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UncleJim 10-12-2012 12:16 AM

Yanmar rocker arm cover oil leak
Ran our recently purchased 1983 Hunter H34 for about 2 hours on Monday to get the feel of the handling and to practice docking in good weather. Today when I went to work on another issue. I checked the engine (3GMF Yanmar) I noticed that there was oil leaking from the top of what I would call the rocker arm cover on a gas engine. There is a round raised spot near the compression release levers and the oil seems to be leaking from that area. In prepping the boat the broker painted over the engine so canít tell if it was a rust area or not. It was not leaking there before and we have run the engine a number of times. Today when I found it, it had been running for about 30 mins at the dock. Any ideas or suggestions, I'll probably need to replace the cover but was wondering what could have been a cause. Any ideas?

arf145 10-12-2012 10:14 AM

Re: Yanmar rocker arm cover oil leak
That cover has a big O ring as a gasket, if I remember correctly. Could just be misaligned or flattened.

UncleJim 10-12-2012 10:20 AM

Re: Yanmar rocker arm cover oil leak
Thanks Tom, but it's not coming from under the cover but from the top. I was able to find a diagram online and it seems that there is a pin that keeps the shaft for the demporession lever in line. the pin seems to go in from the top and that is were the leaks are coming from. Broker is checking with a mechanic but I don't except to here anything back for a few days.

arf145 10-12-2012 12:37 PM

Re: Yanmar rocker arm cover oil leak
Ah yes, I see the pin you're talking about (looking at manual). That pin is just driven in, I guess. Hard to picture much oil making it out of there.

UncleJim 10-12-2012 12:50 PM

Re: Yanmar rocker arm cover oil leak
True not much seems to be coming at at one time, maybe 2 to 3 ml /min times three it can add up if the eng is run for an hour or two. The rate of the leak also varies. sometimes faster sometimes not at all. I'd like to know for sure what is going on and not have to worry about it. May just take it apart and put it back together again. That usually fixes things for me.

arf145 10-13-2012 11:13 AM

Re: Yanmar rocker arm cover oil leak
This may not be relevant--just looking at the diagram--but how about the crankcase breather and hose? All clear there?

UncleJim 10-13-2012 11:19 AM

Re: Yanmar rocker arm cover oil leak
I haven't checked them so not sure. the seller, a broker redid the boat and did a good cleaning on the engine. replaced hoses, belts, had a mechanic look at and replace a number of parts. I would assume it had been checked / cleaned but you know what that means

UncleJim 10-16-2012 10:06 PM

Re: Yanmar rocker arm cover oil leak
:(Just got the email from the mechanic, seems that the leak is coming from the pins on the decommpression levers. The good news is that it is just some epoxy that the factory covers them with that has dried out and is leaking, happens all the time he said. scrapped off the old added new and should not be leaking from that spot again. Now the rear seal on the other hand.......:(

redhead78 10-19-2012 05:03 PM

Re: Yanmar rocker arm cover oil leak
Sounds like u have some good oil pressure and distribution.....Red

UncleJim 10-19-2012 11:10 PM

Re: Yanmar rocker arm cover oil leak
yea oil pressure I got, this is a case of to much of a good thing

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