'78 Merc 1400 compression test

[monk-monk]

I have a '78 Mercury 1400...this motor has not been "turned over" for quite sometime...My question is this, i want to check the compression of this powerhead...i know all about the procedures for doing a compression check...BUT not for a motor that has been sitting for awhile....what should i do to lubricate the powerhead before i engage a starter to crank it...and what about the existing piston rings and the cylinder wall lubrication....hope you see my point....just don't want to start spinning a "dry" motor over..Thanks!

 

[SeaKaye12]

Re: '78 Merc 1400 compression test

Yes; I would take a squezze-trigger oiler and squirt a good bit of TWC-3 oil in there before turning the engine over.

Your compression pressure will be higher; but like you say; you don't want to turn it over dry.

After you get it running I would take another reading without the oil. That will be the accurate reading.

Chuck

 

[riverrat17]

Re: '78 Merc 1400 compression test

If it were me, I would remove the spark plugs and put a GOOD squirt of penetrating oil in each cylinder and let it soak for a few hours. Then you should be able to grab the fly wheel (plugs still out) and spin the motor over by hand. If it binds or don't want to spin, let the oil sit even longer. When every thing is free, (rings an such) it will move freely by hand. After it moves freely, install plugs and run on the muffs for a while and then do your compression test. To get the best numbers on a compression test, warm the engine first, pull the kill switch, throttle wide open, fully charged battery, an see what ya got.
hope this helps........

 

[Chris1956]

Re: '78 Merc 1400 compression test

Monk, Tilt it up, remove the spark plugs and squirt some TCW-III oil into the cylinders. Now turn the flywheel by hand and feel for binding. If no binding, you are ready to test it.

If it is frozen, you can try the penetrating oil, however, you should remove the transfer covers and see which cylinder has the rusty rings. You can use a brass drift thru the plug hole to loosen her up. Then inspect for damage.

 

[monk-monk]

Re: '78 Merc 1400 compression test

Thanks for the help! Both replies have their own merits, but here's my situation: When i acquired this motor, it had a bad internal wiring harness, the Black box was fried, the carbs have not received any service since kitty was a pup...etc.! I have new ignition components and i have the parts to service the carbs, but if i can "get away with it" i'd rather not install all these new parts on this motor to check the compression...I don't want to rebuild a new set of carbs to start the motor when i don't even know the condition of the rest of the fuel system...I agree with both of you on lubricating the pistons and cylinder walls and i will do that, im also going to prime the block and spin it by hand to get some lube to the needle bearings...with all this in mind, do you think i can get a decent reading on the compression....the last thing i want to do is rebuild all the components only to find a "dead" motor....Please understand, im a perfectionist...if i rebuilt the carbs i would have to go through the entire fuel system leading up to the carbs....if i didn't service the leading part of the fuel system i would never trust the condition of the newly rebuilt carbs because of possible contamintation! See my point? I only want to do as much as i have to so i can determine if this motor is viable or not! Thanks!

 

[Chris1956]

Re: '78 Merc 1400 compression test

Spray some 2 cycle oil or fuel mix into the carbs, and then crank her up for the compression test. If the compression is good, do the rest of the repairs.

All you need is a spray bottle, heck wd-40 would work as a bearing lubricant, which BTW, I do not think you even need.

Don't sweat it. You will never ruin the motor taking the compression.