4.6L teardown - strange gasket problems

ozrover · Post by **ozrover** » Mon Dec 11, 2006 4:16 pm

Started stripping down the 4.6 tonight ready for cleaning and re-assembly and came acros some curio's. Motor was running when purchased though had high KM.I noticed the valley cover was stretched/bent indicating excessive blowby preasurising the crankcase a little,though no major leaks and to be expected at 300 000km I thought. Inlet came off no dramas,engine looked super clean for mileage(rangie was serviced religiously and did exclusively highway driving). All the cam lobes are still there,lifters a little concave but all of them popped straight out,very little gum. Got worried when i attacked the headbolts,almost all the outside row (4 bolt heads)were just finger tight. Inner row were nice and tight. Removed the left head was pleasently surprised - no lip at all on bores all 4 pistons rather free of carbon,no steam cleaned ones and the head wasnt too carboned up,the chambers were almost carbon free with no sign of any previous work.The factory composite gaskets are another story.The head litterally slid off with the last bolt,no seal at all,both middle cylinders have a 2 inch section on the lower edge where there is only perforated tin left,the rest is gone. I thought ok the heads have been pulled where the engine was removed. Did the other side,noted however the sludge was still on the 2 endmost innerbolts. No chance they have been off any time recently,and the gasket is the same that side too as was the loose outer bolts. I feared liner problems however the only thing abnormal I can see is 2 liners on 1 side and 1 on the other are raised ever so slightly ABOVE the deck,just enough to catch your fingernail.No sign of water being in any chamber.
Is this common? From what I can see its a case of the stretch bolts coming loose and allowing combustion gases to burn the gasket,but nothing else seems amiss. If so is there a way to secure the liners to prevent potential problems?(without replacing them with tophats)
Im a bit surprised considering the mileage that its so clean apart from inside the rocer covers- bit sludgey)and all 8 bores still have crosshatching.
Opinions appreciated.
Doug

ian.stewart · Post by **ian.stewart** » Mon Dec 11, 2006 5:51 pm

The outer bolts are not a problem, it was realised by Rover the outer bolts were causing deflection in the head and causing gasket failure, later heads dont even have bolt holes in the heads, its probably safe to leave the bolts out alltogether, but fit them to keep the Sh-t out of the block,

toughy V8 · Post by **toughy V8** » Mon Dec 11, 2006 5:53 pm

ive just sold a 4.6 block and the liners definately never stuck up from the deck face, these later blocks are prone to the liners moving. it would be best to have new t top liners put in anyway because even if the liners havent moved yet, they will later on its just about guaranteed.

Post by **katanaman** » Mon Dec 11, 2006 8:12 pm

ian.stewart wrote:The outer bolts are not a problem, it was realised by Rover the outer bolts were causing deflection in the head and causing gasket failure, later heads dont even have bolt holes in the heads, its probably safe to leave the bolts out alltogether, but fit them to keep the Sh-t out of the block,

If I am reading this right it is the later heads he has with the very outer row missing. If I am right then no they shouldn't have been loose and that's as you say is why your gasket is damaged.

adamnreeves · Post by **adamnreeves** » Mon Dec 11, 2006 8:36 pm

I am confused as well. I thought the 4.6 was the later type, i.e. 10 bolt head 28CC. Maybe is is a stroked version. He does say that the outer most bolts all 4 the bolts were loose, the later head has 2 rows of 5 bolts, 10 bolts. The older head has 2 rows of 5 bolts and outer row of 4 bolts making 14 bolts. If it was the new type head and one row of bolts were loose I suspect he would have more than a gasket problem.

katanaman wrote:
ian.stewart wrote:The outer bolts are not a problem, it was realised by Rover the outer bolts were causing deflection in the head and causing gasket failure, later heads dont even have bolt holes in the heads, its probably safe to leave the bolts out alltogether, but fit them to keep the Sh-t out of the block,
If I am reading this right it is the later heads he has with the very outer row missing. If I am right then no they shouldn't have been loose and that's as you say is why your gasket is damaged.

HairbearTE · Post by **HairbearTE** » Mon Dec 11, 2006 9:17 pm

Sounds to me like this engine has had a rebuild at some time. Clear cross hatching after 300 000kms is unusual to say the least. No step in the bore after 300 000kms is impossible imo. In such a high mile motor it would be a suprise if the block hasnt cracked behind the liners. Let me hazard a guess here, are all the raised liners towards the rear of the engine?

ozrover · Post by **ozrover** » Mon Dec 11, 2006 11:03 pm

The heads are the late 10 bolt (4 bolts per cylinder),Motor is a factory p38 4.6 from 1998.The raised liners are only very slight,front 2 on left bank,rear 1 on right bank.I am confused by the cross hatching as well,however its standard bore,the valley end gaskets were hard and brittle like ceramics as you would expect,no aftermarket gaskets or silicone sealant as you would expect on a high mileage unit thats been worked on.As far as I can see its had a new water pump and rocker cover gaskets.The guy I purchased it off( (original owner of rangie) put a second hand motor in with 50 oookm on it in preference to waiting to rebuild this 1.
Doug

badger · Post by **badger** » Tue Dec 12, 2006 9:50 am

Pretty typical of stretch-bolt failure. As I said in another post, stretch bolts are useless - they loose their clamping ability over time, causing head gasket issues. Replace with studs, it's the way forward!

adamnreeves · Post by **adamnreeves** » Tue Dec 12, 2006 10:31 am

I used ARP studs for mine.

GreenV8S · Post by **GreenV8S** » Tue Dec 12, 2006 10:46 am

ozrover wrote:The heads are the late 10 bolt (4 bolts per cylinder)

This makes it seem as if you had the ten bolt heads with the outer line of five bolts loose - which would definitely be a problem. But your original post mentioned the outer four bolts loose, implying that you have the older fourteen bolt heads with the redundant four outer bolts loose - which is perfectly OK. You need to confirm how many bolts were tight on each side. If it's less than ten, that's likely to be the problem. I wonder if the engine has been rebuilt with the new heads by somebody who followed advice to leave the outer row loose?

ozrover · Post by **ozrover** » Wed Dec 13, 2006 6:15 pm

They are the late 10 bolt heads.When I referred to 4 bolts I meant 4 around each cylinder instead of the 5 of the early ones.I tend to agree on the stretch bolt theory meaning studs are the way forward.Still have concerns about the 3 liners being slightly raised even of its not a large amount.I would assume the decks are machined after the liners are fitted meaning they would have started out dead level with the deck.
Doug

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4.6L teardown - strange gasket problems

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