Somewhat clean piston 4.6

[rednaxela]

Hi,

1997 4.6 Gems from a P38 RR.

I bought this engine a few months ago to perhaps put into a Defender. The block possibly seems to have been a factory/warranty replacement in around 2000/2001.

Upon stripping it down I noticed that piston 5 had a relatively clean appearance... Aside from this being the early stage of the piston being 'steam cleaned' from a cracked block, what could all the other possible causes of this be? I've asked on LR4X4, and was told it could be from oil, but would appreciate more views.

The appearance of the exhaust valve serving cylinder 5 is, as you can see, not the best looking either. All other 15 valve faces look as they should, really. The exhaust port for 5 was wet/oily unlike the others which were the correct 'dry' sort of appearance. Looking at the inlet stem for 5, there was a very small bit of 'rusty' looking blemishing on it but it scraped off easily.

Would the dubious condition of the cylinder 5 valves be linked to and be contributing to the piston's appearance?

Would it be possible for there to be a crack within the head bolt female threads, letting coolant work its way up that way, and across into the combustion chambers via going under the gasket? When I cleaned up piston 7 (using a rag and some diesel), the carbon was very quickly removed, unlike the other 6 pistons which took more effort.

Thank you

[ChrisJC]

It does look to me like you have water getting into the cylinder.

I have had a cylinder head crack and water escape into plug threads I think (it was a while ago), but it is very very common (apocryphal stats of 50%) for blocks to crack behind the liner.

So I suggest that the odds suggest you do have a cracked block.

Either way, I would get both block and heads pressure tested before putting it all back together!

Chris.

[garrycol]

Normally indicates a slipped liner with the associated issues this can bring - cracks etc.

[stevieturbo]

I doubt it's oil....it is most likely water.

Or being hopeful, lack of spark causing fuel to wash it clean

[rednaxela]

Thanks all for the suggestions.

Almost could have been that Stevie. When removing the leads from the plugs, one of them broke apart at the crimp due to corrosion. After a bit of tracing, unfortunately I'm certain that it was not plug 5.

With the engine in bits it'd be daft not to get it re-linered. It's just that anything somewhat unforeseen which increases the cost of this conversion makes it harder to justify removing the current engine.

[stevieturbo]

I would not randomly get it linered. I would get it properly inspected and tested first.

Both that the block is true and no liners are moved or split etc.

[rednaxela]

Sorry to link to another forum, but here is the thread I made on lr4x4, one of the photos in the second post shows what I believe to be some movement in cylinder 8.

https://forums.lr4x4.com/topic/110479-t ... derpiston/

Surely top hat liners would be the wisest long term bet, but you mean as in not to give this treatment to a block which may be no good?

[paul c]

I don't know my login for lr4x4, been so long since I've been there.

I have a 300TDi R380 110 and a v8 Auto 110, both have had disco 1.2 transfer gears and 33 tyres, the 300 now has normal 245/70 16s and the v8 is getting a 1.3 transfer when I swap the 3.9 for a 4.6.

For the v8 auto I am getting around 15-18mpg. The 300 gets 25-30 for the same trips. The 300 was tweaked by the previous owner, a LR mechanic.

I bought all the parts to rebuild the 4.6 from Turners and was getting a local shop to do the machining but in the end I gave up on them and bought a short block from Turners, was going to end up cheaper and quicker.

The v8 is a better vehicle and the one I want but the diesel is cheaper to run. They both struggle a bit if heavily laden, hence the 4.6 upgrade.
I am unsure of what the future holds for my 300, if I end up keeping it long term I am quite keen on the 2.8 upgrade kit and VNT Turbo from MD Engineering https://www.mdengineering.co.uk/shop/en ... 2-8-litre/

[ChrisJC]

Surely top hat liners would be the wisest long term bet, but you mean as in not to give this treatment to a block which may be no good?

I'd welcome other views on this, but the only issue with the 4.0 / 4.6l cross-bolted block (i.e. one from a P38 or Disco 2) is the cracked block / slipped liner issue. Both are resolved with top hat liners, so a block with top hat liners is basically as good as it gets for the Rover V8.

I suppose I mean that in general terms, you won't find any other issues with that block, so there isn't really any other way that it can be 'no good'.

Chris.

[rednaxela]

I'd certainly agree, I think Steve meant that I shouldn't assume the block NEEDS re-linered, unless a crack/liner problem is proven.

That's the dilemma Paul. It requires some justification to remove the 300Tdi. And partly due to its mechanical injection and lack of electronic gremlins, I'd be tempted to try to keep a degree of that form with the possible V8 conversion, perhaps deviating from the original plan and using an AVS2 or Edelbrock 500 carb instead of megasquirt. I'd use distributorless ignition, probably megajolt.

Seems up in the air whether a carb will help to give a rawer induction sound. A 4.6 carb, tuned well, is still bound to perform better than the 4.0 GEMS used in the Defender 50th (?).

Back to the piston, for whatever it is worth, from when a crack in the block first allows water into the combustion chamber, how long should it take for the piston to be fully steam cleaned?!

[paul c]

My 4.6 is running carbs, the 4.6 will give much more torque than a 4.0 even though it is only maybe 40hp more, still a lot more than the original 100hp restricted 3.5.

[DaveEFI]

I'd certainly agree, I think Steve meant that I shouldn't assume the block NEEDS re-linered, unless a crack/liner problem is proven.

That's the dilemma Paul. It requires some justification to remove the 300Tdi. And partly due to its mechanical injection and lack of electronic gremlins, I'd be tempted to try to keep a degree of that form with the possible V8 conversion, perhaps deviating from the original plan and using an AVS2 or Edelbrock 500 carb instead of megasquirt. I'd use distributorless ignition, probably megajolt.

Seems up in the air whether a carb will help to give a rawer induction sound. A 4.6 carb, tuned well, is still bound to perform better than the 4.0 GEMS used in the Defender 50th (?).

Back to the piston, for whatever it is worth, from when a crack in the block first allows water into the combustion chamber, how long should it take for the piston to be fully steam cleaned?!

Seems odd to recommend MegaJolt. When mentioning the desire to avoid electronics. It being 2/3rds of the way to full engine management. MegaJolt works very well indeed - but is based around EDIS, which has been obsolete for a long time. If you insist on getting rid of the distributor - which I'm keen on too - I'd consider using a MegaSquirt ignition only, driving smart wasted spark coils. Eliminating the EDIS module, which is getting hard to find new. And if you eventually decide a carb can be bettered to, you've already done much of the work.

[stevieturbo]

Back to the piston, for whatever it is worth, from when a crack in the block first allows water into the combustion chamber, how long should it take for the piston to be fully steam cleaned?!

Guess it depends how dirty they were in the first place, and usage.

Tracking it over time isn't that easy to do I guess. But water in there definitely cleans things, but I doubt it's in a matter of minutes.

[rednaxela]

Seems odd to recommend MegaJolt. When mentioning the desire to avoid electronics.

I know, it's just that needs must. Would hate to use a dizzy in a 1998 vehicle and use the wrong cover for a 4.6 at that.

I've read through some Megasquirt tuning threads which have begun to put me off using aftermarket EFI due to complications with dialling everything in.

[DaveEFI]

Seems odd to recommend MegaJolt. When mentioning the desire to avoid electronics.

I know, it's just that needs must. Would hate to use a dizzy in a 1998 vehicle and use the wrong cover for a 4.6 at that.

I've read through some Megasquirt tuning threads which have begun to put me off using aftermarket EFI due to complications with dialling everything in.

Well, jetting a carb from scratch ain't an easy job either. Rather more difficult than tuning an ECU, I'd say.