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Head Gasket


Guest mariotech

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I suspect I may have a blown head gasket on Crackerjack. We had an overheat last weekend and when checked the same engine seamed to be overpressure on the fresh system which makes me think I have a blown head gasket. Now these BMW/Mercruser engine have six separate heads and gaskets and I need to find which if any is blown. There is no water in the oil or oil in the water so I intend to fit a clear tube where the calorifier water exits the heads and see if any air bubbles are present, after that I will compression test each cylinder. What are anyone's thought on these test or others I could try.

Jonathan :Stinky

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hi,

if yours are the d219 ,i,d just check the compresion of each,

the preassure s should be 348-377 psi(2400-2600 kpa)

the max preassure diff between cylinders is 72psi (500kpa)

ps, you don,t have your tappet clearances by any chance as they are same as miine?? :wave,

fittin a hose won,t show which head has gone,but there is a test you can do by sampling the coolant for fuel/oil but i can,t remember what it,s called.i have a check list at home for dealing with overheating mercs on pdf ,will try and dig it out tonight

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Hi Jonathon

Firstly you need to confirm the head gasket has definitely failed, the best option to test this is with a block tester, you can get these from snap on. it is basically a tube you fill with a blue testing fluid, place onto the filler reservoir header tank if any exhaust gas is in the system it will turn the fluid yellow. If this is confirmed you then have the difficult diagnosis of which cylinder head gasket is leaking. One possible way would be to pull out the injectors or glow plugs if you have them, the leaking cylinder may show signs of a grey/white colouration from the antifreeze. If not it would most probably be best to change all the head gaskets as others may have weakened during the overheat.

Unless it is a very severe leak it is unlikely a compression test will show up which cylinder.

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Hi Jonathon

Firstly you need to confirm the head gasket has definitely failed, the best option to test this is with a block tester, you can get these from snap on. it is basically a tube you fill with a blue testing fluid, place onto the filler reservoir header tank if any exhaust gas is in the system it will turn the fluid yellow. If this is confirmed you then have the difficult diagnosis of which cylinder head gasket is leaking. One possible way would be to pull out the injectors or glow plugs if you have them, the leaking cylinder may show signs of a grey/white colouration from the antifreeze. If not it would most probably be best to change all the head gaskets as others may have weakened during the overheat.

Unless it is a very severe leak it is unlikely a compression test will show up which cylinder.

That sound a little more scientific Colin. I have found this on Ebay.

http://cgi.ebay.co.uk/BT500-TEST-TOOLS- ... 483a3f755c

Would you normally get enough fluid to do two test and do you know the alcohol content of it should they both fail. :cry

My engines have glowplugs so inspecting these would be the next step. I had already discounted the compression test for the same reasons you have given as the leak if any seams small allowing the engines to run up to 3000 rpm with no obvious side effects.

cheers Jonathan

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This was the advice given to someone with the same problem on the same engine :roll: .

I am a great believer that if one leaks then eventually they all will.

VM mercs arent that easy to work on, look at the engine and study it carefully.

You have to remove the water rail from all heads, then the manifolds, look at the spacer under the bolts, each bolt secures 2 heads on each corner, as soon as the bolts loose pressure is off the gasket, the head is unevenly clamped down, it could distort the alloy head and displace the gasket, for the extra work and cost of gaskets as you will ahve to buy all new for the manifolds and water pipes its just not worth leaving them off.

If you are having them skimmed and I always do, make sure the machine shop take off equal amounts, otherwise you may get worse leaks than before.

There are also a few special tools you need to align the ex manifold to the heads as they move around on the face of the block when tighteneing up they need to be partially clamped to the exhaust manifold in order the get a good seal.

All sounds not as straight forward as a good old volvo eh.

Sorry Dave im so busy, otherwise id of come over and done the job for you.

Did you do a compression check, id do one before you strip it and get the valves checked and refaced if req while its all down.

Anyone know any good broads based mechanic with experience of individual heads.

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Hi Jonathon

You will have enough fluid for several tests with the block tester, you can get a bottle of scotch from Tesco's for under a tenner if it is bad news.

I agree if one has failed the others are sure to be weakened. Replacing all gaskets would be the best option.

Out of curiosity why do you feel the gasket has failed, I understand you say the fresh water system had over pressurised, on many marine engines the sealed water system run at a set pressure normally determined by the filler cap to increase the boiling point. In a similar way to cars. If you were in a overheat state the pressure would increase. I am not familiar with your engines though, so could be totally wrong. How bad was the overheat? Do you have any idea what caused the overheat? Did it blow out all of your coolant?

You will be surprised how hot an engine can get before damage to a headgasket occurs. Unless of course the headgasket failed first and caused the overheat.

cheersbar

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Hi Colin the overpressure was compared to the other engine after a run up the river. The overheat was very quick. When I first bought the boat the alarms did not work on the fly so I fitted two full size sirens behind the dash, lets just say running with it on was not an option and it was turned off straight away. The overheat sensors were also changed when I bought the boat. The engine lost about a litre of coolant.Certainly hoping it is not the gasket as first quote for parts ie head gasket manifold gaskets, tappet gaskets and water rail gaskets for one engine £499.34 that's from a BMW parts place still waiting to hear from Mercruiser parts. Anyone know of any good Mercruiser parts places.

Jonathan

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If it is just parts you are after then try CC Marine at Beccles to see if they are in stock, Would not order them through them though as parts seem to take around 4 weeks to turn up.

If they are not in UK stock and you need to order them I would do it yourself from the States, there are a few decent suppliers from there that will get your parts to you in about 7 days. Can't remember the names but sure someone will post them up soon.

Aquapart.co.uk stock Mercruiser stuff by mail order, most are after market parts but may be worth a call.

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Waiting to hear back from tricketts, Keypart may be able to help but need serial numbers.Aquapart don't do diesel. Will look up Prior diesel and contact them as cummins now own mercruiser diesel.

cheers Jonathan

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hi,

been offline for a couple days, may be stating the obvious but ,our engine,s started to overheat when under load,ie @over 3000 rpm ,ours turned out to be blocked weed filters ,you couldn,t see though the glass that they were blocked ,but when i took the tops off they were choker,if the overheat was very quick it could have been a blocked raw water pickup which dropped off when the suction preassure decreased when engine on tickover?,

if you need an expert ,Doug Ashley is your man tel 01493 488000 or 07818040711,before you buy 500 pounds worth of parts,he may be able to pinpoint the problem for a couple of hours work,he,s very approachable and has worked on mercruiser since he was a boy.

hope you get soeted soon

cheers trev

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Turns out a lot of Mercruisers and my BMW are actually VM engines (Vancini and Martelli ) So I have contacted two VM uk parts specialist and both keep all parts in stock at at least half the price. Happy days now just need to find a machine shop that won't charge 6 times more for working 6 single heads rather than one 12 valve head :grin:

Jonathan

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Hi there

As stated in another thread Engine Engineering in Cobholm are a good machine shop at a good price, Alan is the guys name, but you must stay on his case as he is always very busy and can easily be talked into leaving your job and starting another call 01493 442221

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Hi there

As stated in another thread Engine Engineering in Cobholm are a good machine shop at a good price, Alan is the guys name, but you must stay on his case as he is always very busy and can easily be talked into leaving your job and starting another call 01493 442221

I will be hoping to turn the whole job around in ten days so maybe need someone more reliable.

Jonathan

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|Hi Jonathon

If you are unfortunate and it does turn out to be the headgaskets, make sure you advise the machine shop to skim off the bare minimum.

cheersbar

Hi col I have the choice of three thickness's on the gasket 1.41 , 1.51 and 1.61 so will go middle if it has not been done before. I now have a compression tester to help make up my mind if its worth doing. Will be checking breather as well as the engine is definitely burning oil. With a bit of luck will be down to gasket or valves seals and not the rings.

Jonathan :Stinky

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Possible good news after testing today it looks like the exhaust/inlet manifold has cracked. This is hopefully good new as I have sourced one in Wales. Will be stripping it off tomorrow for a better look.

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Hi Jonathan

That will save a lot of work if it is the inlet manifold. Fingers crossed. I presume that the inlet manifold is water cooled.

Did you carry out a block test?

Why do you think it is burning oil, is it breathing heavy. or have you noticed blue smoke out the back? Didn't notice any unusual smoke at Easter.

cheersbar

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