jt_armstrong

jt_armstrong

Well-Known Member
Just about to pull the heads on my 4.6l and would appriciate some advice:-

1) Do I have to get the heads skimmed or is it only of they need it? Primary reason for head coming off is to replace the valve stem oil seals (no leaking or pressurising of cooling system)

2) RAVE states that maximum reface limit is 0.50mm. How do I know if they have previously been skimmed and that this tolerence won't be exceeded if I have to get them skimmed again.

3) Do I need a thicker gasket (if there is such a thing) to compensate for the skimming?

Many thanks everybody.
 
Hi,

I refitted the heads on my 3.9 efi a few years ago after suspecting a leak. Must say they looked ok once off but had a light skim to remove headgasket marks (efi headgasket bits into the alloy). Don't recall how much was taken off but very little non the less.

Haven't had any problems since.

Having said this I don't see why the heads can be left alone and a new gasket used and tourqued correctly. Make sure you go over all the head bolts more than once to check the tourque as i found they 'settled' as you worked round. On the other hand if you find any deep marks you may want to get them skimmed to be safe.

Cant really comment on your other questions...

Colin
 
Thanks guys, I should have them off by this afternoon so will be able to see how they look.
Prius - I need to investigate a slightly reduced compression reading on one of the cylinders - suspect carbon build up due to oil burn - who knows for sure until the heads are off.
 
jt_armstrong said:
Thanks guys, I should have them off by this afternoon so will be able to see how they look.
Prius - I need to investigate a slightly reduced compression reading on one of the cylinders - suspect carbon build up due to oil burn - who knows for sure until the heads are off.
Click to expand...

:behindsofa:

The valve stem seals come with the Head Set.
Grind the valves in whilst the head is stripped and check for worn valve guides.
Check the heads for flatness with a good straight edge or better still on a surface plate. If you don't have this equipment, an engineering shop or engine specialist will do it for you in a few minutes. If you have not had head gasket problems previously, chances are that the heads are ok. Do not skim the heads just because you have taken them off, only needs doing if they are warped outside the flatness spec's or if you are going to increase the compression ratio (Tune up).
Most important thing is replacing the head bolts when you rebuild and applying the correct tightening procedure.
 
A variation of up to10% in compression test readings is acceptable and to be expected in an engine that has covered a few miles.
Check the wear ridge depth at the top of the cylinders.
Apart from worn rings/bores, the usual causes of oil burning are:
Blocked engine breathers/hoses.
Worn Valve stem seals.
Worn Valve guides.
Oil level too high.
Incorrect grade of oil.

Usually, oil burning at cold start up is caused by oil seeping past the valve seals/guides when the engine is left standing for a while and seeping into the cylinders where the valves are open or sitting on the head of the valves when they are closed.
 
Irishrover said:
How did the brake pipe excersise go ??
Click to expand...

Both pipes removed without too much difficulty. I haven't fitted the new ones yet but that doesn't look too complicated. Disks and pads were in a really poor state so decided to change them out for some new OEM replacements.
She also failed the MOT on her emissions which the diagnostics guy put down to oil burn (I hadn't noticed this before and afterwards still didn't think it was too bad - not as if I am having to constantly top her up with oil. Anyway did a compression test and found one cylinder slightly below the 10% threshold. Wammers has suggested that if loss of pressure is through the exhaust valve then an unburned fuel air mixture will be making its way straight to the MOT guys emmision tester. Fingers crossed by the time I have finished climbing this little learning curve that everything is good for another 10 years.....

By the way I am taking plenty of photos so if anyone has to do the same and hasn't done this before I should be able help out.
 
Don't skim the heads at all unless they are warped, which is unlikley as you have had no problems; if you went for a 0.5 mm skim, then I think you would need to get the inlet manifold skimmed too, or you could have problems sealing the valley gasket. Higher compression ratios can lead to all sorts of nasty problems unless you do the maths carefully, problems from holed pistons to bent valves lurk around for the unwary!
 
there is a round cast flat in combustion chamber tha you measure head face from,head bolts can be used several times even if stretchbolts,also check cam lobes for wear as worn inlet lobe can alter compression readings plus change hydraulic tappets
 
I used to skim heads for a living, if the head gasket hasn't blown there's no point skimming it.. To clean the head up, get a decent size sheet of emery cloth and wrap it around a chock of wood, then use it to clean the face up rubbing diagonally across the head face, so that you clean it up evenly.. As long as you do that you shouldn't have any problems. It doesn't need to look perfect, just reasonably clean!
 
Thanks for all the feedback. As soon as I manage to get them off I will do the basic check to ensure there is nothing obvious out of true. If it is all good then no skimming.
Don't really want to do this again (at least not on this car) so I have ordered landrover gaskets. New head bolts as well but they are an aftermarket brand.
From what I can see the cam looks in good shape. She did have a bit of tappet rattle before I started so I might be tempted to replace the tappets anyway.

Is there anything else that should be swapped out when I am this far in?
 
check cam carefully as can be just one lobes worn,and pull rockers to one side to chec k shaft prone to wear on underside
 
Also worth while stripping the rocker shaft assemblies down to check as the shafts wear on the underside where the rockers run. Shaft and replacement rocker arms are not too expensive to replace
 
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