Cylinder head gasket

Post by **minor_hickup** » Sun Jan 14, 2007 10:26 pm

Last night I the cylinder head gasket went on the mog on a run back from Eastbourne. Number 2 cylinder is doing nothing. I managed to nurse it back home, albeit slowly. Im going to find a replacement gasket tomorrow. I just wondered if there was any tips or tricks I should know before I attempt this that the manual neglects to tell me and whether anyone thinks using a sealant is necassary or worthwhile?

Time to test out my brand new torque wrench!

Post by **Kevin** » Sun Jan 14, 2007 10:32 pm

A sealant should not be nessesary.
A piece of card with numbered holes in it for the push rods so they go back in the same order, a straight edge to check the head is flat and remove any carbon deposits at the same time, and if you have the time check that the valves are ok while you have it apart.

Post by **minor_hickup** » Sun Jan 14, 2007 11:06 pm

Yes I was planning to clean up the head while I was at it. Just wanted to make sure there was no withcraft involved! I realise a sealant shouldnt be needed, but wondered if any of the members thought it was either worth it as 'insurance' against a leak or actually a bad idea!?

Post by **bmcecosse** » Mon Jan 15, 2007 7:52 am

If it's just the one cylinder doing nothing - it's unlikely to be the gasket. The car can scarcely move when the gasket goes between two cylinders - and if it goes anywhere else it boils/loses all the water!! More likely to be an exhaust valve that's burned out - best to have another head ready - and stick that on.

Post by **Kevin** » Mon Jan 15, 2007 9:01 am

Just wanted to make sure there was no witchcraft involved!

You will be surprised its quite straight forward just take your time, and as halloween is some way of I dont think witches will cause any problems for you

Post by **bmcecosse** » Mon Jan 15, 2007 10:12 am

Sealant is a 'bad' idea - thin smear of grease on both faces is a 'good' idea. Running an engine with a known blown gasket is of course a very bad idea - it quickly errodes a gap in the head and the block - and if that happens then both faces need machining to make them perfectly flat again. Easy enough on the head - not so easy on the block. Let's hope it's an exhaust valve !

Post by **minor_hickup** » Mon Jan 15, 2007 5:14 pm

Cheers guys, I pulled the head off, it came off really easily. Its obviously been leaking coolant, its been using a fair bit lately! On number 2 cylinder, the exhaust valve has a 'pie slice' missing from it.

Post by **bmcecosse** » Mon Jan 15, 2007 7:38 pm

Phew - lucky day then !! The exhaust valve seat will be in a bit of a state - use another head if you have one.

Post by **minor_hickup** » Mon Jan 15, 2007 8:42 pm

Eek! I haven't taken the valve out yet as I don't have a replacement, the head is unleaded and I don't have a replacement. I just hope its ok. The valves are all rather proud from the head so it looks like I've loads of metal on the seats to sink them in further if needs be.

Post by **bmcecosse** » Mon Jan 15, 2007 9:00 pm

Another 'unleaded' head failure !! Hmmm. The valves will only burn like this if the clearances are allowed to close up - hence I suggest setting at 15 thou on exhausts - and regular checks to make sure they stay at 15 thou.

Post by **minor_hickup** » Mon Jan 15, 2007 9:23 pm

Has this broken as a result of getting too hot? I have been using 12thou for exhaust gaps. I only checked them about 600 miles ago, they've never really moved all the time I've had the car.

Post by **bmcecosse** » Tue Jan 16, 2007 10:14 am

The gap may have closed up - but the combustion chamber is obviously in a bit of a mess - whether this happened after the valve let go - or before, we don't know. Excessive oil can lead to 'detonation' - which may have damaged the valve. It may be the head suppliers will grasp at that straw - but I would refute strongly. If you don't want to make a fuss - just stick a valve in there and grind it in carefully.

Post by **IslipMinor** » Tue Jan 16, 2007 1:13 pm

Rather strange shaped combustion chamber?

Where did the head come from? Is this a 'factory' unleaded head? Where is the 'heart' shape? Or isn't there one on an unleaded head? My 12G940 unleaded 'converted' head has all the traditional shapes and hardened exhaust valve seats.

Also the valve seats look as if they protrude into the chamber with lots of sharp edges - or is that just the photo and lighting?

There seems to be a lot of oil in the No.2 chamber, are inlet valve stem oil seals fitted?

Finally - are bronze guides fitted? These are well known to pick up if not correctly sized.

Sorry about the multitude of questions, but the shape etc. has me puzzled.

Post by **bmcecosse** » Tue Jan 16, 2007 1:27 pm

The heart shape is there ok - nicely hugging the valves to make sure hardly any mixture gets into the cylinders !!

Post by **chickenjohn** » Tue Jan 16, 2007 1:54 pm

Yes grotty looking cyliner head! I do think with old valves, its worth treating the engine a bit more gently to avoid the valves getting burnt, especially with modern fuels.

Post by **minor_hickup** » Tue Jan 16, 2007 3:06 pm

Im not sure about the valve guides, they may be bronze. All the other cylinders look better than no 2 which is all fouled up probably from the drive home.

IslipMinor, the head is a 12g202 1098 head.

Post by **minor_hickup** » Tue Jan 16, 2007 3:08 pm

Can someone wxplain to me how the 'donut' oil seals fit? they seem to be all dropping out as I struggle to remove the exhaust valve with a next to useless valve spring compressor.

Post by **IslipMinor** » Tue Jan 16, 2007 4:00 pm

Wow!! I had forgotten just how close the heart shape is to the valves in the original head design! I looked for a 'sloping back', i.e. unshrouded look, and mistook the heart for a very uneven chamber roof - Dooh!

Start again.

Have you noticed any misfire under load, particularly when the engine is warming up, or pulling hard when warm? Any puffs of smoke under load?

I would:

Clean everything completely - incl valve stems
Check and replace any dodgy looking valves
Lap the valves in
Re-assemble with original stem 'O' ring seal (can't do any harm?) PLUS valve guide seals on the inlets ONLY
Make sure everything is well-lubricated
Re-assemble head to block and do the usual tightening and torquing routines
As suggested, set inlet tappets to normal 0.012", but for the time being exhaust to 0.015" (gives slightly longer on valve seat to aid cooling of valve)
Change oil and filter - use a decent 20W/50 oil like Duckhams or Castrol
Check/reset ignition timing
Start engine, warm up, check/reset mixture (err on being rich if in doubt) and re-torque head studs
If you have a water temperature gauge, what does it read once warmed up thoroughly?

If you are running the standard 95 unleaded, you could try and advance the ignition by 2/3°, or even a little more (unleaded burns slower, but hotter). Check for pinking, and retard if necessary, but not below the standard ignition setting - if you get pinking at this, there is another problem that needs fixing.

Same question once back on the road, are you getting any misfire under load?

Post by **iddy** » Tue Jan 16, 2007 8:10 pm

Make sure engine steady bracket and heater pipe are in place before tightening head down - something I've neglected to do in the past

Iddy

Post by **bmcecosse** » Tue Jan 16, 2007 8:41 pm

chicken - This is 'supposed' to be a no doubt very expensive 'unleaded' head - which should take everything thrown at it!! No point buying such a head - and then taking it gently. The little O ring seals just sit at the base of the collet groove - they often go soft and expand making them useless.
Iddy - my steady and water pipe go on above the head nuts - longer studs with additional nut on top - this allows proper torque to be applied to the head nuts - and then the holding nuts for these extras are just 'nipped up'.