gaz22
regular
Reged: 03/07/2008
Posts: 13
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Can anyone with a VP 2001 engine comment on back pressure from the engine, this one has just had a top overhaul reground valves etc, the rocker box and joint are aligined correctly to allow the engine to breathe normally but it now seems to have more back pressure than before.
Can anyone comment on this or tell me how to somehow measure the back pressure 
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From the only Kingdom
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VicS
regular
Reged: 13/07/2002
Posts: 9247
Loc: Home: Kent. Boat: Chichester
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Not quite sure what you mean by back pressure.
From the exhaust system due to restriction to the flow which can be caused by collapsing hose or choked up water injection elbow.
Or do you mean a build up of crankcase pressure due to wear of piston rings and/or cylinder bore and/or restricted crankcase breathing due to incorrectly fitted top cover gasket.
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Old Chemists never die, they just fail to react
Edited by VicS (05/07/2008 11:35)
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gaz22
regular
Reged: 03/07/2008
Posts: 13
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Yes, crankcase pressure now seems to be exessive through the dip stick or the oil filler cap,
The head was recently removed for the valves to be reground, the engineer who did the job said the piston bore was ok, the engine starts and runs ok and the top cover and joint is aligined ok
have been told to run the engine at 90% in gear for a couple of hours to let the engine run its self in again, not sure about this seems a bit drastic.
cheers for any help or suggestions
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From the only Kingdom
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Bilgediver
regular
Reged: 06/06/2001
Posts: 1400
Loc: Scotland
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Volvo engines usually manage the crankcase pressure by breathing to the intake on these small engines. SOmetimes this is an external hose to the aircleaner however they have also utilized a system of direct breathing from the pushrod space to the inlet bore above the inlet valve.
If your engine has the latter then maybe the breathing valve is partially blocked or stuck....Vic is a dab hand for finding manuals....maybe we can check this however it might require the head to be removed 
These systems can cope with quite worn engines so seems in your case it just isn't doing its job.
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Eastern Scotland and beyond.
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aluijten
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Reged: 26/10/2004
Posts: 429
Loc: Dordrecht, The Netherlands
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A common thing to go wrong with these engines is that the gasket between the cam-shaft (actually rocker box) cover and the cylinder head is mounted in mirrored way. There is a small breather hole that leads the crankcase pressure to the inlet, this hole can be blocked if the gasket is mounted wrong side up.
Cheers,
Arno
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VicS
regular
Reged: 13/07/2002
Posts: 9247
Loc: Home: Kent. Boat: Chichester
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Quote:
There is a small breather hole that leads the crankcase pressure to the inlet, this hole can be blocked if the gasket is mounted wrong side up.
That is what I was referring to when I said "restricted crankcase breathing due to incorrectly fitted top cover gasket"
I did not want to labour the point as Gaz22 seemed to be saying that he knew it was correctly fitted. It is mentioned in the Workshop manual Paragraph 21 in the "assembly" chapter. It is something that should be rechecked I think,
I don't understand the suggestion that it should be run at high speed for a period. After a re-bore one would normally follow a running in procedure of gentle running for a period.
Even if the bores are OK it could still be problem with a piston or rings, but let's not go there just yet.
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Old Chemists never die, they just fail to react
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gaz22
regular
Reged: 03/07/2008
Posts: 13
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cheers the top cover gasket is fitted correctly and the hole is clear inside the top cover
Would need to find more info on the hole in the head with the breather valve as bilgediver said.
if the older style engines had a pipe to the air cleaner where did it suck from (a fitting on the top cover??) this may be an option to let me use the boat this summer and remove the cylinder head this winter if the breather valve is blocked.
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From the only Kingdom
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VicS
regular
Reged: 13/07/2002
Posts: 9247
Loc: Home: Kent. Boat: Chichester
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The earlier ones that I know about had a hose from the oil filler cap to the air intake "frying pan" hose 31 in This diagram of an MD11C for example
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Old Chemists never die, they just fail to react
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Bilgediver
regular
Reged: 06/06/2001
Posts: 1400
Loc: Scotland
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There is a small breather hole that leads the crankcase pressure to the inlet, this hole can be blocked if the gasket is mounted wrong side up.
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I think this may be referring to the cylinder head gasket....Bells are ringing 
I modified an older MD 2 by replacing a blank flange on the upper crankcase with one fitted with a 1/2 " pipe stub which was connected by hose to the air inlet.
Maybe you have a convenient blank as otherwise you might have to get your fella to remove the head and fit a new head gasket the right way round ..
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Eastern Scotland and beyond.
Edited by Bilgediver (06/07/2008 10:39)
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VicS
regular
Reged: 13/07/2002
Posts: 9247
Loc: Home: Kent. Boat: Chichester
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Quote:
get your fella to remove the head and fit a new head gasket the right way round ..
Surely this is not a problem with the head gasket. Won't the crankcase breathe up to the valve cover via the whacking great space where the push rods come through. You cant block that off with the head gasket!
This diagram may not show the push rods but they come though the opening nearest to you in the gasket.
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Old Chemists never die, they just fail to react
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