Last chance saloon for Volvo Penta MD7b

[mdonnelly]

Mentioned on a previous thread that head gasket had gone twice in 2 weeks. The head has been skimmed at least twice and the block once and during a rebuild last year piston heads were also skimmed. Current thoughts are that there is over compression as a result of this, therefore blowing the gasket. Would it be feasable to have a gasket made, say in copper, thicker than the standard volvo head gasket to reduce the compression?

 

[oldsaltoz]

A thicker gasket may provide a little more clearance and possible prevent the gasget being damaged by the top of the piston, but would have very little effect on the compression.

The explosion and expansion that takes place when firing would a whole lot more than compression pressures anyway.

 

[2Tizwoz]

Do you have a picture of the gasket?

Where is it leaking?

 

[mdonnelly]

First gasket failed at one of the studs. Havn't removed the head to see where 2nd gasket failed but at the joint behind the engine there is oil and exhaust fumes leaking.

 

[2Tizwoz]

Is the cooling what it should be?

 

[sailorman]

Has he torqued the head bolts correctly

 

[mdonnelly]

Cooling system is fine. I believe the first gasket failed due to the head not being torqued down properly.

 

[sailorman]

Thats wot i said /forums/images/graemlins/confused.gif

 

[mdonnelly]

But, would overcompression occur due to the skimming and would this cause the gasket to blow?

 

[sailorman]

well you have skimmed the head twice & the block once. that could well be 15 thou or more.

 

[saltwater_gypsy]

Some arithmetic!!
The MD7A has a compression ratio of 20-24 and a stroke of 82mm.
This means that the clearance at the top of the stroke is 3.5 to 4mm.(probably less when the shape of the combustion chamber is taken into account). Anyway, 15thou is about 0.375mm so that in a worst case, the clearance has been reduced to 3.125mm and the compression ratio will have increased to 26.24. This is still not drastic and I don't think that a 9.3% increase in compression is going to wreck your engine.
You are dealing with a historic monument here so its worth trying again and in particular tightening the head bolts to the correct torque in the CORRECT ORDER. You can find the technical manual online via Google

 

[mdonnelly]

Thanks for replies. Having spent almost £2k in the 5 yrs of ownership of the engine basically I am loathe to spend another penny and really need to start a new engine fund. Probably looking for a panacea where none exists.

 

[sailorman]

i have that Tee Shirt /forums/images/graemlins/ooo.gif

 

[AlanRD]

Have you tried Hermatite yet? As stated on the previous posting it has worked for me, albeit with petrol engines.

 

[warrenmarkus1]

Yes you can get copper gaskets, but it would be easier to simply get a compression test done on your engine and compare the values against the manual.
IMHO the gasket failure is an effect of a problem, and not the problem