Cylinder head gasket replacement - difficult job.

[herbiemercman]

Hi Guys, I have just completed the job and it has been hard work and frustrating. You need the special tools, the parts and the know how, also with it being an NAT there are modifications to wiring and pressure pipes.

I downloaded a OEM workshop manual and this was paramount.

 

Disassembly was ok just three problems:

 

1. The crank shaft pulley was seized on and i could not budge it with a 5 ft bar and 340 NM's torque, i contacted a friend who is my Merc specialist, he said jam the wrench bar into the hole in the chassis and then crank the engine, it worked, out came the massive bolt, BUT, the pulley would not come off, so blow torch and tapping with a hammer and carefully levering, it eventually came off.

2. Could not figure out how to remove the timing belt tensioner, once we removed the crank pulley then we could remove the lower timing belt cover and you then see the 3 bolts that hold the belt tensioner.

3. The starter solenoid 12v supply plug is impossible to gain access to without lifting the car, also the rear knock sensor plug is difficult to reach and vunerble to be damaged, mine got caught by somthing and the head broke off. Had to order two new ones and this stopped the reassembly job due to delivery time from USA,# 30 each, the UK sensors are #196 each and 7 days delivery. I have re rooted the supply wires to the starter and the knock sensors which eliminates this problem.

I will do another thread about the re assembly. Herbie.

[tintinmt]

Sounds like a mission.

[badboyz00700]

Sounds like you know what your doing

[Scooter]

Could you clearly see the gasket failure area out of interest. Years ago I took apart a blown NA motor and the cylinder head gaskets are layer steel ones so it would be interesting (well to me!) to see the failure area.

 

Hope if all goes smoothly from here, did you fit the thicker gasket in the end?

[Style]

Do you have to get the crank pulley off just to get to the headgasket? Not something I've done but wondered if it could be done by just getting the engine to TDC and getting the belt off the cam gears?

[WayneW]

How to clean enough the block and head surface without machining them ?

 

I've always asked myself how a new gasket could be 100% effectiv in that case… ?

[Scooter]

Do you have to get the crank pulley off just to get to the headgasket? Not something I've done but wondered if it could be done by just getting the engine to TDC and getting the belt off the cam gears?

 

Yeah if you undid the tensioner you could, but if you want to renew the cambelt it has to come off. Also you might not be able to re-tension the belt properly without the lower cam cover off (can't picture the layout in my head), and that won't come off without the crank pulley being off.

[Scooter]

How to clean enough the block and head surface without machining them ?

 

I've always asked myself how a new gasket could be 100% effectiv in that case… ?

 

I think with the block being steel it's not normally machined? just thoroughly cleaned? Head when off is then normally inspected for flatness and skimmed if necessary from what I've read?

[Mk4Gaz]

I think with the block being steel it's not normally machined? just thoroughly cleaned? Head when off is then normally inspected for flatness and skimmed if necessary from what I've read?

Pretty sure the blocks are cast iron, and you'd always want to check it for flatness, to make sure it doesn't need decking.

 

I wouldn't just skim the head and chuck a new gasket on, without being sure that both mating surfaces were dead flat

 

 

[Scooter]

cast iron yes I agree sorry, not aluminium is more my point like some engines have and if the ali head is measured and doesn't need a skim or only a very minor one then I'd think the cast iron block can't have warped/changed from its original state given the vast difference in strength/elasticity/melting point of the cast iron in comparison? Won't hurt to measure it but I don't think it's common to need decking/maching of the block on these engines is it?

[Mk4Gaz]

cast iron yes I agree sorry, not aluminium is more my point like some engines have and if the ali head is measured and doesn't need a skim or only a very minor one then I'd think the cast iron block can't have warped/changed from its original state given the vast difference in strength/elasticity/melting point of the cast iron in comparison? Won't hurt to measure it but I don't think it's common to need decking/maching of the block on these engines is it?

I think that for a cast iron block to warp, you'd be doing well [emoji23]

 

But always best to err on the side of caution, as it's definitely something you don't want to do twice [emoji106]

 

 

[herbiemercman]

REASSEMBLY: KEY CRITICAL THINGS TO GET RIGHT.

 

1.Checking the flatness of the head and the block, took the head to a friend of mine who has a precision engineering works, i watched him put it on his 'co-ordinate measuring machine', thankfully the flatness was only out .001inches, and you are aloud .004 inches, (0.1 mm).

I did not check the block as it is almost unheard of for this to bow.

All surfaces were cleaned to a mirror finish and the replacement gasket was the thicker high performance one cost big bucks.

The pistons etc had only light carbon deposits and were cleaned with 'scotchbright' cloth and WD40. The no1 pistion was like the bottom of an electric kettle with calcification precipitate,instead of carbon, this was were the gasket had failed.Prior to any further assembly all cylinders were checked for compression, all ok. The 14 off head bolts were all replaced with new ones and the undoing and re tightening procedure of low,med,high was followed.

 

2. The camshafts, these are a real pain, everything was marked and the undoing and tightening procedure is critical and time consuming, you have to tighten each shaft in the low,med and high torque settings and then completely slacken them off in the same sequence, then you have to rotate the shaft 33 deg, this is repeated three times, apparently the process is meant to harmonize the molecular structure.

 

The two end oil seals are replaced and the end bearing caps have silastic sealent smeared underneath them.

 

3. Valve timing and replacement belt and idler, this is quite easy but you need to compress the belt tensioner in your vice and fit the holding pin which keeps the spring compressed, you just remove the pin once it is in place.

We rotated the crank shaft pulley to TDC mark and lined the camshaft pulleys up with the marks on top of the casing.The belt was then fitted, we rotated the engine by hand to ensure all internal components were clearing.

 

4. Tightening up the crankshaft pulley, we had the same problem as we had trying to undo the retaining bolt, it has to be torqued up to 340NM and even with the car in first gear and the wheels chocked, we could not get more than 200 NM, i tried putting some heavy duty 'mole grips' on the outer edge of the 12mm thick pulley and jamming the grips against a bose and a knut on the block, the grips dug in and did not slip, so we achieved the 340NM.The OEM's have a special tool for this problem, but try and find one.(lol).

 

So that just about covers it, i could do another head gasket in half the time now, but it is difficult, nerve wracking at times, expensive and hard on your back, easy to see why garages charge between 1,400 to 2,000 pounds for this operation.I have shelled out circa 500 pounds just for parts etc. I hope all is ok now and if it fails i am buying a box of 'Swan Vestas'. Herbie.

 

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Edited July 26, 2019 by herbiemercman (see edit history)

[Scooter]

Good work getting stuck in, I have had that lower back pain many times reaching over the engine bay for various jobs. It creeps up on you and it's often not until you stop that the aching/stiffening kicks in!

[tintinmt]

Thanks for taking the time to write this up. Sincerely hope that incendiaries are not required.