Crankcase pressure

Yos_Sam

Yos_Sam

Registered
Hi, after I've rebuilt my 99 gen 1
I noticed that it started then once warm, turned it off then it wouldn't restart. Symptoms of a flat battery. OK, bought new battery. Same thing. But also notice extreme crankcase pressure. When I opened the screw cap on clutch cover it hissed like an airline blast, whoooah! It only ticked over for 5 minutes until warm.
What can cause such high pressure?
Pressure relief valve? It's just a spring loaded ball bearing in a tube isn't it? If I accidentally installed it upside down it wouldn't work but is it possible to do?
The engine is in a lotus 7 type car but is pretty standard, other than a shallow billet wet sump and stiffer clutch springs so not greatly different. Internal all stock oem.
Stuck for ideas

DSC_0770.JPG
 
If the timing has jumped one tooth is that enough to clatter the valves (not sure how far it'd need to be to make contact)
 
First thing to check is the crankcase ventilation hose is not blocked or kinked flat so as to block it off.
If it's pressurized as you've described, to be able to hold that amount of pressure for a period of time the vent is NOT freely venting to atmosphere.
If it were blowby from the rings, it would not hold that pressure but would vent it in a few seconds after stopping the engine running. You would typically see an oil residue around the fitting or at the end of the hose and in the airbox where it is vented to.
Remove the vent hose from the pipe fitting on the top of the crankcase and run the engine, put your hand nearby or over the pipe fitting and see if it's 'puffing' gently.
Check the hose for blockage.
Do you have a PCV valve fitted on it? (positive crankcase ventilation valve)
You called it a 'pressure relief valve.
Let us know what you find.
 
Last edited:
Yos_Sam said:
If the timing has jumped one tooth is that enough to clatter the valves (not sure how far it'd need to be to make contact)
Click to expand...
"clatter the valves" (never heard that expression before but I know what you mean by it lol)
Incorrect valve timing will not cause crankcase pressure to build up.
It will run rough and heat up maybe, or not run at all. (bent valves)
 
SSGT_B said:
Dona compression test to check for blow by. 1st place I would start.
Click to expand...
Done a compression test but forgot to do it warm or open throttle.. The results were very low, 90psi, think the book says 171-228psi. I'll redo it tomorrow.
Is there a pressure valve on the oil system? Sorry if I sound dim but I have severe memory problems which is annoying as I forget a lot of things.
Oil pressures are good, on tick over it's around 40psi, climbs very eagerly with a blip.
I don’t understand how pressure could build up that much.
The only thing I can think of is low torque on head bolts. But that would contaminate oil and water, it'd explain the compression low and the case being pressured so much.
 
bigoltool said:
Just to be clear, you have a swinging oil pickup for the low pro oil pan and it was hitting the OEM Breather tube?
Click to expand...
No, I have the shallow swinging arm oil pick up sump, the breather was removed, reading back my phrasing was terrible, apologies
As far as I know there's no pcv valve on it. It should vent through the air/oil housing, which has a hose from the housing to the underside of the airbox.
 
Yos_Sam said:
Done a compression test but forgot to do it warm or open throttle.. The results were very low, 90psi, think the book says 171-228psi. I'll redo it tomorrow.
Is there a pressure valve on the oil system? Sorry if I sound dim but I have severe memory problems which is annoying as I forget a lot of things.
Oil pressures are good, on tick over it's around 40psi, climbs very eagerly with a blip.
I don’t understand how pressure could build up that much.
The only thing I can think of is low torque on head bolts. But that would contaminate oil and water, it'd explain the compression low and the case being pressured so much.
Click to expand...
Wow . . this is not something to be sorted out over a forum, with being modified and in a car . . . I'm out.
 
Yos_Sam said:
No, I have the shallow swinging arm oil pick up sump, the breather was removed, reading back my phrasing was terrible, apologies
As far as I know there's no pcv valve on it. It should vent through the air/oil housing, which has a hose from the housing to the underside of the airbox.
Click to expand...
Correct! crankcase is vented through the hose and into the airbox for recirculation purposes.
 
Yos_Sam said:
Done a compression test but forgot to do it warm or open throttle.. The results were very low, 90psi, think the book says 171-228psi. I'll redo it tomorrow.
Is there a pressure valve on the oil system? Sorry if I sound dim but I have severe memory problems which is annoying as I forget a lot of things.
Oil pressures are good, on tick over it's around 40psi, climbs very eagerly with a blip.
I don’t understand how pressure could build up that much.
The only thing I can think of is low torque on head bolts. But that would contaminate oil and water, it'd explain the compression low and the case being pressured so much.
Click to expand...
There is a pressure relief valve on the oil pump and oil pressure has nothing to do with crankcase ventilation.
 
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