The blowing Rocker Cover gasket!

Submitted: Sunday, Feb 15, 2015 at 13:47
ThreadID: 111122 Views:2433 Replies:8 FollowUps:3
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Gidday good folk.
I've come seeking advice in regards to my Toyota Coaster Motorhome, 1980 model with the modest 20r 4cyl engine.

I'm currently looking at what is the vehicles third busted rocker cover gasket in the past six months.
Allow me to give some background.

I bought the vehicle on Sydney last year and drove it up to Townsville.
Prior to purchase it had had the rocker cover gasket replaced amongst other things, it wasn't more than a few hundred k's from my departure that the gasket blew though!
I managed to keep it all okay with oil top ups and got home.
The percieved issue was that the breather pipe ( next to the oil cap ) was hooked to an aftermarket cannister with no ventilation.
I had the gasket replaced and fitted an oil catch can in between the breather and the already fitted cannister, which I fitted a breather / air filter.

I got a long way south with this set up, however had the issue of a LOT of oil going to the catch can.

Thinking I could avoid it all together and not lose all that oil, I had removed the catch can and hooked the breather up to the intake next to it (where from what I can gather it's supposed to go) but to my despair once the engine was placed under enough load the gasket burst again!
Now I'm stuck with one hell of a leak.

In my mind there's already two possibilities that may need confirming.
One. The hose I fitted from the breather to the intake has a slight bend that will restrict flow, though it appears to still have some flow, could I have just blocked off the ventilation again, causing another blow out?

Two. The pcv is hooked to the rocker cover and the spot on the throttle body it's meant to be, though there is a tree fitting inbetween these two hoses, with the third hose blocked off, is that supposed to run somewhere??

I'd just fit my little k&n breather to the rocker cover if I didn't think it would spew oil from the top of the engine like it did into the catch can ( or will it? )

Has anyone tackled this before?
Any help is appreciated, I'll be replacing the gasket this week and am not interested in doing so again, nor am I interested in losing oil through that breather outlet.

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Reply By: Matthew G5 - Sunday, Feb 15, 2015 at 14:01

Sunday, Feb 15, 2015 at 14:01

AnswerID: 545967

Reply By: Zippo - Sunday, Feb 15, 2015 at 16:21

Sunday, Feb 15, 2015 at 16:21
The PCV valve is meant to pass cylinder blow-by back into the intake. Assuming the PCV valve is OK, the only reason I can see for the blowing gaskets is excessive blow-by and pressure build-up. Catching oil is a separate issue from the cause of the problem.

Check and/or replace the PCV valve. If the gasket problem persists, the engine needs a rebore and rings. Just my 2c worth.
AnswerID: 545975

Reply By: pop2jocem - Sunday, Feb 15, 2015 at 16:27

Sunday, Feb 15, 2015 at 16:27

A couple of questions. How many k's (if you know) has the vehicle done? How is the engine dipstick held in on those engines?

If the dipstick is just a normal push in type and there is some excessive restriction with breather setup, usually the dipstick gets blown out before the rocker cover gasket blows.
What type of gasket do those engines use?

If the engine is getting a little sad condition wise extra crankcase pressure can get generated but usually the breather just has to work a little harder. That is assuming the screen or gauze inside the cover isn't blocked.
If you haven't already, check that the breather system inside the rocker cover isn't blocked when you remove it to fit the new gasket.

AnswerID: 545976

Reply By: Hoyks - Sunday, Feb 15, 2015 at 16:45

Sunday, Feb 15, 2015 at 16:45
The picture is a bit average, but the PCV hose probably shouldn't have a kink in it. I'd get a longer hose, even if it has 1/2 a loop in it, it would be better than being pinched off.

On the inlet duct, how big is the fitting that the vent hose is attached to? It should be at least the same size as the outlet from the rocker cover.

On some one of my old vehicles there was an arrangement of baffles that worked as an oil separator in the rocker cover. If it has one, has that been cleaned?
On my old Ni$$an it had a vent tube that went to an oil separator on the outside of the engine that then drained to the sump and vented into the inlet tract.

What oil are you running, I know on my bike running synthetic causes excessive oil blowing out the crankcase vent, but similar spec mineral oil is fine.

Maybe a compression test could be worth it. It will tell you if compression is low because the engine is bleeding pressure into the sump which would be be the cause of excessive blow-by. An experienced mechanic might be able to look at it and see if you are missing any bits too.

Oh, and as a motorcyclist, please don't vent it to the atmosphere. We have enough people trying to kill us off without finding oil on the road mid corner.
AnswerID: 545978

Follow Up By: Matthew G5 - Sunday, Feb 15, 2015 at 16:58

Sunday, Feb 15, 2015 at 16:58
Hi mate,

The PCV is unkinked, it was the breather that was hooked from rocker to intake that was kinked.

I feel relatively comfortable with that being the cause of the blow out as once I had taken the breathing ability away, I had the trouble almost instantly.

The attatchment sizes are closely similar.

I will be checking the rocker cover tomorrow once I can confirm parts, will keep ya posted.

Am currently running 15w40.

FollowupID: 833647

Reply By: Matthew G5 - Sunday, Feb 15, 2015 at 16:52

Sunday, Feb 15, 2015 at 16:52
Hey Gents.

The dipstick is a push in and the tube had come out with the stick post it's first blow out.

If I am correct the vehicle has done just over 1 mil with a complete engine rebuild 700 thousand ago, she gets by ok ;)

I popped the breather hose that I fitted and can confirm that it probably pinched enough to completely block off the flow, would this have been sufficient to blow her out?

I will be fitting a hose as a replacement that fits properly aswell as removing, cleaning, inspecting and refitting it with the new gasket.
With this attack plan, the engine should breathe fine, leaving my concern being the oil that the breather likes to pump out.. is it likely to run down to my filter? If not will it be okay in the intake?
It is how they came stock afterall?

As far as the gasket is concerned, it's yer usual rubber with a half moon at the front (maybe the back too).

Cheers again for your help, I look forward to hitting the road again!
AnswerID: 545979

Follow Up By: Ron N - Sunday, Feb 15, 2015 at 23:13

Sunday, Feb 15, 2015 at 23:13
Matt - If that engine has done 700,000 kms since it's last overhaul, the diagnosis is simple!

It is totally worn out - and the oil rings are barely doing their job!! What is the oil consumption like?

You will never be able to control blow-by, and blown rocker cover gaskets, until you address the basic problem! - massive blow-by from virtually non-existent oil control, via virtually non-existent oil rings!

The engineered life of the old Toyota engines is 500,000kms. You've got your moneys worth - and someone elses as well!

Cheers, Ron
FollowupID: 833677

Follow Up By: pop2jocem - Monday, Feb 16, 2015 at 18:33

Monday, Feb 16, 2015 at 18:33

I think what Ron has said pretty much covers it, however, just to be clear.
You are saying that the vehicle has done, in round figures, 1,000,000 k's

The engine was rebuilt at 300,000 k's

So since it required a rebuild at 300,000 and it's done twice that plus a bit since then, and assuming the rebuild was complete, surely that should be a clue as to the condition of the engine's internals notwithstanding the fact that "she gets by ok".

Certainly get the breather hoses and other components sorted, but I would think you wouldn't be looking at a much longer lifespan if those kilometer figures are accurate.

FollowupID: 833719

Reply By: Notso - Sunday, Feb 15, 2015 at 21:42

Sunday, Feb 15, 2015 at 21:42
Sounds like bad blow by. Caused by worn/damaged rings.
AnswerID: 546001

Reply By: HKB Electronics - Sunday, Feb 15, 2015 at 23:03

Sunday, Feb 15, 2015 at 23:03
When you have excessive leakage past the rings you'll probably find that you'll have trouble getting a smooth idle due to the foul air form the crank case being feed into the air cleaner assembly, you'll also find rapid dirtying of the air cleaner element due to the same and oil mist getting blown out of the rocker cover.

I would suspect the previous owner removed the breather hose from the air cleaner and routed it through a catch can and then to the atmosphere. The catch can or whatever to prevent the oil being blown out of the breather hose dirtying everything.

Normally with a good engine you'll have a low pressure in the sump caused by the PVC valve, you would only expect to have a positive pressure under very high engine loads.

The only way to prevent a rough idle will probably be to vent to atmosphere again but that is also illegal.


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AnswerID: 546007

Reply By: swampfox - Monday, Feb 16, 2015 at 17:57

Monday, Feb 16, 2015 at 17:57
Check your tappet clearance first

Check with vacumn gage should be steady above 15 inches of vacumn

dry compression test
readings have to be within 10% of each other
equaul winds on str motor 6- 10

wet test will test how the rings are sealing
2 pumps oil then crank 6-10 times
if compression comes up keep record of all cylinders and compare dry to wet

If readings indicate poor health confirm with a leak down test
[u set gage to 100 and check % of drop ]

There is pressure in the crankcase caused by some situation ????
This is assuming the breather is installed correctly ???

swamp fox

AnswerID: 546033

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