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Old 27 February 2012, 15:22   #1
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Honda 50 HO 4-stroke- NO COMPRESSION

So I bought this 14 foot Alliance RIB. It has a Honda 50 ont eh stern. The motor looks great, but it has like 4 pounds of pressure in each hole. Looked at teh Cyl walls and they looked fine. Any ideas on what could have happened or how to fix this?
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Old 27 February 2012, 15:28   #2
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The valves are stuck open.
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Old 27 February 2012, 15:47   #3
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The valves are stuck open.
I just pulled the cover and it appears that everything is going in and out....

Do you know how I would check the timing on a Honda 50hp? How wold I check to see if the valves are stuck?
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Old 27 February 2012, 16:11   #4
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I just pulled the cover and it appears that everything is going in and out....

Do you know how I would check the timing on a Honda 50hp? How wold I check to see if the valves are stuck?
Does it start? She needs to be running to check the timing. Just because the lifters are going up and down doesn't mean the valves are sealing like they should. Zero compression in a 4 stroke suggests stuck valves to me. Or you have no functional rings in there which seems unlikely. Its possible the Honda actually has a decompression feature to help pull start her.

I don't know how to do a valve job on an outboard, that's beyond my pay grade. You'll need a shop manual to start at the very least. That should give you some idea of what you're taking on.
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Old 27 February 2012, 16:43   #5
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Does it start? She needs to be running to check the timing. Just because the lifters are going up and down doesn't mean the valves are sealing like they should. Zero compression in a 4 stroke suggests stuck valves to me. Or you have no functional rings in there which seems unlikely. Its possible the Honda actually has a decompression feature to help pull start her.

I don't know how to do a valve job on an outboard, that's beyond my pay grade. You'll need a shop manual to start at the very least. That should give you some idea of what you're taking on.
It won't start, no compression..

I think I have it narrowed down to two possibilities..
1. The rings are stuck on the piston.
2. The valves are stuck open.

I'm guessing that I have to pull the head to find out? Or is there a way to check without pulling the head?
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Old 27 February 2012, 16:54   #6
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could there be holes in the pistons if the valves and pistons have met at some point?

I guess a flashlight would reveal this?

Could someone have adjusted the valves to such an extent that they never close?
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Old 27 February 2012, 16:58   #7
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You should get more than 4psi compression with stuck rings and stuck rings on all cylinders is unlikely (though possible).


Spray some WD40 down the bores and turn it over a few times by hand then retest it. If the compression jacks up it's the rings.
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Old 27 February 2012, 17:07   #8
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few drops of oil down the spark plug holes into the bores see if that makes any difference,may give enough compression to start it ,
any ideas when it was last run ,,if its been stood a long time compression should come up with running unless its badly worn.
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Old 27 February 2012, 17:15   #9
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few drops of oil down the spark plug holes into the bores see if that makes any difference,may give enough compression to start it ,
any ideas when it was last run ,,if its been stood a long time compression should come up with running unless its badly worn.
Wouldn't want to try that without hand turning/rechecking the compression 1st.

If it's sticky valves you may end up with them contacting the pistons if it fires up on one pot.
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Old 27 February 2012, 18:12   #10
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As Nos says, whip the plugs out and turn the crank/flywheel by hand.
If you remove the valve cover, you can check the valve clearances when the valves appear to be fully closed. If there's excessive clearance, then the valves are likely to be stuck open.
If this is the case then you may be able to free them off by applying some releasing oil on the stems/guides and continue turning the flywheel by hand to work them free.
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