omc engine problems

[firehog6305]

ok guys, had my cabin cruiser out for another two days on the water, everything was going good, just tinkering fixing wires and fishing, on the way back to my slip, one of my 1978 omc 185hp started to tick, and then seem to drop a cyilnder, it still ran but seemed like it was only firing on 7 instead of 8cylinders. I thought oh $%#@& then thought well maybe its a plug or wire, (wishful thinking) did a comp test, and #1 had only 60lbs, all others were very close #120-124lbs, so I'm thinking vavle so I did all the normal tricks on unsticking a vavle, that didnt help so it looks like I need to take the head off and check the valves unless any of you have a bright idea:redface:
and another question for ya, the boats in the slip at my club, I dont have to pull the boat out of the water to replace the head on an old 800 stringer right???

 

[EricR]

Re: omc engine problems

I have not had to pull and engine to pull a head yet. The question is, how much damage did the broken parts of valve do to the piston crown? It does sound good however that this happened at low, idle speed, possibly you will just fine the valve eroded around the edges.

 

[CharlesW]

Re: omc engine problems

ok guys, had my cabin cruiser out for another two days on the water, everything was going good, just tinkering fixing wires and fishing, on the way back to my slip, one of my 1978 omc 185hp started to tick, and then seem to drop a cyilnder, it still ran but seemed like it was only firing on 7 instead of 8cylinders. I thought oh $%#@& then thought well maybe its a plug or wire, (wishful thinking) did a comp test, and #1 had only 60lbs, all others were very close #120-124lbs, so I'm thinking vavle so I did all the normal tricks on unsticking a vavle, that didnt help so it looks like I need to take the head off and check the valves unless any of you have a bright idea:redface:
and another question for ya, the boats in the slip at my club, I dont have to pull the boat out of the water to replace the head on an old 800 stringer right???

You might want to pull the rocker cover off and check the rocker arms first. I don't if the OMC 185 is a Ford or a GM engine, but I once had a rocker arm stud wear and let the rocker arm pivot so it didn't open the valve on a Chevrolet 305 engine in a van. It's pretty easy to see with the rocker cover off and the engine running.

 

[firehog6305]

Re: omc engine problems

yes I need to pull the cover off and take a look see, I have to take it off to remove the head anyways, so we will see. it happened at low rpm's so maybe nothing got to damaged, back to work tomorrow so it will have to wait a few more days

 

[CharlesW]

Re: omc engine problems

yes I need to pull the cover off and take a look see, I have to take it off to remove the head anyways, so we will see. it happened at low rpm's so maybe nothing got to damaged, back to work tomorrow so it will have to wait a few more days

I just reread your post and I doubt that you have the same problem I had. If the rocker arm was bad, the valve wouldn't open. That wouldn't give you the low compression which you have. Sorry for confusing the issue. It's still worth looking at though in case you lost a keeper or valve spring.

 

[aerwin]

Re: omc engine problems

185 hp was the gm 305. you could also have a flat lobe or a worn lifter also. as long as your not pulling the outdrive, the boat can stay in the water. if yo have to pull the engine I would definatly pull the boat out of the water. most likley the outdrive will have to come off

 

[CharlesW]

Re: omc engine problems

185 hp was the gm 305. you could also have a flat lobe or a worn lifter also.

Those wouldn't give him a low compression reading would they? Kind of like my rocker arm thought, those problems would leave the valve closed rather than open to lose compression.
He mentions 120# or more on 7 cylinders, but only 60# on the one.

 

[wire2]

Re: omc engine problems

They would, if the intake valve is opening only partially for any reason, a reduced volume of air will enter the cylinder and lower compression.

 

[aerwin]

Re: omc engine problems

yeah your right about the low compression, I wasnt even thinking about that. just goin by past experiences. would a burned valve cause low compresion? air leaking by? but would a burnt valve tick?

 

[CharlesW]

Re: omc engine problems

They would, if the intake valve is opening only partially for any reason, a reduced volume of air will enter the cylinder and lower compression.

Never thought of it that way, but it does sound logical.

 

[firehog6305]

Re: omc engine problems

ok just an update, I went down to the boat and pulled the valve covers and intake, there is two broken pushrods, looks like the valve stuck and it broke the pushrods, thats what the ticking was. so I'm going to replace all pushrods and lifters, took off all rocker covers and tapped the valves to make sure they were not stuck again, havent put it all back together yet, is there somthing else that I should do before sealing her up??? also I have those two piece ext mainfolds, I had to break them apart to get to a couple of bolts, can I reuse those gaskets you think with proper sealeant, or do I need to change them out??