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Cylinder Head Woes
https://www.ausmini.com/forums/viewtopic.php?f=5&t=1530		 Page 1 of 4
Author:  Anto [ Sat Aug 14, 2004 3:02 pm ]
Post subject:  Cylinder Head Woes
Hi Guys,
I'm in need of some advice, following a blown head gasket on my Mini.
Yesterday on my way to uni I looked at my temp guage and realised it wasnt giving a readout. I pulled up at Autobahn to have a look. The short of it is the coolant was frothing and continually surging. Bugger, blown head gasket. The car still drove normally, the oil showed no signs of infection.

I have since stripped it down and replaced the head gasket. However, after I had finished it is still exactly the same! All I can assume is that the cylinder head is cracked, which is expensive and bloody annoying! So before I pull it apart again, is there any other problems that could cause this? The problem appears to only be in the cooling system. The oil is fine and the car drives the same, isn't any more smoky than usual.

At least I got to have a look at what has been done to the bottom end of the engine (I didn't build it). It is 20 thou over, and shows all signs of in fact being reconditioned about 10000 kays ago, as I thought (I just wasn't sure what the bloke meant by reconditioned). Interestingly enough, three of the pistons are installed backwards!

Cheers,
Anto.
Author:  drmini in aust [ Sat Aug 14, 2004 4:11 pm ]
Post subject: 
You better hope they don't have offset gudgeon pins- can't remember if 1098 does, I thought they did. I got one 1098 piston, will have a look... 8)

On 1275s it doesn't matter really. Piston is symmetrical.

<edit> Just measured a 1098 one, and you are lucky. Pins are central, so OK (phew) :lol:

It's the Hillman Imp ones (68mm) that are offset. They take your 1098 out to 1220.. :P
Author:  Anto [ Sat Aug 14, 2004 5:26 pm ]
Post subject: 
Yeah I figured that the pistons would have to be symmetrical - considering the motor runs fine. I think in this case the only problem is that the writing is upside down :)

I'm guessing I should start thinking about a top end rebuild - I have a pollution control 12G202 head and a few 998 and 850 heads, but none of them look especially good.

At least I know that the bottom end is relatively sound for some performance mods.
Author:  min13k [ Sat Aug 14, 2004 5:49 pm ]
Post subject: 
when the head gasket went last time did you get the head milled ???
makka
Author:  Anto [ Sat Aug 14, 2004 6:37 pm ]
Post subject: 
Makka,
The head went yesterday and since I had little time or money I just put a new gasket on - so the head hasn't been crack tested or milled. When the gasket went, the engine wasn't running hot at all, so I had hoped that it wasn't too bad.
Author:  drmini in aust [ Sat Aug 14, 2004 6:38 pm ]
Post subject: 
If you have a pollution control (smog) head, it is either off a 998 or 1275. They never made a 1098 one..

Check the number under the rocker cover... :wink:

1098 (12G202) head had bigger (and square) ports and inlet valves than the common 998s did. Bit less work to make them GO.. :wink:
Author:  Anto [ Sat Aug 14, 2004 7:03 pm ]
Post subject: 
The pollution control head is off a late model 998 motor. From memory it has 202 sized inlet valves (1.156"), whereas some had normal 998 inlet valves. My old Mini Kingdom catalogue lists the 998 smog heads as having 1.486" inlet valves :)

Maybe during the week I'll pull the valves out of it and see how bad it is. Do you know roughly the cost of crack testing, and milling the head would cost?
Author:  drmini in aust [ Sat Aug 14, 2004 7:16 pm ]
Post subject: 
If it's really cracked you should be able to see it.
Look between the valves, between valves and plug holes, and at the gasket line between cylinders.
Unusual for 202s to crack, I've never seen one go.

More likely it's just not flat now, and is leaking near #1 cylinder, below the thermostat area.

Did you clean the block well around the head studs? It's a good idea to pull them all out to make sure there's no burrs around the threaded holes- these can stop the gasket pulling down properly. Use a countersink bit in a drill, at slow speed.. :wink:

If you can't find a 202 head- I got one here, complete, stock, no cracks. But check yours well first- the freight would be a killer.
Author:  Anto [ Sat Aug 14, 2004 7:29 pm ]
Post subject: 
When I was cleaning up the head I didn't notice any obvious cracks - however, there was a fair bit of carbon deposit build up and I didn't have time to do a complete decoke. Looking at the old gasket, I couldn't tell where it had blown.

My block uses bolts, not studs, so the block face was cleaned up pretty well. Problem with bolts is, it is much harder to get the gasket lined up when putting the head back on. Maybe I can put one or two studs on to make alignment easier next time.

Perhaps I'll pull the head off, get it crack tested and skimmed (it has a pretty low CR at the moment so may as well raise it a bit). I've got new valve stem seals sitting here waiting to be installed.

Problem with crack testing is it's a real 'waste' of money. If it is cracked, you have to throw it away so the money spent on it was pointless, and if it isn't cracked then you didn't need to test it ;)
Author:  drmini in aust [ Sat Aug 14, 2004 7:35 pm ]
Post subject: 
You need to take it to a machine shop for grinding, so get them to do a `dyecheck' test on it, first....

Won't cost you much.

My 1098 has bolts too. I screw 2 studs in temporarily, 1 each end to line it all up.

BTW check the threads on the bolts are not stretched from over-tightening.. and wire brush any crud off the threads. They should screw right in with your fingers. I oil them on assembly.
Author:  Anto [ Sat Aug 14, 2004 7:46 pm ]
Post subject: 
Now that I begin to think about it, are A series motors known to get problems with air pockets, and hot spots? The coolant level had been getting a bit low, maybe that was a contributing factor?
Author:  drmini in aust [ Sat Aug 14, 2004 7:51 pm ]
Post subject: 
It's pretty hard to crack an A series head (except early Cooper S). They ain't Holden Grey motors..

I did crack a 998 one once, casting was faulty (hollow) between #1 & #2 cyls. It had 30 hours of porting done already. So, I gas welded it with bronze.. :wink:

What gasket did you use? Some cheapies are crap..
Author:  9YaTaH [ Sat Aug 14, 2004 9:16 pm ]
Post subject:  Corrosion...
drmini in aust wrote:
It's pretty hard to crack an A series head (except early Cooper S). They ain't Holden Grey motors..(wonderful old pieces of kit!!!! :shock:)

I did crack a 998 one once, casting was faulty (hollow) between #1 & #2 cyls. It had 30 hours of porting done already. So, I gas welded it with bronze.. :wink:

What gasket did you use? Some cheapies are crap..


Except when you have one of the old wax type thermostats and you are honking along...ouch....things can happen very quickly sometimes! :cry:

Anto I haven't said much so far because most times it will be the head (as described by Doc). Go back and have another look - you are not looking for the Grand Canyon - just the finest of hairline cracks.

However, I have this terrible feeling you may have a corrosion problem somewheres....if you have the head gasket refitted and it drives OK, I would maybe think about a coolant system pressure check....good luck (ask some of the old experts in the club before you panic too much - and in this case , I don't mean a drip under pressure!)
Author:  Anto [ Mon Aug 16, 2004 10:24 am ]
Post subject: 
What do you mean by a corrosion problem? I was thinking about a pressure test, I've also heard of making an air adaptor for the spark plug hole and filling it with compressed air, watching what the radiator water does.

I have it on good authority that a cracked cylinder head is the most likely problem, due to my symptoms - most likely at the exhaust valve. I guess I'll look into a replacement head, I wouldn't have thought it was worthwhile welding it (considering it is nothing special, the valves weren't *that* great and the guides were worn etc etc.)
Author:  min13k [ Mon Aug 16, 2004 11:42 am ]
Post subject: 
anto i have a few heads hear i have a bare head that was milled and all that needs to be put back together make me a reasonable offer and it is yours
makka
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