3C - Sources of Crankcase Pressure?

Haggis

Haggis

Hero member
Location
UK
Hi All,

Seem to be getting high crankcase BP even at modest rpm. Where's could it come from?

Spec - Series 1 180 - Ball Type breather (valve) - 120 type (short) cyl-liners

Valve timing bang on (F1 grind)

Breather ball OK (not swollen/bouncy)

Compression OK (171-174psi tested dry WOT)

Not done a leakdown check.

Any ideas?

Cheers

Paul H
 
Hi Paul,
'Seem to be getting high crankcase BP even at modest rpm. Where's could it come from?'
How do you know this? Oil coming out of breather?

Broken oil ring(s)
To much oil in sump.

Cann't think of anything else at the moment,
Andy
 
Thanks Guys, the end of the breather hose is weter than I've know it before (not quite dripping but close). The oil that comes from the head crack is clearly under some pressure, nut a dribble, but a fair flow.

Exhaust colour is darker and oilier than normal.

Suspect rings, but confused by healthy compression reading. (171-174psi all 3)

Paul
 
Hi Paul.
The top two rings will still seal therefore giving good compression.
Why not attach a catchment bottle and go for a ride.Check contents on return?
Down pipes sealing in head OK?

Paul if you decide to take motor out,give me a shout and I'll pop over and give you a hand to lift it out.Your in Bromsgrove yes?

Andy
 
I've just had a another look at photo of crack - crack is on the surface and down the side of where cam cover sits yeah.
I once had a allen bolt that held down cam cover pull out,the oil pissed out.
I would say the back pressure and the amount of oil pissing out off crack are un related.
If the ends of exhurst are oily then the down pipes are not sealing,or oil coming down exhurst valve,or oil coming up pass oil ring(s).
Might be worth checking exhurst ports.

Andy
 
Rings themselves will be fine, hence the good test readings, it's usually the top ring groove that's worn.  Probably won't show up in a leakdown test either...  Allows oil and/or compression pressure to pass in enormous quantities above certain rpm.

piet
 
You might want to try the compression test again with the engine warm. Then two readings per cylinder first one dry then the second wet, the second reading should then be higher. If not then your rings are shot and the reason why compression good on the test you did is that the oil bypassing.

 
I think you have it backwards Brett. If second compression test (with oil) is significantly higher than the first, it indicates leaking rings. If a low test doesn't improve with oil, then it indicates poor sealing of valves.
 
yes and no I guess whilst correct in what you say in that if low it doesnt improve the usually indicates valves... you can also get situations where if you have oil in the cylinders from worn rings you can get false reads on your dry testing.

Then again I have only been a mechanic for near on 40 years so what would I know. Bottom line I guess is if he has crank case pressure then it can only be coming from one place at the end of the day.
 
well we can all be wrong cant we?

I spoke to a motor mechanic friend a day or two ago, he is 74 years old and exteremely well thought of locally as being able to work on and fix anything that fails the main dealers, electronoics, engine management,autotrans, fuel injection you name it, and in passing (me and my sons were erecting a full house scaffold for him) I mentioned that the tow bar on my Chevvy truck was three inches too high for the caravan, and since its a twin axle its doubly important to have the tow ball the right height, he said this was an easy fix, just unbolt the two fixings for the tow ball and fit it upside down, then rotate the tow hitch on the caravan 180 degrees, and hook on from underneath !!!! this was deadly serious and he took some convincing that this  would be very dangerous practice, because
the draw hitch weight on the caravan has to be on the top of the ball with the socket engaged, as the "tongue" underneath is a safey device to stop it coming off, if for any reason it becomes "unloaded", there is a flat under the ball for this to locate under but not actually touch(clearance) so if its upside down, that tongue becomes load bearing and the contact is flat to flat not ball to socket, so I dont actually have all that much faith in him now.
CLEM
 
You lost me there Clem! But you will remember when you helped me with my Jota when It had to come apart ....not least, apart from the pulled studs, because it kicked oil out of the breather nicely aimed at the rear tyre? Looked ok but pistons were well worn as diagnosed by yer man in Tatsfield.
Hi Paul! Sorry to hear of this. Not for general sale but I have a spare set of barrels and just worn in JE pistons with them if you have to go that route.
Nick
 
Hi All, sorry for the late reply - away for the bank holiday weekend.

Thanks Nick, very kind of you, I'm trying to find some spanner time - will PM you.

Thanks Andy, I'm in Lichfield now, but can get the bike down Bromsgrove way easily. As above, I'll see if I can clear the decks of work and get some spanner time. I'll whip the downpipes off and check for a good seal. Yes the crack is in the head - the cam cover is fully seated and is sealing OK.

Thanks Piet and Brett, yes, I suspect rings/groove are contributing. Had to put in the orig Mondials back in at last build. Groove width was OK, but a little wide at the time.

Cheers guys, Paul


 
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