Oil spitting from filler - 2.25 petrol

I've just took my 2A up to Gaydon for the weekend. It was a 2hr 45m run up to the show and it seemed to run as well as usual but when I next looked in the engine bay she'd been spitting some oil out the oil filler.

She didn't have too much oil in.. so as I'd never had the rocker breather off I soaked that in some petrol and gave it a clean out. After the long drive home I checked and she'd still spat some more oil out but it seemed better.. might have imagined it I suppose.. not much for 3hrs driving but it's never spat a drop until now so something's changing..

What causes excess oil pressure? Over-heating? It's not lost any coolant that I can tell (just checking the level under the rad cap).. Someone said to check valve clearances and compression. I could do both, but I'd only be doing as I'm told, I don't know what the connection is between the spitting oil and checking these things.?

I did compression about 250 miles ago and it seemed alright (and she's running as well as she ever has): Results were Front to back (Dry): 120 / 110 / 120 / 125 (air filter off, coil off, all plugs out, throttle pedal on floor). I can check again to see if something's shifted over the long trip there and back, but what else should I be thinking about?

Usual cause of oil being pushed out of breather is crankcase pressurisation. Worn bores or rings causing piston blowby.

Do you get air blowing out of the filler with the cap off.

Bobsticle said:

Do you get air blowing out of the filler with the cap off.

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Do I want to check that if it's spitting oil? With the cap off that could be a face full of oil right?

It is looking like blowby isn't it. Don't know why it's only just started though. Will do a dry and wet compression test this weekend and share results. Could a head gasket split between cylinders cause crankcase compression? But it was running so well all the way home.. it is strange. Anyway, I'll do a test..

scottonthefen said:

Do I want to check that if it's spitting oil? With the cap off that could be a face full of oil right?

It is looking like blowby isn't it. Don't know why it's only just started though. Will do a dry and wet compression test this weekend and share results. Could a head gasket split between cylinders cause crankcase compression? But it was running so well all the way home.. it is strange. Anyway, I'll do a test..

Click to expand...

When I took the head off my diesel there was very little of the copper gasket left. It had breached between cylinders and into a few oil ways.
I couldn’t believe how well it had been running for the past seven years even though a hand over the filler tube identified pressure from the bottom end.

Bobsticle said:

When I took the head off my diesel there was very little of the copper gasket left. It had breached between cylinders and into a few oil ways.
I couldn’t believe how well it had been running for the past seven years even though a hand over the filler tube identified pressure from the bottom end.

Click to expand...

Blimey that's impressive, I didn't know they could get along that well with a ruined head gasket. I'll let you know after the weekend. cheers!

now then.. All cylinders 120 dry, 130 wet. And I’d say it’s puffing gently out the oil filler tube when ticking over, but I don’t know what’s normal?

So it seems the compression and head gasket are both reasonable. Maybe the rocker breather was just blocked after all.. unless there are other ideas here I’ll put a new rocker breather on to be sure and see how it goes from there..

After my rebore and engine build I have air movement at the filler tube (more slight in and out than a blow) but still have oil from the rocker trying to get out of the breather joint. The diesel has a separate filling tube but not sure if yours does. I tried a new O ring on the breather but oil still crept out. Ended up with a smear of engine silicone round it and it seems to be holding.

Right, I've got the head off. It had a composite head gasket on which was still complete when I peeled it off the underside of the head.. it's been on a while but it's not blown.

I need to clean things up for a proper look at the valves and to measure the bores. I don't know what I will do yet. New valves and lap the seats would be worthwhile, surely?. Piston rings would depend on the wear in the bores and I'd need to hone them too.. there's nothing stamped on the piston tops I can see just yet that suggests they're already oversized.

I'm new to engines. I want to improve compression to reduce crankcase pressure. To me that means improving the valves and seats and possibly hone the bores and rings.. anything else I should look at?

As for hardened inserts for unleaded.. the smaller valves are the exhaust, right? Yet what looks like shiny insert metal is on the intake valve seats..? Not sure what I'm looking at here until I clean it up more..

@admins - please move to the Series Engines forum if more appropriate.

..I'm going to post a few updates and questions here over the next few weeks of this engine work..

Its probably too late since the head is off but I wonder if a pressure test would be helpful. Something like threading the hose used for the compression test you did and instead of attaching gauge you hook it up to the air compressor. Perhaps rotate the crank until the piston your testing to have both valves closed , I think that means rocker cover off. But if your compressed air machine can get up to 90 psi like my generic one I would think you could hear air coming out. I'm not sure about this though.
edit: I searched it up, I was describing "leak-down testing"

Try rattling the pistons side to side then front to back. That’ll give you an idea how oval they have gone.
Nowt on mine front to back but a healthy 1mm side to side. That’s as much measuring as I did and phoned the mobile rebore chap to come out and add +20 to the oles.