Oil blow-by - possible reasons and how to fix?

[dom14]

Hi Guys,

High crankcase pressure or blow-by has been an issue with my GQ RB30(carby, dual fuel, naturally aspirated), that has been going on for few years now. It's not catastrophic but creates annoying enough oil blow-by out of the rocker cover gasket and from the PCV hose on top of the rocker cover. These oil leaks from the back of the head near cylinder 5 and 6 are leaking towards the back of the block and into the clutch compartment as well.

I've 'constructed' the following possible causes of it using internet search.


piston ring wear
Worn valve guides
Worn valve seats/valves
Hairline fractures in piston crowns----using ether will cause this!(Indirect injected Diesel engines)
egg shaped cyl bores
intake/valley pan seal leaks
blocked/inoperative CDR(PCV) valve


4 and 6 doesn't apply to RB30 AFAIK.

I've done the following work to address the issue so far without any good results


PCV valve check/test and clean
Rocker cover gasket replacement+using gasket sealant for better seal
Compression test and leak down test,which came out ok on all cylinders



I'm about to do the valve(stem) seals, which I can manage

1)I'm not sure how the worn valve guides affect blow by. I'm guessing if the valve seals are fine that should hold any combustion gases inside the combustion chamber without allowing it to leak into the rocker cover.
Am I correct about that?!!

2)Does the leak down test showing little or no leak, conclusively say that there are no badly worn piston rings(to cause bad enough blow-by)??!!

3) Does the valve guides get replaced with new ones during a typical cylinder head recondition job at head recondition places? Or is it that cost something extra??!!

Thanx in advance for any help, advice.

[kevin07]

so if your handy enough lift the motor and put new rings in may as well tickle the sump at the same time (mild cam). and just redo the head.

[dom14]

so if your handy enough lift the motor and put new rings in may as well tickle the sump at the same time (mild cam). and just redo the head.

Just new rings?
How do I tickle the sump(mild cam)?
Head is good, as far as I can see. Just suspecting bad stem seals, but that's probably not the case.

[Throbbinhood]

Are you blowing oil on startup, or after the cars warm and idling for a while, then given a bootfull. If not, probably not valve stem's.

Have you checked your rocker cover and put a new gasket in? I had the same issue, replaced gasket, fixed issue, after a few months was leaking again, just needed to tighten up the rocker cover bolts as they'd come loose.

[dom14]

Are you blowing oil on startup, or after the cars warm and idling for a while, then given a bootfull. If not, probably not valve stem's.

Have you checked your rocker cover and put a new gasket in? I had the same issue, replaced gasket, fixed issue, after a few months was leaking again, just needed to tighten up the rocker cover bolts as they'd come loose.

I haven't tested to find that out mate. But, I'm about to do it by blocking PCV and observe the blow-by at startup as well as when warmed up.
'Cos I used sealant as well to improve the seal, I'm pretty sure it's excess blow-by, not the gasket.
What I dont know atm is the actual cause of it, but I'm closing in this time. I had enough with having to wash it all the time. Bang Head

[dom14]

Blocked the breathers and observed the blow-by. It didn't look that bad. Basically, I couldn't notice any excess blow-by(on idling and slightly higher rev)

[dom14]

I think I'm going to do the rocker cover gasket again and check the rocker cover for warpage.
I thought it might be a good idea to do the valve stem seals anyway, 'cos it doesn't look like I have to do the head at this stage.
If I have to do the head, I would have it fully reconditioned, but it doesn't look like now is the time.
I'm also checking the rocker cover breathers for any blockage.
There are two of them.
One for PCV and the other for the air filter.

[dom14]

Blocked the breathers and observed the blow-by. It didn't look that bad. Basically, I couldn't notice any excess blow-by(on idling and slightly higher rev)

I blocked the two breather holes on top of the rocker cover with two screwdrivers and a rag. Then opened the oil filler cap to see if there's any violent blow-by. I couldn't see any.
Then I placed the oil filler cap without tightening it. Still couldnt' see any violent move of the oil filler cap.
Apparently there's no bad blow-by, yet oil keeps blowing from the side of the gasket and the breather holes.

Next, I'm gonna remove the rocker cover, see if the breather holes are blocked, & replace the gasket.

https://www.youtube.com/watch?v=398jRvmBuhA&feature=youtu.be

I also revved the engine hard in the above test(not in the video) and still couldn't see any violent blow-by.

Next, I'm going to remove the rocker cover, see if the breather holes are blocked, & replace the gasket.

[dom14]

Breather holes are not blocked. I'll be replacing the rocker cover gasket.
I'm hoping to do the valve stem seals as well.

[Patrol'n]

One of my previous vehicles had a real issue with a leaking rocker cover gasket, took ages to sort out. In the end I bought a high quality thick rubber gasket, and applied an even layer of gasket compound, RTV blue from memory (was a long time ago) to both sides of the gasket. Then tightened the rocker cover bolts down to specs. Then I left it for 24 hours to set properly before I ran it again. Had the car 2 years or so after that, then sold it to a mate, far as I know it didn't leak in the few years he drove it either. I'd tried using gasket compound before that, but it seems like giving it time to set before starting it and not over tightening the bolts made the difference. At least in my case anyway. It also seemed to have blow by (although the gasket was a separate issue), although the engine was healthy. In the end I fitted a small catch can and breather filter on top of it. Never had a problem after that, and it didn't ever actually collect oil in the can that I could find. Mind you that particular engine used to pull very high revs regularly (lots more than my RB30), so that could have caused that problem I guess.

Edit, as pointed out by threedogs, always be careful with gasket sealants and not applying too much, since it can cause problems if any breaks off and clogs an oil gallery etc.

[dom14]

One of my previous vehicles had a real issue with a leaking rocker cover gasket, took ages to sort out. In the end I bought a high quality thick rubber gasket, and applied a generous even layer of gasket compound, RTV blue from memory (was a long time ago) to both sides of the gasket. Then tightened the rocker cover bolts down to specs. Then I left it for 24 hours to set properly before I ran it again. Had the car 2 years or so after that, then sold it to a mate, far as I know it didn't leak in the few years he drove it either. I'd tried using gasket compound before that, but it seems like giving it time to set before starting it and not over tightening the bolts made the difference. At least in my case anyway. It also seemed to have blow by (although the gasket was a separate issue), although the engine was healthy. In the end I fitted a small catch can and breather filter on top of it. Never had a problem after that, and it didn't ever actually collect oil in the can that I could find. Mind you that particular engine used to pull very high revs regularly (lots more than my RB30), so that could have caused that problem I guess.

Hi mate,
Thanx the for the helpful post. The more I discuss and read about this problem, more I come to the conclusion this is partly inherent to RB30 stock engine.
When I used the RTV last time, I applied on both sides and allowed over night to dry. Only thing I can't be sure about is overtightening. I don't think I did initially, when it started leaking from the rear end of the rocker cover, I started tightening the bolts that end bit more. That initially did help then back to square one again.
I will fit in a catch can, new gaket(without sealant) and see how it goes. I'll put off the valve stem seal job for now, as it appears it may not be the cause.
There's definite signs of blow-by. And it doesn't happen in idling. So, I reckon either,
1)blow-by on high revving or
2) blow-by on temperamental basis.
I reckon it's number (1). I will do a high rev blow-by test soon.
At the moment, I got the rocker cover out. I removed the splash guard and degreased all the crap inside the rocker cover and the splash guard.
I'm planning to make my own catch can "apparatus" at home and fit it soon.
I'll have to wait for the warm engine high rev blow-by test as I have the exhaust, manifold, water, etc out to fix exhaust leaks all for once and the leaking welch plug.
Cheers

[threedogs]

Go easy using RTV or any silicon style sealants, too much
and it may break off and clog an oil gallery, a light smear should be
sufficient, if it still leaks look for the reason why something may be warpped

[dom14]

Go easy using RTV or any silicon style sealants, too much
and it may break off and clog an oil gallery, a light smear should be
sufficient, if it still leaks look for the reason why something may be warpped

Thanx threedogs.
I won't be using RTV this time. I was going to test the rocker cover for warpage, but ran out of time today. I'll do it tomorrow.
I gave the rocker cover & splash guard a super clean today.
Splash guard retaining bolts and the edges were caked with some sort of paste, obviously to prevent them form becoming loose and to improve the seat as well.
I'm wondering what I can use that will be resistant to hot oil.
Obviously it can't be any kind of silicon. Something that hardens and resists hot oil forever.
Any suggestions?!

[Patrol'n]

Go easy using RTV or any silicon style sealants, too much
and it may break off and clog an oil gallery, a light smear should be
sufficient, if it still leaks look for the reason why something may be warpped

Good point about too much sealant TD, I should have put that in my post, I wasn't meaning horribly thick layers of the stuff, more just not missing spots which could itself create an uneven thickness seal.

[dom14]

I prefer not to use sealant at all when possible, 'cos oil passages are being bit narrower than water passages, it can easily clog up with broken off RTV sealant bit and pieces.
'cos the rocker cover gasket is made of rubber, it should be able to create a proper tight seal, when the bolts are properly torqued with balance.
Also not to mention the amount of time it can take to clear old sealant stuck between tight spots.
I had to remove all the old RTV bit and pieces from the rocker cover sealing edges(which had a narrow "trench" build into it., as well as on the cylinder head.
It took ages and not fun at all. If you have to have to remove the rocker cover later for other jobs inside the rocker cover, then sealant is probably not a good idea. In my case it was not so much a good idea 'cos it's still leaking.