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rich434
richard markham

(6 posts)

Registered:
07/03/2021 05:01PM

Main British Car:
4.6L v8 bore wear. How much is too much?
Posted by: rich434
Date: January 27, 2022 07:06AM

So given the LR overhaul manual doesn't specify a max bore wear figure, just a max ovality of 0.013mm, how much bore ware is too much?

I have one cylinder that's 94.11mm at its widest (side to side) and 94.08mm long ways. So technically out of round and way past the bore size for type B pistons of 94.030mm.

The rest are OK at around 94.05mm.

There is a max bore to piston clearance of 0.045mm, which is also pretty tight.

Am I going to be ok to just flex hone it and put new rings in, or should I get the whole block rebored by 0.1mm and fit oversize pistons?

(I don't really want to go to all the hassle of fitting top hats. The block has the lip at the bottom to stop the liners dropping)

Cheers!


MGBV8
Carl Floyd
Kingsport, TN
(4485 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: 4.6L v8 bore wear. How much is too much?
Posted by: MGBV8
Date: January 27, 2022 09:44AM

0.045mm = 0.00177"

That is either the minimum or you meant 0.045 inches.


rich434
richard markham

(6 posts)

Registered:
07/03/2021 05:01PM

Main British Car:
Re: 4.6L v8 bore wear. How much is too much?
Posted by: rich434
Date: January 27, 2022 01:43PM

From the LR overhaul manual, 4.6L v8:

Piston to Bore Clearance 0.015mm to 0.045mm (1 to 2 thou)

Admittedly their conversion factor is off but, yes its very tight!

Also from the same manual, max bore (doesn't say max wear) is 94.03mm and min piston width is 93.986mm so that gives a clearance max of 0.044mm

Trust me I've read it a million times!
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MGBV8
Carl Floyd
Kingsport, TN
(4485 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: 4.6L v8 bore wear. How much is too much?
Posted by: MGBV8
Date: January 28, 2022 10:19AM

My 3.5-4.2 manual says max bore is 94.04mm. The 3.9 & 4.2L can be bored to 0.030". A 3.736" bore has been done to accommodate a Chevy 305 piston.

Seems your 4.6L is only supposed to be bored 0.020". If that is not enough, it is time for liners. If considering liners read thru this:

[forum.britishv8.org]


rich434
richard markham

(6 posts)

Registered:
07/03/2021 05:01PM

Main British Car:
Re: 4.6L v8 bore wear. How much is too much?
Posted by: rich434
Date: January 30, 2022 04:42AM

Just trying to weigh up the options. £100 for a DIY hone and ring, £500 for a rebore and pistons, £1000 for new liners!

The bore wear is only on 7&8 so I may just decide to accept a little bit of blow by and oil consumption for now!


roverman
Art Gertz
Winchester, CA.
(3188 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: 4.6L v8 bore wear. How much is too much?
Posted by: roverman
Date: January 31, 2022 02:02PM

In the real world, .001"-.002" max wear is quite acceptable in a re-ring. NOW, if you go moly rings and file to fit, the gaps,
don't expect good ring seal with that overprice "bottle brush".
Good Luck.


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