1980 Mercury 70 hp

[roper]

No fuel getting to #1 cylinder. Runs rough and when I remove spark plug it and inside of # 1 cylinder is completely dry. Both # 2 and # 3 cylinders are wet and seem to be firing.

 

[ODDD1]

Re: 1980 Mercury 70 hp

beg, borrow, or steal a compression tester...you must verify mechanical health before assuming anything....

 

[Trent]

Re: 1980 Mercury 70 hp

As said above..Compression must be tested!! Also have you done a spark test? Does it spark more with the plugs removed or when the plugs are installed?

 

[roper]

Re: 1980 Mercury 70 hp

I have not done a compression test. The only thing I have done is make sure the piston is moving. I'm not sure how to do a spark test. Can you please explain further? Thank you both for your responses.

 

[Rex]

Re: 1980 Mercury 70 hp

You got to have compression to start with<br />then check the runner to number 1.<br />If you got all above you should be ok,<br />but one of the three is not right.<br />Could be a bad plug wire, but I don't think<br />so. COMPRESSION OR SPARK CHECK THEM.<br />REX

 

[petryshyn]

Re: 1980 Mercury 70 hp

Hello roper<br /><br />In answer to "how to check spark"<br />Purchase on of these

at your local auto parts store. They're cheap and you should have one on hand if you're handy!<br />Pull the plug wires off one at a time and install tool(leaving the others connected) Ground tool to block and crank engine. With tool set at 3/8" you should have a whiteish blue spark. This engine was known to foul the bottom plug and prone to pack failures as well. If you don't have a comp. tester, atleast check this first. Wouldn't hurt to change plugs as well, as the permagap plugs foul easily. Check ignition and get back with results. A dry cylinder is sometimes a subjective observation.....<br /><br />Good luck.

 

[roper]

Re: 1980 Mercury 70 hp

OK, I checked the spark and it looks good. The compression on the other hand does not. I didn't get a compression tester, but I used my thumb. Couldn't feel anything on cylinder # 1. # 2 and # 3 blew my thumb back out of the spark plug hole with good force. Can I assume that I need to have a new piston and the block bored? I have a feeling this may be more than this beginner can handle.

 

[Trent]

Re: 1980 Mercury 70 hp

Sounds like major money time..If no compression..Look on the net for a rebuilt powerhead..Then decide if you want to spend the money. A twentyone year old engine if you look at the price guide is not worth much..sorry

 

[catfish]

Re: 1980 Mercury 70 hp

i have a merc 70 also with some problems. if you decide to sell the motor let me know i might buy it. but do not give up the ship to fast the compression test will tell you a good bit about the motor.

 

[roper]

Re: 1980 Mercury 70 hp

Want to trade powerheads??? JK <br /><br />I'm going to send it to the shop and have them tear it down and take a look inside to see if it is worth fixing or if I have a very heavy anchor.<br /><br />Anybody know why it cost $1600 to rebuild a three cylinder outboard, but only $800 to rebuild an eight cylinder car motor? <br />

 

[trevorcday]

Re: 1980 Mercury 70 hp

We see a lot of these older 3 cylinder mercury's with burned pistons at our shop. As a rule of thumb we use $500 per hole to rebuild an outboard. The main reason it costs a lot more to rebuild an outboard vs a car is that the parts are MUCH more expensive. One piston and rings for your motor are probably more than $100. Before you rebuild your p/h make sure you know why it burned the piston in the first place. On these motors the #1 piston sometimes packs-in as a result of overheating but it could also be caused by a lean a/f ratio or an ignition problem. Unless you fix the cause of the problem it will burn the new piston on the first day out. Trust me i have learned this the hard way.

 

[trevorcday]

Re: 1980 Mercury 70 hp

We see a lot of these older 3 cylinder mercury's with burned pistons at our shop. As a rule of thumb we use $500 per hole to rebuild an outboard. The main reason it costs a lot more to rebuild an outboard vs a car is that the parts are MUCH more expensive. One piston and rings for your motor are probably more than $100. Before you rebuild your p/h make sure you know why it burned the piston in the first place. On these motors the #1 piston sometimes packs-in as a result of overheating but it could also be caused by a lean a/f ratio or an ignition problem. Unless you fix the cause of the problem it will burn the new piston on the first day out. Trust me i have learned this the hard way.

 

[roper]

Re: 1980 Mercury 70 hp

Thanks, that is good advice. I told the repair shop that we need to find / fix the orignal problem as well as rebuild the PH

 

[roper]

Re: 1980 Mercury 70 hp

FYI - cylinder #1 was gone. culprit was heat caused by an old water pump. lesson: even if the guy you buy the motor from tells you the water pump is new, replace it anyhow ! Thanks to all that replied, this is a great site.