MD7a cylinder head gasket gone after recent rebuild - Why ?

[nickdick]

After a complete de-coke and rebuild of my Volvo 2 cyl. MD7a and about 40 hrs use the gasket has burnt through to one of the water gallery holes about 15mm from the cylinder wall. Bucklers Hard Boat Builders did the rebuild so don`t think it`s shoddy work. Any ideas about how this can happen. Lots of water out of the back and no reason to think it`s over heated.

 

[michael_w]

Did they make sure that the head hadn't warped?

 

[savageseadog]

It's got to be workmanship. The head should be skimmed and pressure tested. Other than that cleanliness of surfaces, proper thickness of head gasket, new head bolts proper torqueing etc.

 

[DinghyMan]

Don't know about the specified engine but some heads need retourquing (?) again after a few hours running - maybe yours is one that does?

 

[Topcat47]

There are a numbr of reasons this might have happened, apart from poor installation, which has to be top of your list. It's much more likely to be the result of impropper installation than almost anything else after 40 hours. Most head gaskets need to be torqued down after an initial running period, but 40 hours is a bit tight for that.

Impropper installation includes the inclusion of debris between the gasket and the head/barrel, incorrect torque settings etc....

An engine of that age, if it has failed before in the same place in the past, may need to have the head or even the block re-skimmed. We used to get around this in the sixties by fitting two head gaskets, but that was in petrol engines, diesels are a bit more critical in compression ratios.

When the MD7 was designed, head gaskets were copper/asbestos or even in some cases solid copper. A lot of modern replacements are aluminium/some other fibre and these do not work as well. An old solid copper gasket may be annealed and re-used, but if it is re-used without first being heat treated, failure is almost a given.

Finally, if the engine has been run when the water pump is not working propperly, that too can result in failure.

None of this gets your engine working. If it were mine, I'd have the head off and check the head and block for flatness. and try to get a copper or copper composite gasket.

 

[nickdick]

Thanks all, so far. I should say that the head was skimmed as part of the process of de-carboning 40 hours ago and it just come back from another skimming to-day before being re-fitted. The original workshop manual doesn`t mention re-tightening head nuts afetr certain amount of hours but this might be worth investigating. Thanks again.

 

[Bilgediver]

Skimming the head will by virtue of the operation restore it to a flat surface and so take care of any warping present. You have really no choice of gaskets as they will be Volvo volvlo or Volvo though those from some sub contractors vary from others in the MD2 range of engines.

Yes regardless of the manual it is always a good idea to retorque and I usually do it after a few hours. I also check the torque annually and it is surprising how the tension eases with time.

I suspect your problem is the flatness of the block which was not skimmed or the head gasket not installed correctly.

the head could possibly be checked using a straight edge and feelers.


John