The theory is the better compression once a head gasket is done can bring out a worn bearing and then give you rod knock after a few hundred or so miles once all back together

^^ this - every time

it's a new built engine with run in miles and a bit of mapping, it's done nothing and we're talking about head gaskets ??
Trev

Really hope all is OK Rob; how the he'll did this go from a cooling thread to engine out?

bring out a worn bearing ?

so the bearing is already worn and needed replaced no ?

of course if you try to drive with it blown your asking for trouble.

I would say thats got to be pretty rare tho

plenty of headgaskets go and get replaced with no bottom end rebuild and never return.

Has to be a faulty bearing or setup in 1st place imo & will be rebuilt because they are apart. Not because the head gasket failure killed the bottom end.

If any water makes it into a block with head gasket failure or even blowing, 99% of the time you will find score marks on bearings! So is adviseable to check and replace, at same time check heads (cam housings) for score marks too and most likely polish out of 1500 grit.
^^^^thats based if you like to do job as anal as most enthusiasts.
Most don't, and yes never have trouble, but that never means it's probably been sold of changed car etc, doesn't mean that it won't have issues later.
Do it the right way, or fix it quickly and cheaply to get it on road is the choice of you.

Mine only blew a little bit of gasket near turbo side, but I was planning to do bottom end, bought all parts ready, but then decided on a fresh 2.1 instead.

But rob, ignore all these posts until you have fully checked car over.

Yea but if your that anal then you would be stripping the engine every season to replace bearings & check things over anyway

No point in replacing parts just for the sake of it tho.

Heads would usually come off for the gasket to be replaced so yea check them but the odds are they will be fine unless cars been abused when broken...

If your building an engine up thats scored then you shouldnt really expect it to last long so pretty basic that.

You says yourself most don't and never have trouble :)

I said 99% of time if water has entered block then the bearing will have taken some damage

Up to the user on what they replace, but ill take note of not to buy an engine from that user

Subaru engines tend to have head gasket failure when the heads lift, which presurises the water system. They don't tend to put water into the crankcase like a lot of other engines do when they have head gasket failure.

You have to asses each failure on its own merits, blanket statements about what needs to be done isn't much help.

Whether you choose to do it or notnis up to yiu, but given you risk a whole engihe for the price if a few hubdred quid its your choice.

I know people who have found out the hard way and its cost them the thoisands for a second rebuild.

Yes the blanket statement about gaskets blowing killing bottom ends was my issue.

As if majority of head gasket failures result in bottom end failure.

The poor folk who have had gasket failure fixed fine and read it thinking their bottom end will grenade on them.

I am all for doing a job properly, but not for doing unnecessary work :)

Should be up to the competant person doing the build.

Strip & Inspect

If a part has failed or is worn then replace it.

Any decent engine builder wouldn't put their name to something which wont last a few oil changes.

Not worn to need replacing anyway no, It wore in time with the compression naturally lowering over natural wear n tear but to suddenly have more compression and strain on it when hg is done can sometimes then make a big end with 100k on it let go.


Not all do and some dont.
But some do


same with most things on these engines :lol1:

Why would the compression ratio change if you use same thickness gasket or compensate for any decking skimming ?

Obviously a 100k engine would benefit from more than just gaskets but to say it is a must on majority of head gasket failures just isnt true unless car has covered moon miles.

Got to draw the line somewhere or every gasket failure would be solved with a rebuilt cdb & 14mm studs lolol

Didnt say it was a must

It's a possibility

You do or don't

If they do or don't fail that's the theory behind it

:brickwall
Read my first post, 'check and replace'. Basically same as what you just put!
Seems your looking for something that's not there :thumb:
You basically disagreed and questioned my theory, then just agreed lol

Any progress rob

No what i disagree with is saying most if not all (99%) headgasket failures need bottom end replaced which is just not true,

It comes across as tho you shouldn't touch a car which has had gasket failure and no bottom end replacement because it will grenade, which just isn't fair to say,

Blanket statements help nobody, as does throwing away perfectly good parts because scoobynet says so.

You quit trying to get this back on track...........


On another side note did you ever get that map fixed ?

Sigh! No! A bottom end replacement is new pistons, crank etc which I have not said a bottom end replacement, that's come from you not me, I'm taking about bearings here when water has entered block!
You're assuming, I never said they 'NEED', what I did say though is IF water has entered the block due to hg, then 99% of the time you will find wear on bearings and cam housings. That is exactly what I put.(which is true if you check yourself and you will see, water and oil does not make a good lubricant fact).
So it's advisable to check and replace and repair if nessaserly.
If water hasn't entered block then it may well bo ok to just fix without pulling block apart assuming it's just that.
As said, you're trying to assume I'm saying something which I haven't if you care to read my first post clearly.

I give up, if you can't understand what I'm saying, but instead assume I'm saying something else, which you have done with rig also.

Which is not as common as being made out.

As if gaskets and bearings should be sold as a pair...

I don't understand where the water gets in ?? wouldn't a small amount be burned off, a larger amount cause hydrolock ?
Trev

My old hawk sti done it's head gasket @60k and was only skimmed/gaskets replaced (by the guy who built/owns the 10sec OMA Legacy so he knows how to build them)

it was still going 4yrs afterwards and it was a daily driver

On boost the gases/oil will get into to water and then off throttle when hot I presume it would cause a reverse effect no?? Either way it gets in somehow, when you drop the oil, why does it turn milky? Is that not water contamination?

I wouldn't have thought it could get past the piston, the very high temps at the cylinder head, unless there was a fair amount and lubrication would be the least worry. But if coolant is in oil it must come from the jacket.
Trev

No.

When a head gasket fails the cylinder pressure is enough to pass gasses into the water, depending on how severe the failure is you may blow a whole section of gasket material, so when the engine is switched off some water can enter the bore.

Most failures start by lifting the heads, which gives a small pathway for the gasses to pass into the water, but no water will flow the other way, even with the engine switched off because the cylinder pressure was required to overcome the gasket seal.

The oil way passage to the heads is on the outside of the water ways, as is the oil return path, so you never get oil and water mixing unless the head gasket is absolutely annihilated and you have an open path without the head lifting. Water in the oil occurs when the head gasket material between bore and waterway is destroyed enough to leave an open path for the water to drain through when the engine is switched off.

This is why its a good idea to get head gaskets replaced when you start to get issues with the water pressuring under boost, the longer you wait the more likely you will damage the gasket enough to allow the water to pass into the bore when switched off. You can often make it last longer by running lower cylinder pressures so you don't break the seal until you can get it fixed.

Take a look at the photo of my engine block and head gasket, top left is the pathway for the oil feed to the heads. The two big openings at the bottom are the oil return paths from the heads into the crankcase.


https://cimg3.ibsrv.net/gimg/www.sco...4b2bd4eb80.jpg

An issue the early 2.5's used to suffer from was water leaking out of the external part of the gasket to the outside of the engine block, this wasn't a traditional gasket failure issue, the fix was to put a bottle of radweld into the cooling system at every service. :D

The whole thing about rattling engines after replacing a head gasket is from old classics. It will start relating to newage cars now they are getting long in the tooth, though.