one, overheating, is in your care. A new block should give you good service so long as you are kind to it. Fit the low water alarm first.

Originally Posted by INter674

this is all very interesting...and I'm worried now as I've just bought a brand new 4L short motor from Triumph Rover Spares.

On advice from an expert I asked for a top hat motor, but was talked out of that by the TRS rep. He said there will not be a problem with the 4L provided head studs are fitted. He said he'd built hundreds of these and never had a problem.

His reasoning is that the head bolts pull the block metal aroung the cylinder upwards due to the massive tension caused especially by stretch bolts and even by normal head bolts.

Sales spin??? Well I hope not!!! TRS are trustworthy and knowledgeable are they not? Ah well looks like another LR experiment is in progress at my place

TRS firstly are a reputable crowd and would not have passed off a junk block onto you. They are also knowledgable re the head bolt issue. Flanged/ T Hat liners are not cheap hence rarely used other than reuilding cooked blocks.

That said instal a low level coolant alarm as bee utey suggests and don't let it overheat as it only has nominal/min 2.2mm - 2.5mm wall thickness behind the liners.

yes, having owned Discos for several years we are well-versed in their cooling and other foibles and keep one eye permanately glued to the temp guage with an ear out for the assuring cyclical roar of the viscous-coupled fan when towing up hills

But even with this level of trepedation and cautious maintenance, the usual head gasket/welch plug failure happened (again) at 160k, just prior to the unnanounced blocked pick-up 'event' which equally misteriously terminated and siezed the oil pump - even though the oil light flickered for only seconds beforehand - hence the new motor.... Ah the joys of Landrover ownership....a new challenge every day

TRS suggested to me that the porous block syndrome may be caused by localised hot spots developing in the motor. Nothing about head bolts.

Mark Adams believes there may be a correlation between cracking and the use of stretch bolts, but even he concedes nobody is absolutely certain what the cause, or combination of causes, is.

The only thing agreed on is that the only 100% guaranteed solution to the problem is to fit flanged liners.

Like I said before some RV8 specialists in the UK are refusing to guarantee any non top hatted new LR / Coscast blocks due to instances of cracking occuring even on the latest castings.

TRS should know this - they may be just trying to offload old/new stock LR blocks which were all sold off when Coscast took over production.

The suggestion that the "slipped liner" syndrome in 4.0 and 4.6 engines is only caused by overheating is an old wive's tale. It may cause some, but it is not the main cause. Having experienced two, the latest at 53,000 in a 2002 build factory new 4.6, I can swear that the latest engine was never overheated, as I watch it like a hawk using a Scan Gauge 2.

After seeing two of my engines fail from "slipped liners" and reading the Robison blog I am certain that Robison is correct: the problem is poor design and poor manufacture, and manifested firstly by cracking of the block which because of the poor liner design (lack of flange) allows combustion chamber gas into the cooling system and vice versa. The block cracking appears to be caused by the use of bolts which concentrate the stress in less than the maximum threads available, and can be obviated at least to some degree by fitting studs in lieu.

Poor quality manufacture was also evident in the first factory new 4.6 I bought which had been incorrectly machined for the crank and had to be replaced under warranty after 7,000 km.

I have just purchased a rebuilt 4.6 from TRS, and they were adamant about the need for both top hat liners to provide a proper seal with the head gasket, and studs in lieu of the LR stretch bolts. I understand that TRS alone has top hatted some 2-300 LR engines to date.

Based on my experience (see D2 forum), I can only recommend that no-one purchase a 4.0 or 4.6 without top hat liners.