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Broken rocker arm

U

uffeibhster

New member
"Hi experts

Engine;
Marine

"Hi experts

Engine;
Mariner, 4-stroke, 4 hp, outboard from the 80's I guess.

Situation;
The engine keeps braking the rockerarm for the exaust valve. It runs ok at low revs/idle but when giving some throttle the exaust rocker arm brakes after app. 20 seconds.
It looks like the lubrication is ok. When I changed the rocker arm I set the clearance to 0,25mm.
Any suggestions are very velcome. If you need further info I will try and answer.
My thought is that it is not proper able to get rid of the exaust? Any comments to this?
I know a little of engines and have worked on mc and auto, but I have never worked on marine engines before and I have never seen a problem like this.

Thanks for your help
Best regards
Uffe, Denmark"
 
"Cam timing ok? Valve not hitt

"Cam timing ok? Valve not hitting on piston? Hasn't jumped a tooth/link?

Any recent work done? Valve/valve spring replacement, camshaft change? Coil bind is the first thing that comes to my mind. When the valve is fully open is there a gap between the coils?"
 
Thank you for your answer.
In

Thank you for your answer.
In the autumn the engine had a service before I bought the boat. I was planing to call the former owner and the shop who sold the boat to get more info.
I will do that and check with your comments asap.
Have a nice day!
 
"Does anyone have a repair man

"Does anyone have a repair manual for the above engine. additional engine info; Mariner, F4M 1999. S/N OR002078."
 
"stuck exhaust valve or bent,

"stuck exhaust valve or bent, I have no experiance with this engine. Lots of bad valve experiance."
 
"Hi
Further info on this;
Fi

"Hi
Further info on this;
First of all Graham Lamb informs that it is a '99 or '00 engine (year).
I called the Marine Center that did the service - they state that they only worked on the cooling system - nothing else. Sounds reasonable as the former owner says that there where no other problems (I trust that).
So I just removed the valve cover, turned the engine so the piston was in the bottom. Then I tried pushing the exaust valve and there was no resistance from corrosion or like, but it hits something after app. 5mm. Something firm that does'nt move. So this is probably why the rocker arm breaks - but what have suddenly entered the head that feels very firm...?
The inlet valve moves perfect as much as I can push it - not hitting anything.
I feel like there is something the Marine center might not inform - but what could be assembled in a way that this happens when they have only worked on the cooling system?
Any ideas on this problem.
Does anyone have a repairmanual?

Best regards and have a nice weekend
Uffe"
 
"if the valve is bent it will

"if the valve is bent it will hang in the valve guide, that could be the sticking point you feel at 5mm. There could also be something wedged in the spring, but you should see that. I'm sticking with my guess, tear into it and find out.
Is this it, cute little thing.
http://www.crowleymarine.com/mercury_parts/4695.cfm"
 
"I have the service manual for

"I have the service manual for this model - send me an email with your engine (4 horse 4 stroke) as the subject and I'll send you off the chapter (pdf file) on the powerhead.

It may be a couple days, I'm out of town so not on my "outboard" computer at the moment..."
 
Hi

Yes JB - it looks like t

Hi

Yes JB - it looks like that is the engine - thanks!
When I push the valve it feels more like a stop and not like a sticking - like the valve is hitting something.
Anyway - I will try and dismantle as mush as I dare today... Usually as much as I can assemble :eek:)
Thanks Graham - I look forward to getting the pages!

Have a nice day and thanks for info!
Best regards
Uffe
 
Further info;

The exaust pu

Further info;

The exaust push rod feels like it gives a small and a big push. This means that it opens the exaust valve a bit just after the inlet valve has closed.
After explosion the exaust valve opens more and I guess it is here that it hit something inside the head.
Is it intentionally from factory/design that the exaust valve opens like described above?

Best regards
Uffe
 
"I don't know your mechani

"I don't know your mechanical backround so study this if you need to. http://www.maxrules.com/fixtheory1.html
Again I don't know this engine, we must wait for Graham and his library of manuals. I wonder if the engine has a compression release for starting, that would open the exhaust valve a bit at low rpm's. I would remove the spark plug and have a good look at the piston if possible, see if the exhaust valve hit it. Next pull the rocker arms and inspect the pushrods. Last would be to remove the head. Don't do anything major till Graham sends the manual."
 
"I did make it home for a brie

"I did make it home for a brief stop, so got the section of the manual off to you.

Now heading off to Michigan - NASCAR Sprint Cup race tomorrow - wooo hooo.

Hmmmm, wonder if those guys run water separating filters since they run on Ethanol???
"
 
"You aren't that far away

"You aren't that far away JB - stop by - meet me in the parking lot - I'll buy you a beer
"
 
"Changing a tire on an A/C rig

"Changing a tire on an A/C right now, might take a little longer than a nascar pitstop. I'll take you up on the beer later."
 
"Hi

I finally found the ans

"Hi

I finally found the answer to this problem. The valve guide for the excauts valve had moved app. 10mm. Never seen that before.
But it actually makes a little sence as the service in the autumn was regarding a broken impeller and a bad cooling system, so perhaps the area around the guide have been very hot and alloved the guide to move...
Anyway - I got the guide pushed back and are about to assemble the valve system again. Then I'm waiting for gaskets aso. so next weekend I should be up and running.
Thanks for all your help!
Best regards
Uffe"
 
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