VOLVO Penta MD7A

[tutts]

Hi I have a problem with my MD7A engine
The engine air intake alternates between sucking air in and blowing
out engine gasses. This gas smell ends up in the cabin
I have had the problem for some years, so ayear ago I hade new
rings,shells and valves reground in a general overhaul but still
have the problem
Is this normal for the MD7A, if not can anyone advise how to stop it
Thanks

 

[tomboy352]

Volvo have a very good technical help line. You might contact them. It sounds as if you might be exhausting through an inlet valve/or headgasket/or cracked head. A compression test should either confirm or rule out such a problem. If the engine only misbehaves when hot, it might also suggest one of the above.

 

[tomboy352]

Volvo have a very good technical help line. You might contact them. It sounds as if you might be exhausting through an inlet valve/or headgasket/or cracked head. A compression test should either confirm or rule out such a problem. If the engine only misbehaves when hot, it might also suggest one of the above..

 

[johnsomerhausen]

When you had your rings changed, did they check the valves ? I had a similar problem three years ago, but only when the engine refused to start and it disappeared when when the valves seats were rectified and new valves put in.
john

 

[vyv_cox]

I don't know the engine, but it sounds like a problem with the crankcase breather valve. Don't even know if you have one but it is worth having a look.

 

[DaveA]

Dont know the engine but - it sounds like the valve clearance is varying, this can happen if shims are used ,if they have worn tapered ( uneven ) if the rotate any
clearance you set can reduced totally .

 

[Guest]

I had a similar problem with my Bukh engine (not a Volvo but an engine is an engine). Like you I feared expensive things but the cure was actually very simple. Where the exhaust gas and raw water combine in a 'pong box' an internal hose had collapsed and partially blocked the exhaust, thus I was getting back pressure in the cylinder as the exhaust gasses were not venting properly which resulted in 'blow back' when the inlet valve opened.

 

[Trevor_swfyc]

I thought you were having a laugh when I first read your posting. Are you not affected by the exhaust fumes, dizzy spells and feeling faint etc.
As you have had the head off you would have noticed problems that could cause your problem ! (1) Weak inlet valve spring. (2) Damaged head. (3) Badly adjusted valve clearance on inlet valve. (4) Damaged valve / seat.
The idea that the exhaust system pipe could be faulty not sure I understand this mine is about 3" diameter and reinforced how would this collapse ?
Then I have got to agree with the posting that suggested crankcase pressure but this would have been reduced when you had new rings fitted, was it ?
You did not refer to the performance you were getting from the engine, does this problem have an effect on ability to start/run/rev etc.
Finally silly question you have not got a valve lifter active have you !

All the best.
Trevor (Volvo 2002 owner)

 

[scottie]

you could check the valve stem seals
or it could be worn valve sleeves