Hey guys, I have a issue with oil blowing out my valve cover vent line on my 35 gdsd.. it started out small in the beginning and is now pretty thick when I'm at full throttle. I've got about 200 hrs on engine and have no idea where to start. Any ideas will be appreciated!


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Make sure it's not overfilled with the oil. Then possible headgasket failure, rings leaking or valvestem seals. Get a leakdown test done

Ok.. definitely not over filled with oil! Was going to do a compression check, will that tell me anything? Motor runs like a top with no issues!


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Compression test may point you in right direction.
Headgasket leaking is pretty common exspecially since your heads are now seasoned. they have changed shape a bit and likely are not perfectly flat anymore ,'likely leaking into lifter valley. Creating excessive crankcase pressure

Thanks for the info will. I'll start with the compression test first!


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Also check valve seals as well as the drain port possibly being plugged. I have seen some gasket material get in there and prevent all the oil from draining back out of the top of the heads, thus pooling and have no where to go.

With all that's said, if compression test or leak down test check out good would changing out all topend seals and gaskets be my solution?


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You be surprised at how much blowby the stock rings allow past them. Most of your PSI will leak from them.

Should I add rings to the list also, or is that normal?


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Do a leakdown. It will tell you where the issue is. Until then, asking questions will be fruitless, as they can all get answered with that. Our answers without that result are purely speculation.

Ok gotcha


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quick thread jack question, what is a good inexpensive leak down tester? if that is even possible.

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I seen them at harbor freight for 60


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Most of the people i know who've used the hf one with these little engines had no luck, including myself. Preston said the orifice is too large or something.

That otc works very well.

DA that's where I got mine aswell. Those numbers sound about right

Just got done with the same problem. Mine was blowing a lot of oil by at higher RPMs. I ran it until I couldn't anymore. Started with 90 for compression and 3 weeks later it was officially done with 40. Motor was 2.5 years old and warranty had the dealer take it all apart. I just was sent a brand new motor yesterday, all the motor really needed was a new head gasket, it had couple hot spots in the motor but not too bad.

Ok guys, got the tester in and it's not looking to good! Regulated pressure was set at 90# before I do the test.

This is left cylinder with almost all the air coming from exhaust.



This is right cylinder with with air coming from oil cap and carb!

The readings don't go that far down to know percentage.. would you say motor is on its last leg?


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I would honestly say you probably don't have it at TDC.



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On the compression stroke. Valves have to be completely shut.

It was for sure set at tdc.. had a guy help me


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And leakage issues don't mean the motor is on it's last leg. If you have valve leakage, you do a valve job. If you have leakage at the pistons/rings, you hone and replace rings or go to .020 overs if there is a lot of scarring.

I cheated and with air blowing out took a cheater bar and clutch engaged turned the prop until it wouldn't let me then removed air and turned back to that position and returned air to guage.

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Ok I got it now.. this is left cylinder now with mostly air coming out of carb..


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Intake valve leak pal. Pull both heads and get a good Valve job done and your engine will run a lot better.

Thank you guys for all you're help!


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I went back and made sure it was.. left cylinder wasn't and right cylinder was!! Thank y'all again


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Interesting advice on this post. Thanks for sharing this stuff.

50% leak down seems really high.