470 breather oil blowby at high rpm

"Hello, hope everyone is havin

"Hello, hope everyone is having a good boating summer, Kghost get that boat on the water!
’85 SRV255 Sea Ray, twin 470’s, Pertronix & alternator conversion, timing +8 deg. I have an oil leak issue on starboard. Motors will pull to 4200+ wide open, but almost never run this high, usual cruise rpm is 3800. ~1200 hrs on the engines.

Above 3800 rpm starboard motor has started to belch oil out of what appears to be the breather tube to the carb flame arrestor. I also suspect the valve cover gasket somewhat; however there is excess oil inside the spark arrester and carb, the majority of the blow by seems to be running down the rear of the carb body and on. Oil was changed at summarization and I assume to be 10-40W or 20-50, marina did it and don’t have the ticket in front of me. Oil was full to just above the “full dot” stayed that way for about 12 hrs this year till I ran the rpm up. Oil pressures "match" in both engines-per book.

Worked a long time on getting all AF and oil leak issues addressed and now this. Engines use no oil otherwise. (I check before each run). Leak rate at 4200 rpm appears to be about 1 qt/hr. Did a second 5 min run at 4000+ and reconfirmed the blow-by. No blow-by at 3800 rpm after this for another 6 hrs of run time over multiple trips.

Thanks in advance (boat is 2.5 hrs away)"

"Sounds like the rings are wor

"Sounds like the rings are worn on 1 or more cyl's, suggest a compression and leak down test of the cylinders."

"1 qt/hr ?!?

Thats got to b

"1 qt/hr ?!?

Thats got to be more than just worn rings. There must be a few broken ones in there. As Brian said go with the compression and leak down test of the cylinders. Get that rocker cover gasket replaced and look at the oil return holes in the head while the cover is off. If they are plugged up with crap, the oil will fill the rocker arm area faster than it can drain back, and will get sucked up the tube. Make sure all crankcase ventilation hoses (and PCV valve if equiped) are not plugged. If they are, too much crankcase pressure will build and the oil will get pushed out wherever it can.

Wrench"

"Thanks for the feedback.
Qu

"Thanks for the feedback.
Question, on worn or broken rings, if it is a ring problem, why is there no oil consumption below 3800 rpm? I would expect consumption to be proportional to rpm/oil pressure.

I'm very detailed about checking & logging oil (and antifreeze) consumption at start of each run so temp and drain back is consistent. There no loss when run @ or below 3800. Last year in 65 hrs they each went through a 1/4 quart. Same pace this year, except starboard >3800.

Won't be back to the boat for 10 days, will replace gasket and check drain holes (will post findings)
Thanks again."

"Mark:

"...if it is a r

"Mark:

"...if it is a ring problem, why is there no oil consumption below 3800 rpm?"

Pull the spark plugs; if they are oil fouled then you have either worn rings or worn valve guides and seals.

If the plugs aren't fouled, look thru the oil fill cap hole; do you see sludge? Does the oil blacken quickly after it's changed? Then the oil return galleys may be narrowed or plugged w/sludge and/or a piece of gasket material."

"I did a #1 plug check on both

"I did a #1 plug check on both engines at about 10 hours this season and they were not fouled, nice light tan, electrode in excellent shape, gap fine, 90 hrs on plugs.

Boat has 17+ hrs on this oil change; oil is not black but is not golden like new, more like very light brown and can easily see dipstick markings. Boat runs 50% at 12-1400 rpm and 50% 36-3800 rpm.

Will check all four on starboard engine this weekend and replace valve cover gasket as well.

If the oil return holes are restricted, what is a good way to clean them with out messing something up?

Thanks, Mark"

"Let me know if you solve your

"Let me know if you solve your issue. Guy was helping me with the same problem on an 1987 470, never did find the problem. Then when I started the motor this spring, I had antifreeze steam coming out the vent tube along with the oil. Im in the process of installing a 120hp 4cyl, and I tore the 470 down as I was taking it out, and the inside of the motor looked like brand new. The head looked spotless. no rust and no plug-ups. the top of the back piston looked a little bit of a differen color that the other three, but I couldn't find anything visibly wrong,,good luck...Ray"

"before replacing the VC Gaske

"before replacing the VC Gasket, check around just below it with your finger, if' its oily, then it could be loose or needs to be changed... the bolts only get tightened to 25 INCH pounds.. small 1/4 or 3/8 rachet with your hand at the head of the wrench. 1/4 bolts are easily broken."

"Thanks Brian,

It has been

"Thanks Brian,

It has been "wet below" since I had the boat for past 3 yrs., "finger" tightening has been done. Yes, don't want to warp the cover or locally pinch the gasket at the bolts.

Anyone have a suggestion on cleaning the oil return hole with the head in place if it is not VC gasket, valve guides or rings? Thanks.

last season the marina put 10-40 in it and this season made sure they put 20-50, I may switch to a synthetic 10-40 equivalent to see if drain back improves, any thoughts on this?"

It is not a drain back problem

It is not a drain back problem......


Most likey a stuck or broken oil control ring or broken or stuck top two rings.

Blow by is excess combustion gasses entering the oil system. Normally the cumbustion gasses blow by the rings and ad pressure to the oil system IE: the oil pan and then exits where ever it can IE: the PCV valve.

Are you using any excess antifreese?

Are you sure there is not a water leak at the manifolds to exhaust manifold. Raw water runs thru the manifold to the elbow and does over time rot away the manifold.

Not much you can do about it without engine dissembly.

Do a compression check on all 4 cylinders and report back.

That should tell the tail....

"thanks Kg, No anti-freeze con

"thanks Kg, No anti-freeze consumption and again no oil consumption <3800 rpm. Manifolds are original, so borrowed time on those, but no external rust through or external leaks. Just was hoping for a "non-pull the engine solution". Will try and get compression test this weekend or early next week.

What is an expected shop charge for pulling her, rings, manifold, gasket kit, an lower bearings. Since she is a twin it is easier to pull out. Also since she is apart, valve guides and seats cost?

And just got her starting on first crank. Since she is past 1,200 hours MCM will take pity and give parts discounts right....lol
thanks"

sent some emails for your info

sent some emails for your info

"Life is short...summer is sho

"Life is short...summer is short...my opinion...put some STP or other oil thickener in it...enjoy the summer season, baby the motor by keeping the revs down and deal with the overhaul at the end of the season."

"Hello, hope everyone had a go

"Hello, hope everyone had a good 4th.

Compression results are all low 130's, plugs were not oily and no anti-freeze (suprised they were so even) Put new plugs in since they were out and over 100 hours old. As reference Port engine is in low 150's (suprised it was so good).

engine behaved the same in 4 days of running, below 2000 rpm, no blow by, 3800 rpm, 1/4-1/2~quart/hr. runs down flame arrestor and carb body to bilge.

Per Bob, we'll just deal with it for the summer. Any "snake oil" additives to try that anybody has had luck with? STP, Restore, etc...? (not much to lose)

Also my time and tools/place to pull the motor are both nearly zero, so any estimates on a rebuild?

Is there a oil breather cap that will help allow the oil to stay or run back to the valve cover?

Thanks."

Mark

Boat is still in shrin

Mark

Boat is still in shrink wrap. Better cover than the mouring cover with all this rain!!!


I am not sure but do the rocker arms have clips on them to deflect the oil??? Maybe the one nearest the vent hole is allowing the oil to run directley into the vent tube at high speeds.

Pull the valve cover off and look closley. Maybe a rocker arm or push rod has a issue and is allowing excess oil to shoot straight out and is causing this.

If you had a bad ring situation or guide or seal then the plug (s) would be oil fouled.

Reread your plugs again now they are fresh and if you run it again and the oil bath returnes shut the motor down and pull the plugs and look BEFORE you return to cruising speed and allow them to burn any oil contamination off.

"I have a similar problem with

"I have a similar problem with my 1986 MCM 170.
I had a crack in the valve cover also which was loosing a lot of oil. Pull your valve cover and check for cracks near the bolts, if you have them get it welded and then get some spreaders to spread the load when you tighten the bolts. Also you can get a valve cover gasket at Autozone for about 10 bucks for a 460 engine, you will have a spare also.

I have decent compression but have blow by at high RPM's. I am going to try a valve job before I pull the entire engine to rebuild."