Deglazing/honing
 

Building the bottom end of my engine which already has 'B' pistons in it from factory. Cylinders and pistons are within tolerances. Normally would give the cylinders a hone to give it a good crosshatch but was reading the factory manual and:
- The 1998 '3rd edition' of the 4.0 and 4.6L v8 engine overhaul manual says nothing about honing other than 'a' pistons can be replaced with B pistons and cylinder honed over-sized;
- The 2003 '4th edition' of the same book says under piston inspection "CAUTION: DO NOT attempt to de-glaze cylinder bores".

Wondering if anyone knows the details of this? I would think it would be fine as long as you didn't result in the cylinder spec going below the 93.986 mm required for B pistons and you didn't put the piston/cylinder gap out of spec but the book seems clear ... (well at least the new one)

Anyone have any advice?

Forgot to mention I have a 1996 4.0.

I am curious about this as well. I just had my block honed during the overhaul and now I have low compression with lots of blow by. I was told somewhere that honing wasn't good for our blocks, but not why. Hopefully someone comes along with an answer

I'm fairly sure there isn't an issue with honing. What is an issue is the bore being oval and honing will not correct that.

Agreed bore geometry is key. Everyone I talk to (most with no LR v8 experience) says it's fine. But I can't see why they would put it in the FSM for no reason. There must have been a reason to add it between editions sometime in 1998 and 2003.

The best I could find but was just speculation is this advice was put in due to the heat and friction from honing causing sleeves to slip or move enough that they became susceptible to slipping but aluminum engines with sleeves are not unique to LR v8s and haven't found this advice for other engines...

It could be ring materials used, like for instance chrome moly requires a very fine hone. I'm not suggesting Rover used CM rings..... As long as your using new rings I'd blow off the manual, pick a ring and hone and go. I'll read the manual when I get home.

I did mine last year, I used a 3 stone hone on a drill like I always do on blocks I am not getting bored and mine is fine

Yep, I haven't heard these motors are anything exotic.
Tom, have you done a comp test? Love to know your numbers, looking forward to a rebuild of my own.

Yeah nothing exotic. My only thought is they were getting reports of issues with sleeves moving when honing so said not to do it in updated manual.

That said the manual says it's okay to bore if you have A pistons to B size bore so something is inconsistent with that explanation.

Interesting - had another read today and the 3rd edition says "If only new piston rings are to be fitted, break cylinder bore glazing using a fine grit, to produce a 60° cross-hatch finish. Ensure all traces of grit are removed after above operation."

This directly contradicts what I read in the 4th edition which says not to deglaze ...

My rings took like 1500 miles to break in, that said ,I have no idea how long it would take if you don't due glaze


Scouts I never did an after comp test