Damaged block

nigelv8 · Post by **nigelv8** » Fri Apr 08, 2011 8:37 pm

Hi

Have brought a Rover 3.9 block which upon inspection was found to have bad scratches in a few of the bore and, upon taking it apart, a crank that was scratched. The con rods shells had also gone through to the copper in places.

Would post some pictures on here but haven't figured out how to attach pictures.

Any advice how I can proceed? Have taken it to an engineering firm who have attempted to hone the worst bore but the damage at the top of the bore is still there.

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ChrisJC · Post by **ChrisJC** » Sat Apr 09, 2011 6:09 am

I don't think it's possible to rebore the 3.9 because the liner is too thin.

Therefore the only fix is new liners........ Or at least some new liners.

Chris.

DEVONMAN · Post by **DEVONMAN** » Sat Apr 09, 2011 12:49 pm

ChrisJC wrote:I don't think it's possible to rebore the 3.9 because the liner is too thin.

Therefore the only fix is new liners........ Or at least some new liners.

Chris.

A 20 thou rebore is ok for a 3.9 RV8.
I have done it more than once.
The standard liners look thinner than they are due to the chamfer at the top.
Real Steel sell the +20 pistons.
Regards Denis

ChrisJC · Post by **ChrisJC** » Sat Apr 09, 2011 6:42 pm

DEVONMAN wrote:
ChrisJC wrote:I don't think it's possible to rebore the 3.9 because the liner is too thin.

Therefore the only fix is new liners........ Or at least some new liners.

Chris.
A 20 thou rebore is ok for a 3.9 RV8.
I have done it more than once.
The standard liners look thinner than they are due to the chamfer at the top.
Real Steel sell the +20 pistons.
Regards Denis

Interesting. I wonder why you can rebore a 3.9 (with the 3.7" bore), but you can't rebore the 4.0 or 4.6 (with the 3.7" bore).

Chris.

DEVONMAN · Post by **DEVONMAN** » Sat Apr 09, 2011 6:53 pm

Chris.
I've not heard that you couldn't rebore a 4.0 or 4.6.
Real Steel now sell +20 pistons for the 4.6.
I can't see why it's not possible other than +20 pistons were not available till quite recently given lack of demand and the fact that with reringing a standard lump would survive to 200K plus and probably last 17 years which is about now.
Regards Denis

ged · Post by **ged** » Sat Apr 09, 2011 7:41 pm

Hi Dennis & Chris,
My 4.6 was bored to .020" over in 2005. Anyway after about 10K I developed a ticking under load when cold (only lasted a couple of minutes) & even though I new it was bore related I went into denial mode & tried to convince myself it was a leaky follower. So I used to leave it idling for a few minutes before I drove off. Eventually though, it started to pressurise the coolant system & even though it never actually used any coolant the warning light would come on. It never over heated but was forcing just enough air into the system to expose the low coolant probe & so the idiot light would illuminate.

Any way to cut a long story short it turned out to be a crack behind the liner.
The noise was (as my paranoia first thought) the liner moving until heat expansion made it nip.

Eventually I had the block top hatted & no problems since!!

I hope my post is of some use but as I've had a few glasses of wine I've probably got it all wrong.

Regards Ged

DEVONMAN · Post by **DEVONMAN** » Sat Apr 09, 2011 8:23 pm

Hi Ged.
I think what happened to your engine would have happened even without a +20 rebore just like many other RV8's. I don't think the liner thickness has a bearing on the matter but the thickness of the aluminium behind it does.

My only comment on your post is that a loose liner will become looser when the block is hot as ali expands more than iron and the liner will not nip up as the engine heats up, except when the motor is suddenly made to work hard at which time combustion heat expands the liner unevenly.
However, I don't understand why you had the noise when the engine was cold.

I assume you changed the pistons to standard size when you top hatted it.

Regards Denis

ChrisJC · Post by **ChrisJC** » Sun Apr 10, 2011 7:18 am

DEVONMAN wrote:Chris.
I've not heard that you couldn't rebore a 4.0 or 4.6.
Real Steel now sell +20 pistons for the 4.6.

The Land Rover Overhaul Manual only mentions grade A and grade B pistons. It states that a grade A bore can be honed to accept grade B pistons, but it makes no mention anywhere of reboring or oversize pistons.

Chris.

DEVONMAN · Post by **DEVONMAN** » Sun Apr 10, 2011 8:16 am

ChrisJC wrote:
DEVONMAN wrote:Chris.
I've not heard that you couldn't rebore a 4.0 or 4.6.
Real Steel now sell +20 pistons for the 4.6.
The Land Rover Overhaul Manual only mentions grade A and grade B pistons. It states that a grade A bore can be honed to accept grade B pistons, but it makes no mention anywhere of reboring or oversize pistons.

Chris.

Chris
Given the availability of grade B pistons, this is probably the reason that rebores have not been undertaken to date but once the bore wear exceeds the size for Grade B pistons, it will become more common to rebore to +20 and fit oversize pistons.
There is no difference between 3.9 and 4.0/4.6 blocks made after 1994 block (type 38A) and I have had no problems with +20 rebores on two 3.9 blocks since then.
I therefore can't see any reason not rebore a 4.0/4.6 block.

If others on here have reasons why it can't or shouldn't be done, I would be interested to hear them.

Regards

ChrisJC · Post by **ChrisJC** » Sun Apr 10, 2011 7:19 pm

I guess my alarm bells are ringing because the Land Rover overhaul manual gives a standard oversize of 20thou on the 3.5/3.9/4.2 section of the manual (and implies availability of genuine pistons / rings etc).

But the 4.0 / 4.6 manual is conspicuous in it's omission of the relevant section.

Maybe Land Rover decided there would never be a need to rebore the 4.0 / 4.6 engines......

Chris.