Head gasket job on M103 3L, pointers anyone?
Greetings...
I have the intention of changing the head gasket on my 300 straight-six in the coming weekend, and not having done the job before, I was looking for some things to be wary of.
Reason for change: engine has done 102k, and about 3k ago was leaking coolant/steam between cylinder head and block, (requiring frequent coolant top-ups) just below exhaust manifold, towards rear of engine. Some radiator sealant put a stop to that, but I don't want to blow the gasket later on, as that must have been the source of leak. Fortunately no blue smoke or signs of mixing oil/coolant yet.
I have the XZN bits to undo the cylinder bolts, and a new gasket and bolts/washers for the head, and cam cover, and new rubber seal for the cam cover (again another reason for the job, as oil leaks from there as well), and the loctite sealant to cure that leak.
I am yet to get an angle torque wrench, and the tightening torques/instructions, and I understand the gasket is easily damaged in-situ so will be careful with that.
I envisage the process to require removal of the exhaust manifold first, then plugs/leads/distributor, and cam cover. Any best way to keep the cams in place? I hope to have the GWOA tech rep with me in the afternoon to monitor progress and advise on procedures.
Hoping to get it done in a day, possible run-over to sunday, if anyone has the parts from the engine manual (103.987) that cover this, they would be very much appreciated! I have the workshop manual, but only the general maintenance/brake sections.
Thanks in advance!
Anybody is welcome to come and watch of course...to document when things go horribly wrong. I'm just off Junction 23 on the M1.
Did this on my 300SE. Dont expect a days work, the head might need skimming, may need exhaust valve guides doing etc. After all, she will be stripped, so do it right and only have to do it once :wink:
I didnt need skimming/guides, but replaced the valve stem seals as a matter of course. If the dizzy etc is the same, watch for the rotor arm carrier, can be stuck, had to break mine to get it off, there are 2 different ones so have your dealer order both!!!
Check your hydraulic tappets, replace if tired. Check timing chain, replace the tensioner as a matter of course, check guides for wear or brittleness.
At the time I didnt have the w126 workshop manual, but used the w124 Haynes book, covers that engine nicely.
It's a nice job to do, the inlet manifold fixings I seem to remember as awkward to access, prepare for the unexpected then the unexpected cant happen cos it wasnt unexpected?!?!!?
Don't try to do it with the manifolds on, its too bloody heavy!!!!!
Just have some really good sleep the night before, give yourself plenty of time and follow the manual step by step, double-checking as you go along and all will be fine.
best of luck!
Finalllly got this done last weekend, what a pain, but definitely worth it.
Had the able assistance of an experienced merc mechanic, and his tools, I think that was the only way we could finish in 2 days (sat around 10hrs, sun 12hrs!).
We renewed the following:
cam cover seal, cam cover bolts, head bolts, exhaust and inlet manifold gaskets, exhaust manifold studs and nuts, front engine cover oil seal, and of course the gasket itself, after cleaning up the head and block.
I'll try posting some pics later..
The problems we faced were:
-worn out nuts on the exhaust manifold (size 12 i think, but easily worn smooth if tight, due to corrosion)
-one broken exhaust stud in head (fortunately came out with stud extractor after some drilling)
-cracked some of the brittle vacuum hoses in the inlet manifold and to the cam cover, they are mostly 3mm hoses so bought replacements and will fit them later, nothing major, only effect is on transmission upshift (jerky!), they were probably brittle due to old age and engine heat when the engine was losing coolant.
-the exhaust downpipes (we had to remove from manifold due to manifold nuts not coming off in place), are a PAIN to remove, you need a lot of extensions and u-joints at least 3/8" drive, and to make it easier remove the inner wheel lining on that side, then the exhaust shield (a metal piece held in by 5 small bolts and 1 big bolt) to gain access, also don't forget removing the lambda/O2/temp sensor (i forget which one).
-the inlet manifold is huge, best leave it in place..we tried removing it but it wouldn't come off.
-the allen bolt that holds on the fan was apparently put on with a threadlocker (WHY??), making it a royal pain to remove, this is not needed here, just tighten it properly.
be extra careful with the vacuum hoses and removing them from the head/manifold, unless you already have replacements!
having said that, the engine runs beautifully now, no loss of coolant, or oil so far, hope the 2 weeks at the airport won't affect it too much!
if anyone has any questions on the job now that it's been attempted, let me know by message.
A great big THANK YOU goes to our technical rep Rakesh, without whose advice and help this would have not happened, thanks again!
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Thanks for the input, much appreciated!
I've delayed it a few weeks to get some more bits and pieces, and since then I now have the valve stem seals and new gaskets for the inlet/exhaust manifolds (some of the exhaust ones are on the way out), the short rubber hose between the thermostat and head (precautionary measure), and some rubber seals for the pipes that run across the front of the engine (that will need replacing upon removal). Of course that is aside from the rubber valve cover seal and front-of-engine seal..which is the source of the oil leak in the first place.
Also got a valve spring compressor to do the stem seals. The only other bits I need are the valve re-seating kit (halfords?) and some coolant/water to change the coolant after the job is done (along with the oil).
Here's hoping for the best...