Rebores on the 4.6L?

General Chat About Engine Build

Moderator: phpBB2 - Administrators

Post Reply
rich112
Helpful or Confused
Helpful or Confused
Posts: 105
Joined: Fri Jul 02, 2021 7:22 pm

Rebores on the 4.6L?

Post by rich112 »

Reading the specs on the 4.6L, it appears that even a tiny bit of wear means you need a rebore?

From a factory size of 94mm, you get a limit of 0.015mm of wear (a bit over half a thou). Then you can go to a B size piston at 94.016mm.

Another 0.015mm on a 'B' size bore and it's time for new sleeves or a rebore?

I don't quite get why bore wear of only 0.03mm (1 thou) means you need to chomp 20 thou out to fit +20 pistons and rings? I haven't seen +10 pistons anywhere.

Are the cylinder bore wear limits really that tight?

Are there 'real world' bore wear limits? Does loss of compression and blowby and skirt wear get exponentially worse as bore wear and ring gap increases?

Is there sufficient material in the liners for a 0.5mm rebore?

Is another option to keep your pistons, assuming they're not worn out and replace the liners? I think this gets a lot more expensive if fitting top hat liners and needs all the machining work too.


EDIT: After a careful measure with a bore gauge, all my bores are slightly over size and over oval. Not by a lot, the worst being cylinder 8 which is 94.11mm side to side and 94.08mm longways. So as I have B pistons, 0.08mm over size, side to side and 0.05mm over size long ways. Ovality is 0.03mm so double the spec.

Best is 94.04mm by 94.03mm which is very close to spec.

I don't have a calibrated gauge to check my bore gauge on, just a digital caliper. But I did compare with the bottom of the bores and these are 94.01mm so I think my measurements are close.



User avatar
ChrisJC
Top Dog
Top Dog
Posts: 5039
Joined: Mon Nov 20, 2006 1:13 pm
Location: Northants / Cambs
Contact:

Re: Rebores on the 4.6L?

Post by ChrisJC »

When I had top hat liners fitted, I kept my old pistons and just fitted new rings. Both times. It worked fine.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

rich112
Helpful or Confused
Helpful or Confused
Posts: 105
Joined: Fri Jul 02, 2021 7:22 pm

Re: Rebores on the 4.6L?

Post by rich112 »

ChrisJC wrote:
Sun Jan 23, 2022 9:28 pm
When I had top hat liners fitted, I kept my old pistons and just fitted new rings. Both times. It worked fine.

Chris.
Hi Chris, no can do! My pin bores are shot on at least 2 pistons so will be getting new pistons.

Question is: +20 rebore or replace all the liners.

Replacing the liners seems to be very expensive, despite the liners only costing £300, people are telling me to expect a £1000 bill!

I am really struggling to find a definative spec for bore to piston clearance limts with cast pistons. (other than the 0.045mm mentioned in the LR manual)

User avatar
ChrisJC
Top Dog
Top Dog
Posts: 5039
Joined: Mon Nov 20, 2006 1:13 pm
Location: Northants / Cambs
Contact:

Re: Rebores on the 4.6L?

Post by ChrisJC »

I had my liners put in by Turners on both engines.
The total cost (liners + all sundries required for the rebuild) was about £2K.

But on the first engine I did, it lasted for 10 years and did 100K miles, no bother. Still doesn't use oil or water. It has just retired because the rest of the vehicle is knackered.

The other engine has only done 5K miles so it's too early to say.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

Richard P6
Getting There
Getting There
Posts: 238
Joined: Sat Feb 14, 2009 11:04 pm
Location: Yorkshire

Re: Rebores on the 4.6L?

Post by Richard P6 »

rich112 wrote:
Mon Jan 24, 2022 10:44 pm
ChrisJC wrote:
Sun Jan 23, 2022 9:28 pm
When I had top hat liners fitted, I kept my old pistons and just fitted new rings. Both times. It worked fine.

Chris.
Hi Chris, no can do! My pin bores are shot on at least 2 pistons so will be getting new pistons.

Question is: +20 rebore or replace all the liners.

Replacing the liners seems to be very expensive, despite the liners only costing £300, people are telling me to expect a £1000 bill!

I am really struggling to find a definative spec for bore to piston clearance limts with cast pistons. (other than the 0.045mm mentioned in the LR manual)
I just had my 4.0L fitted with top hat liners (same block) and it cost me £850 + vat, i.e. £1,020, so you're not far out.

I also had the spinning bits balanced at the same time and if I had to do the job again, I would do the same.

It is well worth it
Rover P6 4L V8
Megasquirt MS1 EDIS
5 Speed

paul c
Getting There
Getting There
Posts: 265
Joined: Tue Mar 11, 2008 7:41 am
Location: Takaka New Zealand

Re: Rebores on the 4.6L?

Post by paul c »

I originally was going to just rebore +.020 but decided it was worth spending the money and doing the liners as well, it was just a much safer option. If you havent already bought pistons you could either buy used or new standard size, which will mean if ever needed you could still bore the liners oversize.

SuperV8
Guru
Guru
Posts: 947
Joined: Tue Jul 07, 2009 11:25 pm
Location: West midlands

Re: Rebores on the 4.6L?

Post by SuperV8 »

My 4.6 had 3x leaky liners so I went the Top hat liner route - something in the order £1000-1200 I forget, it was a while ago.

My pistons were fine, when doing the liners the engine shop would have bored them out to whatever size I requested - so I was very tempted by going up in size to 5.0 or 5.2 but as my pistons were fine I couldn't justify it.

Now If I needed to buy new pistons as well...
Dax Rush 4.6 supercharged V8 MSII

Post Reply

Return to “Engines Area”