1984 115 mercury no. 2 cyc. Detonation

[backlash49]

hello still need help with this motor. Motor runs fine for the first 20 min. 5500 rpm and then loses no. 2 cyc. will not run over 3000 rpm, for that day. the next day it will do the same thing. will run fine in the drive way all day???? pull no. 2 plug there is alu. on the plug you can see a small pc. has comeff the piston. ????

 

[Faztbullet]

Re: 1984 115 mercury no. 2 cyc. Detonation

Quit running it and repair it Sound like it still has the idle stabilizer box and it has went bad or a pack/trigger has problems as carb will not do this.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

the idle stabilizer box has been removed, both switch boxs have been changed, trigger and stator have been changed all new parts. ???

 

[canoemang]

Re: 1984 115 mercury no. 2 cyc. Detonation

compression test and go from there..

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

compression is 120 all cyc.

 

[CharlieB]

Re: 1984 115 mercury no. 2 cyc. Detonation

Careful inspection of that piston dome should reviel if you have a lean carb/intake leak or advanced timing/detonation.

Either problem MUST BE corrected before you totally destroy that cyl/engine.

Verify ignition timing, test for intake leaks.

I note you have changed almost the entire ignition with the exception of the coil. While I don't recommend you operate the motor you need to test the coil to ensure it is not heating up and failing, thus limiting engine speed running less the one cyl.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

timing has been checked good, carbs was taking off and rebuild with new gaskets, put on new coil for cyc 2, how do you test for intake leaks ?? thanks for your help

 

[CharlieB]

Re: 1984 115 mercury no. 2 cyc. Detonation

With the motor idling on the hose, lightly spray the carb base(s) and crankcase parting lines with most any flammable aerosol, any 'change' in engine speed indicates a leak sucking in the fumes.

NOTE: Be very careful when spraying around the carb bases as too much spray can be sucked in thru the carb throats and falsely make you think you found a leak. Tiny little psst's, wait a minute for the fumes to disperse, move a couple of inches and repeat, until you cover all gasket edges and the crankcase seams.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

thanks for your help, motor will run fine on hose in drive way, you have to run it on the water for 20 mins then it starts running bad, and then the next day it will run fine in drive way until you take it out for 20 min.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

Does anybody know anything about the cylinder block cover. all the bolts where very loose and two bolts had fill out , replaced bolts and tighten up bolts. going to take it out this weekend to see if this fixed my problem

 

[sschefer]

Re: 1984 115 mercury no. 2 cyc. Detonation

Faztbullet gave you the advice you need to follow but for some reason you seem to be determined to destroy this motor. You've thrown parts at it to no avail and still have a piston that's destroyed. If that piston has flashed over bad enough to leave chunks of aluminum on the plug the next thing that's going to happen is you'll stick a ring and tear up a cylinder wall. Even if this last effort does cure the running problem, the euphoria that follows will be short lived. That hole is damaged to the point where it needs attention now.

Not a butt chewin, just trying to save you money and grief.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

hello need help from somebody that knows these motors, i have did everything that all of these people on this forum has told me to do,and none of it has worked, all i need is somebody to tell me whats wrong with this motor and how to fix it ???????? so far i have not got any help from this forum ????????? hopefully their is somebody out there that knows these motors. thanks for all your help

 

[Faztbullet]

Re: 1984 115 mercury no. 2 cyc. Detonation

Quit running it and repair it Sounds like it still has the idle stabilizer box and it has went bad or a pack/trigger has problems as carb will not do this.

If the tightening of transfer port cover didnt fix it the check the timing on that cylinder. It either has bad trigger or bias circuit failure in packs or idle stablizer that was removed after the damage occured. That is preignition and aluminum throw off from eyebrow of piston. If the eyebrow is badly eroded it will cause a lower compression in that cylinder and continued problem ..this is rebuild time.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

Thanks for your help the eyebrow of the piston has a pc. missing the size of the head of a pencel would that be badly eroded, remember this motor runs fine for the first 20 min. 120 lbs compression cold are hot ???

 

[CharlieB]

Re: 1984 115 mercury no. 2 cyc. Detonation

It could also be a good idea to test the overheat alarm to ensure it works. Simply ground the tan wire that connects to the temp sender, and turn the key ON, the alarm should sound.

You may want to remove the exhaust side cover to better inspect the damaged piston, right now, part wise, you may only be looking at replacing the one piston, all the rings, gaskets, and seals.

If allowed to continue you will require cyl boring, and worst case, siezure, broken rod, destroyed cyl sleeve, possibly an engine block.

Re-read Fazt posting and follow his recommendations, positively find the root cause of the problem, or it will repeat itself, and you'd really hate to spend money on parts a second time.

 

[backlash49]

Re: 1984 115 mercury no. 2 cyc. Detonation

I am on this forum to find out what is causing this problem, ???? I have done everything that everybody has told me to do, and still don't know what is causing this problem. this motor does not have a alarm, but you can put your hand on the motor its just warm??????

 

[CharlieB]

Re: 1984 115 mercury no. 2 cyc. Detonation

Fazt has repeatedly told you exactly what and how to test your ignition to identify a problem.

I don't see your response as to the results of those tests.

Look at the timing marks on your flywheel, find the Zero and using a protractor repeat the mark at EXACTLY 60 degree intevals around the flywheel, adding 5 more marks such that you have one for each cyl.

Run the motor and use an inductive timing light begin checking to see if #2 shows your mark in the EXACT same position as it shows the #1 mark.

EVERY big motor has an alarm, many fail to function, which is why we stress TESTING. There is supposed to be a temp sensor in the cyl cover, when grounded and the key turned on, the alarm should sound. If not, you risk frying your motor without warning.